JP2024032657A - Optical measuring device and method for manufacturing the optical measuring device - Google Patents

Abstract

The present invention provides an optical measurement device that can simplify and downsize the device, and a method for manufacturing the optical measurement device. A spectrometer 1A includes a light source unit 2 that emits a laser beam L1, a plane mirror 41 having a mirror surface 41a on which the laser beam L1 is incident, and a plane mirror having a mirror surface 42a opposite to the mirror surface 41a. 42, a mirror section 4 in which the object to be measured is introduced between the mirror surface 41a and the mirror surface 42a, and a laser beam that is multiple-reflected and returned between the mirror surface 41a and the mirror surface 42a. It includes a photodetector section 3 that detects L1. The mirror surface 41a and the mirror surface 42a are arranged so that an optical path OP of the laser beam L1 that reciprocates in the Y-axis direction while undergoing multiple reflections between the mirror surface 41a and the mirror surface 42a is formed when viewed from the Z-axis direction. In some cases, they are arranged non-parallel to each other. The optical path OP of the laser beam L1 between the mirror surface 41a and the mirror surface 42a is inclined with respect to the Z-axis direction. [Selection diagram] Figure 1

Description

The present disclosure relates to a light measurement device and a method of manufacturing the light measurement device.

Mid-infrared light (wavelength 3 μm to 20 μm) is used for absorption spectroscopy (spectrometry) targeting gas molecules because strong absorption derived from the fundamental vibrations of molecules is observed. In addition, as disclosed in Non-Patent Document 1, as a method for improving the sensitivity of the above-mentioned absorption spectroscopy, two concave mirrors are arranged facing each other, and light is multiple-reflected between these two concave mirrors. A technology called the Herriot cell is known, which enables long optical paths.

Donald R. Herriott and Harry J. Schulte, “Folded Optical Delay Lines”, Applied Optics vol.4, pp.883-889, August 1, 1965.

However, gas absorption spectrometers using concave mirrors, such as the Herriot cell disclosed in Non-Patent Document 1, require a high degree of processing precision and assembly precision, resulting in higher costs and larger equipment. The problem was that it was easy.

Therefore, one aspect of the present disclosure aims to provide an optical measurement device that can simplify and downsize the device, and a method for manufacturing the optical measurement device.

The present disclosure includes the following optical measurement devices [1] to [20] and the method for manufacturing the optical measurement device [21].

[1]
a light source unit that emits laser light;
a first plane mirror having a first mirror surface onto which the laser beam emitted from the light source section is incident; and a second plane mirror having a second mirror surface opposite to the first mirror surface; a mirror section in which a measurement object is introduced between the first mirror surface and the second mirror surface;
a light detection unit that detects the laser beam that is multiple-reflected and returned between the first mirror surface and the second mirror surface;
Equipped with
The first mirror surface and the second mirror surface perform multiple reflections between the first mirror surface and the second mirror surface in a second direction perpendicular to a first direction perpendicular to the first mirror surface. are arranged non-parallel to each other when viewed from a third direction orthogonal to the first direction and the second direction, so that an optical path of the laser beam reciprocating is formed;
The optical path of the laser beam between the first mirror surface and the second mirror surface is inclined with respect to the third direction.
Light measurement device.

According to the above-mentioned optical measuring device, the configuration in which two plane mirrors (the first plane mirror and the second plane mirror) are disposed opposite to each other in a non-parallel manner (i.e., compared to the configuration of a Herriot cell etc. using a conventional concave mirror) A long optical path optical measuring device can be realized with a low cost and simple configuration. In addition, by setting the optical path of the laser beam between the plane mirrors to be inclined with respect to the third direction, the outgoing path and the returning path of the laser beam between the plane mirrors can be spatially separated in the third direction. Optical measurement of a measurement target introduced between mirrors (for example, absorbance measurement at a predetermined wavelength (single wavelength), absorption spectrometry at multiple wavelengths, etc.) can be appropriately performed. More specifically, it is possible to prevent the outgoing light and the returning light from interfering between the plane mirrors, prevent the laser light reflected by the mirror from re-entering the light source, and detect the reflected light. be able to guide them appropriately. Therefore, according to the above optical measuring device, it is possible to simplify the device (lower price) and downsize the device.

[2]
The optical path of the laser beam that first enters the first mirror surface is inclined with respect to the third direction,
the first mirror surface and the second mirror surface are parallel to the third direction;
[1] Optical measuring device.
According to the above configuration, by tilting the optical path of the laser beam that first enters the first mirror surface with respect to the third direction, the first plane mirror and the second plane mirror can be tilted with respect to the third direction. Therefore, it is possible to easily realize a configuration in which the optical path of the laser beam between the plane mirrors is inclined with respect to the third direction.

[3]
When viewed from the third direction, the incident angle of the laser beam that first enters the first mirror surface is equal to Adjusted to be a natural number multiple of the inclination angle of the mirror surface,
The optical measuring device according to [1] or [2].
According to the above configuration, the optical path of the laser beam between the plane mirrors can be set so that the outgoing path and the returning path of the laser beam between the plane mirrors overlap when viewed from the third direction. This makes it possible to easily arrange the forward optical system for guiding the laser beam from the light source section to the mirror section and the return optical system for guiding the reflected light from the mirror section to the photodetecting section. Become.

[4]
A distance along the second direction from a position where the laser beam first enters the first mirror surface to an end of the first mirror surface in the outgoing direction of the laser beam is 300 mm or less,
The optical measuring device according to any one of [1] to [3].
According to the above configuration, it is possible to further effectively downsize the device.

[5]
The length of the mirror portion in the third direction is 50 mm or less,
The optical measuring device according to any one of [1] to [4].
According to the above configuration, by suppressing the height of the mirror part in the third direction below a certain level, the apparatus can be made smaller, and the amount of the object to be measured (for example, gas) introduced (filled) between the plane mirrors can be reduced. can be kept below a certain level. That is, by simply introducing a relatively small amount of the object to be measured between the plane mirrors, it is possible to perform optical measurement of the object to be measured.

[6]
An end of the first mirror surface in the backward direction of the laser beam protrudes in the backward direction than an end of the second mirror surface in the backward direction.
The optical measurement device according to any one of [1] to [5].
According to the above configuration, it is possible to make it easier for laser light to enter the first mirror surface. In addition, when the beam diameter of the laser beam expands through long optical path propagation due to multiple reflections between plane mirrors, the laser beam that is finally reflected on the first mirror surface and guided to the photodetector side is It is possible to prevent the reflected light from being blocked by the mirror surface (that is, the beam loss of the reflected light).

[7]
If the incident angle of the laser beam that first enters the first mirror surface when viewed from the third direction is expressed as θ _H , then the second mirror in the return path direction of the laser beam The distance along the second direction from the end of the surface to the end of the first mirror surface in the return direction is the distance between the first mirror surface and the second mirror surface along the first direction. It is set to a value greater than or equal to the distance from the end multiplied by _tanθH ,
[6] Optical measuring device.
According to the above configuration, the return light that is reflected at the end of the second mirror surface in the return direction and travels to the first mirror surface escapes to the outside (return direction side) of the end of the first mirror surface in the return direction. This makes it possible to avoid beam loss caused by

[8]
The distance along the second direction from the end of the second mirror surface in the return direction to the end of the first mirror surface in the return direction is equal to the distance along the second direction from the end of the second mirror surface in the return direction. and the distance between the second mirror surface and the end of the second mirror surface multiplied by _tanθH ,
[7] Optical measuring device.
According to the above configuration, in addition to achieving the effect of [7] above, the protrusion length of the first plane mirror (first mirror surface) with respect to the second plane mirror (second mirror surface) can be adjusted to avoid the above beam loss. By setting the length to a necessary and sufficient length, it is possible to avoid beam loss and downsize the device.

[9]
The inclination angle of the second mirror surface with respect to the first mirror surface when viewed from the third direction is such that the laser beam passing between the first mirror surface and the second mirror surface is tilted from the third direction. It is set to be larger than the divergence angle when viewed,
The optical measuring device according to any one of [1] to [8].
According to the above configuration, when the beam diameter of the laser light expands through long optical path propagation due to multiple reflections between plane mirrors, beam loss of the folded light can be effectively suppressed.

[10]
The light source section and the light detection section are arranged so as to overlap each other in the third direction,
The optical measuring device according to any one of [1] to [9].
By tilting the optical path of the laser beam between the plane mirrors with respect to the third direction, the optical path of the laser beam is guided from the light source section to the mirror section, and the reflected light is guided from the mirror section to the photodetecting section. The optical path can be separated into a third direction. Utilizing this, by arranging the light source section and the light detection section side by side in the third direction, the light source section and the light detection section can be arranged side by side in the third direction. The area required for arranging the detection unit (the area when viewed from the third direction) can be reduced. As a result, it is possible to more effectively downsize the device.

[11]
Further comprising a lens disposed on a side of the light source unit from which the laser beam is emitted and condenses or collimates the laser beam,
The light source section is a quantum cascade laser element,
The distance between the lens and the quantum cascade laser element is shorter than the shortest distance between the first mirror surface and the second mirror surface in the first direction.
The optical measuring device according to any one of [1] to [10].
According to the above configuration, the spread of the laser light emitted from the light source section can be effectively suppressed by the lens. As a result, it is possible to suppress the spread of the beam diameter of the laser light between the plane mirrors, and it is possible to reduce the beam loss of the reflected light due to the spread of the beam diameter.

[12]
The light source section is a quantum cascade laser element,
The photodetector is a quantum cascade photodetector having characteristics corresponding to the quantum cascade laser element.
The optical measurement device according to any one of [1] to [11].
According to the above configuration, by using a quantum cascade laser element and a quantum cascade photodetector that operate in the mid-infrared as the light source section and the photodetection section, strong absorption derived from the fundamental vibration of molecules can be observed, resulting in high sensitivity. This makes it possible to perform optical measurements.

[13]
The characteristic is a characteristic related to the polarization direction,
The light source section and the photodetection section are configured such that the polarization direction of the laser beam that is emitted from the light source section and then enters the photodetection section via the mirror section is different from the polarization direction to which the photodetection section is sensitive. arranged to match,
The optical measurement device of [12].
According to the above configuration, stray light components whose polarization direction is disturbed due to scattering or the like can be prevented from being detected as noise by the photodetector, and the signal-to-noise ratio (S/N) can be improved.

[14]
The characteristic is a characteristic related to wavelength,
The photodetector has a sensitivity wavelength corresponding to the oscillation wavelength of the light source.
The optical measuring device according to [12] or [13].
According to the above configuration, since the quantum cascade photodetector plays the role of a pseudo wavelength filter, it is possible to suppress the influence of background light noise and perform highly sensitive optical measurement.

[15]
a first light guide mirror that guides the laser light to the first mirror surface by reflecting the laser light emitted from the light source;
further comprising a second light guide mirror that guides the laser light to the photodetector by reflecting the folded laser light,
The first light guide mirror and the second light guide mirror are arranged to overlap each other in the third direction,
The optical measuring device according to any one of [1] to [14].
According to the above configuration, by using the first light guide mirror and the second light guide mirror, the degree of freedom in arrangement (layout) of the light source section and the light detection section with respect to the mirror section can be improved. In addition, by arranging the first light guide mirror and the second light guide mirror side by side in the third direction, a comparison is made with the case where the first light guide mirror and the second light guide mirror are arranged without overlapping in the third direction. As a result, the area required for arranging the first light guide mirror and the second light guide mirror (the area when viewed from the third direction) can be reduced, and the device can be downsized.

[16]
The light source section includes a first light source section that emits the laser beam of a first wavelength, and a second light source section that emits the laser beam of a second wavelength different from the first wavelength,
The photodetector includes a first photodetector that detects the laser beam of the first wavelength that is multiple-reflected and returned between the first mirror surface and the second mirror surface, and the first mirror. a second light detection unit that detects the laser beam of the second wavelength that is multiple-reflected and returned between the surface and the second mirror surface;
The first light source section, the second light source section, the first light detection section, and the second light detection section are arranged to overlap each other in the third direction.
The optical measuring device according to any one of [1] to [15].
According to the above configuration, by arranging the first light source section, the second light source section, the first light detection section, and the second light detection section so as to overlap each other in the third direction, the light source section and the light The detection unit can be arranged compactly. Furthermore, by varying the wavelength bands between the systems, absorption spectroscopic measurements of two different wavelength bands can be performed simultaneously.

[17]
The light source section includes a first light source section that emits the laser beam of a first wavelength, and a second light source section that emits the laser beam of a second wavelength different from the first wavelength,
The photodetector includes a first photodetector that detects the laser beam of the first wavelength that is multiple-reflected and returned between the first mirror surface and the second mirror surface, and the first mirror. a second light detection unit that detects the laser beam of the second wavelength that is multiple-reflected and returned between the surface and the second mirror surface;
The first light source section and the second light source section are arranged side by side in the first direction,
The first photodetector and the second photodetector are arranged side by side in the first direction,
The first light source section and the first light detection section are arranged to overlap each other in the third direction,
The second light source section and the second light detection section are arranged to overlap with each other in the third direction.
The optical measuring device according to any one of [1] to [15].
According to the above configuration, by arranging the first light source section and the first light detection section in an overlapping manner in the third direction, and arranging the second light source section and the second light detection section in an overlapping manner in the third direction, , two systems of light source sections and light detection sections can be arranged compactly. Furthermore, by varying the wavelength bands between the systems, absorption spectroscopic measurements of two different wavelength bands can be performed simultaneously.

[18]
further comprising a casing that airtightly accommodates the mirror section,
The measurement target is a gas,
The housing is provided with an opening for introducing the gas from the outside of the housing to the inside of the housing,
The light source section and the light detection section are arranged outside the housing,
The optical measurement device according to any one of [1] to [17].
According to the above configuration, more precise measurements can be performed by introducing gas through the opening after reducing the pressure inside the casing that airtightly accommodates only the mirror portion.

[19]
Further comprising a casing that accommodates the light source section, the light detection section, and the mirror section,
The measurement target is a gas,
The casing is provided with an opening for introducing the gas from the outside of the casing into the inside of the casing.
The optical measurement device according to any one of [1] to [18].
According to the above configuration, by housing the light source section, the light detection section, and the mirror section in one housing, each member constituting the optical measurement device is appropriately protected from external contamination, mechanical shock, etc. be able to.

[20]
The measurement target is a gas,
The light source section is configured to be able to emit the laser light of a first wavelength that is absorbed by the gas and the laser light of a second wavelength that is absorbed by the gas to a smaller degree than the first wavelength. ing,
The optical measuring device according to any one of [1] to [19].
According to the above configuration, it is possible to perform analysis based on the difference between the measured value corresponding to the first wavelength and the measured value corresponding to the second wavelength, that is, measure the gas concentration by differential absorption spectroscopy.

[21]
The light source section is configured to be able to switch and emit the laser light of the first wavelength and the laser light of the second wavelength based on light emitted from a single laser element.
The optical measurement device of [20].
According to the above configuration, the configuration [20] above can be realized using a single laser light source.

[22]
A method for manufacturing an optical measuring device according to any one of [1] to [21],
The light measurement device includes a first light guide mirror that guides the laser light to the first mirror surface by reflecting the laser light emitted from the light source section, and a first light guide mirror that guides the laser light to the first mirror surface, and a first light guide mirror that guides the laser light that is emitted from the light source section. further comprising a second light guide mirror that guides the laser beam to the photodetector by reflecting it,
fixing each of the light source section, the light detection section, the mirror section, and the second light guide mirror;
After the fixing step, adjusting and fixing the position and angle of the first light guiding mirror while emitting the laser light from the light source section so that the light detection intensity in the photodetecting section is maximized. and,
A method of manufacturing an optical measuring device, including:
According to the above configuration, the light source section, the light detection section, the mirror section, and the second light guiding mirror are positioned (fixed) in advance within a mechanical precision range, and then the light detection intensity in the light detection section is maximized. Based on a simple index, it is possible to precisely adjust the angle of the first light guide mirror. The above method is particularly effective when the laser light emitted from the light source is invisible mid-infrared light.

According to one aspect of the present disclosure, it is possible to provide an optical measurement device that can simplify and downsize the device, and a method for manufacturing the optical measurement device.

FIG. 1 is a schematic perspective view of a spectrometer according to a first embodiment. FIG. 2 is a cross-sectional view of the casing taken along line II-II in FIG. FIG. 3 is a diagram used to explain the polarization characteristics of the light source section and the light detection section. FIG. 4 is a diagram showing an example of the oscillation spectrum of the light source section and the sensitivity spectrum of the photodetector section. FIG. 5 is a plan view schematically showing an optical system for laser light before being reflected by a mirror section. FIG. 6 is a plan view schematically showing an optical system regarding laser light after being reflected by a mirror section. FIG. 7 is a diagram showing the optical path of the laser beam passing between the first light guide mirror and the second light guide mirror when viewed from the Y-axis direction. FIG. 8 is a diagram showing the beam shape of the laser light reaching the output light guide mirror. FIG. 9 is a diagram showing the beam diameter of the laser light reaching the output light guiding mirror. FIG. 10 is a diagram showing part of the configuration of a spectrometer according to the second embodiment. FIG. 11 is a plan view schematically showing an optical system related to a laser beam before being reflected by a mirror portion in the configuration of a spectrometer according to a third embodiment. FIG. 12 is a plan view schematically showing an optical system related to laser light after being reflected by a mirror part in the configuration of the spectrometer of the third embodiment. FIG. 13 is a diagram showing part of the configuration of a spectrometer according to the fourth embodiment. FIG. 14 is a schematic perspective view of a spectrometer according to the fifth embodiment. FIG. 15 is a schematic cross-sectional view taken along line XV-XV in FIG. 14. FIG. 16 is a plan view schematically showing the configuration of a spectrometer according to the sixth embodiment. FIG. 17 is a plan view schematically showing the configuration of a spectrometer according to the seventh embodiment. FIG. 18 is a plan view schematically showing the configuration of a spectrometer according to the eighth embodiment. FIG. 19 is a diagram illustrating a configuration example of a spectrometer for optical measurement of a solid measurement target.

Hereinafter, one embodiment of the present disclosure will be described in detail with reference to the drawings. In the following description, the same or equivalent elements will be denoted by the same reference numerals, and overlapping description will be omitted.

[First embodiment]
A spectrometer 1A (light measurement device) of the first embodiment will be described with reference to FIGS. 1 to 9. As shown in FIGS. 1 and 2, the spectrometer 1A includes a light source section 2, a light detection section 3, a mirror section 4, an entrance adjustment mirror 6 (first light guide mirror), and an output light guide mirror. 7 (second light guide mirror) and a support member 8. The mirror section 4 includes a plane mirror 41 (first plane mirror) having a mirror surface 41a (first mirror surface), and a plane mirror 42 (second mirror surface) having a mirror surface 42a (second mirror surface) opposite to the mirror surface 41a. plane mirror). A gas (measurement object) to be subjected to spectroscopic measurement is introduced between the mirror surface 41a and the mirror surface 42a.

As an example, the light source section 2 and the light detection section 3 are housed in the same housing 10. The housing 10 has a substantially rectangular parallelepiped outer shape and is disposed on the side of the mirror section 4 . More specifically, the housing 10 is disposed on the side of the plane mirror 42 on the opposite side of the plane mirror 42 from the side where the plane mirror 41 is located. In other words, the housing 10 is arranged at a position facing the back surface 42f of the plane mirror 42 on the opposite side to the mirror surface 42a.

The support member 8 is formed into a rectangular plate shape and has a planar support surface 8a. The housing 10 and the mirror section 4 are fixed (supported) on the support surface 8a of the support member 8. The plane mirrors 41 and 42 are arranged on the support surface 8a so that the mirror surfaces 41a and 42a are perpendicular to the support surface 8a. The entrance adjustment mirror 6 and the output light guide mirror 7 may also be fixed to the support member 8 via a support member such as a column (not shown).

In the following description, the direction perpendicular to the mirror surface 41a will be referred to as the X-axis direction (first direction), the direction perpendicular to the support surface 8a will be referred to as the Z-axis direction (third direction), and the X-axis direction and the Z-axis direction The direction perpendicular to is expressed as the Y-axis direction (second direction). The plane mirrors 41 and 42 are arranged so that the mirror surface 41a and the mirror surface 42a are non-parallel when viewed from the Z-axis direction (see FIG. 5). More specifically, the mirror surface 41a is inclined with respect to the mirror surface 42a so that the distance between the mirror surface 41a and the mirror surface 42a (distance in the X-axis direction) becomes smaller toward the negative direction of the Y-axis. . In this embodiment, for convenience, the Y-axis negative direction (i.e., the direction in which the distance between the mirror surfaces 41a and 42a narrows) is defined as "rear", and the Y-axis positive direction (i.e., the direction in which the distance between the mirror surfaces 41a and 42a increases). ) is defined as "forward". Further, the side on which each member such as the mirror portion 4 is arranged with respect to the support surface 8a is defined as "upper".

As shown in FIG. 2, the housing 10 hermetically accommodates the lens 11, the lens 12, the heat sink 15, and the Peltier element 16, as well as the light source section 2 and the light detection section 3. As an example, the light source section 2 and the light detection section 3 are fixed to the inner surface of the side wall 10a of the housing 10 via a heat sink 15 and a Peltier element 16. The side wall 10a is a wall portion of the housing 10 that faces the mirror portion 4 (plane mirror 42). The Peltier element 16 is fixed to the inner surface of the side wall 10a, and the heat sink 15 is fixed to the Peltier element 16 on the side opposite to the side of the Peltier element 16 facing the side wall 10a. The light source section 2 and the light detection section 3 are fixed to the heat sink 15 on the side opposite to the side of the heat sink 15 that faces the Peltier element 16 . The Peltier element 16 plays a role of controlling the temperature inside the housing 10. That is, the heat generated in the light source section 2 is absorbed (cooled) by the Peltier element 16 via the heat sink 15, so that the temperatures of the light source section 2 and the light detection section 3 are maintained within a certain range. Note that the arrangement and shape of the light source section 2, photodetection section 3, heat sink 15, and Peltier element 16 are not limited to the above. For example, instead of the heat sink 15, an L-shaped part is formed, which is made up of a flat first part fixed to the side wall 10a and a flat second part extending in the positive direction of the X-axis from the rear end of the first part. A heat sink may also be used. Moreover, when such a heat sink is used, the Peltier element may be arranged so that the cooling surface of the Peltier element faces the rear surface of the second portion. Furthermore, a secondary cooling unit such as a fan may be provided behind (on the heat exhaust side) of the Peltier element arranged in this manner to cool the Peltier element.

The light source section 2 is a light source that emits laser light L1. For example, the light source section 2 is a quantum cascade laser device including an active layer. As an example, the light source section 2 is a distributed feedback quantum cascade laser device (DFB-QCL). In this embodiment, the light source unit 2 is a DFB-QCL that operates in a single mode with a wavelength of 4.6 μm. The active layer is a layer including a quantum well structure in which quantum well layers and barrier layers are alternately stacked, and generates laser light L1. The active layer has, for example, a structure in which a plurality of InGaAs layers and InAlAs layers are alternately stacked along the stacking direction. The light source section 2 is arranged so as to emit the laser beam L1 forward (in the Y-axis positive direction). That is, the light source section 2 has a light emitting surface 2a that faces forward and emits the laser beam L1 forward.

The lens 11 is arranged on the side from which the laser beam L1 of the light source section 2 is emitted (that is, in front of the light source section 2). The lens 11 serves to suppress the spread of the laser beam L1 by focusing or collimating the laser beam L1. As an example, the lens 11 is a collimating lens that collimates the laser beam L1. The lens 11 has an entrance surface 11a into which the laser beam L1 enters, and an exit surface 11b which outputs the laser beam L1 that has passed through the lens to the outside. As an example, the entrance surface 11a is formed in a planar shape, and the exit surface 11b is formed in a convex shape. From the viewpoint of downsizing the housing 10, for example, an aspherical lens made of ZnSe and having a focal length of 10 mm or less can be used as the lens 11. The entrance surface 11a and the exit surface 11b of the lens 11 may be provided with a low-reflection coating that has a transmittance of 90% or more for the wavelength of the laser beam L1. Further, the base material of the lens 11 is not limited to ZnSe, but may be made of other materials that can transmit mid-infrared light (laser light L1) with low loss. In this embodiment, the lens 11 is constituted by a ZnSe aspherical lens having a focal length of 1 mm and a lens diameter (diameter) of 5 mm.

A portion of the front side wall 10b of the housing 10 that faces the emission surface 11b of the lens 11 has an opening for passing the laser beam L1 emitted from the light source section 2 (the laser beam L1 collimated by the lens 11). A section 10c is provided. A window member 13 for transmitting the laser beam L1 is provided in the opening 10c. As the material of the window member 13, for example, ZnSe can be used similarly to the lens 11. Further, a low reflection coating similar to that of the lens 11 may be applied to the inner surface (the surface facing the lens 11) and the outer surface (the surface opposite to the inner surface) of the window member 13.

As shown in FIGS. 1 and 2, the laser beam L1 emitted from the light source section 2 passes through the lens 11 and the window member 13, and then passes through the incident adjustment mirror 6 under a predetermined angle condition (θ _H and θ _V ) and enters the mirror surface 41a of the plane mirror 41 at a position P1. The position P1 is a position where the optical axis of the laser beam L1 that first enters the mirror surface 41a intersects with the mirror surface 41a. Between the plane mirrors 41 and 42, an optical path OP of the laser beam L1 is formed which reciprocates in the front-rear direction (Y-axis direction) while undergoing multiple reflections between the mirror surfaces 41a and 42a. The optical path OP includes an outgoing path OP1 in which the laser beam L1 travels backward (in the outward direction), and a backward path OP2 in which the laser beam L1 (returning light L2) is turned back and proceeds forward (in the backward direction).

The laser beam L1 incident on the mirror surface 41a travels backward (in the Y-axis negative direction) while undergoing multiple reflections between the mirror surface 41a and the mirror surface 42a. That is, between the plane mirrors 41 and 42, an outgoing path OP1 is formed that travels backward (in the outgoing path direction) from the position P1 while being subjected to multiple reflections. Thereafter, the folded light L2, which is the laser beam L1 whose traveling direction is folded back from the rear to the front, travels forward (in the Y-axis positive direction) while undergoing multiple reflections between the mirror surface 41a and the mirror surface 42a. That is, between the plane mirrors 41 and 42, a return path OP2 is formed which travels forward (in the return path direction) from a turning point (in this embodiment, a position P2 (see FIG. 5) to be described later) while being subjected to multiple reflections.

The return light L2 finally reflected at the position P3 of the mirror surface 41a is guided to the housing 10 via the output light guide mirror 7. The position P3 is a position where the optical axis of the reflected light L2 that finally enters the mirror surface 41a intersects with the mirror surface 41a, and is the final destination of the return path OP2.

The light detection unit 3 detects the laser beam L1 (reflected light L2) that is multiple-reflected and returned between the mirror surfaces 41a and 42a as described above. The light detection section 3 has a light detection surface 3a that faces forward and receives (detects) the reflected light L2 incident from the front. For example, the photodetector section 3 is a quantum cascade photodetector (QCD) having characteristics corresponding to a quantum cascade laser element (light source section 2). A quantum cascade photodetector includes an active layer similar to the quantum cascade laser device described above. By using a quantum cascade laser element and quantum cascade photodetector that operate in the mid-infrared as the light source section 2 and photodetector section 3, strong absorption derived from the fundamental vibrations of molecules can be observed, allowing highly sensitive absorption spectrometry. It becomes possible to do this. Note that examples of the above-mentioned characteristics include the characteristics related to the polarization direction and the characteristics related to the wavelength, which will be described below.

(About characteristics related to polarization direction)
The quantum cascade laser element and the quantum cascade photodetector have a common polarization dependence. Therefore, as shown in FIG. 3, the light source unit 2 (quantum cascade laser element) and the photodetector unit 3 (quantum cascade photodetector) The polarization direction D1 of the laser beam L1 (that is, the folded light L2) incident on the photodetector 3 may be arranged so that the polarization direction to which the photodetector 3 is sensitive matches. Here, the polarization direction D1 of the laser beam L1 is the electric field vibration direction of the laser beam L1, and is a direction parallel to the stacking direction D2 of the active layer included in the light source section 2. Further, the polarization direction to which the photodetector 3 is sensitive is a direction parallel to the stacking direction D3 of the active layer included in the photodetector 3. Therefore, the photodetector 3 is configured so that the polarization direction D1 of the reflected light L2 (laser light L1) that enters the photodetector 3 matches the stacking direction D3 (that is, the polarization direction to which the photodetector 3 is sensitive). It is enough if it is placed. According to the above configuration, stray light components whose polarization direction is disturbed due to scattering or the like on the optical path from the light emission surface 2a to the light detection surface 3a are prevented from being detected as noise by the light detection section 3, It is possible to improve the signal-to-noise ratio (S/N).

(About wavelength-related characteristics)
As shown in FIG. 4, the photodetector 3 may have a sensitivity wavelength corresponding to the oscillation wavelength of the light source 2 (for example, 4.6 μm). In FIG. 4, OS indicates the oscillation spectrum of the light source section 2, and SS indicates the sensitivity spectrum of the photodetector section 3. FIG. 4 shows an example in which carbon dioxide (CO ₂ ) is introduced between the plane mirrors 41 and 42 as a gas to be measured. The photodetector 3 is designed to have maximum sensitivity to the oscillation wavelength (4.6 μm) of the light source 2, for example. For example, the oscillation wavelength of the light source unit 2 is set to a value (4.6 μm) near the absorption band in the infrared region of the gas to be measured (in the example of FIG. 4, the absorption band of CO ₂ is 4.3 μm), and , the peak of the sensitivity wavelength of the photodetector 3 may be matched to the oscillation wavelength of the light source 2. As shown in the sensitivity spectrum SS of FIG. 4, the quantum cascade photodetector has a narrower sensitivity wavelength range than a general photodetector. Therefore, the photodetector 3, which is a quantum cascade photodetector, plays the role of a pseudo wavelength filter. Therefore, as described above, for example, by matching the wavelength at which the sensitivity of the photodetector 3 is maximum with the oscillation wavelength of the light source 2, the influence of background light noise can be suppressed and highly sensitive absorption spectrometry can be performed. becomes possible.

The lens 12 is arranged on the side where the reflected light L2 of the photodetector 3 enters (that is, in front of the photodetector 3). The lens 12 is a condensing lens that condenses the reflected light L2. The lens 12 has an entrance surface 12a into which the reflected light L2 enters, and an exit surface 12b which emits the reflected light L2 that has passed through the lens toward the light detection surface 3a. As an example, the entrance surface 12a is formed in a convex shape, and the exit surface 12b is formed in a planar shape. For example, like the lens 11, the lens 12 may be configured with an aspherical lens made of ZnSe and having a focal length of 10 mm or less. Further, the entrance surface 12a and the exit surface 12b of the lens 12 may be provided with a low-reflection coating such that the transmittance for the wavelength of the reflected light L2 is 90% or more. Further, the base material of the lens 12 is not limited to ZnSe, but may be made of other materials that can transmit mid-infrared light (laser light L1) with low loss. In this embodiment, the lens 12, like the lens 11, is composed of a ZnSe aspherical lens having a focal length of 1 mm and a lens diameter (diameter) of 5 mm.

An opening 10d for guiding the reflected light L2 into the interior of the housing 10 is provided in a portion of the side wall 10b of the housing 10 that faces the entrance surface 12a of the lens 12. A window member 14 for transmitting the reflected light L2 is provided in the opening 10d. Window member 14 may be formed of the same material as window member 13. Further, the inner surface (the surface facing the lens 12) and the outer surface (the surface opposite to the inner surface) of the window member 14 may be provided with a low-reflection coating similar to that of the lens 12.

In the housing 10, the light source section 2 and the light detection section 3 are arranged so as to overlap each other in the Z-axis direction. In this embodiment, as an example, the light source section 2 is arranged above the photodetector section 3. As shown in FIG. 2, the optical axis of the light source section 2 (the axis passing through the center of the light output surface 2a) and the optical axis of the light detection section 3 (the axis passing through the center of the light detection surface 3a) are in the Z-axis direction. , and are separated by a distance h. Similarly, the lens 11 and the window member 13 for the light source section are also arranged above the lens 12 and the window member 14 so as to overlap in the Z-axis direction with the lens 12 and the window member 14 for the light detection section, respectively.

The entrance adjustment mirror 6 is disposed at a position facing the light output surface 2a of the light source section 2, and at a position where the laser light L1 that has passed through the lens 11 is incident. The incident adjustment mirror 6 reflects the laser beam L1 emitted from the light output surface 2a of the light source section 2, thereby directing the laser beam L1 to the mirror surface 41a (position P1) of the plane mirror 41 at a predetermined angle (described later). The light is guided so as to be incident at an angle θ _H and an incident angle θ _V ). That is, the incidence adjustment mirror 6 has a function of three-dimensionally adjusting the incident angle of the laser beam L1 with respect to the mirror surface 41a. In this embodiment, the incidence adjustment mirror 6 guides the laser beam L1 so that the laser beam L1 travels backward (in the Y-axis negative direction) and downward (in the Z-axis negative direction). In this embodiment, the incidence adjustment mirror 6 is a plane mirror. However, the incidence adjustment mirror 6 may be a concave mirror. When the incidence adjustment mirror 6 is a concave mirror, the spread of the laser beam L1 can be suppressed.

The output light guide mirror 7 is disposed at a position facing the photodetection surface 3a of the photodetection section 3, at a position where the return light L2 finally reflected by the mirror surface 41a (position P3) is incident. The output light guiding mirror 7 guides the reflected light L2 to the light detection surface 3a of the photodetector 3 by reflecting the reflected light L2. In this embodiment, the output light guiding mirror 7 is a plane mirror. However, the output light guiding mirror 7 may be a concave mirror. When the output light guiding mirror 7 is a concave mirror, the spread of the reflected light L2 can be suppressed.

In this embodiment, when viewed from the Z-axis direction, the outbound path OP1 overlaps (coincides with) the return path OP2, and the outbound path OP1 and the return path OP2 are shifted (separated) in the height direction (Z-axis direction). In addition, the incident angle (θ _H and θ _V to be described later) of the laser beam L1 with respect to the position P1 is adjusted by an incident adjustment mirror 6. Thereby, the entrance adjustment mirror 6 and the output light guide mirror 7 are arranged so as to overlap each other in the Z-axis direction at different height positions. In this embodiment, the entrance adjustment mirror 6 is arranged above the output light guide mirror 7. Further, the optical path of the laser beam L1 from the light source section 2 to the incident adjustment mirror 6, and the optical path of the reflected light L2 from the output light guide mirror 7 to the photodetector section 3, are both along the Y-axis direction. Therefore, as shown in FIG. 7, the distance between the position where the optical axis of the incident adjustment mirror 6 and the laser beam L1 intersect and the position where the optical axis of the output light guiding mirror 7 and the reflected light L2 intersect is 2 and the photodetector 3 in the Z-axis direction. Note that the distance h is set to, for example, 15 mm. In this case, the casing 10 can be configured to be smaller than a cube with sides of 30 mm.

Next, the configuration of the mirror section 4 and the optical path of the laser beam L1 formed by the mirror section 4 will be described in detail with reference to FIG. 1 and FIGS. 5 to 7.

The plane mirror 41 is formed into a rectangular plate shape. The plane mirror 41 is disposed on the opposite side of the plane mirror 42 from the side on which the housing 10 is disposed. The plane mirror 41 has a mirror surface 41a, a lower surface 41b, an upper surface 41c, a front end surface 41d, and a rear end surface 41e. The lower surface 41b is a surface fixed to the support surface 8a. The upper surface 41c is a surface opposite to the lower surface 41b. The front end surface 41d is a surface facing forward (Y-axis positive direction), and the rear end surface 41e is a surface facing rearward (Y-axis negative direction).

The plane mirror 42 is formed into a rectangular plate shape. The plane mirror 42 is arranged between the plane mirror 41 and the housing 10. The plane mirror 42 has a mirror surface 42a, a lower surface 42b, an upper surface 42c, a front end surface 42d, a rear end surface 42e, and a back surface 42f. The lower surface 42b is a surface fixed to the support surface 8a. The upper surface 42c is a surface opposite to the lower surface 42b. The front end surface 42d is a surface facing forward (Y-axis positive direction), and the rear end surface 42e is a surface facing rearward (Y-axis negative direction). The back surface 42f is a surface opposite to the mirror surface 42a.

The mirror surfaces 41a and 42a of the plane mirrors 41 and 42 have surface precision such that, for example, the reflectance for the target wavelength (the oscillation wavelength of the laser beam L1 emitted from the light source section 2) is 90% or more. . Alternatively, the mirror surfaces 41a and 42a may be subjected to surface treatment to achieve the above reflectance. As an example, the mirror surfaces 41a and 42a may be coated with gold.

In the Y-axis direction, the front end 41g of the mirror surface 41a (that is, the boundary between the mirror surface 41a and the front end surface 41d) is the front end 42g of the mirror surface 42a (that is, the boundary between the mirror surface 42a and the front end surface 42d). ) protrudes forward. In this embodiment, the front end portion 41g is located ahead of the front end portion 42g by a distance d3 (d3>0) in the Y-axis direction. On the other hand, in the Y-axis direction, the rear end 41h of the mirror surface 41a (that is, the boundary between the mirror surface 41a and the rear end surface 41e) is located at the rear end 42h of the mirror surface 42a (that is, the rear end 42h of the mirror surface 42a and the rear end 41h of the mirror surface 41a). The position coincides with the position of the boundary portion with the end surface 42e.

As shown in FIGS. 5 and 6, the mirror surface 41a and the mirror surface 42a allow the laser beam L1 to reciprocate in the Y-axis direction (back and forth direction) while being multiple-reflected between the mirror surface 41a and the mirror surface 42a. They are arranged non-parallel to each other when viewed from the Z-axis direction so that an optical path OP is formed. As described above, in this embodiment, an outgoing path OP1 that proceeds backward (in the Y-axis negative direction) and a return path OP2 that proceeds forward (in the Y-axis positive direction) are formed.

As shown in FIG. 5, when viewed from the Z-axis direction, the distance between the plane mirrors 41 and 42 (distance in the X-axis direction between the mirror surfaces 41a and 42a) becomes shorter toward the rear (in the Y-axis negative direction). The plane mirror 42 is inclined with respect to the plane mirror 41 at an angle of inclination α. That is, when viewed from the Z-axis direction, the plane mirror 42 is inclined with respect to the Y-axis direction (YZ plane) so that the mirror surface 42a approaches the mirror surface 41a toward the rear. Therefore, the distance between the mirror surface 41a and the mirror surface 42a in the X-axis direction is the longest distance d1 (longest distance) at the front end portion 42g of the mirror surface 42a. In this embodiment, as an example, the distance d1 is 55 mm.

As shown in FIG. 5, the laser beam L1 is guided by the incident adjustment mirror 6 to the mirror surface 41a along a direction that is inclined with respect to the mirror surface 41a when viewed from the Z-axis direction. That is, the laser beam L1 reflected by the incident adjustment mirror 6 is incident on the mirror surface 41a at a position P1 (initial incident position) at an incident angle θ _H (θ _H ≠0) when viewed from the Z-axis direction. . As described above, the mirror surface 42a is inclined with respect to the mirror surface 41a (that is, the mirror surface 41a and the mirror surface 42a are opposed to each other in a non-parallel manner), and the laser beam L1 is directed at an incident angle _θH with respect to the mirror surface 41a. By making the laser beam L1 incident, it is possible to form an optical path OP of the laser beam L1 that reciprocates in the front-rear direction (Y-axis direction) while undergoing multiple reflections between the mirror surface 41a and the mirror surface 42a.

As shown in FIG. 7, the laser beam L1 is guided by the incident adjustment mirror 6 to the mirror surface 41a along a direction inclined with respect to the Z-axis direction. That is, the laser beam L1 reflected by the incident adjustment mirror 6 is not directed perpendicularly to the Z-axis direction (that is, along the XY plane parallel to the X-axis direction and the Y-axis direction), but in the XY plane. The light is guided to the mirror surface 41a along a direction inclined to the opposite direction. In this embodiment, the laser beam L1 reflected by the incidence adjustment mirror 6 is incident on the mirror surface 41a at a position P1 at an incident angle θ _V (θ _V ≠0) when viewed from the Y-axis direction. Thereby, the height positions of the outbound route OP1 and the return route OP2 can be shifted, and the outbound route OP1 and the return route OP2 can be spatially separated. This prevents the reflected light L2 from re-entering the light exit surface 2a of the light source section 2, and prevents the operation of the light source section 2 from becoming unstable.

As shown in FIG. 5, the position P1 is located behind the front end 41g of the mirror surface 41a. That is, if the distance along the Y-axis direction from the position P1 to the rear end 41h of the mirror surface 41a is d2, then the length d4 of the mirror surface 41a in the Y-axis direction (that is, from the front end 41g to the rear end 41h) ) is longer than the distance d2. From the viewpoint of downsizing the spectrometer 1A, the distance d2 is set to, for example, 300 mm or less. In this embodiment, as an example, the distance d2 is 150 mm. Furthermore, in this embodiment, the Y coordinate of the position P1 matches the Y coordinate of the front end portion 42g of the mirror surface 42a. Therefore, the distance along the Y-axis direction from the position P1 to the front end 41g is the distance d3 along the Y-axis direction from the front end 42g to the front end 41g (that is, the mirror surface of the mirror surface 42a relative to the front end 42g). 41a).

As an example, the incident angle θ _H is set to be a natural number multiple of the inclination angle α. In this case, as shown in FIG. 5, the laser beam L1 incident on the position P1 of the mirror surface 41a travels backward (in the Y-axis negative direction) while being repeatedly reflected between the mirror surface 41a and the mirror surface 42a. , because the mirror surface 42a is inclined by the inclination angle α with respect to the mirror surface 41a, each time the laser beam L1 is reflected by the mirror surfaces 41a and 42a, the laser beam on the mirror surface 41a when viewed from the Z-axis direction is The incident angle of the light L1 decreases by the inclination angle α. As a result, the incident angle of the laser beam L1 with respect to the mirror surface 41a or the mirror surface 42a finally becomes 0 when viewed from the Z-axis direction. That is, when viewed from the Z-axis direction, the laser beam L1 is perpendicularly incident on the mirror surface 41a or the mirror surface 42a. When the incident angle θ _H is an even multiple of the inclination angle α, the laser beam L1 is perpendicularly incident on the mirror surface 41a, and when the incident angle θ _H is an odd multiple of the inclination angle α, the laser beam L1 is incident on the mirror surface 41a. The light is incident perpendicularly to the surface 42a.

FIG. 5 is an example in which the incident angle θ _H is set to an even multiple of the inclination angle α. A position P2 in FIG. 5 is a position where the laser beam L1 is perpendicularly incident on the mirror surface 41a when viewed from the Z-axis direction, and is the final destination of the outgoing path OP1. The outgoing path OP1 is an optical path of the laser beam L1 from the position P1 to the position P2. Note that when the incident angle θ _H is an odd multiple of the inclination angle α, the position P2 is located not on the mirror surface 41a but on the mirror surface 42a.

As shown in FIG. 6, the laser beam L1 (reflected light L2) reflected and returned at the position P2 of the mirror surface 41a forms an optical path (return path OP2) that overlaps the outgoing path OP1 when viewed from the Z-axis direction. As such, the light travels forward (in the positive direction of the Y-axis) while being repeatedly reflected between the mirror surface 41a and the mirror surface 42a. Finally, the folded light L2 reflected at the position P3 of the mirror surface 41a is guided to the output light guiding mirror 7. The return path OP2 is the optical path of the returned light L2 from the position P2 to the position P3.

The inclination angle α and the incident angle _θH are adjusted so that the outgoing path OP1 and the incoming path OP2 overlap when viewed from the Z-axis direction, and as shown in FIG. 7, the optical path OP between the mirror surfaces 41a and 42a is Since it is inclined at an incident angle θ _V with respect to the axial direction, the position P3 is located below the position P1 and overlaps with the position P1 in the Z-axis direction. Note that if the optical path length from the reflection point of the input adjustment mirror 6 to the reflection point of the output light guide mirror 7 via the mirror unit 4 is expressed as D _T , then the relationship “h=D _T ×tanθ _V ” is established. It works.

Furthermore, if the parameters E ₁ and E ₂ are defined as shown in equations (1) and (2) below, then when the incident angle θ _H satisfies the condition of equation (3) below, the The outgoing path OP1 and the incoming path OP2 between the plane mirrors 41 and 42 completely overlap, and the total optical path length of the optical path OP can be maximized. That is, by adjusting the incident angle _θH so as to satisfy the condition of the following formula (3), the position P2, which is the final destination of the outgoing route OP1, is brought as close to the rear end 41h (or the rear end 42h) as possible, and The number of reflections between mirror surfaces 41a and 42a can be maximized.

As an example, the distance d1, the distance d2, and the inclination angle α described above may be set as follows.
・d1=55mm
・d2=150mm
・α=0.3°

When d1, d2, and α are set as above, the incident angle θ _H that maximizes the total optical path length of optical path OP is 9.6° based on equations (1) to (3) above. Desired. In this case, the optical path length of the optical path OP from position P1 to position P3 via the turning position (position P2) is approximately 3.5 m. In addition, the incident angle θ _V only needs to be adjusted so that the center position of the laser beam L1 is shifted by a distance h (15 mm in this embodiment) in the Z-axis direction after passing through an optical path length of 3.5 m. Under the conditions, it is calculated as “θ _V =tan ⁻¹ (15/3500)=0.25°”. Here, although the laser beam L1, which is mid-infrared light, is collimated by the lens 11, it has a longer wavelength than visible light and near-infrared light, so the beam diameter tends to expand as it propagates over long distances. . That is, as shown in FIG. 8, the laser beam L1 (returning light L2) that is finally reflected at the position P3 and directed toward the output light guide mirror 7 is smaller than the beam diameter b1 of the laser beam L1 that first enters the position P1. The beam diameter b2 becomes larger. Note that in the combination of the light source unit 2 (DFB-QCL operating in a single mode with a wavelength of 4.6 μm) and the lens 11 (collimating lens with a focal length of 1 mm) used in this embodiment, the Since the spread angle of the laser beam L1 (width at which the intensity is 1/e ² (width in the Fast direction described later)) is 0.28° on one side, the beam of the laser beam L1 after propagating 3.5 m The diameter b2 is approximately 25 mm.

When the beam diameter b2 becomes relatively large in this way, a part of the reflected light L2 traveling from the position P3 to the output light guide mirror 7 is blocked by the plane mirror 42, resulting in beam loss (the missing portion DE1 indicated by the broken line in FIG. 8). ) may occur. Furthermore, when the reflected light L2 is reflected by the mirror surface 42a of the plane mirror 42 before heading toward the position P3, a part of the reflected light L2 escapes to the outside of the mirror surface 42a, resulting in beam loss (broken line in FIG. 8). There is also a possibility that the defective portion DE2) shown in . As a result, there is a possibility that the beam shape B of the folded light L2 that is finally guided to the output light guiding mirror 7 will be in a state where both sides in the Y-axis direction are missing. That is, the width b of the reflected light L2 having the beam shape B in the Y-axis direction may be smaller than the beam diameter b2.

Here, in beam shape B, in order to secure an area of at least half of the reflected light L2 before the defect (width b is 1/2 or more of the beam diameter b2), the inclination angle α must be adjusted to It may be made larger than the divergence angle (in this embodiment, 0.28°). Further, as shown in FIG. 9, the beam range of the reflected light L2 returned to the output light guiding mirror 7 when viewed from the Z-axis direction is, when the distance d3 is sufficiently long, the front end 42g of the mirror surface 42a. from the portion La that is reflected by the mirror surface 41a to the portion Lb that passes near the front end 42g of the mirror surface 42a (that is, the portion that goes toward the output light guide mirror 7 without being blocked by the front end 42g). range. Here, if the position where the portion La is reflected by the front end 42g of the mirror surface 42a and then enters the mirror surface 41a is defined as the position P4, then the distance d6 along the Y-axis direction between the front end 42g and the position P4 is "d1× tan θ _H ”. Therefore, from the viewpoint of avoiding beam loss of the reflected light L2, it is preferable to set the distance d3 so that the following formula (4) holds true. Furthermore, from the viewpoint of reducing the size of the spectrometer 1A as much as possible (that is, reducing the size of the members (plane mirror 41) constituting the spectrometer 1A) while avoiding the beam loss of the reflected light L2, the following It is preferable to set the distance d3 so that equation (5) holds true.

d3≧d1×tanθ _H …(4)
d3=d1× _tanθH …(5)

Further, from the viewpoint of downsizing the spectrometer 1A, the distance d2 is preferably 300 mm or less. For the same reason, the length d5 (height) of the plane mirrors 41 and 42 in the Z direction is preferably 50 mm or less. Here, for example, if the distance d1 and the distance d2 are set to the same length, the optical path OP can be made to be a long optical path that is significant for gas measurement while realizing a round trip optical path OP that proceeds in the Y-axis direction while performing multiple reflections in a zigzag manner. In order to do so, it may be necessary to make the incident angle θ _H and the inclination angle α so small that they are difficult to control. Furthermore, the smaller the incident angle θ _H and the inclination angle α are, the greater the beam loss of the reflected light L2 (see FIG. 8) that occurs as the beam diameter of the laser light L1 increases. On the other hand, by reducing the ratio of the distance d1 to the distance d2 to a certain extent, the incident angle _θH is increased to a certain extent to reduce the beam loss of the reflected light L2, and the entire Y-axis direction (depth direction) of the mirror section 4 is reduced. It becomes easy to make effective use of this and lengthen the optical path OP. From the above viewpoint, it is preferable that the distance d1 is set to, for example, ⅓ or less of the distance d2. When the dimensions are set as described above, the volume of the space to be filled with the gas to be measured (i.e., the space between the plane mirrors 41 and 42) is at most 300 (distance d2) x 50 (length d5) x 100 (distance d1) mm ³ '' or less, making it possible to perform measurements using a small amount of sample gas. In this embodiment, the length d5 may be set to 30 mm or more, for example, from the viewpoint of avoiding beam loss of the reflected light L2 in the Z-axis direction.

Next, a method for manufacturing the spectrometer 1A will be described. As described above, the laser beam L1 emitted from the light source section 2 and collimated by the lens 11 enters the mirror section 4, forming an outgoing path OP1 and an incoming path OP2 that overlap in the Z-axis direction. Such an optical path OP is established only when the light is incident on the mirror surface 41a at a strictly incident angle _θH . In addition, the positional deviation of the optical path determined by the incident angle _θV (that is, the height position (position in the Z-axis direction) of the laser beam L1 incident on the incident adjustment mirror 6 and the height of the reflected light L2 incident on the output light guide mirror 7) When the distance h between the incident adjustment mirror 6 and the output light guiding mirror 7 in the Z-axis direction corresponds to the distance h in the Z-axis direction, the signal intensity (light detection intensity) at the photodetector 3 becomes maximum. Based on the above, first, each of the light source section 2, light detection section 3, mirror section 4, and output light guide mirror 7 is fixed. For example, each of the light source section 2, the light detection section 3, the mirror section 4, and the output light guide mirror 7 is positioned and fixed to the support member 8 at predesigned positions and orientations. Subsequently, while emitting the laser beam L1 from the light source section 2, the position and angle of the incident adjustment mirror 6 are adjusted and fixed so that the signal intensity at the photodetector section 3 is maximized. According to such a procedure, the light source section 2, the light detection section 3, the mirror section 4, and the output light guiding mirror 7 are positioned (fixed) in advance within a mechanical precision range, and then the signal intensity at the light detection section 3 is determined. Based on the relatively simple index of maximizing the angle, the angle of the incident adjustment mirror 6 can be precisely adjusted. The above method is particularly effective when the laser beam L1 emitted from the light source section 2 is invisible mid-infrared light as in this embodiment.

[Operations and effects of the first embodiment]
According to the spectrometer 1A described above, the configuration is such that the two plane mirrors 41 and 42 are arranged facing each other in a non-parallel manner (that is, the configuration is cheaper and simpler than the configuration of a conventional Herriot cell using a concave mirror, etc.). ), it is possible to realize a long optical path spectrometer 1A. Furthermore, by setting the optical path OP of the laser beam L1 between the plane mirrors 41 and 42 to be inclined with respect to the Z-axis direction, the outgoing path OP1 and the returning path OP2 of the laser beam L1 between the plane mirrors 41 and 42 are Since they can be spatially separated in the axial direction, spectroscopic measurements of the gas introduced between the plane mirrors 41 and 42 can be appropriately performed. More specifically, it is possible to prevent the outgoing light (outgoing path OP1) and the incoming path light (returning path OP2) from interfering between the plane mirrors 41 and 42, and also to prevent the laser beam L1 (returning light L2) that has been turned back by the mirror section 4. ) can be prevented from entering the light source section 2 again, and the reflected light L2 can be appropriately guided to the light detection section 3. Therefore, according to the spectrometer 1A, the device can be simplified (lower in price) and smaller.

In this way, according to the spectrometer 1A, it is possible to fold a long optical path into a small volume by multiple-reflecting light using a pair of plane mirrors disposed opposite to each other in a non-parallel manner. Thereby, it is possible to realize highly sensitive absorption spectroscopy using a long optical path for the gas to be measured introduced into the space sandwiched between the plane mirrors 41 and 42 while employing a compact configuration. Furthermore, since the plane mirrors 41 and 42 are cheaper than spherical (concave) mirrors used in general long-path gas cells, the price of the spectroscopic measurement module can be kept low.

Further, the optical path of the laser beam L1 that first enters the mirror surface 41a is inclined at an incident angle _θV with respect to the Z-axis direction. Further, the mirror surface 41a and the mirror surface 42a are parallel to the Z-axis direction. According to the above configuration, by tilting the optical path of the laser beam L1 that first enters the mirror surface 41a with respect to the Z-axis direction, the plane mirrors 41 and 42 are not tilted with respect to the Z-axis direction (i.e., To easily realize a configuration in which the optical path OP of the laser beam L1 between the plane mirrors 41 and 42 is inclined with respect to the Z-axis direction (by simply arranging the plane mirrors 41 and 42 perpendicularly on the support surface 8a). Can be done.

Furthermore, the incident angle θ _H of the laser beam L1 that first enters the mirror surface 41a when viewed from the Z-axis direction is the inclination angle of the mirror surface 42a with respect to the mirror surface 41a when viewed from the Z-axis direction. It is adjusted to be a natural number multiple of α. According to the above configuration, the optical path OP of the laser beam L1 between the plane mirrors 41 and 42 is adjusted so that the outgoing path OP1 and the return path OP2 of the laser beam L1 between the plane mirrors 41 and 42 overlap when viewed from the Z-axis direction. can be set. Thereby, the outgoing optical system (in this embodiment, the lens 11, the window member 13, the incident adjustment mirror 6, etc.) for guiding the laser beam L1 from the light source section 2 to the mirror section 4, and the It becomes possible to easily arrange the return path optical system (in this embodiment, the lens 12, the window member 14, the output light guide mirror 7, etc.) for guiding the light L2 to the light detection section 3.

Also, in the Y-axis direction from the position P1 where the laser beam L1 first enters the mirror surface 41a to the rear end 41h of the mirror surface 41a (that is, the end of the mirror surface 41a in the outgoing direction of the laser beam L1). The distance d2 (see FIG. 5) along the line is 300 mm or less. According to the above configuration, it is possible to further effectively downsize the device.

Further, the length d5 (see FIG. 7) of the mirror portion 4 (plane mirrors 41, 42) in the Z-axis direction is 50 mm or less. According to the above configuration, by keeping the height of the mirror part 4 below a certain level, it is possible to downsize the device and to suppress the amount of gas introduced (filled) between the flat mirrors 41 and 42 to below a certain level. Can be done. That is, by simply introducing a relatively small amount of gas between the plane mirrors 41 and 42, it is possible to perform spectroscopic measurement of the gas.

Further, the front end 41g of the mirror surface 41a projects further forward (in the Y-axis positive direction) than the front end 42g of the mirror surface 42a. As shown in FIG. 5, in this embodiment, the front end 41g of the mirror surface 41a is located ahead of the front end 42g of the mirror surface 42a by a distance d3. According to the above configuration, it is possible to easily make the laser beam L1 incident on the mirror surface 41a. Furthermore, when the beam diameter of the laser beam L1 expands through long optical path propagation due to multiple reflections between the plane mirrors 41 and 42, it is finally reflected at the mirror surface 41a (position P3) and guided to the photodetector 3 side. It is possible to prevent the emitted laser beam L1 (reflected light L2) from being blocked by the mirror surface 42a (that is, beam loss of the reflected light L2).

Further, the distance d3 along the Y-axis direction from the front end 42g of the mirror surface 42a to the front end 41g of the mirror surface 41a is the distance d1 between the mirror surface 41a and the front end 42g of the mirror surface 42a along the X-axis direction. is set to a value greater than or equal to the value obtained by multiplying by tan θ _H. That is, the distance d3 is set so as to satisfy the above-mentioned equation (4). According to the above configuration, as shown in FIG. 9, the return light that is reflected by the front end 42g of the mirror surface 42a and goes toward the mirror surface 41a passes outside (forward) of the front end 41g of the mirror surface 41a. It becomes possible to avoid beam loss due to storage.

Note that in this embodiment (see, for example, FIGS. 5, 6, and 9), the distance d3 is set longer than the value obtained by multiplying the distance d1 by _tanθH ; It may be set to match the value multiplied by _H. That is, the distance d3 may be set so as to satisfy the above-mentioned formula (5). In this case, the same effect as when satisfying the above formula (4) can be obtained, and the protrusion length (i.e., distance d3) of the plane mirror 41 (mirror surface 41a) with respect to the plane mirror 42 (mirror surface 42a) is By setting the length to be necessary and sufficient to avoid beam loss, it is possible to avoid beam loss and downsize the device at the same time.

Further, the inclination angle α of the mirror surface 42a with respect to the mirror surface 41a is set to be larger than the spread angle of the laser beam L1 passing between the mirror surface 41a and the mirror surface 42a when viewed from the Z-axis direction. ing. According to the above configuration, when the beam diameter of the laser beam L1 expands through long optical path propagation due to multiple reflections between the plane mirrors 41 and 42 (see FIG. 8), beam loss of the reflected light L2 is effectively suppressed. be able to. For example, as described above, in the beam shape B (see FIG. 8), ensure an area that is at least half or more of the reflected light L2 before the defect (that is, the width in the Y-axis direction of the reflected light L2 having the beam shape B). This makes it easy to make b more than half the beam diameter b2. However, in the beam shape B, it is not essential to ensure an area equal to or more than half of the reflected light L2 before the defect. For example, when it is possible to use the photodetector 3 with very high photodetection intensity, it is not necessary to secure an area of half or more of the folded light L2 before the defect in the beam shape B.

In the above embodiment (FIG. 8), it is assumed that the beam diameter of the laser beam L1 is circular, but in reality, the laser beam L1 emitted from the light source section 2, which is a quantum cascade laser element, has a beam spread. It has anisotropy of More specifically, as shown in FIG. 3, the spread angle (radiation angle) of the laser beam L1 along the direction DF (Fast direction) along the stacking direction D2 of the active layer is larger than that in the stacking direction D2. It is larger than the radiation angle of the laser beam L1 along the orthogonal direction DS (Slow direction). The divergence angle assumed in the above embodiment (0.28° on one side) is the divergence angle along the direction DF. In this way, by making the inclination angle α larger than the larger divergence angle (the divergence angle along the direction DF), beam loss can be suppressed or avoided more reliably. In addition, in order to suppress beam loss in the Y-axis direction as shown in FIG. , the position and angle of the incident adjustment mirror 6 may be set.

Furthermore, the light source section 2 and the light detection section 3 are arranged so as to overlap each other in the Z-axis direction. By tilting the optical path OP of the laser beam L1 between the plane mirrors 41 and 42 with respect to the Z-axis direction, the optical path of the laser beam L1 guided from the light source section 2 to the mirror section 4 and the light detection from the mirror section 4 are realized. The optical path of the folded light L2 guided to the section 3 can be separated in the Z-axis direction. By utilizing this and arranging the light source section 2 and the light detection section 3 side by side in the Z-axis direction, the light source section 2 and the light detection section 3 can be arranged in the X-axis direction or the Y-axis direction without overlapping in the Z-axis direction. Compared to the case where the light source section 2 and the light detection section 3 are arranged in a staggered manner, the area required for the arrangement of the light source section 2 and the light detection section 3 (the area when viewed from the Z-axis direction) can be made smaller. As a result, the device can be more effectively miniaturized.

Further, the distance between the lens 11 and the light source section 2 (quantum cascade laser element) (the distance between the light exit surface 2a and the entrance surface 11a) is the shortest distance between the mirror surface 41a and the mirror surface 42a in the X-axis direction (the rear end (distance between the portion 41h and the rear end portion 42h). According to the above configuration, the spread of the laser beam L1 emitted from the light source section 2 can be effectively suppressed by the lens 12. That is, the beam diameter of the laser light L1 can be made sufficiently small. As a result, it is possible to suppress the spread of the beam diameter of the laser light L1 between the plane mirrors 41 and 42, and it is possible to reduce the beam loss of the reflected light L2 due to the spread of the beam diameter.

Further, the spectrometer 1A includes an entrance adjustment mirror 6 and an output light guide mirror 7, and the entrance adjustment mirror 6 and the output light guide mirror 7 are arranged so as to overlap each other in the Z-axis direction. According to the above configuration, by using the incident adjustment mirror 6 and the output light guide mirror 7, the degree of freedom in arrangement (layout) of the light source section 2 and the light detection section 3 with respect to the mirror section 4 can be improved. For example, as in this embodiment, the housing 10 that houses the light source section 2 and the light detection section 3 can be compactly arranged on the side of the mirror section 4. Furthermore, by arranging the entrance adjustment mirror 6 and the output light guide mirror 7 side by side in the Z-axis direction, compared to the case where the entrance adjustment mirror 6 and the output light guide mirror 7 are arranged without overlapping in the Z-axis direction, The area required for arranging the entrance adjustment mirror 6 and the output light guide mirror 7 (the area when viewed from the Z-axis direction) can be reduced, and the device can also be made smaller.

[Second embodiment]
With reference to FIG. 10, a spectrometer 1B according to the second embodiment will be described. The spectrometer 1B includes a combination (system) of a plurality (for example, two) of light sources (light source section 2) and photodetectors (photodetection section 3), and includes a combination (system) of a plurality of (for example, two) light sources (light source section 2) and photodetectors (photodetection section 3), and is installed between plane mirrors 41 and 42. This device is mainly different from the spectrometer 1A in that it is configured to be able to simultaneously perform gas spectrometry measurements in multiple systems. The configuration of the second embodiment can be easily realized by employing a plane mirror pair (mirror section 4) as a configuration for realizing a long optical path.

In the example of FIG. 10, the light source unit 2 includes a light source unit 2A (first light source unit) that emits a laser beam L1A of a first wavelength (for example, an oscillation wavelength of 4.6 μm), and a second wavelength that is different from the first wavelength. (For example, a light source section 2B (second light source section) that emits a laser beam L1B with an oscillation wavelength of 7.4 μm). The photodetector 3 also includes a photodetector 3A (first photodetector) that detects the first wavelength laser beam L1A (returning light L2A) that is multiple-reflected and returned between the mirror surfaces 41a and 42a; It has a light detection section 3B (second light detection section) that detects the second wavelength laser light L1B (reflected light L2B) that is multiple-reflected and returned between the mirror surfaces 41a and 42a. The light source section 2A, the light source section 2B, the light detection section 3A, and the light detection section 3B are arranged so as to overlap each other in the Z-axis direction.

As in the first embodiment, each light source section 2A, 2B may be configured by a quantum cascade laser element (DFB-QCL). Further, each of the photodetectors 3A and 3B may be configured by a quantum cascade photodetector having characteristics (for example, sensitivity wavelength) corresponding to each of the light sources 2A and 2B.

In the spectrometer 1B, the optical path of the first system corresponding to the combination of the light source section 2A and the photodetector section 3A (i.e., from the light source section 2A, passes through the incident adjustment mirror 6, enters the mirror section 4, and is reflected by the mirror section 4). and a second system optical path corresponding to the combination of the light source section 2B and the light detection section 3B (that is, an optical path where the light is guided from the light source section 2B to the light detection section 3A). An optical path in which the light enters the mirror unit 4 via the adjustment mirror 6, is turned back by the mirror unit 4, and is guided to the light detection unit 3B via the output light guide mirror 7) is formed at the same time.

The spectrometer 1B also includes a lens 11A corresponding to the light source section 2A, a lens 11B corresponding to the light source section 2B, a lens 12A corresponding to the photodetector section 3A, and a lens 12B corresponding to the photodetector section 3B. Contains. Each lens is arranged in front of its corresponding member.

The optical axis of the light source section 2A (the axis passing through the center of the light output surface 2a of the light source section 2A) and the optical axis of the light detection section 3A (the axis passing through the center of the light detection surface 3a of the light detection section 3A) are the Z-axis. are spaced apart by a distance h in the direction. Similarly, the optical axis of the light source section 2B (the axis passing through the center of the light output surface 2b of the light source section 2B) and the optical axis of the light detection section 3B (the axis passing through the center of the light detection surface 3b of the light detection section 3B) are , are separated by a distance h in the Z-axis direction. The light source section 2B is arranged between the light source section 2A and the photodetector section 3A. The photodetector 3A is arranged between the light source 2B and the photodetector 3B. The optical axis of the light source section 2B and the optical axis of the photodetector section 3A are separated by a distance h1 in the Z-axis direction. Therefore, in the spectrometer 1B, the distance between the light source section (light source section 2A) located at the top and the light detection section (photodetection section 3B) located at the bottom is the distance h in the spectrometer 1A. It is longer by ``h−h1'' than ``h−h1''.

The mirror section 4, the incident adjustment mirror 6, and the output light guide mirror 7 in the second embodiment can be used in common for the above two systems. That is, the mirror unit 4, the incident adjustment mirror 6, and the output light guiding mirror 7 do not need to be provided individually for each system. Therefore, the configurations of the mirror section 4, the incident adjustment mirror 6, and the output light guide mirror 7 in the second embodiment are the same as those in the first embodiment. However, in the second embodiment, it is necessary to form two systems of optical paths whose positions are shifted from each other in the Z-axis direction. The dimensions need to be larger than those of the first embodiment. For example, since the deviation width of the optical path in the Z-axis direction has increased by "hh1" compared to the first embodiment, the length d5 of the mirror section 4 has been increased by "hh1" compared to the first embodiment. Just make it bigger. Furthermore, the incident adjustment mirror 6 and the output light guide mirror 7 may also have a shape and size that can reflect the two systems of optical paths simultaneously.

By configuring the mirror unit 4, the incident adjustment mirror 6, and the output light guiding mirror 7 as described above, the optical path of the first system and the optical path of the second system are only shifted in the Z-axis direction, and the Z They match perfectly when viewed from the axial direction, and the total optical path length of each optical path also matches.

According to the spectrometer 1B, by arranging the light source section 2A, the light source section 2B, the light detection section 3A, and the light detection section 3B so as to overlap each other in the Z-axis direction, the light sources and detectors of two systems can be made compact. can be placed in Furthermore, by varying the wavelength bands between the systems, absorption spectroscopic measurements of two different wavelength bands can be performed simultaneously. In this embodiment, absorption spectroscopic measurements of, for example, CO, N ₂ O, etc. can be suitably performed using the optical path of the first system (wavelength: 4.6 μm). Furthermore, absorption spectroscopic measurements of, for example, CH ₄ etc. can be suitably performed using the optical path of the second system (wavelength 7.4 μm).

In this way, a configuration in which absorption spectroscopic measurements of a plurality of systems can be performed simultaneously can be easily realized by using the plane mirrors 41 and 42 that are disposed non-parallel to each other and facing each other. On the other hand, methods such as Herriot cell using a concave mirror and cavity ring-down spectroscopy require complicated optical systems. It is not easy to achieve this.

In addition, if the sensitivity wavelengths overlap between the two systems, by arranging the light sources 2A, 2B and the photodetectors 3A, 3B so that the above-mentioned polarization directions are orthogonal between the two systems. , measurements in each system may be prevented from influencing each other. Furthermore, an optical filter may be placed in the optical path of each system to pass only the wavelength range to be measured. Furthermore, the order in which the plurality of systems of light source units 2 and light detection units 3 are arranged in the Z-axis direction and the intervals between each member are not limited to the form shown in FIG. 10. Moreover, the spectrometer 1B may have a combination of three or more light source sections 2 and light detection sections 3.

[Third embodiment]
A spectrometer 1C according to the third embodiment will be described with reference to FIGS. 11 and 12. The spectrometer 1C is similar to the second embodiment in that it includes a combination of multiple systems (two systems as an example) of light sources (light source units 2A, 2B) and photodetectors (photodetectors 3A, 3B). However, the light source sections 2A and 2B are arranged side by side in the X-axis direction instead of the Z-axis direction, and the light detection sections 3A and 3B are arranged side-by-side in the X-axis direction instead of the Z-axis direction. This embodiment is different from the second embodiment in that one lens 11C is commonly used for the light source sections 2A and 2B, and one lens 12C is commonly used for the light detection sections 3A and 3B. In addition, in the spectrometer 1C, the light exit surface 2a of the light source section 2A and the light exit surface 2b of the light source section 2B are shifted not in the Z-axis direction but in the X-axis direction, so the optical path of each system is They do not match when viewed from above.

That is, in the spectrometer 1C, the light source part 2A and the light source part 2B are arranged side by side in the X-axis direction, and the light detection part 3A and the light detection part 3B are arranged in line in the X-axis direction. There is. Furthermore, the combinations of the first system (light source section 2A and photodetector section 3A) are arranged so as to overlap each other in the Z-axis direction, and the combination of the second system (light source section 2B and photodetector section 3B) is arranged so as to overlap with each other in the Z-axis direction. They are arranged so as to overlap each other in the axial direction.

As an example, one light source section 2A is arranged so that the optical path passing through the center of the lens 11C and the optical axis of the light source section 2A (the center of the light exit surface 2a) match. Further, the other light source section 2B is arranged parallel to the light source section 2A at a position slightly shifted from the light source section 2A in the X-axis direction at the same height position as the light source section 2A. The light emitting points of the light sources 2A and 2B (the centers of the light exit surfaces 2a and 2b) are arranged on the focal plane of the lens 11C. The separation width in the X-axis direction between the optical axis of the light source section 2A and the optical axis of the light source section 2B is set to, for example, about 0.5 mm. The photodetectors 3A and 3B are also arranged so that the positional relationship between the photodetectors 3A and 3B when viewed from the Z-axis direction is the same as the positional relationship between the light source units 2A and 2B when viewed from the Z-axis direction. be done.

As shown in FIG. 11, a lens having a longer focal length and a larger lens diameter than the lens 11 of the first embodiment is used as the lens 11C. For example, the focal length of the lens 11C is 5 mm, and the lens diameter (diameter) of the lens 11C is 15 mm. Further, as shown in FIG. 12, the lens 12C is also a lens having a longer focal length and a larger lens diameter than the lens 12 of the first embodiment, similarly to the lens 11C. For example, the focal length of the lens 12C is 5 mm, and the lens diameter of the lens 12C is 15 mm.

As shown in FIGS. 11 and 12, in the first system, the laser beam L1A that is emitted from the light output surface 2a of the light source section 2A and collimated by the lens 11C is reflected by the incident adjustment mirror 6, and then reflected in the Z-axis direction. When viewed from above, the light enters the mirror surface 41a of the plane mirror 41 at a position P1A at an incident angle θ1, and travels backward (Y-axis negative direction) while undergoing multiple reflections between the mirror surfaces 41a and 42a. Further, the laser beam L1A (reflected light L2A) that is reflected by the mirror portion 4 and proceeds forward (in the Y-axis positive direction) is finally reflected at the position P3A of the mirror surface 41a, and is reflected by the output light guide mirror 7 and the lens 12C. The light reaches the photodetection surface 3a of the photodetection section 3A via the photodetection section 3A.

On the other hand, in the second system, the laser beam L1B that is emitted from the light output surface 2b of the light source section 2B and collimated by the lens 11C is reflected by the incident adjustment mirror 6, and then has an incident angle θ1 when viewed from the Z-axis direction. is incident on the mirror surface 41a of the plane mirror 41 at a position P1B at a different incident angle θ2, and propagates backward (in the Y-axis negative direction) while undergoing multiple reflections between the mirror surfaces 41a and 42a. Further, the laser beam L1B (reflected light L2B) that is reflected by the mirror portion 4 and proceeds forward (in the Y-axis positive direction) is finally reflected at the position P3B of the mirror surface 41a, and is reflected by the output light guide mirror 7 and the lens 12C. The light reaches the light detection surface 3b of the light detection section 3B via the light detection section 3B.

Laser light emitted from a light source placed on the focal plane of the lens 11C toward the entrance surface 11a of the lens 11C is collimated and propagated in a direction passing through the center of the lens 11C. Therefore, as shown in FIG. 11, when viewed from the Z-axis direction, the optical path of the laser beam L1B emitted from the light source section 2B is different from the optical path of the laser beam L1A emitted from the light source section 2A. It is inclined by "tan ^-1 (0.5 mm/5 mm) = 5.7°". Therefore, the incident angle θ1 of the first system is smaller than the incident angle θ2 of the second system by 5.7°. For example, as in the first embodiment, consider a case where the distance d1 is 55 mm, the distance d2 (see FIG. 5) is 150 mm, and the inclination angle α is 0.3°. Further, consider a case where the incident angle θ2 is adjusted so that, for example, the optical path of the second system of laser light L1B becomes the longest (that is, so that formula (3) in the first embodiment is satisfied). In this case, the incident angle θ2 is determined to be 9.6°, similar to _θH in the first embodiment, and the incident angle θ1 is 3.9°. Here, the incident angles θ1 and θ2 are both natural number times the inclination angle α. Therefore, the forward path (laser light L1A shown in FIG. 11) and the backward path (return light L2A shown in FIG. 12) of the first system match when viewed from the Z-axis direction. Similarly, the outward path (laser light L1B shown in FIG. 11) and the return path (return light L2B shown in FIG. 12) of the second system coincide when viewed from the Z-axis direction.

According to the spectrometer 1C, the light source section 2A and the light detection section 3A are arranged in an overlapping manner in the Z-axis direction, and the light source section 2B and the light detection section 3B are arranged in an overlapping manner in the Z-axis direction. Two systems of light source units and light detection units can be arranged compactly. Furthermore, similarly to the second embodiment, by making the wavelength bands different between the systems, absorption spectroscopic measurements of two different wavelength bands can be performed simultaneously. In addition, one lens 11C can be shared by multiple light source units 2A, 2B, and one lens 12C can be shared by multiple photodetectors 3A, 3B, making it possible to simultaneously measure multiple systems. At the same time, the device can be made smaller.

Note that the optical path lengths of the laser beams L1A and L1B between the plane mirrors 41 and 42 depend on the incident angles θ1 and θ2, respectively. In the above example, the optical path lengths of the laser beams L1A and L1B between the plane mirrors 41 and 42 are 1.4 m and 3.5 m, respectively. For example, when performing absorption spectroscopic measurements on gases in multiple wavelength bands using the spectrometer 1C, the optical path of the system with the oscillation wavelength corresponding to the gas with a large absorption coefficient is changed to the optical path with the shorter optical path length. , and the optical path of a system having an oscillation wavelength corresponding to a gas with a small absorption coefficient may be set to the optical path with a longer optical path length. According to the above configuration, the optical path length of each system can be appropriately adjusted according to the absorption coefficient of the gas to be measured. In addition, the spectrometer 1C uses a lens 11C with a longer focal length than the spectrometer 1A, but by using the lens 11C with a longer focal length in this way, beam spread during long-distance propagation is suppressed. Therefore, beam loss caused by beam expansion as shown in FIG. 8 can be suppressed.

Further, the front end portion 42g of the plane mirror 42 may be set to be located between the position P1A and the position P1B of the plane mirror 41 in the Y-axis direction. Thereby, it is possible to avoid an extremely large beam loss of the laser light on one optical path. Further, the distance between the front end portion 41g of the plane mirror 41 and the position P1A may be set to be greater than or equal to the distance along the Y-axis direction between the position P5 and the position P1A, where the laser beam L1A is first reflected on the mirror surface 42a. . Further, the spectrometer 1C may have a combination of three or more light source sections 2 and light detection sections 3, similarly to the spectrometer 1B.

[Fourth embodiment]
A spectrometer 1D according to the fourth embodiment will be described with reference to FIG. 13. The spectrometer 1D differs from the spectrometer 1A in that it includes a casing 51 that airtightly houses the mirror section 4. The other configuration of the spectrometer 1D is the same as that of the spectrometer 1A. FIG. 13 illustrates only the housing 51 in which the mirror section 4 is housed in the spectrometer 1D. In the example of FIG. 13, the casing 51 has a side wall (portion shown by hatching in FIG. 13) that stands upright on the support surface 8a of the support member 8 (see FIG. 1) so as to surround the mirror part 4. and a ceiling wall (not shown) provided so as to close the upper end of the side wall. In other words, the housing 51 hermetically surrounds only the mirror portion 4 on the support surface 8a.

In the spectrometer 1D, a housing 10 in which the light source section 2 and the light detection section 3 are housed is arranged on the side of the housing 51. That is, the light source section 2 and the light detection section 3 are arranged outside the housing 51. In this embodiment, a housing 10 that accommodates the light source section 2 and the light detection section 3, the entrance adjustment mirror 6, and the output light guiding mirror 7 are arranged outside the housing 51 in the same manner as in the spectrometer 1A. has been done.

A gas introduction port 51b (opening) for introducing the gas to be measured from the outside of the housing 51 to the inside of the housing 51 is provided in the side wall of the housing 51. Further, a gas exhaust port 51c for exhausting the gas filled inside the housing 51 to the outside of the housing 51 is also provided on the side wall of the housing 51. The position, shape, and size of the gas inlet 51b and the gas exhaust port 51c are not particularly limited. The gas inlet 51b and the gas exhaust port 51c have the functions of maintaining the pressure inside the casing 51 and replacing the gas inside the casing 51. As shown in FIG. 13, in order to realize efficient gas replacement, the gas inlet 51b and the gas exhaust port 51c are spaced sufficiently apart from each other in the longitudinal direction (Y-axis direction) of the housing 51. In addition, it is preferable that they be arranged at positions close to both ends of the housing 51 in the longitudinal direction.

Further, a portion of the side wall of the housing 51 that is not blocked by the plane mirror 42 and faces the position P1 of the mirror surface 41a is provided with a laser beam guided from the incidence adjustment mirror 6 to the mirror surface 41a (position P1). A light transmitting window 52 that transmits L1 is provided. The light transmission window 52 may be formed of, for example, CaF2, ZnSe, or the like. Further, the inner surface (the surface facing the inside of the casing 51) and the outer surface (the surface facing the outside of the casing 51) of the light transmission window 52 are coated with a low reflection coating similar to the window members 13 and 14 of the first embodiment. may be applied. Alternatively, the low reflection coating may be omitted by adjusting the incident angle of the laser beam L1 to the light transmission window 52 to be the Brewster angle. Similarly, a portion of the side wall of the casing 51 that is not obstructed by the plane mirror 42 and faces position P3 of the mirror surface 41a (see FIG. 1, etc.) has a portion that is reflected by the mirror surface 41a (position P3) and guided out. A light transmission window (not shown) is also provided to transmit the reflected light L2 toward the light mirror 7. The configuration of the light transmission window for transmitting the reflected light L2 is similar to the configuration of the light transmission window 52 described above.

According to the spectrometer 1D, by providing the casing 51 that airtightly houses only the mirror section 4, the interior of the casing 51 is depressurized, and then gas is introduced from the gas inlet 51b to improve precision. This makes it possible to perform accurate measurements. More specifically, by reducing the pressure inside the housing 51, the absorption line of the gas introduced into the housing 51 becomes narrower, making it possible to perform measurements while avoiding the influence of interfering gases. . Further, by airtightly accommodating only the mirror section 4 in the housing 51, it becomes easy to apply highly accurate measurement methods such as phase sensitive detection.

[Fifth embodiment]
A spectrometer 1E according to the fifth embodiment will be described with reference to FIGS. 14 and 15. The spectrometer 1E is different from the spectrometer 1A in that it includes a casing 61 that accommodates a light source section 2, a light detection section 3, and a mirror section 4. In this embodiment, the casing 61 of the spectrometer 1E includes a support member 8 (see FIG. 1) as a bottom wall of the casing 61, and a side wall 62 erected at the peripheral edge of the support surface 8a of the support member 8. and a ceiling wall 63 that closes the upper end of the side wall 62, forming a rectangular parallelepiped shape. The configurations of the casing 10 (light source section 2 and light detection section 3), mirror section 4, entrance adjustment mirror 6, and output light guiding mirror 7 arranged inside the casing 61 are the same as those of the spectrometer 1A. .

The housing 61 may be formed of a material that can protect the internal structure and maintain its shape, such as metal or plastic. In this embodiment, the bottom wall of the casing 61 also serves as a base member (support member 8) that supports each component, but the support member 8 is configured as a separate member from the bottom wall of the casing 61. It's okay. In that case, the support member 8 may be fixed on the bottom wall of the housing 61, for example.

The housing 61 is provided with vents 61 a and 61 b (openings) for introducing gas to be measured from the outside of the housing 61 to the inside of the housing 61 . In this embodiment, as an example, two ventilation holes 61a and 61b are provided in each of the wall portions of the side wall 62 that face each other (wall portions that face each other in the Y-axis direction in this embodiment). However, the number, position, size, and shape of the vents provided in the housing 61 are not limited to the above example. The number, position, size, and shape of the vents can be arbitrarily designed as long as the strength of the housing 61 is not significantly impaired. For example, one vent hole may be provided in the ceiling wall 63. Further, it is preferable that the portions of the housing 61 other than the vents 61a and 61b have airtightness. Further, the casing 61 may include an exhaust or intake fan for replacing the gas inside the casing 61. Further, the ventilation holes 61a and 61b may be provided with dust filters to prevent dust and the like from entering the housing 61 from outside.

According to the spectrometer 1E, by housing the light source section 2, the light detection section 3, and the mirror section 4 in one housing 61, each member constituting the spectrometer 1E can be protected from external contamination and mechanical damage. can be properly protected from physical impact, etc.

[Sixth embodiment]
With reference to FIG. 16, a spectrometer 1F according to the sixth embodiment will be described. The spectrometer 1F is different from the spectrometer 1A in that it includes a light source section 2F instead of the light source section 2, and a diffraction grating 6F instead of the incident adjustment mirror 6.

The light source section 2F is configured to be able to emit laser light L _on having a wavelength λ _on (first wavelength) and laser light L _off having a wavelength λ _off (second wavelength) different from the wavelength λ _on . The degree to which the laser beam L _on is absorbed by the gas to be measured introduced between the plane mirrors 41 and 42 is higher than the degree to which the laser beam L _off is absorbed by the gas. For example, the wavelength λ _on is a wavelength that is absorbed by the gas to be measured (e.g., a wavelength corresponding to the absorption band of the gas), and the wavelength λ _off is the wavelength at which the absorption by the gas to be measured is lower than the wavelength λ _on . A small wavelength (eg, a wavelength outside the absorption band of the gas). The light source section 2F may be configured by, for example, a distributed feedback quantum cascade laser device (DFB-QCL) similar to the light source section 2. The light source section 2F is configured to be capable of wavelength sweeping in a wavelength range including at least the wavelength λ _on and the wavelength λ _off by changing the amount of current injected into the light source section 2F. In this way, in this embodiment, the light source unit 2F distinguishes between laser light L _on and laser light L _off based on the light emitted from a single quantum cascade laser element (DFB-QCL in this embodiment). It is configured so that it can be emitted by switching. That is, the spectrometer 1F does not require a plurality of laser elements as a light source, and by controlling the wavelength of light emitted from a single laser element (in this embodiment, the light source section 2F), the spectrometer 1F can generate laser light L _on A configuration is realized in which the laser beam is emitted by switching between the laser beam and the laser beam L _off .

The diffraction grating 6F is a reflection type diffraction grating. The incident surface of the laser beams L _on and L _off in the diffraction grating 6F is a diffraction grating surface on which a grating structure such as a blazed grating is formed, for example. The traveling direction of the laser beam reflected by the diffraction grating 6F and directed toward the plane mirror 41 (that is, the incident angle θ _H with respect to the mirror surface 41a of the plane mirror 41) changes depending on the wavelength of the laser beam incident on the diffraction grating 6F. For example, when wavelength sweeping is performed between the wavelength λ _on and the wavelength λ _off , the incident angle θ _H is the incident angle θ _{on of the laser beam L on with} the wavelength λ _on and the laser beam L _off with the wavelength λ _off . The incident angle θ _off changes continuously between Here, the incident angle θ _on and the incident angle θ _off are set to satisfy the condition of being a natural number multiple of the inclination angle α, and other angles (i.e., between the incident angle θ _on and the incident angle θ _off angle) is preferably set so as not to satisfy the above conditions. According to such a configuration, when the wavelength is swept between the wavelength λ _on and the wavelength λ _off and the reflected light L2 is detected by the photodetector 3, the wavelength λ _on and the wavelength λ _off are respectively corresponded to. It becomes possible to easily observe the detection results. More specifically, since signals corresponding to laser beams with wavelengths other than the wavelength λ _on and the wavelength λ _off are not detected by the photodetector 3 (even if detected, they are few), the wavelength λ _on and the wavelength λ _off Two peak values corresponding to can be observed. As a result, analysis based on the difference between two peak values (differential absorption spectroscopy described below) can be easily performed.

According to the spectrometer 1F, it is possible to measure gas concentration by differential absorption spectroscopy (for example, differential absorption lidar (DIAL), etc.). For example, as described above, by performing a wavelength sweep between the wavelength λ _on and the wavelength λ _off , the laser beam L _on and the laser beam L _off are alternately switched and emitted, and each signal (detected by the photodetector 3 By analyzing the difference (that is, the difference between the absorption amount for the wavelength λ _on and the absorption amount for the wavelength λ _off ), the gas molecules to be measured introduced between the plane mirrors 41 and 42 are analyzed. It becomes possible to measure the concentration distribution with high accuracy. In other words, by calibrating the measured value corresponding to the wavelength λ _on using the measured value corresponding to the wavelength λ _off as a reference value, it is possible to eliminate fluctuations (noise) derived from the environment, and the concentration distribution of gas molecules can be corrected. can be performed with high precision. Examples of the above noise include blurring of the light source section 2F, dirt on the surfaces of the plane mirrors 41 and 42 (mirror surfaces 41a and 42a), misalignment of the optical path from the light source section 2F to the light detection section 3, and Examples include the influence of absorption by gases other than gas. In other words, since the measurement value corresponding to the wavelength λ _on can be calibrated with the measurement value corresponding to the wavelength λ _off at any time, it is possible to cancel noise due to the influence of the atmosphere in the measurement environment and achieve highly accurate measurement. It can be carried out. Further, by using a diffraction grating 6F with a fixed angle as the diffraction grating instead of a movable member like a movable diffraction grating 6H of a spectrometer 1H described later, a stable configuration with high mechanical strength can be realized.

Furthermore, since the sweep width of DFB-QCL is relatively narrow, the wavelength λ _on and the wavelength λ _off have relatively close values. Therefore, the difference between the incident angle θ _on and the incident angle θ _off becomes relatively small, and the deviation (difference) between the optical path length of the laser beam L _on and the optical path length of the laser beam L _off between the plane mirrors 41 and 42 also becomes relatively small. Becomes relatively small. Therefore, by performing wavelength sweeping between the wavelength λ _on and the wavelength λ _off using the DFB-QCL as the light source section 2F, it becomes possible to perform the measurement by the differential absorption spectroscopy described above with high precision.

[Seventh embodiment]
With reference to FIG. 17, a spectrometer 1G according to the sixth embodiment will be described. The spectrometer 1G differs from the spectrometer 1A in that it includes a light source section 20G composed of a single quantum cascade laser element 2G (hereinafter referred to as "QCL element 2G") and a diffraction grating 21. There is. Similarly to the spectrometer 1F, the spectrometer 1G does not require multiple laser elements as a light source and can control the wavelength of light emitted from a single laser element (QCL element 2G in this embodiment). This realizes a configuration in which laser light L _on and laser light L _off are switched and emitted.

The light source section 20G, like the light source section 2F, is configured to be able to emit laser light L _on having a wavelength λ _on and laser light L _off having a wavelength λ _off . The above-mentioned spectrometer 1F has a configuration in which the laser beam L _on and L _off can be switched by providing a DFB-QCL capable of wavelength sweeping with a single QCL element as the light source section 2F. On the other hand, the spectrometer 1G is equipped with an external cavity quantum cascade laser (EC-QCL) composed of a QCL element 2G and a diffraction grating 21 as a light source section 20G. A configuration is realized in which the light L _on and L _off can be switched.

The QCL element 2G has an end surface 2Ga facing the incidence adjustment mirror 6, and an end surface 2Gb on the opposite side to the end surface 2Ga. Moreover, the diffraction grating 21 is housed in the housing 10 together with the QCL element 2G, and is disposed at a position facing the end surface 2Gb. The diffraction grating 21 is a reflective diffraction grating similar to the diffraction grating 6F. That is, the surface of the diffraction grating 21 facing the end surface 2Gb is a diffraction grating surface on which a grating structure such as a blazed grating is formed, for example.

The light emitted from the end face 2Gb enters the diffraction grating 21, is diffracted and reflected, and returns to the end face 2Gb. Thereby, a Littrow-type external resonator is configured between the end face 2Ga of the QCL element 2G and the diffraction grating 21. By changing the angle (inclination) of the diffraction grating 21 with respect to the QCL element 2G, the wavelength of the light that returns from the diffraction grating 21 to the QCL element 2G can be changed. Thereby, the wavelength of the output light (that is, the light amplified by resonance) emitted from the end face 2Ga to the incidence adjustment mirror 6 can be changed.

According to the spectrometer 1G, the same effects as the above-mentioned spectrometer 1F are achieved. Furthermore, in the spectrometer 1G, the incidence adjustment mirror 6 is used instead of the diffraction grating 6F. Therefore, in the spectrometer 1G, there is no difference in optical path length between the laser beams L _on and L _off . That is, since the laser beams L _on and L _off enter the incident adjustment mirror 6 in the same direction and are reflected at the same angle, the incident angle θ _on of the laser beam L _on is equal to the incident angle θ off _of the laser beam L _off . matches. Therefore, in the spectrometer 1G, the optical path length of the laser beam L _on between the plane mirrors 41 and 42 matches the optical path length of the laser beam L _off . Therefore, according to the spectrometer 1G, it is possible to carry out the measurement by the differential absorption spectroscopy described above with higher precision than when using the diffraction grating 6F like the spectrometer 1F.

In addition, in the spectrometer 1F, the incidence adjustment mirror 6 may be used instead of the diffraction grating 6F. Furthermore, in the spectrometer 1G, a diffraction grating 6F may be used instead of the incidence adjustment mirror 6. As described above, when the diffraction grating 6F is used, by adjusting only the incident angles θ _on and θ _off to be a natural number multiple of the inclination angle α, the wavelengths λ _on and λ _off can be adjusted. The advantage is that the results (two peak values) can be observed. On the other hand, when the incidence adjustment mirror 6 is used, the optical path lengths of the laser beams L _on and L _off can be matched, so there is an advantage that measurement by differential absorption spectroscopy can be carried out with higher precision. can get. More specifically, when the incidence adjustment mirror 6 is used in the spectrometer 1F that uses a DFB-QCL that continuously sweeps the wavelength as a light source, light with wavelengths other than the two target wavelengths λ _on and λ _off However, by using the diffraction grating 6F, such a disadvantage can be avoided and only two peak values can be observed. On the other hand, in the spectrometer 1G using EC-QCL as a light source, since the two wavelengths λ _on and λ _off can be appropriately selected on the light source (EC-QCL) side, the incidence adjustment mirror 6 There is no disadvantage (that is, light having wavelengths other than the two target wavelengths λ _on and λ _off will also be detected by the photodetector 3) when using this method. That is, according to the spectrometer 1G, by using EC-QCL, the above-mentioned disadvantages caused by using the incident adjustment mirror 6 can be avoided, and the above-mentioned advantages (i.e., the optical path lengths of the laser beams L _on and L _off can be matched) (Improvement of measurement accuracy) can be obtained by

[Eighth embodiment]
With reference to FIG. 18, a spectrometer 1H according to the eighth embodiment will be described. The spectrometer 1H differs from the spectrometer 1A in that it includes a light source section 20H composed of a single quantum cascade laser element 2H (hereinafter referred to as "QCL element 2H") and a movable diffraction grating 6H. ing. The movable diffraction grating 6H constitutes an external resonator with the QCL element 2H, and also plays the role of guiding the laser beam emitted from the QCL element 2H to the mirror surface 41a of the plane mirror 41 (that is, the role of the incident adjustment mirror 6). have. That is, the spectrometer 1H is different from the spectrometer 1A in that it includes a movable diffraction grating 6H instead of the incident adjustment mirror 6.

The light source section 20H, like the light source section 2F, is configured to be able to emit laser light L _on having a wavelength λ _on and laser light L _off having a wavelength λ _off . Similar to the spectrometer 1G, the spectrometer 1H includes an external cavity quantum cascade laser (EC-QCL) constituted by a QCL element 2H and a movable diffraction grating 6H as a light source 20H. As a result, a configuration in which the laser beams L _on and L _off can be switched is realized. However, whereas the spectrometer 1G includes a diffraction grating 21 separate from the incident adjustment mirror 6 in the housing 10, the spectrometer 1H has a movable diffraction grating that also serves as the input adjustment mirror 6. 6H is provided outside the housing 10 (that is, at a position corresponding to the incident adjustment mirror 6).

The QCL element 2H has an end surface 2Ha facing the movable diffraction grating 6H, and an end surface 2Hb opposite to the end surface 2Ha. Moreover, the movable diffraction grating 6H is arranged at a position facing the end surface 2Ha (that is, a position corresponding to the incidence adjustment mirror 6 in the spectrometer 1A). The movable diffraction grating 6H is a reflection type diffraction grating similar to the diffraction grating 21, but by rotating around the Z axis, the surface of the movable diffraction grating 6H (diffraction grating surface) of the laser beam emitted from the end face 2Ha is ) is different from the diffraction grating 21 in that the angle of incidence relative to the grating 21 is configured to be variable.

The light emitted from the end surface 2Ha enters the movable diffraction grating 6H, is diffracted and reflected, and returns to the end surface 2Ha. Thereby, a Littrow-type external resonator is configured between the end surface 2Hb of the QCL element 2H and the movable diffraction grating 6H. As described above, by changing the angle (inclination) of the movable diffraction grating 6H with respect to the QCL element 2H, the wavelength of the light that returns from the movable diffraction grating 6H to the QCL element 2H changes. Thereby, the wavelength of the output light (that is, the light amplified by resonance) emitted from the end surface 2Ha can be changed. Further, a part of the light emitted from the end surface 2Ha and incident on the movable diffraction grating 6H is mirror-reflected on the surface of the movable diffraction grating 6H as zero-order light, and heads toward the mirror surface 41a of the plane mirror 41. In the spectrometer 1H, such zero-order light corresponds to laser beams L _on and L _off . In other words, the spectrometer 1H is configured to be able to perform measurement by differential absorption spectroscopy by using such zero-order light.

In the spectrometer 1H, the angle of the movable diffraction grating 6H changes in order to perform wavelength sweeping. Therefore, in the spectrometer 1H, the incident angle θ _on of the laser beam L _on is different from the incident angle θ _off of the laser beam L _off , as in the spectrometer 1F. Therefore, in the spectrometer 1H, as in the spectrometer 1F, the incident angle θ _on and the incident angle θ _off are set to satisfy the condition of being a natural number multiple of the inclination angle α, and the other angles ( That is, the angle between the incident angle θ _on and the incident angle θ _off is preferably set so as not to satisfy the above condition. According to the above configuration, similarly to the spectrometer 1F, when the reflected light L2 is detected by the photodetector 3 by sweeping the wavelength between the wavelength λ _on and the wavelength λ _off , the wavelength λ _on and the wavelength It becomes possible to observe two peak values corresponding to each of λ _off .

According to the spectrometer 1H, the same effects as the spectrometer 1F described above are achieved. In addition, in the spectrometer 1H, the movable diffraction grating 6H used instead of the incidence adjustment mirror 6 can function as an external resonator with the QCL element 2H, so the diffraction grating 21 in the spectrometer 1G is unnecessary. . This makes it possible to reduce the number of parts and downsize the package (casing 10).

