JPH0560691A - Laser emission spectral analysis method - Google Patents

Abstract

PURPOSE:To obtain sufficient sensitivity and analysis accuracy even at an analysis of a trace component by obtaining a large quantity of sample vapor expressly in a laser emission spectral analysis to increase the intensity of an element spectrum. CONSTITUTION:A giant pulse laser light B is made to irradiate a sample 100 while irradiating the sample 100 with a multi-mode laser light A to generate a large quantity of sample vapor expressly. This enables the ensuring of sufficient intensity of an element spectrum in an spectral analysis of a trance component thereby obtaining sufficient sensititvity and analysis accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser emission spectroscopic analysis method for separating light that is excited and emitted when a sample is irradiated with laser light into a spectrum by a spectroscope and quantitatively analyzing the constituent elements of the sample by the spectral intensity. In particular, the present invention relates to a laser emission spectroscopic analysis method suitable for trace component analysis.

[0002]

2. Description of the Related Art With the progress of laser technology in recent years, a laser emission spectroscopic analysis method using laser light as an excitation source for emission analysis has been devised.

FIG. 5 shows a conventional example.

Reference numeral 20 denotes a laser oscillator that oscillates a strong laser beam, and irradiates the laser beam from the laser oscillator 20 through a condenser lens 21 so as to focus on the surface of the sample 100.

The surface layer of the sample 100 is rapidly heated by the laser light. In particular, if the laser light is in the form of a pulse of several tens of nanoseconds, heat will be locally injected before the heat diffuses into the sample 100.
Melting or evaporation in the surface layer of the sample 100 instantaneously occurs, the vapor is excited by laser light, and becomes laser plasma 101 to emit light.

The light emitted from the laser plasma 101 is introduced into the spectroscope 9 through the condenser mirror 8.

The light introduced into the spectroscope 9 passes through the entrance slit 10, reaches the diffraction grating 12 through the reflecting mirror 11, and
The light is dispersed by the diffraction grating 12 into a spectrum.

The spectrum intensity is detected by the detector 14 through the emission slit 13, and the content of the target element in the sample 100 is examined by the signal processor 22 and the computer 23.

According to this method, there is an advantage that the spectroscopic analysis can be carried out in a non-contact state with the sample 100, and the spectroscopic analysis can be carried out even if the sample 100 is a non-conductive substance or in a molten state.

However, continuous light is emitted together with each element spectrum from the laser plasma 101 generated by the laser light irradiation, and this continuous light is the main factor of the background.

Therefore, the above-mentioned conventional method has a drawback that the signal-to-background ratio (S / B ratio) is deteriorated and the analysis accuracy and accuracy are remarkably inferior.

As a means for removing the continuous light which is the main factor of this background, the applicant of the present invention has disclosed in Japanese Patent Laid-Open No. 57-10.
It has already been disclosed in Japanese Patent No. 0323.

This is because the laser plasma 101 immediately after being irradiated with laser light first emits light whose main component is continuous light, and then emits an elemental spectrum, and then separates the measurements in terms of time. It was done.

Specifically, 1 μse from the time of laser light irradiation
After the elapse of c, the light emitted during the time from the irradiation of the laser beam to the time of 16 μsec elapses is analyzed spectroscopically to obtain
We are trying to improve the ratio.

However, the removal of continuous light by this time-resolved measurement method has the following problems.

Since the emission times of continuous light and elemental spectra partially overlap, in order to separate them with high accuracy, a very high speed gate circuit of several tens of nanoseconds, a high speed photodetector, etc. Special equipment is required.

Further, since the intensity of continuous light is larger than that of the elemental spectrum, the gain of the photodetector or amplifier is limited by the peak intensity of continuous light, and the analysis accuracy can be improved only to some extent. In particular, in order to increase sensitivity when measuring trace element spectra,
It is necessary to increase the gain of the above element, but even if the gain of each element is increased, each element will be saturated by the peak intensity of continuous light, so it is not possible to increase each element to the required gain. However, it is not possible to obtain sufficient sensitivity to trace elements. As a result, there has been a problem that particularly sufficient sensitivity and analysis accuracy cannot be obtained during the analysis of trace components.

To solve this problem, the present inventors have disclosed an invention relating to spatially resolved measurement in which only the peripheral portion of laser plasma generated by laser light irradiation is used for spectroscopic analysis in Japanese Patent Laid-Open No. 63-18249. Disclosure.

That is, the S / B ratio is improved by removing the light mainly from the continuous light emitted from the central portion of the laser plasma and using only the light from the peripheral portion mainly emitting the element spectrum for analysis. Trying to improve.

[0020]

In the above invention, in order to improve the S / B ratio, only the light in the peripheral portion of the laser plasma needs to be used for analysis.

However, in the peripheral part of the laser plasma,
As the continuous light decreases, the amount of sample vapor also decreases, and the elemental spectrum intensity decreases toward the periphery.

Therefore, in order to secure a certain level of elemental spectrum intensity in the spectroscopic analysis, there is no choice but to measure the part where the continuous light and the elemental spectrum are emitted with a certain level of intensity, and as a result, the continuous light is completely removed. There was a problem that I could not do it.

The present invention has been made in order to solve the above-mentioned conventional problems. By obtaining a remarkably large amount of sample vapor, the element spectrum intensity is increased, and sufficient sensitivity is obtained even in the analysis of trace components. It is an object of the present invention to provide a laser emission spectroscopic analysis method capable of obtaining analysis accuracy.

[0024]

In order to achieve the above object, the present invention provides a laser emission spectroscopic analysis method for concentrating and irradiating a sample with a laser beam and spectroscopically analyzing the excited and emitted light. While irradiating laser light,
It is characterized by irradiating a giant pulse laser beam.

[0025]

According to the laser emission spectral analysis method of the present invention,
While irradiating the sample with the multi-mode laser light, the sample is irradiated with the giant pulse laser light, so that a significantly large amount of vapor can be generated. Can be secured.

[0026]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a block diagram of an apparatus for carrying out a laser emission spectroscopic analysis method according to an embodiment of the present invention.

The oscillation modes of laser light include a normal pulse mode and a giant pulse mode, and both modes are used in this embodiment.

Reference numeral 1 denotes a normal pulse mode laser oscillator, and this normal pulse mode laser oscillator 1
As shown in FIG. 3A, the multi-spike normal pulse laser light A having a long pulse width (several tens of msec) and a small peak output (several W) is oscillated.

Reference numeral 2 denotes a giant pulse mode laser oscillator for instantaneously melting and evaporating the sample 100 and further exciting the vapor cloud of the sample 100. From this giant pulse mode laser oscillator 2, FIG.
As shown in Fig. 2, the giant pulse laser beam B has a short pulse width (tens of nanoseconds) and a large peak output (several MW).
Is oscillated.

In this giant pulse mode laser oscillator 2, an optical shutter (not shown) arranged in an optical path in an internal resonator (not shown) is closed until the population inversion density in the laser oscillator 2 becomes maximum. The giant pulse laser beam B is emitted by stopping the laser oscillation and instantly opening the optical shutter at the time when the population inversion density becomes maximum to cause the laser oscillation at once. As the optical shutter, a Q-switching element such as Pockels cell is used.

Reference numeral 4 is a reflecting mirror for reflecting the normal pulse laser light A oscillated from the normal pulse mode laser oscillator 1 toward the sample 100, and 5 is a giant pulse laser oscillated from the giant pulse mode laser oscillator 2. Reference numeral 6 is a half mirror that reflects the light B toward the sample 100 and transmits the normal pulse laser light A, and 6 represents the normal pulse laser light A and the giant pulse laser light B.
It is a condenser lens that focuses on the surface of. A beam stopper 7 is arranged to trap the giant pulse laser beam B transmitted through the half mirror 5.

Reference numeral 8 is a condenser mirror for condensing the light C of the laser plasma 101 generated on the sample 100 on the entrance slit 10 of the spectroscope 9, and the reference numeral 12 in the spectroscope 9 is
Light C reaching through the entrance slit 10 and the reflecting mirror 11
Is a diffraction grating that disperses and disperses into a spectrum.

Reference numeral 14 is a detector for detecting the intensity of the spectrum from the diffraction grating 12 incident through the exit slit 13, and is composed of a photographic film, a photomultiplier tube, a photodiode or the like.

Numeral 15 is a signal processor for subjecting the spectrum intensity detected by the detector 14 to signal processing such as integration and integration and then A / D conversion and outputting, and 16 is a signal processor 15
It is a computer that calculates the element concentration based on the spectrum intensity value from.

Reference numeral 17 is a normal pulse mode laser oscillator 1 and a giant pulse mode laser oscillator 2.
Is a control system for controlling the oscillation timings of the oscillators 1 and 2 via a delay circuit 18 for delaying the oscillation time of and, and is operated by a command from the computer 16. The delay time can be set by inputting the delay time D into the computer 16.

Specifically, as shown in FIG. 2 (a), a pulse-shaped control signal is output from the control system 17 to the normal pulse mode laser oscillator 1, and as shown in FIG. 2 (b). A pulsed control signal from the control system 17 is output to the giant pulse mode laser oscillator 2 by a delay circuit 18 with a delay time D. Therefore, if the delay time D is set to be positive,
As shown in (b) and (b), after the normal pulse mode laser oscillator 1 oscillates the normal pulse laser beam A, the giant pulse mode laser oscillator 2 oscillates the giant pulse laser beam B with a delay time D. If the delay time D is set to a negative value, the normal pulse mode laser oscillator 1 does not oscillate, but only the giant pulse mode laser oscillator 2 oscillates the giant pulse laser light B.

Next, the operation of this embodiment will be described.

The control signal shown in FIG. 2 (a) is input to the normal pulse mode laser oscillator 1 and the normal pulse laser light A is supplied to the normal pulse mode laser oscillator 1.
Is output first.

The normal pulse laser light A is irradiated onto the sample 100 so as to focus on the surface of the sample 100 by the condenser lens 6 via the reflecting mirror 4 and the half mirror 5.

This normal pulse laser light A is shown in FIG.
As shown in (a), because of the long width and the small peak output, melting and evaporation mainly occur continuously in the surface layer of the sample 100 for a time corresponding to the pulse width of the normal pulse laser light A.

Then, when the delay time D elapses from the oscillation of the normal pulse mode laser oscillator 1, FIG.
) And (b) are input to the giant pulse mode laser oscillator 2, and the giant pulse laser beam B is oscillated from the giant pulse mode laser oscillator 2 to irradiate the surface of the sample 100.

This giant pulse laser beam B is
As shown in Fig. 3 (b), since it is a powerful laser beam with a short width (tens of nanoseconds) and a small peak output (several MW), sample 10
Melting and evaporation at zero surface layer occurs instantaneously. And
The vapor cloud and the vapor cloud generated by the normal pulse laser light A generated during the delay time D are excited by the giant pulse laser light B, the laser plasma 101 is generated, and the light C is emitted. Since the intensity of the light C corresponds to the sum of the amount of vapor by the normal pulse laser light A and the amount of vapor by the giant pulse laser light B, it becomes larger than that when only the giant pulse laser light B is applied to the sample 100. .

This light C is introduced into the spectroscope 9 by the condenser mirror 8, dispersed into a spectrum by the diffraction grating 12, and detected by the detector 14 as elemental spectrum intensity.

Therefore, since this elemental spectrum intensity corresponds to the vapor amount of the sample 100 at the time of laser irradiation, a large vapor amount can be obtained by increasing the delay time D and lengthening the irradiation time of the normal pulse laser light A. As a result, the elemental spectrum intensity can be increased.

FIG. 4 shows the delay time D when the sample 100 is iron.
And the element spectrum intensity of iron having a wavelength of 271.4 nm was measured as the signal intensity. At the same time, the intensity at a wavelength where the iron spectrum is not generated near the wavelength of 271.4 nm was measured as the background intensity.

As shown in FIG. 4, according to the laser emission spectroscopic analysis method of this embodiment, when the delay time D is increased, the signal intensity, that is, the element spectrum intensity is greatly increased compared to the background intensity. Strength is
Giant pulsed laser light B with negative delay time D
It can be seen that the intensity is much higher than the elemental spectrum intensity obtained by irradiating only the sample 100 with the sample.

Therefore, the sample 10 containing a trace amount of elements to be analyzed
In the case of spectroscopic analysis of 0, if the delay time D is increased, a large amount of vapor is generated from the sample 100 and a large elemental spectrum intensity can be obtained. Obtainable.

[0049]

As described above, according to the laser emission spectral analysis method of the present invention, the sample is irradiated with the giant pulse laser light while the sample is irradiated with the multi-mode laser light. It is possible to generate a sample vapor, and it is possible to obtain a sufficient elemental spectral intensity even when performing a spectroscopic analysis of a small amount of component elements.
As a result, there is an excellent effect that sufficient sensitivity and analysis accuracy can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an apparatus for carrying out a laser emission spectroscopic analysis method according to an embodiment of the present invention.

FIG. 2 is a time chart diagram showing control signals for controlling the normal pulse mode laser oscillator and the giant pulse mode laser oscillator used in FIG.

FIG. 3 is a time chart diagram showing pulsed laser light emitted from a normal pulse mode laser oscillator and a giant pulse mode laser oscillator.

FIG. 4 is a diagram showing changes in elemental spectrum intensity and background intensity when the delay time is changed.

FIG. 5 is a block diagram showing an example of a conventional laser emission spectral analysis method.

[Explanation of symbols]

 1 ... Normal pulse mode laser oscillator, A ... Normal pulse laser light, 2 ... Giant pulse mode laser oscillator, B ... Giant pulse laser light, 4 ... Reflecting mirror, 5 ... Half mirror, 6 ... Condensing lens, 7 ... Beam stopper , 8 ... condenser mirror, 9 ... spectroscope, 10 ... entrance slit, 11 ... reflecting mirror, 12 ... diffraction grating, 13 ... exit slit, 14 ... detector, 15 ... signal processor, 16 ... calculator, 17 ... control System, 18 ... Delay circuit, 100 ... Sample, 101 ... Laser plasma, C ... Light.

Claims (1)

[Claims] 1. A laser emission spectroscopic analysis method for concentrating and irradiating a sample with a laser beam and spectrally analyzing the light emitted by excitation, wherein the sample is irradiated with a giant pulse laser beam while being irradiated with a multimode laser beam. A laser emission spectral analysis method characterized by: