JPS6148733A - Spectrophotometer - Google Patents

Abstract

PURPOSE:To shorten a measurement time by separating high-order diffracted light, such as primary diffracted light, secondary diffracted light, and tertiary diffracted light, which is obtained at the same time from the projection light of a spectroscope using a diffraction grating into light beams of respective degrees, and detecting time individually. CONSTITUTION:For example, when a diffraction grating spectroscope is used and a wavelength dial is set to 1,000nm, light obtained from its projection slit is light of 500nm in wavelength as secondary diffracted light, light of 333.3nm as tertiary diffracted light, etc., in addition to light of 1,000nm as primary diffracted light. The primary diffracted light and its high-order diffracted light obtained from the projection slit 9 are separated through an optical system by degrees and they are detected individually by photodetectors 14 and 15. Consequently, the distance of wavelength scanning is shortened and the measurement time is shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a spectrophotometer for measuring the power spectrum of radiation.

Conventional Structure and Problems Conventional spectrophotometers can be divided into two types depending on their spectral dispersion elements. One is a spectrophotometer that uses a prism as a spectral dispersion element, and the other one uses a diffraction grating or interference as a spectral dispersion element. Spectrophotometers using prisms have a wavelength scale that is not linear and is highly dependent on wavelength. Therefore, when performing spectrophotometry over a wide wavelength range from the short wavelength side to the infrared region, wavelength correction of the slit mechanical width must be performed for each wavelength, which is complicated. Further, as the wavelength becomes longer, the dispersion becomes smaller, and the longer the measurement wavelength range becomes, the more difficult it is to obtain a certain degree of measurement accuracy over the entire wavelength range.

In addition, in spectrophotometers that use diffraction gratings or interference elements,
Diffraction grating spectrometers, which have a large dispersion ability, can linearize the wavelength scale by sine bar scanning, and therefore the slit width correction for the measurement wavelength is also much smaller than that of prism spectrometers. However, removal of higher-order diffracted light poses a problem. When the wavelength scale of the spectrometer is set to 11000n, the wavelength 60 that comes out simultaneously with the radiation of wavelength 11000n
It is necessary to remove radiation of 0 nm and 333 nm, which is one-third of that, and when measuring a wide wavelength range, this work is complicated, and there are also problems in reproducing the position of the optical system (such as an optical filter) for removing higher-order light. becomes.

Furthermore, whether a prism spectrometer or a diffraction grating is used, one thing in common is that the wider the measurement wavelength range, the longer the measurement takes. Therefore, it is necessary to keep the standard light source and the radiation source to be measured, as well as the measurement system such as the photodetector, stable for a relatively long period of time.

Purpose of the Invention The present invention uses an optical system to separate the first-order diffracted light and the higher-order diffracted light obtained simultaneously from the output slit of a spectrometer using a diffraction grating or an interference element, and detect them individually. The aim is to shorten the wavelength scan distance and measurement time while maintaining accuracy.

Structure of the Invention In order to achieve the above object, the spectrophotometer of the present invention uses a spectral dispersion optical system that utilizes diffraction or interference, and thereby) simultaneously obtains first-order diffracted light and its higher-order diffracted light to It consists of multiple detectors that detect each.

DESCRIPTION OF EMBODIMENTS Hereinafter, as an embodiment of the present invention, an embodiment using a diffraction grating spectrometer will be described with reference to the drawings.

Figure 1 shows an optical model of spectral dispersion of a diffraction grating.

1 is a diffraction grating, and the incident light 3 is
Suppose that it is incident at an angle of incidence α. At this time, the diffracted light 4 having the wavelength λ is emitted at a diffraction angle β with respect to the normal 2. Zero-order light 6 emerges at an angle α on the opposite side of the incident light 3 with respect to the normal 2. If the interval between the lines of the diffraction grating is d, and the order of the diffracted light is m, then the following relationship holds true between the incident angle α and the diffraction angle β for light of wavelength λ.

mλ= d・(ginα+sinβ)・・・・・・・
...(1) m = O, ±1. ±2・・・・・・・・・
At this time, if light is incident on the diffraction grating so that the incident angle is α1 and the diffraction angle is β1, and the diffracted light is outputted as m
= 1, that is, when the wavelength is λ1 for primary light, light of wavelength λ2, where m = 2, is obtained at the same time in the direction of the diffraction angle β1. At this time, λ1 and λ2 are.

λ2−2λ1 ・・・・・・・・・(
It becomes a merit. Similarly, in the case of first-order diffracted light, the diffraction angle β1
In the direction of , light of wavelength λ is obtained, and the following equation holds true for λ1.

λm−−λ1 ・・・・・・・・・
(3) In other words, in the case of a diffraction grating spectrometer, for example, if the wavelength dial is set to 1100Qn, the light obtained from the output slit will be at the -next wavelength of 11000Qn.
In addition to the n light, at the same time, there is a second-order diffracted light with a wavelength of 500
It is possible to obtain light with a wavelength of 333.3 nm and third-order diffracted light with a wavelength of 333.3 nm. The first-order diffracted light and its higher-order diffracted light obtained from this exit slit are separated into each order by an optical system, and each is individually detected by a photodetector. Figure 2 shows the optical system. In the figure, 5 is a spectroscope, 6 is a collimator mirror that guides the light from the entrance slit 7 to the diffraction grating 1, and forms an image at the end of the entrance slit on the diffraction grating, and 8 is a collimator/mirror that guides the light from the entrance slit 7 to the diffraction grating 1. This is a focusing mirror that guides the diffracted light to the exit slit 9 and forms an image formed by the diffracted light at the exit slit onto the exit slit 9. The exit slit 9
As shown above, the emitted light 10 consists of the first-order diffracted light 12 and the higher-order diffracted light 13, and when it is incident at an angle of 46 degrees to the normal to the cold mirror 11, it has a wavelength of 700 nm or more. If you use a cold mirror that transmits light with a wavelength of 700 nm or less and reflects light with a wavelength of 700 nm or less in a 46-degree direction, the first-order diffracted light 12 with a wavelength of 700 nm or more and the wavelength 3
Second-order diffracted light 1 from 5 Q nm to wavelength 700 nm
The optical path can be separated into three. Figure 3 shows cold mirror 1.
1 shows an example of spectral transmittance at an incident angle of 46°. The separated first-order diffracted light 12 and second-order diffracted light 13 are detected individually and simultaneously by a first-order diffracted light photodetector 14.
The second-order diffracted light is detected by the moonlight detector 16. Outgoing light 1
The third-order diffracted light contained in the zero and the diffracted light of higher orders are made using a cold mirror 11 that does not transmit light with a wavelength of 233 nm or less, and the components reflected on the surface of the cold mirror 11 are also The detector 14 has a wavelength of 2
It is removed by using a material that is not sensitive to light of 33 nm or less.

By configuring a spectrophotometer with the above optical system, it is possible to simultaneously detect light at a set wavelength (the set value of the spectrometer's wavelength dial) and light at a wavelength half that wavelength. For example, if the set wavelength range is set to 700 nm, When it is 1400nm from
Spectrophotometry from 350 wavelengths to 1400 nm becomes possible.

In addition, in the embodiment shown above, a three-wavelength spectrophotometer was shown that removes third-order or higher-order diffracted light, but based on the same principle, -
By separating and individually detecting higher-order diffracted light such as first-order diffracted light, second-order diffracted light, and third-order diffracted light, it is also possible to configure a spectrophotometer that detects multiple wavelengths simultaneously, such as a three-wavelength spectrophotometer. be.

Further, as an example of separating the diffracted light of each person, a case where a cold mirror is used is shown, but it can also be realized by a dichroic mirror or the like. In addition, a composite light-receiving element in which a Si photodiode and a PbS photoconductive cell are arranged coaxially detects light with a wavelength of 1.1 Atm or less with the Si photodiode, and detects light with a wavelength of 1.1 μm or more with a PbS photoconductive cell through the Si photodiode. Can be detected in cells. If this element is used, the -order diffracted light, which has a wavelength of 1.111 m, can be
．． Light up to 2 μm is detected by a PbS photoconductive cell, and wavelength 5
A three-wavelength spectrophotometer that detects light from 5 onm to 1.1 μm using a Si photodiode can be realized. FIG. 4 shows the spectral sensitivity of the composite element.

Effects of the Invention In addition to the above, the present invention allows the first-order diffraction light and the higher-order diffraction light such as the second-order diffraction light and the third-order diffraction light, which are simultaneously obtained from the output light of a spectrometer using a diffraction grating, to be By separating each light and detecting each light individually, it is possible to shorten the wavelength scan distance and shorten the measurement time. For example, when detecting -order diffraction light and second-order diffraction light at the same time, at the set wavelength (the setting value of the wavelength setting dial of the spectrometer),
When scanning from ○○ nm to 1400 nm, spectrophotometry can be performed at wavelengths from 350 nm to 1400 nm.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of a spectral dispersion optical system of a diffraction grating, and Fig. 2 is a system diagram of an optical system of a spectrophotometer which is an embodiment of the present invention.
FIG. 3 is a diagram showing the relationship between the spectral transmittance and wavelength of the cold mirror used in the example, and FIG. 4 is a diagram showing the relationship between the spectral sensitivity and wavelength of the composite element. 1... Diffraction grating, 5... Spectrometer, 6...
...Collimator mirror, 7...Incidence slit, 8...Focusing mirror, 9...
・Exit slit, 11...Cold mirror, 14
......-Photodetector for second-order diffracted light, 15...
Photodetector for second-order diffracted light. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2

Claims (1)

[Claims] A spectral dispersion element using a diffraction grating or an interference element, an optical system that separates the primary dispersion light and its higher order dispersion obtained from the dispersion element into individual order lights, and individually detects the separated lights. A spectrophotometer is a spectrophotometer that can simultaneously measure light at multiple wavelengths.