[Modified example]
Although some embodiments and some modifications of the present disclosure have been described above, the present disclosure is not limited to the configurations shown in each of the embodiments and modifications described above. The materials and shapes of each structure are not limited to the specific materials and shapes described above, and various materials and shapes other than those described above can be employed. Furthermore, some of the configurations included in each of the above embodiments and modifications may be omitted or changed as appropriate, or may be combined arbitrarily. For example, the embodiments relating to the formed optical path (first to third and sixth to eighth embodiments) can be combined with the embodiments relating to the accommodation form of the spectrometer (fourth and fifth embodiments). Moreover, the fourth embodiment and the fifth embodiment can also be combined. That is, the mirror section 4 may be housed in the housing 51 disposed within the housing 61.

Further, the positional relationship between the light source section 2 and the light detection section 3 may be reversed. That is, in the embodiment described above, the light source section 2 is arranged above the light detection section 3, but the light detection section 3 may be arranged above the light source section 2. In this case, the positional relationship between the entrance adjustment mirror 6 and the output light guide mirror 7 is also reversed. Further, the sign (direction) of the incident angle θ _V is reversed, and the outgoing path OP1 is located above the incoming path OP2.

Moreover, the entrance adjustment mirror 6 and the output light guide mirror 7 may be omitted. However, in that case, it is necessary to adjust the position and orientation of the light source section 2 with high precision so that the laser beam L1 is incident at the incident angles θ _H and θ _V with respect to the position P1. Similarly, it is necessary to accurately adjust the position and orientation of the photodetector 3 so that the return light L2 reflected at the position P2 enters the photodetection surface 3a. By using the entrance adjustment mirror 6 and the output light guiding mirror 7, it is possible to simply arrange the light source section 2 and the light detection section 3 in parallel to the Y-axis direction as in this embodiment. Further, the light source section 2 and the light detection section 3 (in this embodiment, the housing 10 that houses them) can be arranged compactly on the side of the mirror section 4.

Further, the light source section 2 is not limited to a quantum cascade laser element, and the photodetector section 3 is not limited to a quantum cascade photodetector. Furthermore, the laser light L1 emitted from the light source section 2 is not limited to mid-infrared light. For example, the wavelength band of the laser beam L1 may be in the visible light region. Furthermore, in cases where the divergence angle of the laser beam L1 emitted from the light source section 2 is relatively small, the lenses 11 and 12 may be omitted.

Furthermore, the incident angle θ _H does not necessarily have to satisfy the above formula (3). For example, as described in the above embodiment, the laser beam L1, which is mid-infrared light, has a longer wavelength than visible light and near-infrared light, so multiple reflections between the plane mirrors 41 and 42 are used. As the laser light L1 propagates over a long distance, the beam diameter of the laser light L1 tends to expand. For this reason, if the folding position P2 is brought too close to the rear end 41h, a portion of the laser light L1 whose beam diameter has expanded will protrude rearward beyond the rear end 41h, which may cause loss of the laser light L1. In order to suppress such a loss of the laser beam L1, the incident angle θ _H may be intentionally set to be smaller than the angle that satisfies the above formula (3).

Further, the incident angle θ _H does not necessarily have to be set to a natural number multiple of the inclination angle α. That is, the outbound path OP1 and the return path OP2 do not necessarily need to completely match (overlap) when viewed from the Z-axis direction. In this case, when viewed from the Z-axis direction, the optical path of the folded light L2 does not match the optical path of the laser beam L1 before folding, but even in such a case, for example, the position and angle of the output light guide mirror 7 can be adjusted. By doing so, the reflected light L2 can be guided to the photodetector 3. However, by designing the outgoing path OP1 and the incoming path OP2 to overlap in the Z-axis direction, the layout design of the optical system (incidence adjustment mirror 6, output light guide mirror 7, etc.) is facilitated, and the same Another advantage is that it becomes easy to arrange the input adjustment mirror 6 and the output light guide mirror 7 in a compact manner, overlapping each other in the Z-axis direction.

Further, the optical system included in the spectrometer is not limited to that shown in the above embodiment. For example, a collimating lens for suppressing beam spread of the laser beam L1 may be placed at any position on the optical path except between the plane mirrors 41 and 42 of the laser beam L1.

Further, in the second embodiment and the third embodiment, the wavelengths (first wavelength and second wavelength) of the laser beams L1A and L1B emitted by the light source units 2A and 2B are different from the wavelength λ _on in the sixth to eighth embodiments. and the wavelength λ _off . In this case, in the second embodiment and the third embodiment, based on the difference between the signal detected by the photodetector 3A and the signal detected by the photodetector 3B, the Measurement of gas concentration by differential absorption spectroscopy can be carried out.

Furthermore, in each of the embodiments and modifications described above, the gas introduced between the two plane mirrors 41 and 42 is the object to be measured, but the object to be measured is not limited to gas. The measurement target only needs to be placed on the optical path of the laser beam between the two plane mirrors 41 and 42, and may be a solid or a liquid (for example, a liquid stored in a container that transmits light). ).

FIG. 19 is a diagram showing a configuration example of a spectrometer 1A when a solid sample S is used as a measurement target. In the example of FIG. 19, the sample S is a thin film-like substance, and is fixed on mirror surfaces 41a and 42a of plane mirrors 41 and 42. As shown in FIG. 19, the laser beam is A distance for passing through the sample S can be secured. Although the sample S may be provided on only one of the mirror surfaces 41a and 42a, by placing the sample S on both the mirror surfaces 41a and 42a, the distance through which the laser beam passes through the sample S can be reduced. This can be secured more suitably. Further, the sample S does not necessarily have to be fixed to the mirror surfaces 41a and 42a. For example, a light-transmitting member that transmits laser light may be placed between the plane mirrors 41 and 42, and the sample S may be fixed to the surface of the light-transmitting member. However, as in the example of FIG. 19, by using the mirror surfaces 41a and 42a as members for fixing the sample S, the above-mentioned light-transmitting member can be omitted, which simplifies the device configuration required for measurement. This makes it possible to reduce the number of parts.

Further, in each of the embodiments and modifications described above, a light measurement device (spectrometry devices 1A to 1H) configured to perform absorption spectrometry with respect to a plurality of wavelengths has been described, but the light measurement device of the present disclosure The device may be used for single wavelength measurements (eg, absorbance measurements for a particular wavelength). For example, there may be a need to understand the transparency of a certain material to terahertz waves (for example, light with a wavelength within the range of 0.1 THz to 0.3 THz). In such a case, the light source unit may be configured as a light source with a fixed wavelength so as to emit light of a specific single wavelength included in the terahertz region.

1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H... Spectrometer (light measurement device), 2, 2F, 20G, 20H... Light source section, 2A... Light source section (first light source section), 2B... Light source part (second light source part), 2G, 2H... quantum cascade laser element, 3... photodetection part, 3A... photodetection part (first photodetection part), 3B... photodetection part (second photodetection part), 4 ...Mirror part, 6...Incidence adjustment mirror (first light guide mirror), 7...Output light guide mirror (second light guide mirror), 11...Lens, 41...Plane mirror (first plane mirror), 41a...Mirror surface (first mirror surface), 42...plane mirror (second plane mirror), 42a...mirror surface (second mirror surface), 51b...gas inlet (opening), D1...polarization direction, L1, L1A, L1B, L _on , L _off ... Laser light, L2, L2A, L2B ... Returned light (laser light), OP ... Optical path, OP1 ... Outward path, OP2 ... Return path, S ... Sample (object to be measured), α ... Inclination angle, θ _H ...Incidence angle, θ _V ...Incidence angle, θ1, θ2...Incidence angle.

Claims (22)

a light source unit that emits laser light;
a first plane mirror having a first mirror surface onto which the laser beam emitted from the light source section is incident; and a second plane mirror having a second mirror surface opposite to the first mirror surface; a mirror section in which a measurement object is introduced between the first mirror surface and the second mirror surface;
a light detection unit that detects the laser beam that is multiple-reflected and returned between the first mirror surface and the second mirror surface;
Equipped with
The first mirror surface and the second mirror surface perform multiple reflections between the first mirror surface and the second mirror surface in a second direction perpendicular to a first direction perpendicular to the first mirror surface. are arranged non-parallel to each other when viewed from a third direction orthogonal to the first direction and the second direction, so that an optical path of the laser beam reciprocating is formed;
The optical path of the laser beam between the first mirror surface and the second mirror surface is inclined with respect to the third direction.
Light measurement device. The optical path of the laser beam that first enters the first mirror surface is inclined with respect to the third direction,
the first mirror surface and the second mirror surface are parallel to the third direction;
The optical measuring device according to claim 1. When viewed from the third direction, the incident angle of the laser beam that first enters the first mirror surface is equal to Adjusted to be a natural number multiple of the inclination angle of the mirror surface,
The optical measuring device according to claim 1. A distance along the second direction from a position where the laser beam first enters the first mirror surface to an end of the first mirror surface in the outgoing direction of the laser beam is 300 mm or less,
The optical measuring device according to claim 1. The length of the mirror portion in the third direction is 50 mm or less,
The optical measuring device according to claim 1. An end of the first mirror surface in the backward direction of the laser beam protrudes in the backward direction than an end of the second mirror surface in the backward direction.
The optical measuring device according to claim 1. If the incident angle of the laser beam that first enters the first mirror surface when viewed from the third direction is expressed as θ _H , then the second mirror in the return path direction of the laser beam The distance along the second direction from the end of the surface to the end of the first mirror surface in the return direction is the distance between the first mirror surface and the second mirror surface along the first direction. It is set to a value greater than or equal to the distance from the end multiplied by _tanθH ,
The optical measuring device according to claim 6. The distance along the second direction from the end of the second mirror surface in the return direction to the end of the first mirror surface in the return direction is equal to the distance along the second direction from the end of the second mirror surface in the return direction. and the distance between the second mirror surface and the end of the second mirror surface multiplied by _tanθH ,
The optical measuring device according to claim 7. The inclination angle of the second mirror surface with respect to the first mirror surface when viewed from the third direction is such that the laser beam passing between the first mirror surface and the second mirror surface is tilted from the third direction. It is set to be larger than the divergence angle when viewed,
The optical measuring device according to claim 1. The light source section and the light detection section are arranged so as to overlap each other in the third direction,
The optical measuring device according to claim 1. further comprising a lens disposed on a side of the light source unit from which the laser beam is emitted and condenses or collimates the laser beam;
The light source section is a quantum cascade laser element,
The distance between the lens and the quantum cascade laser element is shorter than the shortest distance between the first mirror surface and the second mirror surface in the first direction.
The optical measuring device according to claim 1. The light source section is a quantum cascade laser element,
The photodetector is a quantum cascade photodetector having characteristics corresponding to the quantum cascade laser element.
The optical measuring device according to claim 1. The characteristic is a characteristic related to the polarization direction,
The light source section and the photodetection section are configured such that the polarization direction of the laser beam that is emitted from the light source section and then enters the photodetection section via the mirror section is different from the polarization direction to which the photodetection section is sensitive. arranged to match,
The optical measuring device according to claim 12. The characteristic is a characteristic related to wavelength,
The photodetector has a sensitivity wavelength corresponding to the oscillation wavelength of the light source.
The optical measuring device according to claim 12. a first light guide mirror that guides the laser light to the first mirror surface by reflecting the laser light emitted from the light source;
further comprising a second light guide mirror that guides the laser light to the photodetector by reflecting the folded laser light,
The first light guide mirror and the second light guide mirror are arranged to overlap each other in the third direction,
The optical measuring device according to claim 1. The light source section includes a first light source section that emits the laser beam of a first wavelength, and a second light source section that emits the laser beam of a second wavelength different from the first wavelength,
The photodetector includes a first photodetector that detects the laser beam of the first wavelength that is multiple-reflected and returned between the first mirror surface and the second mirror surface, and the first mirror. a second light detection unit that detects the laser beam of the second wavelength that is multiple-reflected and returned between the surface and the second mirror surface;
The first light source section, the second light source section, the first light detection section, and the second light detection section are arranged to overlap with each other in the third direction.
The optical measuring device according to claim 1. The light source section includes a first light source section that emits the laser beam of a first wavelength, and a second light source section that emits the laser beam of a second wavelength different from the first wavelength,
The photodetector includes a first photodetector that detects the laser beam of the first wavelength that is multiple-reflected and returned between the first mirror surface and the second mirror surface, and the first mirror. a second light detection unit that detects the laser beam of the second wavelength that is multiple-reflected and returned between the surface and the second mirror surface;
The first light source section and the second light source section are arranged side by side in the first direction,
The first photodetector and the second photodetector are arranged side by side in the first direction,
The first light source section and the first light detection section are arranged to overlap each other in the third direction,
The second light source section and the second light detection section are arranged to overlap with each other in the third direction.
The optical measuring device according to claim 1. further comprising a casing that airtightly accommodates the mirror section,
The measurement target is a gas,
The housing is provided with an opening for introducing the gas from the outside of the housing to the inside of the housing,
The light source section and the light detection section are arranged outside the housing,
The optical measuring device according to claim 1. Further comprising a casing that accommodates the light source section, the light detection section, and the mirror section,
The measurement target is a gas,
The casing is provided with an opening for introducing the gas from the outside of the casing into the inside of the casing.
The optical measuring device according to claim 1. The measurement target is a gas,
The light source section is configured to be able to emit the laser light of a first wavelength that is absorbed by the gas and the laser light of a second wavelength that is absorbed by the gas to a smaller degree than the first wavelength. ing,
The optical measuring device according to claim 1. The light source section is configured to be able to switch and emit the laser light of the first wavelength and the laser light of the second wavelength based on light emitted from a single laser element.
The optical measuring device according to claim 20. A method for manufacturing the optical measuring device according to claim 1, comprising:
The light measurement device includes a first light guide mirror that guides the laser light to the first mirror surface by reflecting the laser light emitted from the light source section, and a first light guide mirror that guides the laser light to the first mirror surface, and a first light guide mirror that guides the laser light that is emitted from the light source section. further comprising a second light guide mirror that guides the laser light to the photodetector by reflecting it,
fixing each of the light source section, the light detection section, the mirror section, and the second light guide mirror;
After the fixing step, adjusting and fixing the position and angle of the first light guiding mirror while emitting the laser light from the light source section so that the light detection intensity in the photodetecting section is maximized. and,
A method of manufacturing an optical measuring device, including:

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