JPS6318134B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for measuring laser-excited fluorescence, and more particularly to a method and apparatus for measuring laser-excited fluorescence suitable for monitoring rapidly changing plasma distribution.

In conventional laser-excited fluorescence measurement methods and devices, in order to remove noise and improve the S/N ratio,
Box integrators and lock-in amplifiers are used. However, with both box integrators and lock-in amplifiers, the measurement phenomenon must exhibit regular periodicity, and since the plasma material that is the subject of plasma monitoring changes its luminescence state from moment to moment, it is difficult to detect a single luminescence phenomenon. Must be measured. Therefore, it is necessary to create a device that can generate fluorescent light from the plasma material once with a single pulse of laser light and measure it accordingly. However, with such conventional laser-excited fluorescence measurement methods and devices, it has been impossible to monitor rapidly changing plasma distribution.

The present invention was made in view of the drawbacks of the conventional laser-excited fluorescence measurement method and apparatus, and an object of the present invention is to provide a laser-excited fluorescence measurement method and apparatus that can accurately monitor rapidly changing plasma distribution. It is said that

In order to avoid noise generated at the start of pulsed laser oscillation, the laser-excited fluorescence measurement method of the present invention includes the following steps:
The start time of measuring the intensity of the fluorescent light excited by the pulsed laser light is delayed by a predetermined period of time, and the intensity of the pulsed laser light and the intensity of the fluorescent light excited by the pulsed laser light are integrated separately, and the intensity of the pulsed laser light is integrated. It is characterized in that the accuracy of determining the fluorescence intensity is improved by taking the ratio of the value to the integrated value of the fluorescence intensity.

Furthermore, the laser-excited fluorescence measuring device of the present invention includes a first means for starting measurement by delaying the intensity of the fluorescence excited by the pulsed laser light for a predetermined period of time in order to avoid noise generated at the start of pulsed laser oscillation. , a second means for digitally converting and integrating an electrical signal indicating the fluorescence intensity outputted from the first means; and a third means for detecting the intensity of the pulsed laser beam as an electrical signal, digitally converting it, and integrating it. and a fourth means for correcting the fluorescent light intensity by taking the ratio of the integrated value of the fluorescent light intensity output from the second means based on the integrated value of the pulsed laser light intensity output from the third means. It is characterized by having the following.

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

FIG. 1 shows a plasma distribution monitor incorporating the laser-excited fluorescence measuring device of the present invention. In the figure, in the dye laser 1 for ultraviolet rays, when a discharge tube 22 discharges and emits light due to a trigger from a control unit 17, the dye is pumped, and a pulsed laser beam 24 is emitted from a laser oscillation tube 23.

The laser beam 24 is transmitted to the scanning device 3 on the one hand.
The light is scanned two-dimensionally and is incident through the entrance window 4 of the plasma utilization device 5. The laser beam 24 incident on the plasma utilization device 5 excites the plasma substance 6 and generates fluorescence 25 . The fluorescent light 25 is the measurement window 7
is emitted, is received two-dimensionally by the scanning device 8, is incident on the spectrometer 9, and is emitted to the detector 26.
is converted into an electrical signal. This electrical signal is amplified by an amplifier 10, then converted to a digital signal by an analog-to-digital converter 11, and then converted to a digital signal by an integrator 1.
2 is input.

On the other hand, the laser beam 24 is reflected by the half mirror 2, enters the monitoring detector 13, and is converted into an electric signal. This electrical signal is amplified by an amplifier 14 and is input to an integrator 16 via an analog-to-digital converter 15 on the one hand, and a level detector 18 on the other hand to activate a timer 19. After the timer 19 has counted a predetermined time, the control unit 17 starts photometry of the detector 26,
Further, a trigger is sent to the discharge tube 22, and after the fluorescence intensity is measured, the control unit 17 controls the scan device 3,
8 to the next measurement location.

When the waveform of one pulse of the laser beam 24 is viewed from the output waveform of the monitoring detector 13, it becomes a waveform as shown in FIG. 2a. In FIG. 2a, a waveform 30 is noise caused by the discharge of the discharge tube 22 used to pump the dye, and a waveform 31 is the waveform of the laser beam itself. When the fluorescence intensity waveform is viewed as the output waveform of the detector 26, the waveform is as shown in FIG. 2b.
In FIG. 2b, a waveform 32 is the noise caused by the discharge of the discharge tube 22, and a waveform 33 is the waveform of the fluorescent light itself. The intensity of waveform 30 is relatively weak compared to the intensity of waveform 31, but since the fluorescence intensity itself is weak,
The intensity of the waveform 32 is stronger than the intensity of the fluorescent waveform 33, and in some cases, the intensity is reversed. Therefore, the fluorescence intensity cannot be accurately measured unless the noise waveform 32 based on the discharge tube 22 is removed.

Therefore, in this embodiment, the controller 17 triggers the discharge tube 22, and the level detector 18, which monitors the intensity of the oscillated laser beam, detects when the intensity of the laser beam 24 exceeds a certain level. At this time, a trigger is applied to the fluorescence intensity measurement circuit. In addition, the time constant of the detector 26 is predetermined to an optimum value, so that fluorescence measurement is started with a further delay corresponding to the time constant. Detector 2 obtained in this way
The output waveform of No. 6 is shown in FIG. 2c.

On the other hand, at the same time as a trigger is applied to the fluorescent light intensity measuring circuit, a trigger is also applied to the integrator 16, and the laser beam 2
Measure the intensity waveform of step 4. Both the integral signal of the fluorescence intensity and the integral signal indicating the intensity of the laser beam 24 obtained in this way are inputted to the arithmetic unit 20, and arithmetic processing such as various corrections and calculations is performed to calculate the ratio of the two integral signals. The results are displayed on the display device 21.

The integrators 12 and 16 perform sampling on a time division basis of 17 ns at maximum, and are capable of sampling up to 1024 channels, thus measuring a time change of 17×1204=17 μs. Normally, the pulse width of the laser beam and the lifetime of the fluorescent light to be measured are on the order of several microseconds, so this integrator is sufficient for measurement. However, if the fluorescence intensity gradually weakens after the start of measurement and reaches the same level as the background intensity, even if you measure in this state, the S/N ratio will deteriorate, so it is necessary to Integrate the fluorescence intensity.

As is clear from the above description, according to the present invention, the influence of noise caused by the dye laser excitation discharge tube can be completely eliminated, and the fluorescence intensity can be measured accurately and quickly as a single phenomenon. Therefore, it is suitable for monitoring rapidly changing plasma distribution, and has the effect of improving the accuracy of detection from 20 to 30% in the prior art to several percent.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a plasma distribution monitor incorporating the laser-excited fluorescence measuring device of the present invention;
Figure 2a shows the output waveform of the detector for monitoring laser light, Figure 2b shows the output waveform of the fluorescence detector before noise is removed, and Figure 2c shows the output waveform of the fluorescence detector before noise is removed. FIG. 3 is a diagram showing an output waveform of a fluorescence detector after the above-mentioned detection. 1...Dye laser for ultraviolet light, 2...Half mirror, 3, 8...Scan device, 5...Plasma utilization device, 6...Plasma material, 9...Spectroscope, 1
0,14...Amplifier, 11,15...Analog
Digital converter, 12, 16... Integrator, 13
...Monitoring detector, 17...Control unit, 18...
Level detector, 19...Timer, 20...Arithmetic unit, 21...Display device, 22...Discharge tube, 23...
...laser tube, 24...laser light, 25...fluorescence.

Claims (1)

[Claims] 1. The measurement start timing of the fluorescence excited by the pulsed laser beam is delayed by a predetermined period from the start of the pulsed laser emission, and the intensity of the pulsed laser beam and the fluorescence excited by the pulsed laser beam are further adjusted. A laser-excited fluorescent lamp characterized in that the fluorescence intensity is measured by integrating the respective intensities separately and taking the ratio of the integrated value of the fluorescence intensity with the integrated intensity value of the pulsed laser beam as a reference. Light measurement method. 2. A first means for starting the measurement of the intensity of the fluorescent light excited by the pulsed laser beam by a predetermined time delay from the start of pulsed laser emission, and a digital electric signal indicating the fluorescent light intensity output from the first means. a second means for converting and integrating; a third means for detecting the intensity of the pulsed laser light as an electrical signal, converting it into a digital signal and integrating; and an integrated value of the pulsed laser light intensity output from the third means; 2nd based on
and fourth means for correcting the fluorescence intensity by calculating the ratio with the integrated value of the fluorescence intensity output from the means.