JPH0261529A - Double grating type spectroscopic apparatus - Google Patents

Abstract

PURPOSE:To measure a light level stably and accurately by equivalently rotating the vibration direction of light outputted from the first dispersion type spectroscopic element by 90 deg. before inputting the same to the second dispersion type spectroscopic element. CONSTITUTION:Dispersion type spectroscopic elements 13, 19 equal in diffraction efficiency are used to spectrally diffract light (a) to be measured. In this case, the polarized component (S-component), which is vertical to the slit line direction of the element 13, of the light emitted from the element 13 is incident in parallel to the slit line direction of the element 19 and the polarized component (P-component) parallel to the slit line direction is incident at right angles to the slit line direction of the element 19. That is, the light emitted from the element 13 is equivalently rotated by 90 deg. in its vibration direction to be incident to the element 19. As a result, the incident light component receiving the effect of one diffraction efficiency P (lambda) of the element 13 receives the effect of the other diffraction efficiency S (lambda) in the element 19. Contrarily, the incident light component receiving the effect of the diffraction efficiency S (lambda) of the element 13 receives the effect of the diffraction efficiency P (lambda) in the element 19. Therefore, since any component of incident light equally receives the effects of diffraction efficiencies P (lambda), S (lambda), the effect of the polarization state of incident light can be removed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a double grating type spectroscopic device in which two dispersive spectroscopic elements are inserted in series with respect to an optical path.

[Prior Art] A double grating type spectrometer in which two dispersive spectroscopic elements such as diffraction gratings are inserted in series in the optical path of light to be measured is configured as shown in FIG. 2, for example. That is, the measured light a inputted from the outside is converted into parallel light beams by the first collimator mirror 2 through the entrance slit 1, and then enters the first diffraction grating 3. The light to be measured that has been separated by the first diffraction grating 3 is focused by a first camera mirror 4 made of a concave mirror, and is incident on a second collimator mirror 6 via an intermediate slit 5. This second collimator mirror 6
The light to be measured, which is again converted into a parallel beam, is passed through the second diffraction grating 7.
is input to. The light to be measured further separated by the second diffraction grating 7 is focused by a second camera mirror 8 made of a concave mirror,
The light enters through the output slit 9 into a light receiver 10 consisting of a photodiode arranged on the back side of the output slit 9.

Generally, in such a double grating type spectrometer, the direction of the grooves of the first diffraction grating 3 and the second
The direction of the ruled lines of the diffraction grating 7 is made to coincide with that of the diffraction grating 7. Therefore, the entrance slit 1. The slit directions of the intermediate slit 5 and the exit slit 9 are also the same as the first one. This coincides with the direction of the ruled lines of the second diffraction gratings 3 and 7. Then, the two spectrometers configured as described above have the same structure, and in FIG.
The diffraction gratings 3.7 are rotated in conjunction with one or two drive mechanisms (not shown) so that they coincide with each other. Therefore, the wavelengths λ at the center positions of the separated lights incident on the camera mirrors 4 and 8 from each diffraction grating 3.7 are the same.

In a double grating spectrometer with such a configuration, the n1 constant light a input through the entrance slit 1
is separated by the first diffraction grating 3, and the separated measured light is further separated by the second diffraction grating 7.

In general, the spectral performance of a diffraction grating is limited to a single wavelength. When the reference light of Lattice 7
By performing spectroscopy, it becomes possible to further attenuate the light level attenuated by the first diffraction grating 3 existing in wavelength regions on both sides of the center wavelength λ0. Therefore, by using the two diffraction gratings 3 and 7 in conjunction so that the incident angle θ always matches, the measured light a
The spectral performance can be significantly improved.

[Problems to be solved by the invention] However, even with the double grating type spectrometer shown in Fig. 2, which uses two diffraction gratings 3.7 to improve spectral performance, the following problems still remain. . That is, as shown in FIG. 3(b), the direction of vibration of the light of the n1 constant light a generally oscillates in an arbitrary direction. Therefore, at the time of incidence on the diffraction grating 3.7, there is an arbitrary angle α between the vibration direction of this incident light a and the score line direction of the diffraction gratings 3 and 7.
exists. In general, in a diffraction grating, as shown in FIG. 3(a), the diffraction efficiency is P(λ) in the direction parallel to the ruled lines and S(λ) in the direction perpendicular to the ruled lines.
The wavelength characteristics differ between the two. Therefore, even if spectroscopic analysis is performed on the measured light a containing the same wavelength component, if the vibration direction of the measured light a differs, the polarization component (P component) parallel to the ruled line on the diffraction grating 3.7 ) and the polarized wave component (S component) perpendicular to the ruled line changes, so the light level at each wavelength λ on the obtained spectral characteristics does not always have a correct value.

Furthermore, even if one measured light a is incident, the component ratio will differ depending on the vibration direction, so the wavelength characteristics of the diffraction efficiency will differ depending on whether the S component is large or the P component is large. It is impossible to perform a strict level comparison of each light level between each wavelength on the obtained spectral characteristics.

In this way, with conventional double grating spectrometers, it is possible to accurately determine at which wavelength λ position the peak exists, but the light level of the peak waveform is determined by the vibration direction of the light of the corresponding wavelength. It was difficult to obtain the correct light level because the light level varied greatly depending on the light intensity.

The present invention was made in view of these circumstances, and
By equivalently rotating the vibration direction of the light output from the first dispersive spectroscopic element by 90'' and inputting it to the second dispersive spectroscopic element, the light level obtained at each measurement wavelength can be determined by The purpose of the present invention is to provide a double grating type spectrometer that can remove fluctuation components that depend on the vibration direction of the light source, perform stable and accurate light level measurements at all times, and improve the measurement accuracy of the entire device. .

[Means for Solving the Problems] In order to solve the above problems, the present invention provides two dispersive spectroscopic elements having equal diffraction efficiencies in the direction parallel to the scored lines and in the direction perpendicular (perpendicular) to the scored lines. A double method in which the light to be measured, which has been manually inputted using a dispersive spectrometer, is dispersed using a first dispersive spectroscopic element, and the light to be measured that has been spectrally dispersed by the first dispersive spectroscopic element is further spectrally dispersed using a second dispersive spectroscopic element. The grating type spectrometer is a grating-type spectrometer, and the light having a polarization component that is output from a first dispersive spectroscopic element and is perpendicular to the ruled line direction of the first dispersive spectroscopic element is transferred to a second dispersive spectroscopic element in the ruled line direction. , and the light of a polarization component that is output from the first dispersive spectroscopic element and is parallel to the ruled line direction of the first dispersive spectroscopic element is directed in the ruled line direction of the second dispersive spectroscopic element. It is designed to be incident vertically.

1 Effect] In a double grating spectrometer with such a configuration, the light is incident on the first dispersive spectroscopic element, and the vibration direction is at an arbitrary angle α with respect to the ruled line direction of the first dispersive spectroscopic element. The light to be measured, which has the following characteristics, is spectrally dispersed by this first dispersive spectroscopic element. The light separated by the first dispersive spectroscopic element is incident on the second dispersive spectroscopic element. In this case, the polarized wave component (S component) perpendicular to the ruled line direction of the light output from the first dispersive spectroscopic element is incident on the second dispersive spectroscopic element in parallel to the ruled line direction. Further, a polarized wave component (P component) parallel to the ruled line direction of the light output from the first dispersive spectroscopic element is incident perpendicularly to the ruled line direction of the second dispersive spectroscopic element. That is, the vibration direction of the light output from the first dispersive spectroscopy element is equivalently rotated by 90'' and then enters the second dispersion spectroscopy element.

As a result, the diffraction efficiency P(
The incident light component affected by λ) is affected by the other diffraction efficiency S(λ) at the second dispersive spectroscopic element. Conversely, the incident light component affected by the other diffraction efficiency S(λ) of the first dispersive spectroscopic element is affected by the one diffraction efficiency P(λ) in the second dispersive spectroscopic element. Therefore, any component of the incident light has both diffraction efficiencies P(λ), S(λ)
Therefore, the influence of the polarization state of the incident light can be removed from the separated light output from the second dispersive spectroscopy element.

Therefore, the measurement accuracy of each light level at each wavelength λ of the obtained spectral characteristics is improved.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing a double grading type spectrometer according to an embodiment. The βj-constant light a incident from the outside is converted into a parallel light beam by the first collimator mirror 12 through the entrance slit 11, and is incident on the first diffraction grating 13. 1st
The measured light a that has been separated by the diffraction grating 13 is focused by a first camera mirror 14 made of a concave mirror, further reflected by a first plane mirror 15, and passes through an intermediate slit 16. The measured light a passing through the intermediate slit 16 passes through the second plane mirror 17
The light is reflected by the beam and enters the second collimator mirror 18. The light a to be measured is converted into a parallel beam by the second collimator mirror 18 and is input to the second diffraction grating 19 . The light to be measured a that has been further separated by the second diffraction grating 19 is condensed by a second camera mirror 20 made of a concave mirror, and is condensed by the exit slit 21.
The light enters a light receiver 22 made of a photodiode arranged on the back side of the output slit 21.

The first diffraction grating 13 and the second diffraction grating 19 have the same configuration. Therefore, the diffraction efficiency P, (λ) in the direction parallel to the ruled lines in the first diffraction grating 13 and the diffraction efficiency P2 (λ) in the direction parallel to the ruled lines in the second diffraction grating 19 (
λ) is equal to Moreover, the diffraction efficiency S+ (λ) in the direction perpendicular to the ruled lines in the first diffraction grating 13 and the diffraction efficiency S2 (λ) in the direction perpendicular to the ruled lines in the second diffraction grating 19
) is equal to

Further, the direction of the score lines of the second diffraction grating 19 is rotated by 90° with respect to the direction of the score lines of the first diffraction grating 13. Furthermore, the angle formed by the first collimator mirror 12, the first diffraction grating 13, and the first camera mirror 14, and the angle formed by the second collimator mirror 1
8, the angle formed by the second diffraction grating 19, and the second camera mirror 20 are made equal. Each of the diffraction gratings 13, 19 is rotatably provided around each axis 13a, 19a parallel to the direction of the score line. Each diffraction grating 13.19 is rotated in conjunction with one driver groove (not shown) so that the incident angle θ of the measured light a with respect to each diffraction grating 13.19 is always the same as shown in the figure. Ru. Therefore, the wavelengths λ at the center positions of the separated lights incident on each camera mirror 14.20 from each diffraction grating 13.19 are the same.

1st. In order for the second diffraction gratings 13 and 19 to obtain each of the above-mentioned spectral characteristics, the slit directions of the entrance slit 11 and the intermediate slit 16 are made to coincide with the ruled line direction of the first diffraction grating 13.

Further, the slit direction of the output slit 21 and the ruled line direction of the second diffraction grating are made to coincide with each other.

In the double grating type spectrometer having such a configuration, the a1 constant light a that enters through the entrance slit 11 is split in the vertical direction by the first diffraction grating 13. The M1 constant light a that has been split in the vertical direction is sent to the first camera mirror 14.
First plane mirror 15. Intermediate slit 16. second plane mirror 1
7 and the second collimator mirror 18 to enter the second diffraction grating 19 . Then, the light to be measured a is further separated in the horizontal direction by this second diffraction grating 19. The horizontally separated measured light a is incident on the light receiver 22 via the second camera mirror 20 and the output slit 21 .

Therefore, the target M1 that is spectrally analyzed by the first diffraction grating 13
When the constant light a is incident on the second diffraction grating 19, the vibration direction is rotated by 90'' with respect to the ruled line when viewed from the second diffraction grating 19 side.

The light intensity of the polarized wave component (S component) perpendicular to the ruled line direction of the first diffraction grating 13 of the measured light a is defined as IX, and the light intensity of the polarized wave component (P component) parallel to the ruled line direction is defined as IX. Let IY be the light intensity I of wavelength λ output from the first diffraction grating 13
l (λ) is expressed as equation (1).

1+ (λ)-IX(λ) Sl (λ)+IX-(λ
)PI(λ)...(1) Then, the measured light a with the light intensity 11 (λ) output from this first diffraction grating 13
is incident on the second diffraction grating 19 with its vibration direction rotated by 90'', so the light intensity 12 (λ) of the wavelength λ output from the second diffraction grating 19 is expressed by equation (2).

12 (λ)-1x(λ)S, (λ)P2 (λ)+I
Y (λ) Pl (λ) S2 (λ)...(2
) As mentioned above, the first diffraction grating 13 and the second diffraction grating 1
9 has the same configuration, so it becomes Sl (λ)-32(λ)-8(λ) Pl (λ)-P2 (λ), so (
Equation 2) is expressed as equation (3).

12 (λ)−11x(λ)+1y(λ))×(P(
λ)S(λ)) ...(3) Also, the light intensity of the measured light a! (λ) is the light intensity Ix (λ) of the S component incident on the first diffraction grating 13 and the light intensity IY (λ) of the P component incident on the first diffraction grating 13.
λ), so equation (3) becomes equation (4).

12 (λ)-1(λ)P(λ)S(λ)...(4
) Therefore, the light is separated by the second diffraction grating 19 and sent to the light receiver 22 via the second camera mirror 20 and the output slit 21.
Light intensity at each wavelength λ of the measured light incident on the! (
As shown in equation (4), λ) is the product of the light intensity I (λ) at each wavelength λ of the measured light a incident on this spectrometer and the diffraction efficiency of each diffraction grating 13, 9 in each direction [ P (λ)
S(λ)].

Diffraction efficiency P(λ
), S(λ) are known as shown in FIG. 3(a), so the product [P(λ)S(λ)] at each wavelength λ is aesthetically determined. As a result, the light intensity 2 (λ) at each wavelength λ of the light incident on the light receiver 22 is
API constant, light intensity at each wavelength λ of light a! (λ)
It does not depend on the vibration direction of the measured light a, that is, the ratio of the P component to the S component with respect to the first diffraction grating 13.

Therefore, the influence of the polarization state of the incident light can be completely removed from the light level (light intensity I(λ)) at each wavelength λ of the obtained spectral characteristics, which greatly improves the measurement accuracy of each light level at each wavelength λ. can be improved.

[Effects of the Invention] As explained above, according to the double grating spectrometer of the present invention, the vibration direction of the light output from the first dispersive spectroscopic element is equivalently rotated by 90' to obtain the second dispersion. The type spectroscopic element is manually applied. Therefore, it is possible to remove the fluctuation component that depends on the vibration direction of the light to be measured from the light level at each measurement wavelength, and it is possible to always carry out stable and accurate light level measurement, thereby improving the measurement accuracy of the entire apparatus.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the general configuration of a double grating type spectrometer according to an embodiment of the present invention, FIG. 2 is a schematic diagram showing the schematic configuration of a conventional double grating type spectrometer, and FIG. 3(a) 2 is a characteristic diagram showing each diffraction efficiency in the diffraction grating, and FIG. 3B is a diagram showing the relationship between the vibration direction of the light to be measured and the ruled line direction of the diffraction grating. DESCRIPTION OF SYMBOLS 11... Incidence slit, 12... First collimator mirror, 13... First diffraction grating, 14... First camera mirror, 15... First plane mirror, 16... Intermediate slit, 17... Second plane mirror, 18... Second collimator mirror, 19... Second diffraction grating, 20... Second camera mirror, 21... Output slit, 22 ...Receiver.

Claims (1)

[Claims] Two dispersive spectroscopic elements (13, 19
), the input light to be measured is separated by a first dispersive spectroscopic element (13), and the light to be measured separated by this first dispersive spectroscopic element is passed to a second dispersive spectroscopic element (19). ), the double grating spectrometer further spectrally separates light using the first dispersive spectroscopy element, the light having a polarization component perpendicular to the ruled line direction of the first dispersion spectrometer output from the first dispersion spectrometer 2
The light is incident parallel to the score line direction of the dispersive spectroscopy element, and the light of a polarized wave component output from the first dispersion spectrometer and parallel to the score line direction of the first dispersion spectrometer is transmitted to the first dispersion spectrometer. 2. A double grating type spectrometer characterized in that the light is incident perpendicularly to the line direction of the dispersive spectroscopic element.