JP2014048096A - Two-dimensional spectral measurement device, and two-dimensional spectral measurement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate an interferogram on an image formation surface when an object S to be measured is a low scattering body or a low diffusivity body such as a liquid.SOLUTION: A two-dimensional spectral measurement device comprises: an object lens which light emitted from an object to be measured enters; a phase shifter disposed at the rear of the object lens; an imaging lens which light reflected at the phase shifter enters; a detector disposed on an image formation surface of the imaging lens; and an optical element which is disposed at the front of the object lens and which diffuses light transmitted through the object to be measured which is a low scattering body or a low diffusivity body. The light transmitted through the object to be measured is scattered by the optical element to enter the object lens. The entering light is interfered by the phase shifter, thus an interferogram is generated on the image formation surface.

Description

  The present invention relates to a two-dimensional spectroscopic measurement apparatus and a two-dimensional spectroscopic measurement method for measuring a high-resolution two-dimensional spectroscopic image of a measurement object using a low scatterer such as a liquid or a low diffusivity object.

  As a typical method for analyzing light emitted from an object or transmitted through an object by using a spectroscopic technique, there is Fourier spectroscopy. In typical Fourier spectroscopy, object light is split into two by a beam splitter such as a half mirror, the respective light beams are reflected by a mirror, reach the half mirror again, and the two light beams are merged to observe an interference phenomenon. A mirror that reflects one of the two branched light beams (reference light) is called a reference mirror. In Fourier spectroscopy, the reference mirror is moved with high accuracy at a resolution shorter than the wavelength of light to change the interference light intensity, detect a so-called interferogram, and mathematically Fourier transform the interferogram. Obtain spectral characteristics.

  However, since this Fourier spectroscopy is a point measurement, it cannot know the geometrical arrangement of the object to be measured.

  Therefore, a phase shifter composed of a fixed mirror and a movable mirror is arranged between the objective lens and the imaging lens, and interference light is generated from object light by the phase shifter to generate an interferogram on the imaging plane. A two-dimensional spectroscopic measurement apparatus has been proposed (Patent Document 1).

  FIG. 1 is a schematic configuration diagram of this two-dimensional spectroscopic measurement apparatus.

  In the figure, when light is irradiated to the object to be measured S from a light source (not shown), scattered light, fluorescent light emission and the like are generated radially from one bright spot of the object to be measured S, and this light beam group (also referred to as object light). ) Enters the objective lens 1 and is converted into a parallel light beam. The parallel light beam that has passed through the objective lens 1 reaches the phase shifter 2. The phase shifter 2 includes a flat fixed mirror 20 and a movable mirror 21. The phase shifter 2 has a reflection surface inclined by 45 degrees with respect to the central axis of the objective lens 1 (the optical axis of the parallel light beam). The drive unit 3 drives the movable mirror 21 to reciprocate at an angle of 45 degrees with respect to the arrow direction in the figure, that is, the central axis of the objective lens 1. With such a configuration, the movement (vector) amount (length) of the movable mirror 21 in the optical axis direction is 1 / √2 of the drive amount (length) of the drive unit 3.

  The reflected light of the phase shifter 2 enters the imaging lens 4. The reflection surface of the phase shifter 2 is also inclined 45 degrees with respect to the central axis of the imaging lens 4. A detection unit 5 including a two-dimensional CCD camera is disposed on the imaging surface of the imaging lens 4. The control unit 6 drives the drive unit 3 so that two types of light incident on the phase shifter 2, that is, light incident on the fixed mirror 20 and light incident on the movable mirror 21 (light whose optical path difference is changed) and Thereby interferograms are generated on the imaging plane. The control unit 6 acquires the spectral characteristics of the object to be measured S by Fourier transforming the interferogram.

According to the above-described two-dimensional spectroscopic measurement device, a group of bright spots that are optically conjugate is formed as an image on the imaging plane using a lens, so that the geometrical arrangement of the object to be measured can be known.
JP 2008-309706 A

  However, when the object to be measured is an optical bright spot group, the two-dimensional spectroscopic measurement apparatus forms an optically conjugate bright spot group as an image on the imaging plane using a lens. Therefore, there is no problem when light rays are emitted in various directions radially from the object to be measured, but when a low scatterer or low diffusivity body such as a liquid is used for the object to be measured, or from a mirror body In the case of the reflected light, no image is formed. This problem will be described with reference to FIGS.

  In FIG. 2A, when the object to be measured S is a liquid sealed in a transparent container, the light from the light source 7 is transmitted as it is without being scattered when it enters the object to be measured S. At this time, since the light from the light source 7 is a parallel light beam or a light beam close thereto, the light is collected on the phase shifter 2 by the light collecting action of the objective lens 1. As a result, even when the movable mirror 21 is driven, no light interference occurs on the phase shifter 2, and no image can be formed on the detection unit 5 as shown in FIG. The gram cannot be generated. FIG. 3A shows this state. The left side of the figure shows that no interferogram has been generated on the image plane, and the right side of the figure shows that no spectral characteristics of the object to be measured can be obtained even after Fourier transformation. ing.

  As shown in FIG. 2B, the same problem occurs when the object to be measured S1 is a mirror body such as a mirror. In the figure, a beam splitter 30 is disposed between the objective lens 1 and the mirror. The light from the light source 7 is reflected by the beam splitter 30 and specularly reflected by the mirror. The specularly reflected light passes through the beam splitter 30 and enters the objective lens 1 as parallel light. Therefore, similarly to FIG. 2A, the detector 5 cannot form an image and an interferogram cannot be generated on the image plane.

  The above problem is caused by the measurement object S being a low scatterer or a low diffusivity material such as a liquid. The same problem occurs when the object to be measured S is reflected by the mirror body.

  Accordingly, an object of the present invention is to generate an interferogram on the imaging plane even when the object to be measured S is a low scatterer or low diffusivity body such as a liquid or reflected light from a mirror body. It is to give a device that can be done.

The present invention includes a first conversion unit that converts light generated from an object to be measured into a parallel luminous flux,
A phase shift unit for phase shifting a part of the parallel luminous flux;
A second converter for condensing a parallel light beam including the phase-shifted phase-shifted light;
A two-dimensional spectroscopic measurement unit that generates an interferogram by the phase shift on an imaging plane on which the light collected by the second conversion unit forms an image;
And a light scattering part that is disposed between the object to be measured and the first conversion part and scatters light that has been transmitted through the object to be measured or light that has been reflected by a specular body. .

  For example, the first conversion unit and the second conversion unit each include an objective lens and an imaging lens. The phase shift unit phase-shifts a part of the parallel light flux converted by the first conversion unit, thereby causing the lights to interfere with each other, thereby generating an interferogram on the imaging plane.

  A light scattering unit that scatters light that has passed through the measurement object such as a low scatterer or a low diffusivity body or reflected by a mirror or the like is provided between the measurement object and the first conversion unit.

  In the present invention, the light is scattered to the surroundings by the light scattering portion that scatters the light transmitted through the object to be measured. Further, even when the object to be measured is reflected by a mirror or the like, it is scattered by the light scattering portion. As a result of the light scattering around, the object to be measured can be replaced with one equivalent to an optical bright spot group. In the present invention, scattering of light means converting light into a luminous flux having a spread.

  In the present invention, an imaging optical system can be constructed that forms a luminescent spot group that is optically conjugate using a lens as an image on the imaging plane as shown in FIG. The interferogram can be generated on the image plane by the action of the unit.

  FIG. 3B shows that an interferogram can be generated on the imaging plane according to the present invention. The left side of the figure shows that an interferogram has been generated on the imaging plane, and the right side of the figure shows that the spectral characteristics of the object to be measured can be obtained by Fourier transform as a result.

  Various optical elements can be used. For example, a perforated filter, a diffraction grating, a fly-eye lens, a diffusion plate, and the like are conceivable.

  According to the present invention, two-dimensional spectroscopic measurement is performed on an object to be measured such as a liquid or a mirror by disposing a light scattering unit that scatters light between the object to be measured and the first conversion unit. Can do. In this case, since the arrangement position of the light scattering portion may be between the object to be measured and the first conversion portion, the arrangement position of the light scattering portion has a degree of freedom and is easy to attach.

Schematic configuration diagram of a two-dimensional spectroscopic measurement device Diagram explaining problems when the object to be measured is liquid A diagram comparing the prior art and the present invention regarding the presence or absence of interferogram generation Schematic configuration diagram of an embodiment of the present invention The figure which shows the control procedure of embodiment External view of perforated filter 10 External view of diffraction grating 11 Front view and side view of fly-eye lens 12 External view of diffusion plate 13 Schematic configuration diagram of another embodiment of the present invention Schematic configuration diagram of still another embodiment of the present invention

  FIG. 4 shows an embodiment of the present invention. In the figure, the two-dimensional spectroscopic measurement apparatus includes a two-dimensional spectroscopic measurement unit M and an optical element 8 that diffuses light.

  The two-dimensional spectroscopic measurement unit M is configured as follows.

  A phase shifter 2 (phase shift unit) is disposed behind the objective lens 1 (first conversion unit) that receives light from the object S to be measured. The phase shifter 2 is configured so that the reflecting surface is the same surface in the normal state (when the movable mirror 21 is not moving) of the fixed mirror 20 and the movable mirror 21 that are optically mirror-finished, and the objective lens. The reflecting surface is inclined 45 degrees with respect to the optical axis of the parallel luminous flux from 1. The phase shifter 2 has a rectangular shape as a whole, and the upper half rectangular area is constituted by a fixed mirror 20 and the lower half rectangular area is constituted by a movable mirror. The movable mirror 21 (second conversion unit) is reciprocally driven by the drive unit 3 in the direction of the arrow in the figure, that is, at an angle of 45 degrees with respect to the central axis of the objective lens 1 and 90 degrees with respect to the phase shifter 2. (Extension drive). With such a configuration, the movement (vector) amount (length) of the movable mirror 21 in the optical axis direction is 1 / √2 of the drive amount (length) of the drive unit 3. The drive of the movable mirror 21 requires a resolution shorter than the wavelength of light, and the drive amount depends on the spectroscopic measurement capability, but is approximately 50 nm in the visible light region. The movement (vector) amount (length) of the movable mirror 21 in the optical axis direction is 1 / √2 of the drive amount (length) by the drive unit 3, so that the drive amount by the drive unit 3 is 2 by 2 The optical path difference between the light beams (the light beam reflected by the fixed mirror 20 and the light beam reflected by the movable mirror 21) changes.

  The imaging lens 4 is disposed behind the phase shifter 2, that is, in the lower part of the phase shifter 2 in FIG. 4, and the detection unit 5 is disposed on the imaging surface below the imaging lens 4. The light reflected by the phase shifter 2 is converged by the imaging lens 4 and enters the imaging plane. A CCD light receiving surface of a two-dimensional CCD camera is disposed on the image plane.

  In FIG. 4, the upper half region of the phase shifter 2 is a fixed mirror 20 and the lower half region is a movable mirror 21 so that half of the light is incident on each mirror. The fixed mirror 20 may be arranged so as to be concentric around the circular shape. Further, the positions of the fixed mirror 20 and the movable mirror 21 may be reversed. Also in this case, it is preferable that the respective incident light amounts are the same.

  Next, the operation of the two-dimensional spectroscopic measurement unit M will be described. FIG. 5 shows a control procedure of the control unit 6 of the measurement unit M.

  The light source 7 disposed in front of the measurement object S made of a low scatterer or low diffusivity body such as a liquid is turned on, and then the movable mirror 21 is driven (reciprocated in the direction of the arrow) by the drive unit 3. .

When the movable mirror 21 moves, the reflected light of light of various wavelengths from the objective lens 1 changes in optical path length (changes in phase) and interferes with the reflected light of the fixed mirror 20 whose optical path length is fixed. . Thereby, a waveform of an interference light intensity change called an interferogram as shown in the left diagram of FIG. 3B is obtained (imaging intensity observed on the imaging plane). In the figure, the horizontal axis indicates the optical path length difference between the movable light reflected by the moving movable mirror 21 and the fixed light reflected by the fixed mirror 20, and the vertical axis indicates the imaging intensity at one point on the imaging plane. By performing Fourier transform on the interferogram by the control unit 6, the spectral characteristics for each wavelength of the light emitted from one bright spot of the object S to be measured can be obtained as shown in the right side of FIG. it can.

  A specific method for generating an interferogram is well known in various documents, but is described in detail in, for example, Japanese Patent Application Laid-Open No. 2008-309706.

  The optical element (light scattering unit) 8 disposed in front of the two-dimensional spectroscopic measurement unit M has an optical property of converting a parallel light beam into a broad light beam. Due to the nature of the optical element 8, even if a parallel light beam or a light beam close thereto is incident from the object S placed in front of the optical element 8, light equivalent to a bright spot can be emitted due to the light scattering effect. Therefore, when the object to be measured S is a liquid (such as a colored liquid), the light is scattered by the optical element 8 even if the light from the light source 7 is transmitted as it is or slightly diffused. Thus, an optical imaging system as shown in FIG. 1 is realized. The optical element 8 may be disposed between the objective lens 1 and the object S to be measured, but may be attached to the surface of the object to be measured on the object lens side.

  The first embodiment of the optical element 8 is a perforated filter. FIG. 6 is an external view of the perforated filter 10. As illustrated, innumerable holes 10b are formed in the flat substrate 10a. By opening an infinite number of holes, light is diffracted at the positions of the holes, and bright spots can be generated. Thereby, an imaging optical system is constructed, and an interferogram can be generated on the imaging plane by the action of the phase shifter 2.

  It is best to design the hole diameter so that it has the same size as the pixel when imaged. When the design is made so that it is less than or greater than the pixel, the light utilization efficiency is lowered. The pitch of the hole diameter is directly related to the section resolution of the object to be measured.

  The disadvantage of this perforated filter is that the spatial measurement points become discrete.

  The second example is a diffraction grating. FIG. 7 is an external view of the diffraction grating 11. A phase difference is given to the diffracted light spread on the phase shifter 2 by generating the diffracted light. Here, of the diffracted lights to be interfered on the phase shifter 2, one of the ± 1st order diffracted lights (+ side primary diffracted light or −side primary diffracted light) is incident on the movable mirror 21, and the other is fixed mirror 20. The width of the diffraction grating is set so as to diffract the light so that it is incident on. For the objective lens 1, a lens having a numerical aperture NA that can acquire the long wavelength α2 and the short wavelength α1 of ± 1 next-order analysis light is selected. When the diffraction grating is used, light can be widely distributed on the reflecting surfaces of the fixed mirror 20 and the movable mirror 21 by the diffracted light, and an interferogram can be generated on the imaging surface by the action of the phase shifter 2.

  The diffraction grating has the advantage that the spatial measurement point is the same as the pixel size and the light utilization efficiency is good. However, the optical design is complicated, and there is a demerit that the accuracy of spectral characteristics is slightly inferior due to interference between diffraction lights.

  The third embodiment is a fly-eye lens. 8A and 8B are a front view and a side view of the fly-eye lens 12, respectively. The fly-eye lens is a lens body (lens array) in which identical single lenses are arranged vertically and horizontally. By placing this lens between the object to be measured S and the objective lens 1 and setting a pseudo object surface 13 on the back focal plane of the fly-eye lens 12, a pseudo object surface 13 is set on the pseudo object surface 13. A plurality of bright spot images are created. Thereby, an imaging optical system is constructed, and an interferogram can be generated on the imaging plane by the action of the phase shifter 2.

  When the fly-eye lens 12 is used, the spatial resolution of the spectral imaging seems to be determined by the spatial pitch of each lens. This is because the light incident on each lens in the fly-eye lens is averaged to create a bright spot image on the pseudo object surface.

  The fly-eye lens has high light utilization efficiency, but since it is a lens, there is a possibility that spectral characteristics may be deteriorated due to aberration. However, it is possible to reduce the influence of aberration by reducing the numerical aperture NA of the lens.

  The fourth embodiment is a diffusion plate. FIG. 9 is an external view of the diffusion plate 13. The diffusion plate 13 is created by processing one side of a glass substrate into a ground glass surface or forming a milky white film. The light transmitted through the object to be measured S is optically diffused by the diffusion plate 13. As a result, a state equivalent to the bright spot image can be generated. However, since the optical characteristics of the diffusion plate are not uniform for each diffusion plate, there is a problem in terms of reproducibility that measurement points differ depending on the diffusion plate.

  As described above, each of the first to fourth embodiments has merits and demerits. In either case, the optical element 8 converts the transmitted light that has passed through the object to be measured S into a light beam having a spread. Even when a low scatterer or a low diffusivity body is used as an object to be measured, an interferogram can be generated on the imaging plane of the two-dimensional spectroscopic measurement unit M.

  Still another embodiment of the present invention will be described with reference to FIG.

  In the embodiment shown in FIG. 10, the half mirror 16 is disposed between the objective lens 1 and the phase shifter 2, and the phase shifter 2 is disposed in a face-to-face relationship with the parallel light beam from the objective lens 1. The phase shifter 2 includes a fixed mirror 20 that specularly reflects a part of the transmitted light from the half mirror 16, and a movable mirror 21 that can move a position relative to the fixed mirror 20 and specularly reflect the remainder of the transmitted light from the half mirror 16. The movable mirror 21 is driven (reciprocated) by the drive unit 3 in the optical axis direction. A part of the light (transmitted light) transmitted through the half mirror 16 from the objective lens 1 is specularly reflected by the fixed mirror 20, and the remaining part is specularly reflected by the reflecting mirror 21. At this time, since the movable mirror 21 is driven in the optical axis direction, an optical path difference occurs between the light beam reflected by the fixed mirror 20 and the light beam reflected by the movable mirror 21, and as a result, the light beams interfere with each other. The interference light returns to the half mirror 16 again, is reflected here, and is condensed on the imaging surface via the imaging lens 4 to generate an interferogram.

  Also in the embodiment using the above-described half mirror 16, an interferogram can be generated on the image plane of the detection unit 5 by the same operation as the embodiment shown in FIGS.

  The optical element 8 may be of any type as long as it has an optical characteristic that turns light transmitted through a low scatterer or low diffusivity body such as a liquid into a spread light beam.

  Still another embodiment of the present invention will be described with reference to FIG.

  The embodiment shown in FIG. 11 shows a configuration diagram of a two-dimensional spectroscopic measurement apparatus when a mirror is used as the object S1 to be measured. Between the object to be measured S1 made of a mirror and the objective lens 1, the beam splitter 30 and the optical element 8 are arranged in this order from the objective lens 1 side. A light source 7 is disposed above the beam splitter 30. The beam splitter 30 reflects light from the light source 7 at a right angle, guides it to the optical element 8, and then guides it to the object S1 to be measured. Since the device under test S1 is a mirror, the light reflected by the device under test S1 is reflected as regular reflected light to become a parallel light beam. The parallel light beam is scattered by the optical element 8 and guided to the beam splitter 30, passes therethrough, and enters the objective lens 1. Thereafter, similarly to FIG. 4, an interferogram is generated on the imaging plane of the detection unit 5 by passing through the phase shifter 2.

  Thus, when the object S1 to be measured is a mirror, an interferogram can be generated by using the beam splitter 30.

DESCRIPTION OF SYMBOLS 1 ... Objective lens 2 ... Phase shifter 20 ... Fixed lens 21 ... Movable lens 4 ... Imaging lens S ... Measuring object 8 ... Optical element 10 (10a, 10b) ... -Hole filter 11 ... Diffraction grating 12 ... Fly eye lens 13 ... Diffuser

Claims (7)

A first converter that converts light generated from the object to be measured into a parallel light beam;
A phase shift unit for phase shifting a part of the parallel luminous flux;
A second converter for condensing a parallel light beam including the phase-shifted phase-shifted light;
A two-dimensional spectroscopic measurement unit that generates an interferogram by the phase shift on an imaging plane on which the light collected by the second conversion unit forms an image;
And a light scattering part that is disposed between the object to be measured and the first conversion unit and scatters light that has passed through the object to be measured or light that has been regularly reflected by the object to be measured. A two-dimensional spectroscopic measurement device. The phase shift unit includes:
The two-dimensional spectroscopic measurement apparatus according to claim 1, further comprising a phase shifter disposed behind the first conversion unit and causing an optical path difference in the parallel light flux. The phase shifter is
Behind the first conversion unit, the reflection surface is inclined by 45 degrees with respect to the central axis of the parallel light flux,
3. The two-dimensional spectroscopic measurement apparatus according to claim 2, comprising: a fixed mirror that reflects a part of the parallel light beam; and a movable mirror that is movable with respect to the fixed mirror and reflects the remaining part of the parallel light beam.   3. The two-dimensional spectroscopic measurement apparatus according to claim 2, further comprising a half mirror that is disposed between the first conversion unit and the phase shifter and transmits and reflects a parallel light beam from the first conversion unit.   The phase shifter includes a fixed mirror that specularly reflects a part of the transmitted light from the half mirror, and a movable mirror that can move a position relative to the fixed mirror and specularly reflect the remainder of the transmitted light from the half mirror. The two-dimensional spectroscopic measurement apparatus according to claim 4.   The first conversion unit is disposed between the first conversion unit and the light scattering unit, reflects light from a light source to guide the light scattering unit, and transmits light from the light scattering unit to transmit the first conversion. When the object to be measured is a specular body, the specularly reflected light that is specularly reflected from the light source by the specular body is scattered by the light scattering unit, and the scattered light is The two-dimensional spectroscopic measurement apparatus according to claim 1, which passes through a beam splitter and enters the first conversion unit.   The light generated from the object to be measured is converted into a parallel light beam by the first conversion unit, and this parallel light beam is a phase shifter arranged behind the first conversion unit, and reflects a part of the parallel light beam. When guiding to a phase shifter including a fixed mirror and a movable mirror that can move a position relative to the fixed mirror and reflects the remaining part of the parallel light beam, the movable mirror is moved along the optical axis and a part of the parallel light beam is moved Two-dimensional spectroscopic measurement that generates an interferogram on the imaging plane by producing an optical path difference between the first and second portions, condensing these lights at the second conversion section and forming an image on the imaging plane. Method.

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