JP2001050811A - Optical system and spectrophotometer using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical system capable of reducing spherical aberration at every part of a diffraction grating, and capable of enhancing its resolution. SOLUTION: This is an optical system which comprises a diffraction grating for resolving incident light into each wavelength component, and condenses each wavelength light resolved by the diffraction grating on a specific position. The diffraction grating 110 has a plurality of divided grating surfaces 110, and each divided grating surface 116, 118, 120, 122 is manufactured separately independently in consideration with holographic manufacturing conditions. In the optical system 110, each of these grating surfaces 116, 118, 120, 122 is arranged so that a similar incident light image may be formed on each grating surface 116, 118, 120, 122 separately independently, and that the linear dispersion of each of these grating surface 116, 118, 120, 122 may coincide at the above specific condensing position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system and a spectrophotometer using the same, and more particularly to an optical system capable of reducing spherical aberration in all parts of a diffraction grating.

[0002]

2. Description of the Related Art There are various devices for measuring the light intensity for each wavelength, and a typical one is a diffraction grating 10 as shown in FIG. 1 and a multi-channel detector (MC).
D) is combined with 12 to project, for example, a radiated light beam as the incident light L onto the diffraction grating 10 through the incident slit 14;
The intensity of each wavelength light separated by the diffraction grating 10 is referred to as MCD1.
2. There is a spectrum measuring device for measuring according to 2.

[0003] Such a multi-channel spectrophotometer has the advantages that the configuration can be simplified and the device can be miniaturized. Since wavelength scanning is not required, various characteristics of the sample at each wavelength can be simultaneously measured in real time. Recently, in such a multi-channel spectrophotometer, a holographic concave grating (HCG) made by utilizing interference of laser light is used as the diffraction grating 10.

[0004]

The above-mentioned HCG
In 10, the wavelengths of light split at each portion of the concave grating are condensed almost uniformly to each wavelength-corresponding portion of the MCD 12 by controlling the interval between grooves cut on the spherical mirror, the shape of the groove lines, and the like. Like that. However, the HCG1
In the case of 0, since a spherical mirror is used, spherical aberration depending on the F number occurs, and the resolution is reduced. That is, if a large-area spherical mirror is used to brighten the optical system, the spherical aberration becomes a size that cannot be ignored.

In the above-mentioned HCG 10, in a normal case,
Since grooves are collectively formed on the entire mirror surface by holography on the spherical mirror, it is necessary to appropriately select holographic manufacturing conditions, mainly the radius of curvature of the spherical mirror, exposure conditions, etc., which are optimal for the optical system. However, such optimization is not optimal for all parts on the spherical mirror, but can be performed only on average. The spherical aberration is very small in the vicinity of the center 10a, but is small in the peripheral part 10b. Becomes large. For this reason, the conventional HCG
In No. 10, in order to reduce the influence of the spherical aberration of the peripheral portion 10b, it is necessary to adopt a manufacturing condition or the like at the cost of optimizing the vicinity of the center 10a.

As a result, a slit image I formed on the light receiving surface of the MCD 12 from the central portion 10a of the HCG 10 is formed.
_A deviation occurs between _10a (see FIG. 2A) and the slit image I _10b from the peripheral portion 10b (see FIG. 2B). For this reason, in this type of field, although there has been a strong demand for the development of a technique capable of reducing spherical aberration in all parts of the diffraction grating, there is still an appropriate technique for solving this. Did not.
The present invention has been made in view of the problems of the prior art, and reduces spherical aberration for all portions of the diffraction grating,
An object of the present invention is to provide an optical system capable of improving the resolution and a spectrophotometer using the same.

[0007]

Means for Solving the Problems As a result of intensive studies conducted by the present inventors to achieve the above object, the grating surface of the diffraction grating is divided into a plurality of grating surfaces, and each of the divided grating surfaces is separately and independently formed.
For example, considering the curvature radius of the concave lattice surface, the shape of the groove cut into the lattice surface, that is, optimization of the groove shape according to the location of each part, and further, considering the holographic manufacturing conditions such as the exposure conditions at the manufacturing stage To manufacture. That is, by considering the combination of the shape, curvature, and the like of the grooves on each lattice plane, the light is produced so that light from each lattice plane can be guided to a desired position.

Then, similar incident light images are formed separately and independently on each lattice plane thus formed, and the line dispersion of each lattice plane coincides with the specific light condensing position. As described above, it has been found that the above optimization can be performed for all portions of the diffraction grating by devising the arrangement of the respective grating surfaces, and the present invention has been completed.

That is, the optical system according to the present invention includes a diffraction grating that separates incident light for each wavelength, and the optical system that condenses each wavelength light separated by the diffraction grating at a specific position. The grating is formed by dividing a grating surface into a plurality of parts, and each of the divided grating surfaces is manufactured separately and independently in consideration of holographic manufacturing conditions, and similar incident light images are separately and independently formed on the respective grating surfaces. And the respective grating surfaces are arranged such that the linear dispersion of the respective grating surfaces coincides with each other at the specific light condensing position.

As the diffraction grating of the present invention, for example, a holographic concave grating can be used. Further, in the optical meter, it is also preferable to place a detector at the specific condensing position, or to place an exit slit. Here, the detector receives light of each wavelength or light of a specific wavelength separated by the diffraction grating, and measures the intensity of the light. As the detector of the present invention, for example, a multi-channel detector that receives light of each wavelength separated by the diffraction grating and measures the intensity of light at each wavelength can be used.

The emission slit extracts light of a specific wavelength from the light of each wavelength separated by the diffraction grating. Further, in the optical system, the respective lattice planes are the same,
Or it is also suitable to have different blaze wavelengths. Further, in the optical system, it is also preferable that each of the grating surfaces is held by each holding mechanism or one holding mechanism. Further, in the optical system, it is preferable that the shapes of the respective grating surfaces are the same or different types.

The shape of the grating surface referred to here means, for example, the outer shape of the diffraction grating defined by the width, height and the like. The holographic manufacturing conditions referred to herein include, for example, the design of the radius of curvature of the lattice surface, the shape of the groove, the interval between the grooves, the shape of the groove line, and the like, and the exposure conditions for realizing the design. Say. Examples of the shape of the groove include a classical lattice, an echelette lattice, an echelon lattice, an echelle lattice, a lamina lattice, a lamella lattice, a sinusoidal lattice, and a trapezoidal lattice. There are regular and irregular intervals between the grooves. The shape of the groove line is, for example, a curve group in a concave diffraction grating, but a straight line group is also possible.

Next, an example of a method of manufacturing each lattice plane referred to herein will be described below. In the present invention, the design of the curvature radius of the concave lattice plane, the shape of the groove, etc. Holographic manufacturing conditions such as exposure conditions for realizing the design are taken into account. Then, a lattice groove having a substantially sinusoidal cross section is formed in the thin film on the concave substrate by holography. When the convex substrate is replicated from the concave substrate, a substantially sinusoidal lattice groove is also formed on the transfer surface of the concave substrate.

Next, an ion beam is irradiated at the same angle of incidence from the obliquely above the concave substrate to the entire convex surface from above the convex substrate to perform etching.
Serrated grooves having the same blaze angle are formed on the convex substrate. Then, by forming a replica using the convex grating as a substrate, each concave echelette grating can be obtained.

According to the present invention, similar incident light images are formed separately and independently on each of the grating surfaces such as each of the concave-shaped echelette gratings separately formed in this manner, and the respective grating surfaces are formed. Each of the grating planes is arranged by devising such that the linear dispersion of the light is coincident at a specific light condensing position, thereby completing the optical system of the present invention. In order to achieve the above object, a spectrophotometer according to the present invention uses the optical system according to the present invention.

[0016]

FIG. 3 shows a schematic configuration of an optical system according to an embodiment of the present invention. Note that FIG.
The parts corresponding to and are denoted by reference numeral 100, and description thereof is omitted. In the optical system 110 shown in the figure, the incident light L enters the diffraction grating 110 via the incident slit 114, and is wavelength-resolved. As a result, the MCD set on the slit image plane
Since a slit image for each wavelength is formed on the light receiving surface of the light 112, the intensity of light for each wavelength is measured by the MCD 112.

Here, in the present embodiment, as described above, the diffraction grating 110 divides the grating surface into four, and each grating surface 116,
118, 120, 122 (for example, length 20 mm x width 20 m
m, etc.) are separately manufactured in consideration of the holographic manufacturing conditions such as the curvature radius of the grating surface, the shape of the groove, and the exposure conditions for realizing the design.

[0018] On top of that, in the present embodiment, when light is incident L ₁₁₆ ~L ₁₂₂ of various incident angles on the diffraction grating 110, than the first slit image is made across a plurality of lattice plane And each of the lattice planes 116, 118, 120,
At 122, independent slit images I116-I122 are created and each of the lattice planes _{116, 118} , 12
The grating planes 116, 118, 120,.
The arrangement of 122 is devised by each corresponding holding mechanism (not shown).

The optical system according to the present embodiment is generally configured as described above, and its operation will be described below. First, the incident light L is transmitted through the entrance slit 114 to the diffraction grating 1.
The light is projected onto the diffraction grating 10 and separated by the diffraction grating 110 for each wavelength. Here, conventionally, as such a diffraction grating,
In general, a single spherical mirror having grooves formed on the entire mirror surface by holography is used.

However, if such a diffraction grating is used, a large spherical aberration occurs, for example, in the peripheral portion of the grating surface as described above. Therefore, in the present embodiment, in order to reduce spherical aberration and improve resolution in all portions of the diffraction grating, a grating surface is divided into four as a diffraction grating, and each of the divided grating surfaces 116, 118, and 1 is used.
20, 122 are manufactured independently taking into account holographic manufacturing conditions such as the radius of curvature, the shape of the groove, and the exposure conditions.

Then, incident light L _{116 having} various incident angles is formed.
To L ₁₂₂ are incident on the diffraction grating 110, similar slit images I _{116 to} I ₁₂₂ are formed on the respective grating surfaces _{116 and} 11.
8, 120, 122, and the line dispersion of each of the lattice planes 116, 118, 120, 122 is
The arrangement of each of the lattice planes 116, 118, 120, and 122 is devised so as to coincide at each wavelength corresponding portion of the MCD 122. That is, the incident light L at various incident angles
_{When 116 to} L ₁₂₂ are incident on the diffraction grating 110,
One slit image is not formed over a plurality of lattice planes, but similar slit images I ₁₁₆ , I ₁₁₈ , I ₁₂₀ , and I ₁₂₂ are formed on each lattice as shown in FIGS. The surfaces 116, 118, 120, and 122 are made separately and independently.

The respective lattice planes 116, 11
As shown in FIG. 4D, the linear dispersions from 8, 120, and 122 are matched at each wavelength-corresponding portion of the MCD 112, and therefore, regardless of the incident angle of the incident light L with respect to the diffraction grating 110, It is possible to greatly reduce the spherical aberration on the grating surface and improve the resolution. Further, in the present embodiment, each of the lattice planes 116, 118, 120, 122 is maintained without changing the F number of the optical system 110 as a whole.
Of the optical system 11 can be increased.
Sufficient brightness can be obtained without increasing the size of 0.

In the present embodiment, during the manufacture of the diffraction grating 110, the blaze wavelength of each of the grating surfaces 116, 118, 120, 122 is controlled so as to be different or the same according to the purpose of use. Thereby, it becomes easy to improve the degree of freedom such as uniformly dispersing or concentrating the incident light in a wide wavelength range or giving a plurality of peaks. Next, in order to verify the resolution in the case where the optical system according to the present embodiment is used, how the linear dispersion formed on the light receiving surface of the MCD 112 changes depending on the size of each of the grating surfaces 116 to 122 will be described. Examined.

That is, FIG. 5 shows each of the lattice planes 116-1.
FIG. 6 shows an example of the linear dispersion when the size of each of the samples 22 is 80 mm × 80 mm.
FIG. 7 shows an example of the line dispersion in the case of 20 mm × 20.
An example of linear dispersion in the case of mm is shown. As is clear from FIGS.
FIG. 5 showing a case where the size of each 122 is 80 mm × 80 mm and FIG. 6 showing a case where the size of each 122 is 40 mm × 40 mm are compared with FIG. 195.1, 195.
It is understood that the aberration can be significantly reduced for each wavelength such as 2,159.3, 159.4, and 159.5 nm.

As described above, the grating surface of the diffraction grating 110 is divided into a plurality of portions as in the present embodiment, and each of the divided portions 116 is divided.
１２２122 are manufactured separately and independently in consideration of holographic manufacturing conditions and the like, whereby the same optimization can be performed for each part of the diffraction grating. As a result, it can be said that the spherical aberration can be significantly reduced in all parts of the diffraction grating and the intensity of light for each wavelength can be measured with high resolution, as compared to a case without such a device.

As described above, according to the optical system of the present embodiment, the grating surface of the diffraction grating is divided into a plurality of parts, and each of the divided grating surface parts is manufactured independently by devising manufacturing conditions and the like. As a result, the same optimization can be performed for each part of the diffraction grating, so that the spherical aberration can be significantly reduced and the resolution can be significantly improved for all the grating surface parts. In the present embodiment, the diffraction grating 110
During the manufacture of the laser, the blaze wavelength of each grating surface is appropriately controlled according to the purpose of use, etc., so that the incident light can be dispersed or concentrated uniformly over a wide wavelength range, or multiple peaks can be obtained. It is easy to improve the degree.

