JP2002005739A - Zernitana type spectrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct an image surface curve in a Zernitana type spectrometric optical system. SOLUTION: In this Zernitana type spectrometer, the diffused incident light from an incident slit 1 is reflected by a collimate mirror 2 to form a parallel luminous flux, which is then incident on a reflecting type flat diffraction grating 3, and the reflected parallel spectral light divided by the diffraction grating 3 is reflected by an imaging mirror 4 and imaged and received by a light receiving line sensor 5. In this device, the line sensor 5 is arranged with an inclination from the angle orthogonal to the optical axis B of the imaging mirror 4. The line sensor 5 is arranged also with an inclination from the angle orthogonal to the optical axis of the converged spectral light of middle wavelength incident from the imaging mirror 4 on the center of the line sensor 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called Czernitana-type spectrometer using two spherical reflecting mirrors.

[0002]

2. Description of the Related Art FIG. 1 is a schematic view of a conventional spectral optical system of the so-called Zernnitana type (for example, Japanese Patent Application Laid-Open No. 56-37527). The diffused light incident from the entrance slit 1 'is converted into a parallel light by the first concave mirror 2' (reflective concave mirror / collimator mirror) and is diffracted by the reflection type diffraction grating 3 ', and each diffraction spectrum light is converted into the second concave mirror 4' ( An image is formed by the light receiving section 5 '(line sensor) by the imaging concave mirror. In the figure, an exit slit is provided in the light receiving section 5 ', and only monochromatic light is extracted.

[0003] In a Czern-Turner-type spectroscopic optical system, which is a reflection optical system, chromatic aberration does not occur, but a light beam obliquely enters the concave mirrors 2 'and 4', so that coma aberration and astigmatism occur. Among these aberrations, the coma which is an asymmetric aberration tends to be canceled out when the directions of incident light on the two concave mirrors 2 ′ and 4 ′ are opposite to each other, but the astigmatism which is a symmetric aberration The aberration is amplified by the second concave mirror 4 ′ and further increased, and the image is formed in the sagittal direction perpendicular to the meridional direction with respect to the image forming point (image forming position) in the spectral direction (meridional direction) of the diffraction grating 3 ′. The image point (imaging position) is shifted in a direction away from the second concave mirror 4 '. For this reason, on the light receiving surface of the line sensor 5 'installed in accordance with the image forming position in the meridional direction, each spectrum is received as an image long in the sagittal direction (imaging point group diffused in the sagittal direction), and the light receiving efficiency is reduced. The decline was coming. FIG. 5 shows this state, and the image forming point group in the spectrum light of the specific wavelength appears as diffused as shown in the figure.

However, as described above, when the diffracted light diffuses in the sagittal direction, the light receiving efficiency is reduced. Therefore, some attempts have been already made to prevent the diffusion of the light beam due to astigmatism. For example, in JP-B-63-41413 and JP-A-57-60232, diffusion of diffracted light is suppressed by making the surface of the diffraction grating a cylindrical surface. In Japanese Patent Application Laid-Open No. 57-54826, a concave mirror having a toric surface is used.
No. 0 and Japanese Patent Application Laid-Open No. 2-216019 attempt to overcome the above drawbacks by making the pitch of the diffraction grating unequal. Further, Japanese Patent Application Laid-Open No. 54-15508
No. 6 and JP-A-55-087925, a first slab lens-like medium having a negative refractive power in the sagittal direction is combined with a second slab lens-like medium having a positive refractive power in the sagittal direction. Thus, means for suppressing astigmatism have been proposed.

In the conventional spectroscopic device, as shown in FIG. 1, the line sensor 5 'is formed to be long in the spectral direction (meridional direction) of the diffraction grating 3'. That is, in order to ensure a balance between the light receiving intensity on the short wavelength light receiving side and the long wavelength light receiving side,
The light receiving surface of the line sensor 5 'is set so as to be orthogonal to the optical axis A' of the intermediate wavelength spectrum light that enters the center of the line sensor 5 'from the second concave mirror 4' in the longitudinal direction.

This is described in Japanese Patent Application Laid-Open No. 55-08792.
The same applies to the configuration shown in FIG. 1 of Japanese Patent Application Laid-open No. 5 (1993) -205, in which the bonding surface between the slab lens-shaped medium (5) and the output optical fiber bundle (7) is a line sensor (light-receiving sensor). Part), where the light-receiving surface performs the same function as
Optical axis of intermediate wavelength spectrum light is slab lenticular medium
It is set to be orthogonal to (5).

[0007]

The first problem of the prior art is that the light receiving surface of the line sensor 5 'has an intermediate wavelength spectrum which is incident from the second concave mirror 4' to the center in the longitudinal direction of the line sensor 5 '. That is, it is set so as to be orthogonal to the optical axis A ′ of light. When the angle is set in this manner, the light receiving intensity at the center of the line sensor 5 'can be optimized, so that the light receiving intensity as a whole becomes favorable and a balance can be secured. However, the imaging point in the meridional direction is slightly different depending on the wavelength of the spectral light. The spectral light on the short wavelength side is imaged at a position far from the second concave mirror 4 ′, and the spectral light on the long wavelength side is the second concave mirror. Since an image is formed at a position close to 4 ', if the light receiving intensity is set with priority as in the related art, field curvature occurs on the line sensor 5'. The second problem is that the means taken as a measure against astigmatism has a problem in manufacturing and setting. In other words, diffraction gratings with a cylindrical surface, diffraction gratings with unequal pitch, and reflecting mirrors with a toric surface are very expensive to manufacture, and because setting parameters increase, errors tend to occur in the settings, and corrections can be made. It will be difficult. In the case of using a slab lens-like medium, a first lens having a negative refractive power in the sagittal direction is used.
A slab lenticular medium and a second slab lenticular medium having a positive refractive power in the sagittal direction must be used in combination.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its object to correct the curvature of field on a line sensor in a Zernarter-type spectroscopic optical system by a simple means. It is an object to correct astigmatism in an optical system by a simple means.

[0009]

According to the present invention, diffused incident light from an entrance slit 1 is reflected by a collimating mirror 2 to be incident on a reflection type planar diffraction grating 3 as a parallel light beam, and the light is split by the diffraction grating 3. The reflected parallel-spectral light thus reflected is formed on an imaging mirror 4 inclined with respect to the reflected parallel-spectral light.
And a light receiving line sensor 5 to form an image and receive the image. The line sensor 5 is arranged in a Zernnitana type spectroscopic device inclined at an angle perpendicular to the optical axis B of the image forming mirror 4. Numeral 5 denotes a Zernnitana arranged to be inclined from an angle perpendicular to the optical axis A of the condensed spectrum light of the intermediate wavelength that enters the center of the line sensor 5 from the imaging mirror 4 in order to correct the field curvature. This is a configuration of a spectroscopic device. Also, the present invention
In the above-described apparatus, the optical path from the imaging mirror 4 to the line sensor 5 does not have a refractive power in the optical path from the imaging mirror 4 to the line sensor 5 in the spectral direction. A cylindrical lens 6 having a positive refractive power is provided in a direction orthogonal to the spectral direction, and the cylindrical lens 6 is arranged to be orthogonal to the optical axis A of the condensed spectral light. This is a configuration of a spectroscopic device.

[0010]

FIG. 2 shows a first embodiment of the present invention.
The divergent light condensed by the objective lens 7 and incident from the entrance slit 1 is converted into parallel light by the collimator mirror 2 which is the first spherical reflecting mirror, and is incident on the reflection plane diffraction grating 3. The spectral luminous flux reflected by the diffraction grating 3 is condensed by an imaging mirror 4 which is a second spherical reflecting mirror, and forms an image on a line sensor 5 which is a light receiving element. Since the spectral luminous flux reflected by the diffraction grating 3 has a different diffraction angle depending on the wavelength, it enters the image forming mirror 4 as a group of parallel rays having different incident angles according to the wavelength.
For this reason, the spectrum light is received by the sensor 5, which is the image plane, at different positions depending on the wavelength.

The cylindrical lens 6, which is a feature of the present invention, is placed between the light receiving element of the line sensor 5 and the imaging mirror 4, and collects light incident on the line sensor 5. The cylindrical lens 6 used in the present invention has no refracting power in the meridional direction (spectral light distribution direction). In this direction, the cylindrical lens 6 does not affect the light condensing action of the image forming mirror 4, but has an influence on the meridional direction. It has a positive refractive power in the vertical sagittal direction. Due to the sagittal refracting power, a light beam in the sagittal direction that forms an image far from the position where the line sensor 5 is originally installed due to astigmatism is formed on the element of the line sensor 5.

FIG. 3 is an optical arrangement diagram of a second embodiment of the present invention. The diffused light condensed by the objective lens 7 and emitted from the entrance slit 1 is reflected at an acute angle by the first plane mirror 9 and is reflected by the collimator mirror 2 to become parallel light. The parallel light is reflected by the second plane mirror 10 and is diffracted and reflected by the reflection type diffraction grating 3. The diffracted light is condensed by the imaging mirror 4 and enters the one-dimensional line sensor 5 via the secondary light cut filter 8 as spectral light corresponding to the wavelength. In the second embodiment, the entrance slit 1 is provided via a plane mirror 9 serving as a first folding mirror, and the one-dimensional line sensor 5 is provided with an imaging mirror 4.
, Are inwardly convoluted around the plane mirror 10 serving as a second folding mirror, respectively, and have a very compact configuration. Further, since the light beam can be taken long and the light beam does not cross, the arrangement of the light shielding plate becomes easy, and stray light can be effectively prevented.

FIG. 4 is a diagram showing the arrangement of the line sensor 5 and the cylindrical lens 6 of the optical system according to the present invention.
The cylindrical lens 6 is disposed perpendicularly to the optical axis A of the intermediate-wavelength spectral light flux incident on the center of the line sensor 5.
Attach it at α degrees. In addition, the line sensor 5
As shown in FIG. 4, is tilted from an angle perpendicular to the optical axis A of the spectral light flux of the intermediate wavelength incident on the center of the line sensor 5 and is installed non-parallel to the cylindrical lens 6. This is to correct the field curvature which is a shift of the image point in the meridional direction caused by the image forming mirror 4 being inclined with respect to the incident light. By shifting the long-wavelength light receiving side of the line sensor 5 closer to the imaging mirror 4 and slightly inclining the short-wavelength light-receiving side away from the imaging mirror 4, the deviation of the imaging point can be corrected.

Incidentally, the cylindrical lens 6 is mounted so as to be movable by a predetermined distance in the direction of the optical axis A. This is to make it possible to adjust the focusing state of the light beam on the line sensor 5.

[0015]

The line sensor 5 according to the present invention is shown in FIG.
As shown in the above, the light is inclined at an angle perpendicular to the optical axis A of the intermediate wavelength spectrum light incident on the center of the line sensor 5 and is installed non-parallel to the cylindrical lens 6. For this reason, the curvature of field, which is the shift of the imaging point in the meridional direction caused by the imaging mirror 4 being inclined with respect to the incident light, can be adjusted by adjusting the set angle without affecting other configurations. Can be easily corrected.

FIG. 5 shows the operation of the conventional apparatus (FIG. 1) which does not use the astigmatism correcting means corresponding to the cylindrical lens 6 of the present invention. Due to the influence, the light is diffused in the width direction of the line sensor (sagittal direction of the diffraction grating). FIG. 6 shows the operation of the present invention, in which the diffusion of the luminous flux in the sagittal direction is corrected by inserting the cylindrical lens 6 capable of correcting astigmatism, and the image forming point group is concentrated at the center of the line sensor 5. I understand.

[0017]

As described above, according to the present invention, the diffused incident light from the entrance slit 1 is reflected by the collimating mirror 2 to be incident on the reflection type plane diffraction grating 3 as a parallel light beam, and separated by the diffraction grating 3. The reflected parallel spectrum light is reflected by the imaging mirror 4 arranged obliquely with respect to the reflected parallel spectrum light, and is imaged and received by the light receiving line sensor 5. The line sensor 5 is located on the optical axis B of the imaging mirror 4. In a Czerni-Turner-type spectroscopic device arranged to be inclined from an angle perpendicular to the line, the line sensor 5 is a collection of intermediate wavelengths incident on the center of the line sensor 5 from the imaging mirror 4 in order to correct field curvature. The configuration of the Czernita-type spectroscopic device arranged so as to be inclined from the angle orthogonal to the optical axis A of the light spectrum light is also used, so-called Czernita using two spherical reflecting mirrors In the type of spectroscopic optics, Yuizokyo 4
Can be accurately and easily corrected, which is a shift of an image forming point in the meridional direction, which is caused by oblique light with respect to incident light. The present invention also provides the apparatus, wherein in the optical path from the imaging mirror 4 to the line sensor 5, in the optical path from the imaging mirror 4 to the line sensor 5, A cylindrical lens 6 having no refractive power but having a positive refractive power in a direction orthogonal to the spectral direction is provided, and the cylindrical lens 6 is orthogonal to the optical axis A of the condensed spectrum light. With the configuration of the Zell-Nitana-type spectrometer arranged as described above, diffusion of an image caused by astigmatism can be prevented, and good light-collecting characteristics can be obtained. In particular, since it is not necessary to use a special diffraction grating or a reflecting mirror as in the above-described conventional example, the above-described effect can be achieved with an extremely simple configuration.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a Zernnitana-type spectroscopic optical system.

FIG. 2 is an explanatory diagram of a first embodiment of the present invention.

FIG. 3 is an explanatory diagram of a second embodiment.

FIG. 4 is a layout diagram of a cylindrical lens and a light receiving line sensor.

FIG. 5 is a diagram illustrating a light receiving state of a sensor when a cylindrical lens is not used.

FIG. 6 is a diagram illustrating an effect of the cylindrical lens.

[Explanation of symbols]

1, 1 '... entrance slit, 2 ... collimating mirror, 2'
... Concave mirror, 3, 3 '... Reflection type diffraction grating, 4 ... Imaging mirror, 5
... Line sensor, 5 '... Light receiving part (line sensor), 6 ...
A cylindrical lens, 7 an objective lens, 8 a secondary light cut filter, 9 a first plane mirror, 10 a second plane mirror,
A, A ': optical axis of the intermediate wavelength spectrum light, B: optical axis of the imaging mirror.

Claims (2)

[Claims] 1. A diffused incident light from an entrance slit 1 is reflected by a collimating mirror 2 to be incident on a reflection type planar diffraction grating 3 as a parallel light flux, and the reflected parallel spectrum light separated by the diffraction grating 3 is reflected parallel spectrum. The light is reflected by the imaging mirror 4 arranged obliquely with respect to light, and is formed and received by the light receiving line sensor 5. The line sensor 5 is inclined from an angle perpendicular to the optical axis B of the imaging mirror 4. In the arranged Zernnitana spectrometer, the line sensor 5
Is a Zernnitana type arranged to be inclined at an angle perpendicular to the optical axis A of the condensed spectral light of the intermediate wavelength that enters the center of the line sensor 5 from the imaging mirror 4 in order to correct the field curvature. Spectroscopy device. 2. An optical path from the imaging mirror 4 to the line sensor 5 in the optical path from the imaging mirror 4 to the line sensor 5, A cylindrical lens 6 having no refractive power but having a positive refractive power in a direction orthogonal to the spectral direction is provided, and the cylindrical lens 6 is orthogonal to the optical axis A of the condensed spectrum light. Cernitana-type spectrometer arranged like this.