JP2576284B2 - Polychromator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a polychromator that uses a diffraction grating and is capable of changing a measurement wavelength range in a wide and narrow range.

(Prior Art) FIG. 3 shows a basic configuration of a conventional polychromator using a diffraction grating. In this figure, 1 is an entrance slit, and 2 is a plane mirror which reflects light incident from the entrance slit 1 toward the diffraction grating 3. The diffraction grating 3 is a concave diffraction grating, and a photodetector 4 is arranged along a spectral image plane formed by the diffraction grating.
Is arranged. As the photodetector 4, one in which a large number of light receiving elements are arranged in an array is used. When the central ray of the rays shown in the figure enters the diffraction grating 3 at an incident angle α, the wavelength λ of the diffracted light is sin α + sin x = Nmλ where x is the diffraction angle, N is the number of grating grooves, and m is the diffraction order. It is represented by Maximum measurable wavelength λl determined by device configuration
Light forms an image in the direction of x = β, and light of the shortest wavelength λs
An image is formed in the direction of γ. When the photodetector 4 is fixed, β and γ are also fixed values. Therefore, when it is desired to widen the measurement wavelength range or conversely improve the wavelength resolution by improving the wavelength resolution, the number of grooves in the diffraction grating is increased. Replace it with a different one,
It was necessary to replace the diffraction gratings with different focal lengths and to move the photodetector closer or farther. However, changing or converting the positions of the components of the polychromator in this way is not only a cumbersome operation but also requires that the reproducibility of the positions of the components of the polychromator be sufficiently good. Otherwise, measurement accuracy and measurement reproducibility will be insufficient.

(Problems to be Solved by the Invention) The present invention aims to make it possible to switch the width of the measurement wavelength range without moving or converting the components of the polychromator.

(Means for Solving the Problems) A pre-spectrometer using a diffraction grating having a narrow entrance slit is arranged on the light entrance side of the polychromator, and its spectral image is formed on the plane of the entrance slit of the polychromator. At the same time, the width of the entrance slit of the polychromator was widened, and the direction of the diffraction grating of the pre-spectrometer was changed, so that the order of diffraction of the spectrum image on the entrance slit was switched between positive and negative.

(Operation) According to the above-described configuration, a spectral image is formed on the entrance slit of the polychromator by the diffraction grating of the pre-spectrometer, and the incident points of the light of each wavelength to the polychromator are different on the entrance slit surface. Thus, the angle of incidence on the diffraction grating of the polychromator differs depending on the wavelength.
Therefore, the + 1st order spectral image of the pre-spectrometer is formed on the entrance slit surface of the polychromator using the code of FIG. 3 as it is, and the incident angle α to the diffraction grating of the polychromator increases. If the spectral image is formed such that the wavelength becomes shorter in the direction, the maximum value of the incident angle to the diffraction grating of the polychromator is α1, and the minimum value is α2.
<Α <α1, and the longest wavelength λl ′ within the measurement range is sin α2 + sin β = Nmλl ′ <Nmλl (1) The shortest wavelength λs ′ is sin α1 + sin γ = Nmλs ′> Nmλs (2) The measurement wavelength region becomes narrower than in the case of a single spectroscope, and the wavelength resolution is improved. When the diffraction grating of the pre-spectrometer is turned and the diffraction order of the spectrum image on the entrance slit surface of the polychromator is set to −1, the wavelength arrangement on the slit is opposite to the above, and the measurement wavelength region is It is enlarged.

(Embodiment) FIGS. 1 and 2 show an embodiment of the present invention. FIG. 1 shows a state in which the wavelength resolution is increased, and FIG. 2 shows a state in which the measurement wavelength region is enlarged. In these figures, reference numeral 1 denotes an intermediate slit, which is the entrance slit of the main spectroscope, and the right side in the figures is the main spectroscope. The main spectrometer has the same configuration as the conventional polychromator shown in FIG.
Denotes a diffraction grating, 4 denotes a photodetector, and an array-type element is used. The left side of the intermediate slit 1 in the figure is connected to a pre-spectroscope, and the intermediate slit 1 is also an exit slit of the pre-spectroscope. The entrance slit 1 of the main spectroscope has a wide slit width and a variable width.
In the pre-spectrometer, 5 is its entrance slit, which is as narrow as a normal spectrometer. Reference numeral 6 denotes a plane mirror, and reference numeral 7 denotes a concave diffraction grating which is a spectroscopic element of a pre-spectrometer, which can rotate in an axis passing through the center of the grating plane and perpendicular to the plane of the drawing, and can take two directions. A plane mirror 8 reflects the light diffracted by the diffraction grating 7 in the direction of the intermediate slit 1. With this configuration, a spectral image of the pre-spectroscope is formed on the opening of the intermediate slit 1 of the main spectroscope.
In the figure, only the center lines of the light beams of the three wavelengths are shown. In the case of FIG. 1, the spectrum of the -1st-order diffracted light of the diffraction grating 7 is formed on the intermediate slit 1 by the pre-spectrometer, and the upper edge side has a long wavelength and the lower edge side has a short wavelength in the diagram of the intermediate slit 1. Therefore, the angle of incidence on the diffraction grating 3 of the main spectroscope is large on the long wavelength side and small on the short wavelength side. Therefore, the wavelength range of the spectral width developed within the entire width of the photodetector 4 is wider than that of the conventional type in this case, as described in the operation section. In the state shown in FIG. 2, the direction of the diffraction grating 7 of the pre-spectrometer is changed so that a plus first-order diffraction spectrum image is formed on the intermediate slit 1. In this case, the upper edge side of the intermediate slit 1 is used. Is a short wavelength, the lower edge is a long wavelength, and the incident angle to the diffraction grating 3 of the main spectrometer is large on the short wavelength side and small on the long wavelength side, and as described in the operation section, the full width of the photodetector 4 The wavelength range of the spectrum inside is narrower than the conventional one, and the wavelength resolution is improved.

In the above embodiment, the width of the entrance slit 1 of the main spectroscope is 10 mm.
And 5.6mm can be switched. In the pre-spectrometer, the focal length of the diffraction grating is 110 mm and the number of grooves is 150 lines / mm. The diffraction grating 3 of the main spectrometer has 600 grooves / mm and an entrance slit 1
Angle of incidence α on the diffraction grating 3 for a ray passing through the center of
25.0 {β and γ are β = 3.3 ° and γ = 11.2 °, respectively, and the optical path length from the center of the diffraction grating 3 to the center of the entrance slit 1 is 9
With a conventional polychromator, the shortest wavelength on the photodetector 4 is about 380 nm and the longest wavelength is about 800 nm.

FIG. 1 shows a case where the pre-spectrometer forms a -1st-order diffraction spectrum on the entrance slit 1 of the main spectroscope as described above. The entrance slit 1 is selected to have a width of 10 mm. In the pre-spectrometer, the incident angle δ to the diffraction grating is 12.574 °, the exit angle ε of the central ray of the diffracted light is 17.845 °, and the shortest wavelength on the photodetector 4 is
301,370nm, the longest wavelength is 877.678nm and the measurement wavelength range is about 57
6 nm.

FIG. 2 shows that the direction of the diffraction grating 7 of the pre-spectrometer was changed to +1.
When the next diffraction spectrum light is incident on the main spectroscope, the entrance slit 1 is switched to one having a width of 5.6 mm in conjunction with the rotation of the diffraction grating 7. If the width of the entrance slit is switched to the narrow one at a width of 10 mm, light having a wavelength near the edge of the opening of the entrance slit 1 comes out of the photodetector 4 by the main spectroscope and is measured. It is simply to increase the stray light level of the main spectrometer, so that light of such wavelengths does not enter the main spectrometer,
The wavelength range of the + 1st-order diffraction spectrum of the pre-spectrometer formed in the width of 5.6 mm of the entrance slit 1 is developed on the photodetector 4. In the case of FIG. 2, the incident angle δ and the outgoing angle ε to the diffraction grating 7 of the pre-spectrometer are replaced with those in FIG. 1, and the incident angle δ is 17.845 ° and the outgoing angle ε is 12.574 °. The shortest wavelength on the vessel is 424.73 nm, the longest wavelength is 75
It becomes 6.21 nm, and the measurement wavelength range becomes 331.48 nm.

When the pre-spectrometer is removed as described above (the entrance slit 1 is assumed to be a normal narrow one), it is approximately 42 from 380 nm to 800 nm.
By attaching a pre-spectrometer and making the primary light incident, a range of about 580 nm from about 300 nm to 880 nm,
Also, the range of 330 nm from 424 nm to 756 nm and the measurement wavelength range can be switched in three steps so that the +1 order light is incident.

(Effects of the Invention) According to the present invention, by attaching one prespectrometer without changing the optical element of the main spectroscope or its position at all, the measurement wavelength region as a polychromator can be changed by the main spectroscope alone. By turning the diffraction grating of the pre-spectrometer, the main spectrometer is completely fixed, and the wide or narrow case can be changed by attaching an adapter to a conventional polychromator as an adapter. It is possible to perform both measurement in the wavelength region and measurement with increased wavelength resolution.

[Brief description of the drawings]

FIG. 1 is a plan view of a polychromator according to one embodiment of the present invention, FIG. 2 is a plan view of another embodiment, and FIG. 3 is a plan view of a conventional polychromator. DESCRIPTION OF SYMBOLS 1 ... Intermediate slit, 2 ... Plane mirror, 3 ... Diffraction grating of main spectroscope, 4 ... Photodetector, 5 ... Entrance slit of pre-spectroscope, 7 ... Diffraction grating of pre-spectroscope, 8 …… a plane mirror.

Claims (1)

(57) [Claims] 1. A pre-spectroscope having a narrow entrance slit and a rotatable diffraction grating is arranged in front of an entrance slit of a main spectroscope constituting a polychromator, and a spectrum image of the pre-spectroscope is obtained by using the main spectroscope. Along with being formed on the entrance slit surface, the width of the entrance slit of the main spectrometer is increased,
A polychromator characterized in that the order of diffraction of the spectrum image of the pre-spectrometer formed on the entrance slit can be switched between positive and negative by rotation of the diffraction grating of the pre-spectrometer.