JPH08292096A - Spectroscope - Google Patents

Abstract

PURPOSE: To enable it to compensate any slippage of focus position in this spectroscope due to thermal expansion and contraction in a base plate due to a temperature change, inexpensively and accurately. CONSTITUTION: In this spectroscope, installing an inlet slit 3, a collimator mirror 4, a diffraction grating 5, a camera mirror 6 and an outlet slit 7 on one base plate 1, making a light 2 inputted from the inlet slit 3 incident into the diffraction grating 5 via the collimator mirror 4, having this light dispersed by this diffraction grating 5 image on the outlet slit 7 with the camera mirror 6, and detecting the intensity of the light imaged on this outlet slit 7 through a photo detector 9, the collimator mirror 4 is made so as to be rectilinearly shiftable along an optical path L.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spectroscope used in, for example, an induction wave coupled high frequency plasma (ICP) optical emission spectrometer.

[0002]

2. Description of the Related Art As one of the above-mentioned spectroscopes, there is a Zerniter type spectroscope, which is constructed as shown in FIG.
That is, in FIG. 3, reference numeral 31 denotes a substrate, and this substrate 31
Optical components such as an entrance slit 33 into which light 32 from the outside of the substrate 31 is input, a collimator mirror 34, a diffraction grating 35 as a dispersive spectroscopic element, a camera mirror 36, an exit slit 37, a lens 38, and a photodetector 39. A system member is provided.

In the spectroscope having the above structure, the measured light 32 input from the outside enters the collimator mirror 34 through the entrance slit 33. The measured light 2 that has entered the collimator mirror 34 is converted into parallel light by the collimator mirror 34, and is rotated around a predetermined axis.
Is illuminated at an incident angle. The diffraction grating 35 splits the measured light 32 incident at a certain incident angle into a plane orthogonal to a marking line (not shown) parallel to the axis. Diffraction grating 35
The light dispersed by is condensed by the camera mirror 36 and is imaged on the exit slit 37. The light that has passed through the exit slit 37 enters the photodetector 39 through the lens 38.

When the diffraction grating 35 is rotated, the incident angle changes corresponding to the rotation angle. Then
The central wavelength of the light that has been split and condensed on the exit slit 37 changes. Therefore, by measuring the intensity of the light received by the photodetector 39 while rotating the diffraction grating 35, the spectrum at each wavelength of the measured light 32 can be obtained.

By the way, in the spectroscope having the above structure,
In order to improve the resolution of each wavelength on the measured spectral characteristics, it is necessary to narrow the slit width of the exit slit 37 and minimize the wavelength width of the wavelength contained in the light passing through the exit slit 37. . However, if the slit width is narrowed, the intensity of light incident on the photodetector 39 via the lens 38 is reduced. When the light intensity decreases, the S / N of the light intensity signal output from the photodetector 39 decreases, and the measurement accuracy of the entire spectroscope decreases. Therefore, since it is necessary to collect as much light as possible on the narrow slit width, it is necessary to strictly adjust the positional relationship between the optical members 33 to 37 on the substrate 31.

[0006]

However, in general, when the ambient temperature of the spectroscope changes, the substrate 31 made of, for example, aluminum expands or contracts due to the temperature rise or temperature drop, and the optical path L from the entrance slit 33 to the exit slit 37 is expanded. Even if the positional relationship between the optical members 33 to 37 on the substrate 31 is strictly adjusted as described above due to the change in the length,
A shift that cannot be ignored occurs in the positional relationship between them, and a shift in focus occurs due to a temperature change, and as a result, the measurement accuracy of the entire spectroscope decreases.

Therefore, in a spectrometer requiring high precision, conventionally, a low expansion alloy having a thermal expansion coefficient smaller than that of aluminum is used as the material of the substrate 31, or the entire spectrometer is housed in a constant temperature bath. I was trying to control the temperature.

However, in addition to the problem that the low expansion alloy is considerably expensive, there are the following problems. That is, an ICP emission spectrometer or the like requires a high-resolution spectroscope, but the high-resolution spectroscope has a considerably large focal length, and therefore the spectroscope itself becomes large, so that the thermostatic chamber itself also becomes large. However, it was difficult to make an accurate correction because it was necessary to adjust the temperature to the same temperature as when using it during adjustment, and to adjust the temperature when not using it.

On the other hand, it is conceivable to adjust the tilt angle of the diffraction grating 5 and the tilt angles of the collimator mirror 4 and the camera mirror 6, but a mechanism for adjusting these angles and its control are required. Extremely complex and expensive.

The present invention has been made in consideration of the above matters, and is capable of reliably and inexpensively correcting the shift of the focal position in the spectroscope caused by the thermal expansion and contraction of the substrate due to the temperature change. The purpose is to provide a vessel.

[0011]

In order to achieve the above object, the present invention provides an entrance slit, a collimator mirror, a dispersion type spectroscopic element, a camera mirror, and an exit slit on one substrate, and inputs from the entrance slit. The dispersed light is made incident on the dispersive spectroscopic element through the collimator mirror, and the light dispersed by the dispersive spectroscopic element is imaged on the exit slit by the camera mirror,
In a spectroscope in which the intensity of light imaged on the exit slit is detected by a photodetector, either or both of the collimator mirror and the camera mirror can be linearly moved along the optical path.

[0012]

In consideration of the amount of expansion and contraction of the substrate due to the temperature change, one or both of the collimator mirror and the camera mirror are finely moved along the optical path to correct the positional deviation due to the expansion and contraction of the substrate. The correction amount at this time is calculated by the CPU linked with the photodetector, and based on the result, one or both of the collimator mirror and the camera mirror are finely moved to adjust to the optimum condition.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. In FIG. 1, reference numeral 1 is a substrate made of, for example, aluminum, on which an entrance slit 3 for receiving light 2 from the outside of the substrate 1 and a collimator mirror 4 are provided. A diffraction grating 5 as a dispersive dispersive element rotatably supported in the direction of the arrow about an axis in the direction perpendicular to the paper surface by a rotating mechanism 5a, a camera mirror 6 formed of a concave mirror, an exit slit 7, a lens 8 and a photodetector such as a photomultiplier tube or a photodiode 9
Is provided. The configuration so far is no different from that of the conventional spectroscope shown in FIG.

A major difference of the spectroscope of the present invention from the conventional spectroscope is that either or both of the collimator mirror 4 and the camera mirror 6 are linearly moved along the optical path. In the embodiment shown in FIG. 1, the camera mirror 6 can be finely moved along the optical path L by the actuator 10.

That is, the actuator 10 is provided on the substrate 1 and has a movable base member 11 for mounting the camera mirror 6, and a pulse motor 12 which rotates in either forward or reverse directions. The movable base member 11 includes a spline shaft 13 meshed with a meshing portion 11a formed at one end of the movable base member 11. Then, by a control signal from the driver 17 described later,
When the motor 12 rotates in a predetermined direction, the movable base member 11 is translated in the direction of arrow A or B, and the camera mirror 6 can be linearly moved (finely moved) along the optical path L. . In addition, in the movable base member 11,
A position fixing device is provided which can securely fix this at its stop position.

Further, in FIG. 1, 14 is an AD converter for converting a signal output as an analog amount from the photodetector 9 into a digital amount, and 15 is a CP for controlling the entire spectroscope.
U and 16 are I / O, and 17 is a driver.

Next, the operation of the spectroscope having the above structure will be described. Assuming now that the dimensions and positions are in a standard temperature state (probably 0 ° C.) with the state indicated by the solid line in FIG. 1, when the ambient temperature rises, as indicated by the chain double-dashed line 1A in the figure. Then, the substrate 1 expands, and accordingly, the collimator mirror 4 and the camera mirror 6 are displaced as shown by the chain double-dashed line. The spectroscope is as shown in FIG.
The substrate 1 is long in the arrow X direction and short in the arrow Y direction. Therefore, it is sufficient to consider only the arrow X direction and correct only this direction.

Now, as an example, the spectroscope 0
The focal length f _{0 at} ℃ is 560 mm,
Assuming that the ambient temperature of the spectroscope rises from 0 ° C. to 45 ° C., the linear expansion coefficient α of the aluminum forming the substrate 1 is 2
Since it is 3.1 × 10 ⁻⁶ (at 293K), the focal length f ₄₅ of the spectroscope at 45 ° C. is 560.582 mm.
Becomes

That is, the substrate 1 is thermally expanded due to the temperature rise, and the collimator mirror 4 and the camera mirror 6 are made to enter the entrance slit 3.
And away from the exit slit 7 side (reference numerals 4A, 6A
By this), the optical path length from the entrance slit 3 to the exit slit 7 is slightly increased. Therefore, if it is attempted to correct this by only the fine movement of one of the collimator mirror 4 and the camera mirror 6 (camera mirror 6 in this embodiment), the correction amount at that time is (560.582-560) × 2. = 1.164 mm. That is, in a spectroscope having a focal length of 560 mm, when there is a temperature change of 45 ° C., the motor 12 is rotated in a predetermined direction by a predetermined amount to move the camera mirror 6 by 1.164 mm, and the position is indicated by reference numeral 6B in the figure. Need to move in a straight line.

Then, as the camera mirror 6 moves,
It suffices to feed back the degree of focusing at the exit slit 7 using the photodetector 9 and fix the camera mirror 6 at a position where the focus is clearly focused.

As a means for observing the degree of focus using the photodetector 9, light from a standard light source such as a mercury lamp is made incident through the entrance slit 3 and the diffraction grating 5 is slightly rotated to adjust the center wavelength. The wavelength profile may be changed and processed by the CPU 15. In this case, as means for changing the central wavelength, instead of rotating the diffraction grating 5, an optical shifter such as quartz may be provided in the optical path from the entrance slit 3 to the exit slit 7.

As described above, according to the above configuration, even if the optical path length is extended due to a temperature change, the camera mirror 6 is moved in the direction of the exit slit 7 along the optical path, and the predetermined distance is provided on the exit slit 7. You can focus on the position of.

The substrate 1 does not need to be made of an expensive material such as a low expansion alloy, and it is not necessary to take into consideration the problem of temperature change during use and during adjustment, and adjustment can be performed easily. It can be carried out.

In particular, since the CPU 15 is used to feed back the degree of focus adjustment, the accuracy of correction is high and reliable.

In the above-described embodiment, the camera mirror 6 is finely moved to correct the focus error due to the temperature change, but instead of this, the collimator mirror 4 may be moved similarly. Good. Further, as shown in FIG. 2, both the collimator mirror 4 and the camera mirror 6 are moved to the movable base member 1.
The mirrors 4 and 6 may be moved in the first position. In this case, the movement amount Δa is half as compared with the case where only one of the collimator mirror 4 and the camera mirror 6 is moved.

Although the above-mentioned embodiments are all based on the feedback method, a temperature sensor for detecting the temperature in the vicinity of the spectroscope is provided, and the collimator mirror 4 is added while taking the temperature information into consideration.
Alternatively, the amount of movement of the camera mirror 6 may be determined. In that case, adjustment can be performed without using a detector while the spectroscope is open.

Further, in the above-mentioned embodiment, the case where the substrate 1 expands due to thermal expansion is illustrated, but it goes without saying that the present invention can also be applied to the case where the substrate 1 contracts due to a temperature drop.

[0028]

As described above, according to the present invention, it is possible to inexpensively and surely correct the shift of the focal position in the spectroscope caused by the expansion and contraction of the substrate due to the temperature change, and to correct the wavelength over a wide temperature range. Measurement accuracy can be maintained. Therefore, a spectroscope with high measurement accuracy can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a configuration of a spectroscope according to an embodiment of the present invention.

FIG. 2 is a diagram schematically showing a configuration of a spectroscope according to another embodiment of the present invention.

FIG. 3 is a diagram schematically showing a configuration of a conventional spectroscope.

[Explanation of symbols]

1 ... Substrate, 2 ... Measured light, 3 ... Entrance slit, 4 ... Collimator mirror, 5 ... Dispersive spectroscopic element (diffraction grating), 6 ... Camera mirror, 7 ... Exit slit, 9 ... Photodetector, L ... Optical path .

Claims (1)

[Claims] 1. An entrance slit, a collimator mirror, a dispersive spectroscopic element, a camera mirror, and an exit slit are provided on one substrate, and light input from the entrance slit is incident on the dispersive spectroscopic element via the collimator mirror. In the spectroscope in which the light dispersed by the dispersive spectroscopic element is imaged on the exit slit by the camera mirror and the intensity of the light imaged on the exit slit is detected by the photodetector, the collimator mirror is used. A spectroscope characterized in that either or both of the camera mirror and the camera mirror can be moved linearly along the optical path.