JPS63201539A - Spectrochemical analyzer - Google Patents

Abstract

PURPOSE:To permit elimination of influence of second order diffracted light and to reduce the length of an array detector to about half by rotating a diffraction grating by a rotary shaft so that the incident angle of light to the diffraction grating can be changed over in two steps. CONSTITUTION:Incident light L from an inlet slot 1 is diffracted by the diffraction grating 2 and enters the array detector 3, where the spectral distribution of the diffracted light is detected. The diffraction grating 2 is fixed on the front end of the rotary shaft 5 driven by a low-speed motor or the like and is so constituted that the grating can be freely inverted 180 deg.. A filter 6 for cutting short wavelength provided on the incident side of the inlet slit 1 is so constituted that said filter is rotated by a gear system 7 cooperatively with the diffraction grating 2.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a so-called polychromator type diffraction grating spectrometer using an array detector.

(Prior Art) This type of spectrometer uses an array detector composed of multiple cells instead of moving the exit slit of a diffraction grating spectrometer to simultaneously measure a wide wavelength range. The wider the wavelength range covered, the greater the number of elements in the array detector and the higher the cost. For example, when measuring using one array detector in the measurement wavelength range of 200 to 700 nm, in the wavelength range of 400 nm or more, 20 nm
Accurate measurements may not be possible because the second-order diffracted light of 0 to 350 nm overlaps with the first-order diffracted light.

As a countermeasure, the conventional method was to first use 20 to 4
00nm wavelength range, then for example 350nm wavelength range.
A sharp cut filter that blocks light of wavelengths below m was inserted on the incident side of the entrance slit to measure wavelengths of 400 to 700 nm. In this case, in each measurement, the measured values of about half of the cells in the array detector are not used, so the effective utilization rate is 50%, which is extremely uneconomical.

Therefore, in order to be able to measure the entire wavelength range with a single array detector that covers about half of the measurement wavelength range, there is a method in which measurements are performed twice by moving the position of the array detector, or a method in which the diffraction grating is One possible method is to rotate the array detector by a small angle in a plane that includes the axis, but in reality there is a problem with the accuracy of the mechanism that slides the array detector or the mechanism that rotates the diffraction grating by a small angle, so it is difficult to achieve good reproducibility. was not obtained.

(Problems to be Solved by the Invention) In view of the above points, the present invention provides a spectroscopic analyzer that can switch the measurement wavelength range in 2° steps using an array detector that covers about half of the total wavelength range. The purpose is to provide an extremely simple structure with high reproducibility.

(Means for Solving the Problems) In order to achieve the above object, a spectroscopic analyzer according to the present invention includes an artificial slit 1, a diffraction grating 2, and an array detector 3. The diffraction grating 2 can be rotated 180 degrees by the rotation axis 5, which is provided at a constant angle θ with the normal N of the diffraction grating surface in a plane that includes the optical axis of the spectrometer. The incident angle can be freely switched in two stages.

(Function) According to the above configuration, the diffraction grating has 1 in the plane perpendicular to the optical axis.
Since it rotates by 80 degrees, the influence of variation in the stopping position on the angle of incidence can be almost ignored.

(Embodiment) FIG. 1 shows an embodiment of the present invention, in which light incident from the entrance slit l is diffracted by the diffraction grating 2 and enters the array detector 3, as shown by the arrow. , where the spectral distribution of the diffracted light is detected. The diffraction grating 2 is fixed to the tip of a rotating shaft 5 that is rotationally driven by a low-speed motor 4 or the like, and is configured to be able to rotate 180 degrees. As shown in FIG. 2, the rotation axis 5 is located on the back side of the approximate center of the diffraction grating 2 and within a plane that includes the optical axis of the spectrometer, that is, the center line of each of the incident and output beams of the diffraction grating. They are provided so as to form a constant angle θ with the normal N of the diffraction grating surface in a plane including
It is configured to stop at two positions that are reversed. Further, a short wavelength cutting filter 6 provided on the entrance side of the entrance slit 10 is configured to rotate in conjunction with the diffraction grating 2 via a gear system 7.

In the example of FIG. 2(a), the lattice constant is soo/m.

The inclination angle θ of the rotation axis 5 with respect to the normal N of the diffraction grating 2 is set to 1.
25 degrees, the incident angle α of the light from the entrance slit 1 at the long wavelength region measurement position is set to 110 degrees, and the direction of the array detector 3, that is, the main diffraction angle β1 is set to 120 degrees. Light of approximately 645 nm is emitted in the direction of . Further, in this state, as shown in FIG. 1, the short wavelength cutting filter 6 is inserted on the entrance side of the entrance slit 1. Next, when the diffraction grating 2 is reversed from this state and switched to the short wavelength range measurement position as shown in the same figure (b), the Rowland circle moves from the broken line position to the solid line position, and the incident angle
2.5 degrees, the upper fold angle β is 2.5 degrees, which is about 325 degrees.
nm light will be detected at the center of the array detector 3.

In the above example, the diffraction grating 2 with equally spaced grooves is used, and although the array detector 3 will be slightly deviated from the detection surface along the Rowland circle, the effect on detection sensitivity is small, and It is also possible to reduce this error by shifting the extended position of the rotating shaft 5 from the center point of the diffraction grating.

Furthermore, if a diffraction grating 2 with unevenly spaced grooves manufactured by holography is used, the position of the array detector 3 can always be made to coincide with the detection surface.

(Effects of the Invention) As described above, the spectroscopic analyzer according to the present invention rotates the diffraction grating by 180 degrees with the rotation axis that is provided to form a constant angle with the normal to the grating surface, so that light is transmitted to the diffraction grating. The angle of incidence is 2
Since it is designed to switch in stages, it is possible to eliminate the influence of second-order diffracted light compared to when measuring the entire wavelength range at once, and since the length of the array detector is about half, the number of elements can be reduced. The advantage is that the resolution can be reduced by about half, or the resolution can be doubled with the same number of elements.Moreover, since the diffraction grating is rotated in a plane perpendicular to the optical axis, the wavelength error is reduced by the rotation of the diffraction grating. Since the angle setting error is proportional to the square of the angle setting error caused by the angle setting error, there is an advantage that the influence of fluctuations in the stopping position on the incident angle is extremely small and measurement can be performed with high reproducibility.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing an embodiment of the present invention, Fig. 2(a)
and (b) is an explanatory diagram of the same operation. l...Artificial slit, 2...Diffraction grating, 3...Array detector, 4...Low speed motor, 5...Rotating shaft, 6
... Filter for short wavelength cut, 7... Gear system.

Claims (1)

[Claims] (1) In a spectrometer equipped with an entrance slit, a diffraction grating, and an array detector, a rotation is provided on the back surface of the diffraction grating so as to form a constant angle with the normal to the diffraction grating surface in a plane that includes the spectrometer optical axis. A spectroscopic analysis device in which the diffraction grating can be rotated 180 degrees around the shaft, and the angle of incidence of light on the diffraction grating can be switched in two stages.