JPH11264762A - Echelle type spectroscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the totally uniform and bright spectral image without affected by the shading by a plane mirror for converting an optical path. SOLUTION: A reflection type Schmidt plate 5 is used, a rotary shaft y1 forming a curved surface of a reflection face of the Schmidt plate and a rotary shaft y2 forming a curved surface of a reflection face of a spherical mirror 6 are same as each other, and the arrangement of the optical elements is determined so that the rotary shaft y2 is shifted from an axis of the incident light of the spherical mirror 6. A spectral image is focused on a detection surface of an optical-detector 7 through the spherical mirror 6, when the luminous flux including the two-dimensional spectral of which the wavelength is dispersed by the echelle diffraction grating 3 and diffraction grating 4 is introduced to the Schmidt plate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an echelle spectroscope used for a spectroscopic analyzer such as a plasma emission analyzer.

[0002]

2. Description of the Related Art In an echelle diffraction grating, which is a kind of diffraction grating, a groove having a large blaze angle is formed.
Higher-order (for example, several tens to hundreds or more) diffracted light with respect to incident light can be obtained as output light. Since a large number of high-order diffracted lights are superimposed on light obtained at a certain exit angle, this echelle diffraction grating is usually used in combination with an order separating optical element that disperses light in the order direction. Many.

FIG. 2 is a schematic diagram showing an example of an optical path of a conventional general echelle spectroscope. This configuration is based on a so-called Zernnitana mountain arrangement, in which a diffraction grating 4, a transmission type Schmitt plate 8, a plane mirror 10, and a spherical mirror 9 are arranged substantially in a straight line. In the case of an emission spectrometer, light containing an emission line spectrum from a light source such as a plasma torch or an arc is emitted. It passes through and is introduced into the spectroscope.

The light passing through the entrance slit 1 is converted into a parabolic mirror 2
And wavelength-dispersed by the echelle diffraction grating 3 in a direction perpendicular to the longitudinal direction of the entrance slit 1 (hereinafter referred to as “horizontal direction”). Next, the dispersed light is dispersed in the direction perpendicular to the horizontal direction (hereinafter, referred to as “vertical direction”), that is, in the order separation direction, by the order separation diffraction grating 4, and the transmission type Schmitt plate 8 is separated. It passes through and strikes the spherical mirror 9. The reflected light from the spherical mirror 9 is reflected by the plane mirror 10 and forms an image on the detection surface of a photodetector (for example, a CCD imager) 7 disposed outside the light beam incident on the spherical mirror 9.

The Schmidt plate 8 is mainly composed of a spherical mirror 9
An optical element for correcting spherical aberration, coma, and astigmatism caused by, formed from a material such as quartz glass in order to transmit ultraviolet rays with minimal loss,
The element surface is processed by polishing or the like so as to have a curved surface corresponding to the distortion or the like of the spherical mirror 9. Thereby, it is possible to prevent the diffracted lights of different orders that are temporarily separated in the vertical direction by the diffraction grating 4 from overlapping due to aberration at the time of image formation.
High resolution is guaranteed.

[0006]

However, in the optical path configuration of the above-mentioned conventional Echelle spectroscope, since the plane mirror 10 is disposed on the optical path between the Schmitt plate 8 and the spherical mirror 9, the light passes through the Schmitt plate 8. A part of the luminous flux is shielded by the plane mirror 10 (that is, the shadow of the plane mirror 10 is projected on the spherical mirror 9). For this reason, the light reflected from the spherical mirror 9 does not include information corresponding to the shielded light flux, and as a result, the photodetector 7 cannot obtain spectral information of some wavelength regions. .

In order to reduce the influence of the light shielding, each of the optical elements such as the parabolic mirror 2, the echelle diffraction grating 3, the diffraction grating 4, and the spherical mirror 9 is enlarged, and the light beam transmitted from the diffraction grating 4 to the spherical mirror 9 is used. Should be increased to relatively reduce the influence of light shielding. However, such a method does not necessarily prevent shading, so that a spectral image is darker in some wavelength regions to be shielded than in other wavelength regions, and sensitivity and accuracy of spectrometry are deteriorated. . In addition, when each optical element is enlarged, there is a problem that the cost of the element increases and it is difficult to reduce the size of the entire spectroscope.

The present invention has been made to solve such problems, and a first object of the present invention is to:
It is an object of the present invention to provide an echelle spectroscope capable of obtaining a spectrum image with uniform brightness in all wavelength regions to be analyzed. A second object is to provide an echelle spectroscope capable of obtaining a spectral image with less aberration. A third object is to provide an inexpensive echelle spectroscope that is easy to manufacture.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an echelle diffraction grating for dispersing incident light in one direction, and a light beam from the echelle diffraction grating in a direction substantially perpendicular to the direction. In the echelle spectroscope provided with an order separating dispersion element for dispersing the light, a) light reflected on the element surface of the order separating dispersion element is incident, and the incident optical axis and the output optical axis are different from each other. A) a reflection-type aberration correcting optical element disposed at a position; b) a photodetector disposed outside the reflected light beam from the aberration correcting optical element; and c) reflected light from the aberration correcting optical element is incident. And a spherical mirror for condensing light on the detection surface of the photodetector.

In order to realize the above-mentioned optical configuration,
The curved surface of the reflecting surface of the aberration correction optical element is a curved surface obtained by rotating a curve by a multidimensional function in a certain plane around a certain axis included in the plane, and the curved surface of the reflecting surface of the spherical mirror is A curve formed by a quadratic function in a plane is a curved surface obtained by rotating about a certain axis included in the plane, and both rotation axes are aligned in the same direction, and the rotation axes are set as aberration correction optical elements. From the optical axis of the light sent from the lens to the spherical mirror.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In this optical configuration, a reflective Schmitt plate or a reflective meniscus can be used as a reflective aberration correcting optical element. For example, a reflective Schmidt plate has a curved surface obtained by a predetermined function around a certain rotation axis as a reflective surface.

When a light beam having a two-dimensional spread from the order separating dispersion element is sent to the aberration correcting optical element, the aberration correcting optical element reflects light in a direction different from the optical axis of the incident light beam. The reflected light hits the spherical mirror, and forms a spectral image on the detection surface of the photodetector located outside the light beam incident on the spherical mirror. That is, according to this configuration, it is not necessary to insert an element that causes light shielding, such as a conventional reflector, in the optical path from the wavelength dispersion element to the photodetector. If the curvature of the reflection surface of the aberration correcting optical element is determined so that the aberration on the focal plane of the photodetector is the best in the area where the light beam hits, the aberration on the detection surface of the detector can be reduced. A small number of spectral images can be formed.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the echelle spectrometer according to the present invention will be described below with reference to FIG. FIG. 1 is a schematic configuration diagram illustrating an optical path by the echelle spectroscope of the present embodiment. In the spectroscope of this embodiment, the optical path configuration from the entrance slit 1 to the diffraction grating 4 is the same as the conventional one shown in FIG. 2, and the configuration of the optical path after the diffraction grating 4 is different.

That is, in FIG.
Is converted into a parallel light beam having no aberration by the parabolic mirror 2 and is applied to the echelle diffraction grating 3. The echelle diffraction grating 3 disperses light in the horizontal direction, and the diffraction grating 4 further disperses the dispersed light in the vertical direction to obtain spectral light having a two-dimensional spread. This dispersed light is sent to the reflective Schmitt plate 5, and the light reflected by the Schmitt plate 5 is sent to the spherical mirror 6 located in a direction different from the optical axis of the incident light. The light reflected by the spherical mirror 6 is collected on the detection surface of the photodetector 7 located outside the incident light beam.

Such an optical path configuration is achieved by satisfying the following conditions. The reflection type Schmitt plate 5 is formed by depositing aluminum or the like on the surface of a base made of glass, synthetic resin, or the like processed into a predetermined curved surface to form a mirror surface. In the three-dimensional coordinate system Q1 composed of x1, y1, and z1 axes orthogonal to each other, the curved surface forms a curve of a predetermined function in a plane including the x1 axis and the y1 axis by y.
It has a shape that rotates around one axis. On the other hand, the reflecting surface of the spherical mirror 6 uses the y2 axis as a rotation axis in a three-dimensional coordinate system Q2 including x2, y2, and z2 axes orthogonal to each other.

The respective rotation axes, ie, the y2 axis and the y1 axis, are aligned in the same direction. The axis direction is set so that the focal plane due to the reflected light from the spherical mirror 6 is outside the incident light beam.
It is shifted from the direction of the optical axis of the incident light beam. Further, the irradiation point C1 of the central light on the reflecting surface of the Schmidt plate 5
The distance between the coordinate system Q1 and the origin of the coordinate system Q1, and the distance between the irradiation point C2 of the central light on the reflecting surface of the spherical mirror 6 and the origin of the coordinate system Q2 are substantially equal to each other. The arrangement is determined.

The curvature of the reflecting surface of the Schmitt plate 5 is set so that the aberration on the detecting surface of the photodetector 7 becomes the best within a range where the light beam hits the reflecting surface of the Schmitt plate 5, B is determined. ^{y1 = A · x1 4 + B} · x1 6 It should be noted that such curvature of the specified details on how can be by various techniques known in the art.

Due to the shape and arrangement of the respective optical elements, a two-dimensional spectrum having small aberration is provided on the detection surface of the photodetector 7 without placing an obstacle in the optical path from the diffraction grating 4 to the photodetector 7. An image can be formed.

The same optical path configuration can be obtained by using a reflective meniscus instead of a Schmidt plate as the aberration correcting optical element. Furthermore, the dispersion directions of the echelle diffraction grating and the diffraction grating may be directions orthogonal to each other, and the echelle diffraction grating may be dispersed in the vertical direction, and then may be dispersed in the diffraction grating in the horizontal direction.

The above embodiment is merely an example, and it is apparent that modifications and variations can be made within the spirit of the present invention.

[0021]

As described above, according to the echelle spectroscope according to the present invention, the light is guided to the photodetector by the optical path off the optical axis. Never. Therefore, a two-dimensional spectral image with uniform brightness can be obtained on the detection surface of the photodetector.
Analysis accuracy and sensitivity can be improved.

Further, according to the echelle spectroscope according to the present invention, an optical element such as a reflector for optical path conversion becomes unnecessary, and a small optical element such as an echelle diffraction grating can be used. . Therefore, the size of the entire spectroscope can be reduced.

Further, in the conventional echelle spectroscope, it is necessary to use a transmission type aberration correcting optical element. However, in the transmission type, there is a limitation on materials in order to pass ultraviolet light having a short wavelength without attenuation (for example, It is necessary to use a material having a high transmittance in the ultraviolet region such as quartz glass), that is, mass production by the so-called replica method cannot be performed. On the other hand, in the present invention, since the reflection type aberration correcting optical element is used, it is possible to manufacture the aberration correcting optical element by a replica method using a material such as a synthetic resin. Therefore, there is an advantage that the cost can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an optical path according to one embodiment of an echelle spectroscope of the present invention.

FIG. 2 is a schematic configuration diagram showing an optical path by a conventional echelle spectroscope.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 entrance slit 2 parabolic mirror 3 echelle diffraction grating 4 diffraction grating 5 reflective Schmidt plate 6 spherical mirror 7 photodetector

Claims (1)

[Claims] 1. An echelle spectroscope comprising: an echelle diffraction grating for dispersing incident light in one direction; and an order separating dispersion element for dispersing light from the echelle diffraction grating in a direction substantially perpendicular to the direction. a) a reflection type aberration correcting optical element in which light reflected by the element surface of the order separating dispersion element is incident, and the incident optical axis and the output optical axis are arranged to be different; b) the aberration correction A photodetector disposed outside the light beam reflected from the optical element, c) a spherical mirror to which reflected light from the aberration correction optical element is incident and condenses light on a detection surface of the photodetector, An echelle-type spectrometer comprising: