JP2000356550A - Spectroscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide spectroscope where an optical system can be configured without using any aspherical optical elements and the generation of asymmetrical aberration (astigmatism and coma) is reduced. SOLUTION: The spectroscope is provided with a collimated optical system 13 for collimating light from light source parts 11 and 12, a dispersion element 14 for dispersing light from the collimated optical system 13, and a condensation optical system 15 for condensing light from the dispersion element 14 on a specific surface 17a. In this case, the collimated optical system 13 and the condensation optical system 15 are composed by each spherical mirror, and parallel plane plate glass 16 is arranged while being inclined for a light path in at least one light path between the light source parts 11 and 12 and the collimated optical system 13 and between the condensation optical system 15 and the specific surface 17a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spectroscope used for separating light having a wide wavelength distribution such as white light.

[0002]

2. Description of the Related Art Conventionally, in a spectroscope using a dispersive element such as a diffraction grating or a prism, collimated light is incident on the dispersive element, and the dispersed light obtained from the dispersive element is condensed on a predetermined surface. Spectroscopy. Since the direction of the dispersed light obtained from the dispersive element differs depending on the wavelength, the condensing position of the dispersed light on a predetermined surface also differs depending on the wavelength.

Now, in such a spectroscope, for example, when light including two wavelengths is separated, a predetermined surface has
Two spectral lines at different positions according to the wavelength should be formed.

However, if the image forming performance of the collimating optical system and the condensing optical system constituting the spectroscope is poor, it becomes impossible to separate the two supposed spectral lines and distinguish them (spatial resolution is low). . As a result, it becomes impossible to separate the wavelength component of the light to be split into two (the wavelength resolution is low). Therefore, in order to maintain the wavelength resolution of the spectroscope at a high value determined by the performance of the dispersive element, it is necessary to enhance the imaging performance of the collimating optical system and the condensing optical system.

FIG. 2 shows an example of the most common spectroscope. In FIG. 2, a collimating optical system 13 and a condensing optical system 15 are decentered optical systems using spherical mirrors. Further, as can be seen from FIG. 2, in the case of this optical system,
Light L from the entrance slit 12 enters the optical axis of the spherical mirror (collimating optical system 13) at an angle. For this reason, astigmatism and coma occur in the spherical mirror (collimating optical system 13). Furthermore, astigmatism and coma also occur when the light emitted from the diffraction grating 14 is condensed by a spherical mirror (condensing optical system 15). In the case of such decentered optical systems, it is inevitable that asymmetrical aberrations occur in the optical axes of these optical systems.

As spectroscopes for correcting these aberrations, there are a spectroscope 20 shown in FIG. 5 and a spectroscope 30 shown in FIG. In the spectroscope 20, the collimating optical system 23 and the condensing optical system 2 are used to correct the above astigmatism and coma.
5 and 5 use an off-axis parabolic mirror. Further, in the spectroscope 30, a cylindrical lens 33 is disposed in the optical path, thereby correcting astigmatism and the like.

[0007]

However, an off-axis parabolic mirror constituting the collimating optical system 23 and the condensing optical system 25 of the spectroscope 20 (FIG. 5) and the spectroscope 30 (FIG. 6). Since the cylindrical lens 33 is an aspherical optical element, it is very difficult to manufacture it, and it is also difficult to adjust the assembling, resulting in an increase in cost.

It is an object of the present invention to provide a spectroscope in which an optical system is configured without using an aspherical optical element and in which the occurrence of asymmetric aberrations (astigmatism and coma) is reduced. .

[0009]

According to a first aspect of the present invention, there is provided a spectroscope including a collimating optical system including a spherical mirror, a dispersion element, a condensing optical system including a spherical mirror, and a plane-parallel plate glass. Things. The plane-parallel plate glass is disposed at an angle to the optical path between at least one of the optical paths between the light source unit and the collimating optical system and between the light-collecting optical system and the predetermined surface.

Thus, the light from the light source passes through the plane-parallel plate glass before reaching the predetermined surface via the collimating optical system, the dispersion element, and the condensing optical system. The plane-parallel sheet glass generates asymmetric aberration depending on its thickness, refractive index, and inclination angle with respect to the optical path. By canceling out the asymmetric aberration caused by the plane-parallel plate glass and the asymmetric aberration caused by the spherical mirror (the collimating optical system and the condensing optical system), a spectroscope having no asymmetric aberration can be obtained.

The invention described in claim 2 is the first invention.
Wherein the dispersion element is rotatably supported, and the dispersion of the plane-parallel plate glass is corrected by the rotation angle of the dispersion element.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings.

This embodiment corresponds to claims 1 and 2. As shown in FIG. 1A, the spectroscope 10 of this embodiment includes an entrance slit 12 and a collimating optical system 13.
, A diffraction grating 14, a condensing optical system 15, a plane-parallel plate glass 16, and an exit slit 17. In addition, the light source 11 is disposed in front of the entrance slit 12,
A detector 18 is arranged downstream of the exit slit 17.

The entrance slit 12 is an opening for guiding light from the light source 11 into the inside of the spectroscope 10. Here, the entrance slit 12 and the light source 11 correspond to the “light source unit” in claim 1. The collimating optical system 13 outputs the light L guided into the spectroscope 10 through the entrance slit 12.
11 is a concave mirror that reflects and collimates the light, and is specifically constituted by a spherical mirror. The light collimated by the collimating optical system 13 is referred to as a collimated light L12. The collimating optical system 13 is arranged to guide the collimated light L12 in a direction inclined by an angle 2α from the traveling direction of the light L11 (see FIG. 1B). Light L1 at this time
The incident angle of 1 is α.

The diffraction grating 14 (FIG. 1A) is a dispersion element that diffracts and disperses the collimated light L12.
The light dispersed by the diffraction grating 14 is called a diffracted light L13. The condensing optical system 15 is a concave mirror that reflects the diffracted light L13 and condenses the diffracted light L13 on the arrangement surface 17a of the exit slit 17, and is specifically formed of a spherical mirror. The light condensed by the condensing optical system 15 is referred to as condensed light L14. The condensing optical system 15 guides the condensed light L14 in a direction inclined by an angle 2β from the traveling direction of the diffracted light L13 (FIG. 1C).
See). At this time, the incident angle of the diffracted light L13 is β. The arrangement surface 17a corresponds to the "predetermined surface" in the first aspect.

The plane-parallel plate glass 16 is arranged to be inclined with respect to the optical path of the above-mentioned condensed light L14. The inclination angle θ of the parallel flat plate glass 16 is, as shown in FIG.
It is represented based on a state (shown by a dotted line) in which the parallel flat plate glass 16 is orthogonal to the optical path of the condensed light L14. The exit slit 17 (FIG. 1A) is an opening for selectively passing a part of the condensed light L14 transmitted through the parallel flat plate glass 16 and guiding it to the detector 18.

In the spectroscope 10 configured as described above, the diffraction angle of the diffracted light L13 differs depending on the wavelength.
Arrangement surface 17 of exit slit 17 via condensing optical system 15
The position of the condensed light L14 condensed on a also differs depending on the wavelength. Then, only the light of the wavelength imaged at the position of the exit slit 17 can be extracted. The light detected by the detector 18 can be changed to a different wavelength by rotating the diffraction grating 14 around a slit direction (a direction perpendicular to the paper surface).

The features of the spectroscope 10 of this embodiment are as follows.
The collimating optical system 13 and the condensing optical system 15 are constituted by spherical mirrors, and a parallel flat plate glass 16 is provided between the converging optical system 15 and the exit slit 17 (in the optical path of the condensed light L14).
Is located at an angle. Therefore, if the parallel flat plate glass 16 is removed from the spectroscope 10 of the present embodiment (the state of FIG. 2), the collimating optical system 13 composed of a spherical mirror is used.
The condensed light L14 in which the asymmetric aberration has occurred through the light condensing optical system 15 and the condensing light
Will be collected. Hereinafter, the conventional spectroscope of FIG. 2 in which the parallel flat plate glass 16 is removed from the spectroscope 10 is referred to as a "spectroscope 40".

Incidentally, the spectroscope 10 of this embodiment (FIG. 1)
The parallel flat plate glass 16 provided in (a) generates an asymmetric aberration (astigmatism or coma) according to the thickness t, the refractive index n, and the inclination angle θ. According to such a plane parallel plate glass 16, by optimizing the combination of the thickness d, the refractive index n, and the inclination angle θ, the spectroscope 40 can be used.
The opposite asymmetric aberration that cancels the asymmetric aberration in FIG. 2 can be generated.

When the refractive index n of the plane-parallel plate glass 16 is assumed to be the above optimization,
Is determined according to the amount of asymmetric aberration in the spectroscope 40 (FIG. 2). Further, the inclination angle θ of the plane-parallel plate glass 16 is determined according to the directionality of the asymmetric aberration in the spectroscope 40 (FIG. 2).

Therefore, according to the spectroscope 10 (FIG. 1 (a)) of the present embodiment, the spectroscope 10 is formed by the parallel flat plate glass 16 in which the combination of the thickness d, the refractive index n, and the inclination angle θ is optimized. 40 (FIG. 2), that is, a spherical mirror (collimating optical system 13, condensing optical system 15)
Can cancel the asymmetric aberration generated through the above, and can eliminate the asymmetric aberration as a whole.

Here, the effect of reducing the asymmetric aberration by the plane-parallel plate glass 16 will be specifically described. FIG.
FIG. 2 is a diagram illustrating aberrations generated in the spectroscope 10 (FIG. 1A) of the present embodiment by wavefront aberrations. FIG.
FIG. 2 is a diagram showing aberrations generated in a conventional spectroscope 40 (FIG. 2) in which the parallel flat plate glass 16 is removed from (FIG. 1A) by wavefront aberration.

3 and 4, the vertical axis represents the wavefront aberration (unit is wavelength), and the XY axes represent the coordinates of the pupil. Also, X
A circular portion in the Y plane corresponds to a stop (not shown) of the spectroscopes 10 and 40. Details of the data used for obtaining the aberration data of FIGS. 3 and 4 are shown in Table 1 below.

[Table 1] Table 1 shows the radius of curvature r1 of the collimating optical system 13, the radius of curvature r2 of the condensing optical system 15, the distance A1 from the entrance slit 12 to the center of the collimating optical system 13, and the distance of the diffraction grating 14 from the center of the collimating optical system 13. Distance A to center
2. A distance A3 from the entrance slit 12 to the center of the diffraction grating 14, a condensing optical system 1 from the center of the collimating optical system 13.
5, a distance A4 from the center of the condensing optical system 15 to the exit slit 17, an incident angle α of the light L11,
The incident angle β of the diffracted light L13, the thickness t of the parallel flat plate glass 16, the refractive index n, and the inclination angle θ are shown.

As shown in Table 1, the radius of curvature r1 of the collimating optical system 13 is equal to the radius of curvature r2 of the focusing optical system 15. Further, the distances A1 to A5 and the thickness t of the parallel flat plate glass 16 are standardized by a radius of curvature r1 (= r2). As can be seen from FIG. 4, in the spectroscope 40 (FIG. 2) in which the parallel flat plate glass 16 is removed from the spectroscope 10 (FIG. 1A), asymmetric aberrations (astigmatism and coma) occur. are doing. Incidentally, the height difference of the wavefront aberration is about four wavelengths.

Therefore, in the optical path of the condensed light L14 of the spectroscope 40 (FIG. 2, Table 1) where this asymmetric aberration occurs, the thickness t = 0.004 × r1, and the refractive index n = 1.46. When the parallel flat plate glass 16 is disposed at an inclination angle θ = 46.7 ° (FIG. 1D), as shown in FIG. 3, the wavefront aberration becomes almost flat in a circular portion corresponding to the stop. this is,
This means that no asymmetric aberration (astigmatism or coma) is generated in the spectroscope 10 (FIG. 1A) of the present embodiment. Incidentally, the height difference of the wavefront aberration is 0.1 wavelength or less.

The thickness t of the above-mentioned parallel flat plate glass 16
(= 0.004 × r1), the refractive index n (= 1.46), and the inclination angle θ (= 46.7 °), the opposite asymmetric aberration that cancels the asymmetric aberration shown in FIG. It is optimized to be generated on the plane-parallel plate glass 16. Thus, the spectroscope 10 of this embodiment (FIG. 1)
According to (a)), a predetermined asymmetric aberration is intentionally generated by the parallel flat plate glass 16 in which the combination of the thickness d, the refractive index n, and the inclination angle θ is optimized.
6 and the spherical mirror (collimating optical system 1)
3, asymmetrical aberration caused by the condensing optical system 15) (for example, FIG. 4)
Can be completely corrected to completely correct asymmetric aberration as a whole (for example, FIG. 3).

According to the spectroscope 10 (FIG. 1A) of the present embodiment having no asymmetric aberration, the spatial resolution (imaging performance) of the optical system is enhanced, and the wavelength resolution is determined by the performance of the dispersion element. It can be maintained at a high value. Furthermore, according to the spectroscope 10 of the present embodiment, the spherical optical elements (the collimating optical system 13 and the condensing optical system 15) and the parallel flat plate glass 16 are used instead of the aspheric optical element in the optical system. Therefore, it can be manufactured easily, the assembly and adjustment can be easily performed, and the cost can be reduced.

That is, the spectroscope 10 of the present embodiment can simplify the configuration and reduce the cost while maintaining high optical performance (imaging performance). In the spectroscope 10 of the present embodiment, the condensed light L
There is no unnecessary reduction in the amount of light due to the part of 14 being cut off. Also, when the spectroscope 10 is used as a light source of another device, it is effective because it is not necessary to correct asymmetric aberration.

Here, in the spectroscope 10 of the present embodiment, since the parallel flat plate glass 16 is disposed at an angle in the condensed light L14, the dispersion of the parallel flat plate glass 16 causes the light exiting from the exit slit 17 to disperse. The wavelength is parallel plate glass 16
This is different from the conventional spectroscope without spectrometer (spectrometer 40 in FIG. 2). When such a wavelength shift becomes a problem, the diffraction grating 1
4 can be dealt with by changing the rotation angle of the conventional spectroscope (spectroscope 40). Alternatively, the rotation angle of the diffraction grating 14 may be the same as that of the conventional spectroscope (spectroscope 40), and the position of the exit slit 17 may be moved within the arrangement surface 17a.

Further, in the above embodiment, the parallel flat plate glass 16 is disposed between the condensing optical system 15 and the exit slit 17, but the same parallel flat plate glass is disposed between the collimating optical system 13 and the entrance slit 12. , A spectroscope free of asymmetric aberration can be constructed. Also,
The plane-parallel plate glass is composed of a condensing optical system 15 and an exit slit 1.
7, the collimating optical system 13 and the entrance slit 12
May be arranged on both sides.

Further, in the above-described embodiment, the example of the spectroscope 10 using the diffraction grating 14 as the dispersion element has been described. However, a similar parallel flat plate glass can be used in a spectroscope using a prism instead of the diffraction grating 14. By arranging, a spectroscope in which asymmetric aberration is corrected can be configured.

[0032]

As described above, according to the first and second aspects of the present invention, it is possible to realize a low-cost, high-performance spectroscope with good imaging performance.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a spectroscope 10 of the present embodiment.

FIG. 2 is a diagram showing a state in which the parallel flat plate glass 16 is removed from the spectroscope 10 (the configuration of the spectroscope 40).

FIG. 3 is a diagram illustrating aberration of the spectroscope 10 of the present embodiment by wavefront aberration.

FIG. 4 is a diagram in which aberrations in a state where the parallel flat plate glass 16 is removed from the spectroscope (spectroscope 40) are represented by wavefront aberrations.

FIG. 5 is a configuration diagram showing a conventional spectroscope 20.

FIG. 6 is a configuration diagram showing a conventional spectroscope 30.

[Explanation of symbols]

 10, 20, 30, 40 Spectroscope 11, 21, 31 Light source 12, 22, 32 Incident slit 13, 23, 34 Collimating optical system 14, 24, 35 Diffraction grating 15, 25, 36 Condensing optical system 16 Parallel flat plate glass 17, 26, 37 Exit slit 18 Detector 33 Cylindrical lens

Claims (2)

[Claims] 1. A collimating optical system for collimating light from a light source unit, a dispersing element for dispersing light from the collimating optical system, and a condensing optical system for condensing light from the dispersing element on a predetermined surface. Wherein the collimating optical system and the condensing optical system are each configured by a spherical mirror, between the light source unit and the collimating optical system, and between the condensing optical system and the predetermined surface. A spectroscope, wherein a parallel flat plate glass is arranged at an angle to the optical path in at least one of the optical paths. 2. The spectroscope according to claim 1, wherein the dispersion element is rotatably supported, and dispersion of the parallel flat plate glass is corrected by a rotation angle of the dispersion element. vessel.