JPH0458893B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a spectrometer used to measure the power spectrum of radiation or obtain monochromatic light.

BACKGROUND OF THE INVENTION A diffraction grating spectrometer can change the wavelength range used by replacing the attached diffraction grating.
However, when replacing the diffraction grating, the reproducibility of the position when attaching the diffraction grating to the spectrometer has a large effect on the accuracy of the set wavelength of the spectrometer. That is, a deviation may occur between the wavelength indicated by the spectrometer and the center wavelength of the diffracted light actually obtained from the output slit. Conventionally, therefore, wavelength calibration has been performed using an emission line light source or the like when replacing a diffraction grating.

Problems to be Solved by the Invention When calibrating the wavelength of a spectrometer using an emission line light source, an emission line light source of the required wavelength must be prepared for each diffraction grating. In addition, there are wavelength regions in the ultraviolet and infrared wavelength regions where it is difficult to obtain bright line light sources.
In this case, the absorption spectrum of the substance may be used, but as the slit of the spectrometer is made narrower to increase the vector resolution, the amount of diffracted light obtained from the output slit of the spectrometer becomes smaller. There was a problem in that it was difficult to obtain sufficient wavelength setting accuracy.

Means for Solving the Problems In the present invention, in a diffraction grating spectrometer, the zero-order light emitted from the diffraction grating is reflected in the same direction as the incident light when the spectrometer has a certain set wavelength, and is observed from the entrance slit. Taking advantage of this fact, the zero-order light at this wavelength is detected outside the entrance slit.

Effects The above configuration makes it easy to calibrate the wavelength of a spectrometer using an easily available general light source and a photoreceiver sensitive to that light source, regardless of the wavelength range used by the diffraction grating.
Moreover, the density can be well controlled.

Embodiment Hereinafter, as an embodiment of the present invention, an embodiment of a spectrometer using a diffraction grating for visible wavelength range spectroscopy will be described with reference to the drawings.

FIG. 1 shows an optical path system of a spectrometer which is an embodiment of the present invention. In the figure, radiation from a light source 1 is introduced into the spectrometer through an entrance slit 2 and directed by a first plane mirror 3 to a collimating mirror 4. At this time, the collimator mirror 4 converts the incident light from the entrance slit 2 into parallel light and guides it onto the diffraction grating 5. The diffracted light emitted from the diffraction grating 5 is guided to the output slit 8 by the focusing mirror 6 and the second plane mirror 7, and an image of the input slit composed of the diffraction light is focused onto the output slit 8. Image. The spectrometer rotates the diffraction grating 5 to change the incident angle and diffraction angle (output angle) of radiation to diffracted photons.
The wavelength of the emitted light emitted from the emitting slit 8 is changed.

When the incident angle of the radiation entering the diffraction grating 5 from the collimator mirror 4 is 0°, that is, it coincides with the grating surface normal of the diffraction grating 5, the 0th order light coming out of the diffraction grating travels backward along the incident optical path and passes through the collimator mirror. 4 and the entrance slit 2 by the first plane mirror 3.
is guided to form an image of the entrance slit 2 onto the entrance slit 2. The zero-order light that has passed through the entrance slit 2 is separated from the incident optical path by a half mirror 9 placed in front of the entrance slit 2, and detected by a detector 10. If the wavelength of the spectrometer when the light incident on the diffraction grating 5 coincides with the normal line of the surface of the diffraction grating 5 is λ, then when the wavelength feed of the spectrometer is turned to rotate the diffraction grating, the detector 10 When the output obtained from the spectrometer is at its maximum, diffracted light of wavelength λ is obtained from the output slit 8 of the spectrometer.

Next, FIG. 2 shows an optical model of spectral dispersion of a diffraction grating. In the figure, the normal 1 to the grating plane of the diffraction grating 5
1, the incident light 12 is incident at an incident angle α. At this time, the diffraction light 13 having the wavelength λ is emitted at a diffraction angle β with respect to the normal 11 to the grating plane of the diffraction grating 5. If the line interval of the diffraction grating 5 is d, and the order of the diffracted light 13 is m, the following relationship holds true between the diffraction angle β of the incident angle α for light of wavelength λ.

mλ=d・(sinα+sinβ) m=0, ±1, ±2 ...(1) In equation (1), β=−α, that is, the direction of the angle −α with respect to the normal 11 of the grating plane of the diffraction grating 5. To,
Undispersed light with m=0 is emitted. This is 0
The second light is 14. In the spectrometer of this embodiment, the optical system other than the diffraction grating 5 is fixed, and the wavelength is changed by rotating the diffraction grating 5 and changing the incident angle α and the diffraction angle β. As the angle α changes, the emission angle −α of the zero-order light 14 also changes. If the angle formed by the incident light 12 and the diffracted light 13 is 2Υ, then 2Υ=β−α (2), which is a value specific to the device and determined by the arrangement of the optical system within the spectrometer. In the spectrometer of this example, the optical system was arranged so that 2Υ=30°.

Next, the optical system for detecting the zero-order light mentioned above will be explained. The diffraction grating 5 attached to the spectrometer at this time is for visible spectrometry measurement, and has a line density of 600.
Book/mm. When the incident light 12 is perpendicularly incident on the grating plane of the diffraction grating 5, that is, when α=0, the 0th order light 14 travels in the opposite direction to the direction in which the incident light 12 came, and is reflected by the collimator through the mirror 3. It is guided to the entrance slit 2, and an image of the entrance slit 2 formed by the zero-order light 14 is formed on the entrance slit 2.
A beam splitter 9 separates the zero-order light 14 emitted from the entrance slit 2 from the incident optical path, and a light receiver 10 detects it. At this time, if the wavelength of the diffracted light 13 obtained from the output slit 8 of the spectrometer is λ, then
When m = 1, λ = d/m (sin (0°) + sin (30°)) = 833.3 (nm) ...(3), and the diffracted light 13 with a wavelength of 833.3 nm enters the output slit of the spectrometer. 8, the output of the photoreceiver 10 is maximum.

When performing wavelength calibration, prepare a light source with a radiation spectrum within the range of the spectral sensitivity distribution of the photoreceiver 10, and direct the radiation from the light source to the input slit 2.
into the spectrometer. Then, the wavelength can be calibrated by turning the wavelength setting dial of the spectrometer to transmit the wavelength, and adjusting the wavelength indication value of the spectrometer to 833.3 nm when the output of the photoreceiver 10 is at its maximum.

Next, a description will be given of wavelength calibration when the diffraction grating 5 in the spectrometer of the present invention is replaced with a diffraction grating for infrared spectroscopy with a line density of 300 lines/mm and a blaze wavelength of 1 μm. At this time, the angle 2Υ formed by the incident light 12 and the diffracted light 13 is a constant specific to the device and determined by the arrangement of the optical system of the spectrometer, and therefore does not change even if the diffraction grating is replaced. Therefore, the wavelength λ of the diffracted light 13 obtained from the output slit 8 of the spectrometer when the zero-order light 14 returns to the input slit 2 and the output of the photodetector 10 becomes maximum is 1666.6 from equation (1). nm.
At this time, the wavelength calibration is performed in the same way as the method described above.
This can be achieved by adjusting the wavelength indication value of the spectrometer to 1666.6 nm when the output of the photodetector 10 is maximum.

The zero-order light 14 detected by the photoreceiver 10 is radiation that is not spectrally dispersed, that is, has the same spectral distribution as the radiation introduced from the entrance slit 2. The amount of incident light can be sufficiently large. Furthermore, even if a diffraction grating for infrared spectroscopy or a diffraction grating for ultraviolet spectroscopy is attached to the spectrometer according to the embodiment of the present invention, the light receiver 1
0, an _Si photodiode sensitive in the visible wavelength range is used, and wavelength calibration can be easily performed using a relatively easily available light source with a spectrum in the visible wavelength range, such as an incandescent light bulb.

Effects of the Invention The present invention is a diffraction grating spectrometer that has a function of detecting the direction of emission of zero-order light emitted from a diffraction grating when diffraction light of a certain wavelength is obtained from an emission slit. Yes, it has the following effects.

(1) Wavelength calibration of a spectrometer can be easily and accurately performed using generally easily available light sources such as incandescent light bulbs, without the need for special light sources such as bright line light sources.

(2) Unlike wavelength calibration, which is performed by detecting diffracted light,
Since this method detects the emission direction of the zero-order light emitted from the diffraction grating, wavelength calibration can be achieved if the light receiver that detects this zero-order light has sensitivity to the light source used for wavelength calibration.For example, visible wavelength Even when using a light source that has a spectral distribution only in the ultraviolet wavelength range or the infrared wavelength range and installing a diffraction grating for use in the ultraviolet wavelength range or the infrared wavelength range in the spectrometer of the present invention, wavelength calibration can be easily and accurately performed.

(3) Since wavelength calibration detects zero-order light that is not spectral dispersion, the amount of light to be detected can be sufficiently larger than when detecting diffracted light, so the entrance slit can be narrowed down, and the wavelength in wavelength calibration Setting accuracy can be improved compared to conventional wavelength calibration methods that detect diffracted light.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an optical system of a spectrometer in an embodiment of the present invention, and FIG. 2 is a diagram of an optical system for spectral dispersion of a diffraction grating. 1...Optics, 2...Incidence slit, 3...First
plane mirror, 4... collimator mirror, 5...
...Diffraction grating, 6...Focusing mirror, 7...
...Second plane mirror, 8...Output slit, 9...
...Beam splitter, 10...Receiver.

Claims (1)

[Claims] 1. An input slit and collimator optical system for converting light from a light source into parallel light, a reflective diffraction grating spectral dispersion element that disperses the parallel light according to wavelength, and a wavelength dispersion element using the reflective diffraction grating spectral dispersion element. an imaging optical system that images diffraction light separated into each band onto an output slit; and an imaging optical system that images the diffraction light separated into each band onto an output slit; a wavelength setting mechanism that sets a center wavelength of the diffracted light focused on the output slit by changing the angle and the output angle of the diffracted light;
When the wavelength of the spectrometer is set so that the incident optical path to the reflection type diffraction grating spectral dispersion element surface matches the normal line of the reflection type diffraction grating spectral dispersion element surface, the 0th order comes out from the input slit. It has a wavelength calibration mechanism consisting of a beam splitter that separates the analyzed light from the incident optical path and a light receiver that detects the separated zero-order light, and extracts light in the target wavelength band through the output slit. A spectrometer characterized by: