JPH10132659A - Spectroscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spectroscope with high measurement accuracy with an improved S/N ratio inexpensively without making the configuration complex. SOLUTION: An incidence angle adjustment element 5 is arranged between an entrance slit 4 and a dispersion type spectral element 9 where light L from a light source 1 is inputted, a small-wavelength region is selected and scanned by the dispersion type spectral element 9, and the incidence angle adjustment element 5 is modulated at the selected small-wavelength region. A modulation angle and the output of a photo detector 13 are paired and are read by a computer part 16 and the computer part 16 performs the n-order differential calculation of the data of the selected small-wavelength region above.

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, a high frequency inductively coupled plasma (ICP) emission spectrometer.

[0002]

2. Description of the Related Art As one of the above-mentioned spectroscopes, there is a Czernitana type spectroscope, which is configured as shown in FIG.
That is, in FIG. 4, reference numeral 41 denotes an optical surface plate. On the optical surface plate 41, an entrance slit 43 into which light 42 from the outside of the optical surface plate 41 is input, a first concave mirror 44, and a diffraction as a dispersion type spectral element. Optical members such as a grating 45, a second concave mirror 46, an exit slit 47, a lens 48, and a photodetector 49 are provided.

In the spectroscope having the above configuration, the light to be measured 42 input from the outside enters the first concave mirror 44 through the entrance slit 43. The measured light 42 incident on the first concave mirror 44 is converted into parallel light by the first concave mirror 44,
The diffraction grating 45 rotating about a predetermined axis is irradiated at an incident angle. The diffraction grating 45 splits the measured light 42 incident at a certain incident angle into a plane orthogonal to a notch (not shown) parallel to the axis. The light split by the diffraction grating 45 is collected by the second concave mirror 46 and is imaged on the exit slit 47. The light that has passed through the exit slit 47 enters a photodetector 49 via a lens 48.

When the diffraction grating 45 is rotated, the incident angle changes according to the rotation angle. Then
The center wavelength of the light that has been split and collected on the exit slit 47 changes. Therefore, by measuring the intensity of the light received by the photodetector 49 while rotating the diffraction grating 45, a spectrum 50 at each wavelength of the measured light 42 as shown in FIG. 5 is obtained.

[0005] By the way, in the spectroscope having the above configuration,
Since the change in the wavelength due to the rotation angle of the diffraction grating 45 is extremely large, the influence of the interference cannot be avoided, thereby lowering the S / N and lowering the measurement accuracy of the spectroscope.

As a method of correcting the interference effect, a wavelength peak (indicated by a in FIG. 5) and a background peak (FIG.
, And the difference is obtained. As shown by an imaginary line in FIG. 4, for example, a light transmissive wavelength modulation plate 51 is provided between the entrance slit 43 and the first concave mirror 44, and this is modulated using a sine wave. As the diffraction grating 45, a high-resolution diffraction grating having, for example, 5000 slits per 1 mm is used. There is such a technique.

[0007]

However, in the above-mentioned method, it is a problem to determine a reference when measuring each peak, and it is particularly difficult to determine a background. In the above method, an optical element for modulation and an electric circuit for controlling the optical element are required,
Since the obtained spectrum is distorted, it is necessary to correct the spectrum profile. In the above-mentioned method, the focal length of the first concave mirror 44 becomes large, the darkness becomes high, and the higher the resolution becomes, the more expensive it becomes. Moreover, there is a limit in manufacturing technology, and it is not practical. There are problems such as.

The present invention has been made in consideration of the above-mentioned matters, and has as its object to provide an inexpensively high-accuracy spectroscope with improved signal S / N without complicating the configuration. It is to be.

[0009]

In order to achieve the above object, according to the present invention, a first concave mirror, a dispersion type spectroscopic element, a second concave mirror, and an exit slit are provided at a stage subsequent to an entrance slit to which light from a light source is inputted. Is disposed, and the light input to the entrance slit is made incident on the dispersion type spectroscopic element via the first concave mirror,
In a spectroscope that forms an image of the light split by the dispersive spectroscopic element on an exit slit with a second concave mirror and detects the intensity of the light formed on the exit slit with a photodetector, Arranging an incident angle adjusting element between the dispersion type spectral element, performing selection and scanning of a minute wavelength region in the dispersion type spectral element, modulating the incident angle adjusting element in the selected minute wavelength area, The modulation angle at that time and the output of the photodetector are taken as a pair into a computer section, and the computer section performs n-order differentiation on the data in the selected minute wavelength region.

According to the above configuration, a high-resolution spectrum can be obtained around a certain selected wavelength. Therefore, the S / N is improved, and the measurement accuracy of the spectroscope is improved.

[0011]

DETAILED 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 this figure, reference numeral 1 denotes a plasma light source for ICP emission spectral analysis, for example. Reference numeral 2 denotes a spectroscope main body, which is configured as follows. Reference numeral 3 denotes an optical surface plate made of a material having a low expansion coefficient, and the following members are provided on the optical surface plate 3. Reference numeral 4 denotes an entrance slit into which the light L from the light source 1 is input, and at the subsequent stage, an element 5 for adjusting an incident angle of the light L passing through the entrance slit 4 is provided. Is used. The incident angle adjusting mirror 5 is configured to swing by a small angle in a direction indicated by a double arrow 7 by a driving mechanism 6 provided outside the optical surface plate 3.

A first concave mirror 8 which receives the light L from the incident angle adjusting mirror 5 and converts it into a parallel light beam, and the light L from the first concave mirror 8 is incident on the optical surface plate 3. A diffraction grating 9 is provided as a dispersive spectroscopic element. The diffraction grating 9 is swung by a small angle in a direction indicated by a double-headed arrow 11 around a predetermined axis by a driving mechanism 10 provided outside the optical surface plate 3, and is parallel to the axis. It is configured to split the light into a plane perpendicular to the inscribed line (not shown) and to select and scan the wavelength.

Further, on the optical surface plate 3, a second concave mirror 11 receiving the light L from the diffraction grating 9, a second concave mirror 1 is provided.
An exit slit 12 for outputting the reflected light L from 1 is provided. The first concave mirror 8 and the second concave mirror 1
As 1, for example, there are a spherical mirror, a collimator mirror, a camera mirror and the like.

Reference numeral 13 denotes a photodetector comprising a photomultiplier tube provided outside the optical platen 3 behind the exit slit 12;
Is a preamplifier provided at the subsequent stage of the photodetector 13.
Reference numeral 15 denotes a circuit for A / D converting the output of the photodetector 13 and the angle information signal from the drive mechanism 6 for the incident angle adjusting mirror 5.

Reference numeral 16 denotes a computer unit for controlling the spectroscope main body 2, which comprises a CPU 17, a memory 18, a display unit 19, an operation unit 20, interfaces 21 and 22, and the like. C
The PU 17 is configured to control the entire spectroscope based on software, perform calculations based on input signals and signals from the A / D conversion circuit 15, and perform n-order differentiation. As the calculation software, for example, S
It is preferable to use the one based on the avittzky-Golay method.

In the spectroscope having the above configuration, the driving mechanism 1 receiving the control signal from the CPU 17 while the light L from the plasma light source 1 is being input to the entrance slit 4.
With 0, the diffraction grating 9 selects a minute wavelength region and performs scanning in the selected wavelength region. Then, a control signal is output from the CPU 17 to the drive mechanism 6 to modulate the incident angle adjustment mirror 5 in the selected minute wavelength region. As the modulation signal waveform at this time, an appropriate one of a triangular wave, a sawtooth wave, a sine wave and the like is preferably used.

The modulation angle when the incident angle adjusting mirror 5 is modulated and the output of the photodetector 13 obtained at that time are taken by the CPU 17 through the A / D conversion circuit 15 as a pair. The captured output of the photodetector is C
The PU 17 performs the n-th order differentiation. As a result, a signal with an improved S / N is obtained as the output of the spectroscope.

In the above-described embodiment, the output of the photodetector obtained by one-time modulation is differentiated by the CPU 17, but instead, the modulation angle is changed little by little. Each time, a large number of data of the modulation angle and the output of the photodetector may be collected, and after collecting all the data, the CPU 17 may differentiate the output of the photodetector by the nth order. In this case, S /
N can be further improved.

Then, after collecting all the above data,
In the case where the output of the photodetector is differentiated by the nth order in the CPU 17, the original spectrum can be superimposed on the wavelength axis and drawn using appropriate software, so that the spectrum can be viewed in a state where the peak position is clear. FIG. 2 is a diagram for explaining this. FIG. 2A is a waveform showing the original spectrum, and the first derivative of the waveform gives a waveform as shown in FIG. Is further differentiated (second order differentiation), the position of the peak P becomes clear as shown in FIG.

The present invention is not limited to the above-described embodiment. For example, background processing may be included in software for performing an n-th order differentiation.
As an incident angle adjusting element, a transmissive element 23 may be used instead of the plane mirror 5 as shown in FIG. 3A, and a polygon mirror 24 as shown in FIG.
May be used. The positions of the transmission type element 23 and the polygon mirror 24 are the same as those of the plane mirror 5.

[0022]

The present invention is embodied in the above-described embodiment and has the following effects.

In the present invention, a high-resolution spectrum is obtained around a selected wavelength, instead of the method of differentiating all the wavelengths of the spectroscope at the nth order at a time, so that the configuration is complicated. Without signal S /
N can be improved, and a spectroscope with high measurement accuracy can be obtained at low cost.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating an example of a processing method performed in a computer unit.

FIG. 3 is a diagram for explaining another example of the incident angle adjusting element.

FIG. 4 is a diagram showing a main part of a conventional spectroscope.

FIG. 5 is a diagram for explaining a problem of the related art.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Light source, 4 ... Entrance slit, 5, 23, 24 ... Incidence angle adjustment element, 8 ... 1st concave mirror, 9 ... Dispersion-type spectroscopic element, 11
... second concave mirror, 12 ... exit slit, 13 ... photodetector,
16: Computer part, L: Light.

Claims (1)

[Claims] 1. A first concave mirror, a dispersive spectroscopy element, a second concave mirror, and an exit slit are provided at a stage subsequent to an entrance slit to which light from a light source is inputted, and light inputted to the entrance slit is transmitted to the first slit. The light is incident on the dispersion type spectroscopic element via the concave mirror, the light separated by the dispersion type spectroscopic element is imaged on the exit slit by the second concave mirror, and the intensity of the light imaged on the exit slit is detected. In the spectroscope to detect with a spectroscope, an incident angle adjusting element is arranged between the entrance slit and the dispersion type spectral element, and the minute wavelength region is selected and scanned in the dispersion type spectral element, and the selected minute wavelength is selected. The incident angle adjusting element is modulated in the area, the modulation angle at this time and the output of the photodetector are paired and taken into a computer section, and the data of the selected minute wavelength area is converted into the nth order data in the computer section. A spectroscope characterized in that it is differentiated.