Also, by using the optical system according to the present embodiment for the optical system of a spectrophotometer, the intensity of light at each wavelength can be measured with good resolution, and thus the invention is devised as in the present embodiment. This makes it possible to perform more accurate spectroscopic measurement as compared with an optical system that does not use an optical system. In addition,
In the present embodiment, an example in which the grating surface of the diffraction grating 110 is divided into four parts has been described. However, the present invention is not limited to this, and other plural divisions may be made according to the purpose of use.

Further, in this embodiment, an example in which the incident light L from the incident slit 114 is directly projected on the diffraction grating 110 has been described.
Alternatively, a light source may be placed, and the light from the light source may be directly projected on the diffraction grating 110, or a reflecting mirror or the like may be interposed between them. In the present embodiment, each wavelength light split by the diffraction grating 110 is directly transmitted to the MCD 11.
Although the example in which the light is received at 2 has been described, a reflecting mirror or the like may be interposed between the diffraction grating 114 and the MCD 112.
In the present embodiment, the blaze wavelengths of the respective grating surfaces 116 to 122 may be the same or different.

In this embodiment, each lattice plane 1
Although the example in which 16 to 122 are held by the corresponding holding mechanisms has been described, they may be held together by one holding mechanism. Further, in the present embodiment, each lattice plane 1
The shapes of 16 to 122, that is, the outer shapes of the diffraction gratings may be of the same type or different.

[0030]

As described above, according to the optical system of the present invention, the grating surface is divided into several parts, and each part is separately and independently made in consideration of holographic manufacturing conditions. Since the same incident light images are formed on the grating planes separately and independently, and such that the line dispersion of each grating plane coincides at a specific light-condensing position, the respective grating planes are arranged. The spherical aberration can be significantly reduced and the resolution can be improved for all portions of the diffraction grating, which has been extremely difficult in the past. In addition, during manufacture of the diffraction grating, by controlling the blaze wavelength of each of the grating surfaces, it becomes easy to uniformly disperse, concentrate, or have a plurality of peaks over a wide wavelength range. Further, according to the spectrophotometer according to the present invention, as described above, the optical system according to the present invention, which has a reduced spherical aberration at each grating surface and an excellent resolution, is used. The resolution can be further improved as compared with an optical system using no optical system.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a schematic configuration of a conventional optical system.

FIG. 2 is an explanatory diagram of a slit image when the optical system shown in FIG. 1 is used.

FIG. 3 is an explanatory diagram of a schematic configuration of an optical system according to an embodiment of the present invention.

FIG. 4 is an explanatory diagram of a slit image when the optical system shown in FIG. 3 is used.

FIG. 5 is a view showing an example in which each grating surface of the optical system shown in FIG.
It is an example of the linear dispersion when it is set to 0 × 80 mm.

FIG. 6 shows each lattice plane of the optical system shown in FIG.
It is an example of the linear dispersion when it is set to 0 × 40 mm.

FIG. 7 shows each lattice plane of the optical system shown in FIG.
It is an example of the linear dispersion when it is set to 0 × 20 mm.

[Explanation of symbols]

 110: diffraction grating 112: MCD (detector) 114: entrance slit 116, 118, 120, 122: each grating surface

Continuation of the front page (72) Inventor Kazuhiro Kawasaki 2967 Ishikawa-cho, Hachioji-shi, Tokyo F-term in Japan Spectroscopy Co., Ltd. 2G020 CC05 CC06 CC11 CC04 CD24 CD24

Claims (6)

[Claims] 1. An optical system including a diffraction grating that separates incident light for each wavelength and condensing each wavelength light separated by the diffraction grating at a specific position, wherein the diffraction grating has a plurality of grating surfaces. Divided, each of the divided lattice planes is manufactured independently and in consideration of holographic manufacturing conditions, and a similar incident light image is formed on each of the lattice planes separately and independently. An optical system, wherein each of the lattice planes is arranged such that the linear dispersion of the light beams coincides with the specific light condensing position. 2. The optical meter according to claim 1, further comprising a detector that receives each wavelength light or a specific wavelength light split by the diffraction grating and measures the intensity of the light at the focusing position. An optical system, comprising: an output slit for extracting light of a specific wavelength from light of each wavelength separated by the diffraction grating. 3. The optical system according to claim 1, wherein
An optical system, wherein each of the grating surfaces has the same or different blaze wavelength. 4. The optical system according to claim 1, wherein each of said grating surfaces is held by a respective holding mechanism or a single holding mechanism. 5. The optical system according to claim 1, wherein said grating surfaces have the same or different shapes. 6. A spectrophotometer using the optical system according to claim 1.