JPS59220633A - Plasma monitor - Google Patents

Abstract

PURPOSE:To achieve a highly accurate measurement with a high sensitivity for a long time by providing a first means of detecting changes in the wavelength of a narrow band laser light and a second means of correcting the output of a fluorescent detector according to the wave changes detected therewith. CONSTITUTION:In a plasma utilizer 4, a laser light 2 excites a measuring chemical seed to generate a fluorescence 6, which leaves an optical window 5c, focused by a focusing system 7 and then, converted into an electrical signal proportional to the intensity of the fluorescence with a fluorescence detector 8. On the other hand, the same measuring chemical seed is sealed into a cell 9 at a constant density and likewise, a fluorescence detector 12 outputs an electrical signal proportional to the intensity of fluorescence. Outputs of both the devices are inputted into a fluorescence generation rate arithmetic unit 13 to correct variations based on changes in the wavelength of the laser light 2 among outputs of the fluorescence detector 8. A correct fluorescence generation rate in the plasma utilizer 4 is computed, outputted and indicated on a display 14.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a plasma monitor attached to a plasma utilization device, and more specifically, the present invention relates to a plasma monitor attached to a plasma utilization device. The present invention relates to a plasma monitor that uses a fluorescent method to make measurements with high sensitivity and accuracy over a long period of time.

[Background of the invention]

BACKGROUND OF THE INVENTION Conventionally, a laser excitation fluorescence method has been known as a means for detecting trace amounts of atoms, diatomic molecules, etc. with high sensitivity. When this laser-excited fluorescence method is used to measure chemical species such as atoms and diatomic molecules in plasma in a plasma utilization device and a plasma monitor is configured, the following problems have occurred with the conventional technology. In other words, the chemical species in the plasma to be measured are:
Since it has a sharp absorption spectrum, it is necessary to use a gold piece with a narrow linewidth and high wavelength stability as the excitation laser beam. However, the oscillation wavelength of normal laser light varies to some extent, and therefore, when a plasma monitor using a laser excitation method is used for a long time, the measurement accuracy of the above chemical species decreases.

That is, in FIG. 1, F is the absorption curve of the chemical species to be measured, and S1, S2 . S3 indicates the spectrum of the excitation laser beam. When the wavelength of the excitation laser beam is adjusted to match the absorption wavelength of the chemical species to be measured by adjustment before the start of measurement, the laser beam spectrum becomes like that of Sl9, and the excitation efficiency of the laser beam for the chemical species to be measured is maximized. However, if measurements are continued over a long period of time, the wavelength of the laser light may become too long to be measured with a spectrometer due to the influence of ambient temperature, etc.
If the laser light spectrum changes slightly by 1/, for example, S2,
It changes like 83. In this case, the excitation efficiency of the measured chemical species by the laser light decreases, and even if the concentration of the measured chemical species is the same, the amount of fluorescence generated decreases, resulting in a decrease in the measurement accuracy of the chemical species by the plasma monitor. It turns out.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and aims to provide a plasma monitor that is highly sensitive and capable of measuring accurately over a long period of time. The plasma monitor excites only a specific chemical species with a narrow band laser beam irradiated into a plasma utilization device, and detects the fluorescence generated at that time with a fluorescence detector. a first means for irradiating said narrowband laser light onto said specific chemical species km and detecting a change in the wavelength of said narrowband laser light; and a first means for detecting by said first means. Depending on the wavelength change made,
and a second means for correcting the output of the fluorescence detection device, thereby eliminating wavelength changes of the narrow band laser beam and enabling highly accurate measurement over a long period of time.

[Embodiments of the invention]

The present invention will be described in more detail below with reference to embodiments shown in the accompanying drawings.

FIG. 2 is a block diagram showing a first embodiment of the present invention. In the figure, a laser beam 1 emits a laser beam 2 having the same oscillation wavelength as the absorption wavelength of the chemical species to be measured. Laser light 2
The beam is split into two directions by the beam splinter 3, and is incident on the plasma utilization device 4 through the optical window 5a' on one side, and incident on the cell 9 on the other side. In the plasma utilizing device 4, the laser beam 2 excites the chemical species to be measured to generate fluorescence 6, and then exits through the optical window 5b.

The generated fluorescent light 6 exits from the plasma utilization device 4 through the optical window 5c, is collected by the condensing system 7, and is converted by the fluorescent light detection device 8 into an electrical signal proportional to the fluorescent light intensity.

On the other hand, the same chemical species as the measurement species in the plasma utilization device 4 is sealed in the cell 9, and the cell 9 has an optical surface that can introduce and guide the laser beam 2 from the beam splinter 3. . Therefore, two laser beams from the beam splitter 3 are received, and a fluorescent light 10 is generated. The fluorescent light 10 is a condensing system 11
The fluorescence is incident on the fluorescence detection device 12 by the fluorescence detection device 1.
2 outputs an electrical signal proportional to the fluorescence intensity. Since the concentration of chemical species within the cell 9 is constant, the intensity change of the fluorescent light 10 is based on the change in the wavelength of the laser beam 2. In the plasma utilization device 4, a change in the intensity of the fluorescent light 6 occurs in exactly the same way based on a change in the wavelength of the laser beam 20, which causes a decrease in measurement accuracy.
The output of 12 is input to the fluorescence generation rate calculation unit, and the change in the output of the fluorescence detection device 8 based on the change in the wavelength of the laser beam 2 is corrected, and the correct total fluorescence generation rate in the plasma utilization device 4 is determined. Calculate and output. Then, the value is displayed on the display device 14.
is displayed.

As is clear from the above description, according to the first embodiment shown in FIG.
．． It is possible to correct measurement errors due to minute changes in the wavelength of the laser beam 2 that occur at a temperature of about 1° C.), and as a result, it is possible to perform highly accurate measurements over a long period of time.

The fluorescence detection device 12 can be constructed at low cost without requiring expensive equipment such as a spectrometer, since the fluorescence measurement in the cell 9 can be carried out without interference from plasma light or the like.

FIG. 3 is a block diagram showing a second embodiment of the present invention, and the same parts as those in the first embodiment shown in FIG. 2 are given the same reference numerals and their explanations will be omitted. The difference between this second embodiment and the first embodiment is that the laser beam 2 from the beam sinter 3 is divided into two parts by a half mirror 15, and is irradiated directly onto a perfect photoelectric converter 16, while the other is The laser beam 2 is irradiated to the photoelectric converter 17 through the cell 9, inputted to the output total absorption rate calculator 18 of the photoelectric converters 16 and 17, and is absorbed by the measured chemical species at a constant concentration in the cell 9. It is to find the proportion.

This rate of absorption is the same for the chemical species to be measured within the plasma utilization device 4, and the amount of fluorescent light is proportional to the absorption scene. Therefore, by inputting the output of the absorption rate calculation unit 18 and the output of the fluorescence detection device 8 to the fluorescence generation rate calculation unit 13, and correcting the output of the fluorescence detection unit 8 with the output of the absorption rate calculation unit 18. Second, it becomes possible to correct measurement errors based on minute changes in the wavelength of the laser beam 2.

FIG. 4 is a block diagram showing a third embodiment of the present invention.
, parts that are the same as those in the second embodiment shown in FIG. The difference from the second embodiment shown in FIG. 3 is that the laser light source 1 is formed by a pulse 1/- laser light source, and the cell 9 is provided with a sonic wave detector ]9. In this third embodiment, a pulsed laser beam 2 is introduced into a cell 9, and the intensity of the sound wave generated when the pulsed laser beam 2 is absorbed by a chemical species to be measured in the cell 9 is measured. The absorption rate of the measured chemical species is determined from the output of the photoelectric converter 16, and the output of the fluorescence detection device 8 is corrected. The reason why sound waves are generated in the cell 9 is that by absorbing the pulsed laser light, the absorbed energy is converted into heat, and as a result, the gas expands rapidly. In that case, the intensity of this sound wave is proportional to the absorption rate of the laser beam 2. Therefore, the intensity of the laser beam 2 is determined using the photoelectric converter]6,
The absorption rate is calculated by determining the intensity of the sound wave with the sound wave detector 19 and inputting both to the absorption rate calculator 18. Therefore, by correcting the output of the fluorescence detection device 8 with the output of the absorption factor calculator 1B, it becomes possible to correct errors caused by minute changes in the wavelength of the laser beam 2.

〔Effect of the invention〕

According to the present invention, it is possible to correct for changes in the excitation efficiency of the measured chemical species caused by subtle changes in the oscillation wavelength of the laser light caused by temperature changes within the laser light source, so that high sensitivity and high performance can be achieved over a long period of time. This has the effect of making it possible to measure accuracy.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the absorption curve of the measured chemical species and the spectrum of the excitation laser beam, FIG. 2 is a diagram showing the first embodiment of the present invention, and FIG. 3 is a diagram showing the second embodiment of the present invention. FIG. 4 is a diagram showing a third embodiment of the present invention. 1. Laser light source, 2. Laser light, 3. Beam splinter, 4. Plasma utilization device. , 6.10・
... Fluorescent light, 7.11... Light collection system, 8, 12... Fluorescence detection device, 9... Cell, 13... Fluorescence generation rate calculator, 14... Display device, 15...Half mirror-116
, 17... Photoelectric converter, 18... Absorption rate calculator, 1
9...Sound wave detector. Agent Patent Attorney Tadashi Akimoto Figure 1 Figure 2 Cause 4;;j Figure 3'';, r, S Figure 4

Claims (1)

[Claims] 1. By exciting only a specific chemical species with a narrow band laser beam irradiated into a plasma utilization device and detecting the fluorescence generated at that time with a fluorescence detector), the above In a plasma monitor for measuring the concentration of a specific chemical species, a first means for irradiating the narrow band laser beam onto a cell encapsulating the specific chemical species and detecting a change in the wavelength of the narrow band laser beam;
A plasma monitor comprising second means for correcting the output of the fluorescence detection device according to the wavelength change detected by the means. 2. The first means is comprised of a fluorescence detection device that measures the intensity of fluorescence generated by irradiating the cell with narrowband laser light, and detects changes in the intensity of the measured fluorescence using the narrowband laser light. 2. The plasma monitor according to claim 1, wherein the plasma monitor detects the change in wavelength as a change in wavelength. 3. The first means is characterized in that it is comprised of a means for measuring the absorption rate of laser light absorbed within the cell, and that the change in the measured absorption rate is regarded as a change in the wavelength of the entire narrowband laser beam. A plasma monitor according to claim 1. 4. The bandpass laser beam is a pulsed laser beam, and the means for measuring the absorption rate includes a sonic detector that detects all the sound waves generated within the cell by laser excitation and a photoelectric converter that detects the intensity of the pulsed laser beam. A plasma monitor according to claim 3, characterized in that it is comprised of: