JPH06100544B2 - Laser emission spectroscopy analyzer - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

TECHNICAL FIELD The present invention relates to a laser emission spectroscopic analyzer, and in particular, it is suitable for use in trace component analysis, and separates light emitted when a sample is irradiated with laser light into a spectrum by a spectroscope to obtain spectral intensity of each element. The present invention relates to improvement of a laser emission spectroscopic analysis device for quantitatively analyzing component elements.

2. Description of the Related Art With the progress of laser technology in recent years, various attempts have been made in various fields to utilize it as an excitation source for spectroscopic analysis. In such an attempt, for example, as shown in FIG.
The surface of the sample 10 is rapidly heated by irradiating the surface of the sample 10 with a strong laser beam focused by a suitable condenser lens 12 from a laser oscillator 14. In particular, if the laser light is pulsed for several tens of nanoseconds, energy will be locally injected before heat is diffused into the sample,
Melting and evaporation occur in 10 surface layers. The vapor is further excited by laser light to become plasma 16 and emits light. The light emitted from the plasma 16 is converted into an appropriate light introduction system 18
After being transmitted to the spectroscope 20 using a condensing mirror 19 (in FIG. 3) and separated into spectra by the diffraction grating 22 or the like, the spectral intensities of the respective elements are photographed film, photomultiplier tube 24. The content of the target element is examined by detecting with a photo diode or the like. In the figure, 26 is an entrance slit of the spectroscope, 28 is a reflecting mirror, 30 is an exit slit, 32 is a signal processor, and 34 is a calculator. Such a laser emission spectroscopic analysis method enables analysis without contacting the sample 10, and has the advantage that the sample 10 can be analyzed even when it is a non-conductive substance or in a molten state, while the signal-to-background ratio is high. (Hereinafter referred to as S / B ratio) is bad,
It had a drawback that the analysis accuracy and precision were extremely poor. This is the plasma generated by laser light irradiation.
This is because continuous light is emitted from 16 along with each element spectrum, and this continuous light is the main cause of the background in this method. The applicant has already proposed that the continuous light should be removed.
57-100323 is disclosed. This is because, based on the knowledge that the light mainly composed of continuous light is emitted from the plasma immediately after the laser light irradiation, and then the element spectrum is emitted, the measurement is temporally separated and the laser light irradiation is performed. 1
After the elapse of μsec, the light emitted during the period from the irradiation of the laser beam to the elapse of 16 μsec is spectroscopically analyzed to obtain S / B.
This is intended to improve the ratio.

[Problems to be Solved by the Invention]

However, the removal of continuous light by this time-resolved measurement method has the following problems. That is, the emission times of continuous light and elemental spectra partially overlap with each other.
A special device such as a very high speed gate circuit or a high speed response photodetector is required. Further, since the intensity of continuous light is higher than that of the element spectrum, the gains of the photodetector and the amplifier are limited by the peak intensity of continuous light. Therefore,
For example, when measuring a trace element spectrum, even if the gain is increased to increase the sensitivity, each element is saturated with the peak intensity of continuous light, and sufficient sensitivity cannot be obtained for trace element elements. It is not possible to increase the gain. Therefore, there has been a problem that the analysis accuracy can be improved only to some extent, and sufficient sensitivity and accuracy cannot be obtained especially when a trace component analysis is performed. On the other hand, Japanese Patent Laid-Open No. 58-219438 discloses a ring-shaped condensing mirror which has a hole at the center and a reflection surface at the periphery for light emitted from plasma formed by irradiating a sample with laser light. However, when a ring-shaped condenser mirror is used, strict optical axis adjustment is required to accurately align the optical axis of the laser and the optical axis of the received light coaxially. It is necessary and needs to be cleaned because the mirror surface (usually a vapor deposition film of aluminum) is contaminated by evaporative substances from the sample when used for a long time, but it is easily scratched and difficult to maintain. Had. The present invention has been made to solve the above-mentioned conventional problems, does not require a special device such as a high-speed response element or strict optical axis adjustment, is simple in maintenance, and is sufficient even for trace component analysis. It is an object of the present invention to provide a laser emission spectroscopic analysis method and device that can obtain various sensitivities and precisions.

[Means for solving problems]

The present invention relates to a laser emission spectroscopic analyzer that separates light emitted when a sample is irradiated with laser light into a spectrum with a spectroscope and quantitatively analyzes component elements from the spectral intensities of the respective elements. The light introduction system to be introduced into
Among the plasma formed on the sample surface, the light emitted from the central part is excluded, and only the light emitted from the peripheral part is selectively introduced into the spectroscope as a light selection means. The above object is achieved by providing a condensing lens which is provided and which has been subjected to a transmission treatment in the peripheral portion. In another embodiment of the present invention, the light selecting means is a slit instead of the condenser lens.

[Action]

In the device shown in FIG.
0, the light introduction system 18 and the spectroscope 20 are fixed, and the laser light axis is moved to measure the light emitted from the central portion and the peripheral portion of the plasma 16. It was found that continuous light, which is the ground, is mainly emitted, whereas continuous system emission is extremely small in the peripheral part of the plasma, and the element spectrum used for spectroscopic analysis is mainly emitted. The present invention was made based on such findings,
The light emitted when the sample is irradiated with laser light is separated into spectra with a spectroscope, and when quantitatively analyzing the constituent elements from the spectral intensity of each element, the plasma is emitted from the center of the plasma formed on the sample surface. The emitted light is excluded and only the light emitted from the peripheral portion is selectively introduced into the spectroscope for spectroscopic analysis. Therefore, the S / B ratio is improved, and sufficient sensitivity and accuracy can be obtained even in the analysis of a trace amount of components, without requiring a special device such as a high-speed response element. Here, not only the slit but also the condensing lens having the central portion subjected to the anti-transmission treatment can eliminate only the light emitted from the central portion of the plasma in the point source where plasma is theoretical. Instead, it has a certain size (about 3 mm diameter). That is, due to the geometrical positional relationship between the position of the emitted light in the plasma, the incident slit of the spectroscope, and the transmission prevention processing section of the condenser lens, the emitted light from the central part of the plasma is not taken into the spectroscope. .

【Example】

Embodiments of the present invention will be described in detail below with reference to the drawings. As shown in FIG. 1, the first embodiment of the present invention is similar to the prior art example shown in FIG. 3 in the laser emission spectroscopic analyzer, but instead of the condenser mirror 19 of the light introducing system 18, As shown in FIG. 1, a condensing lens 42 is provided in which the central portion of the lens is subjected to a permeation-preventing treatment and the peripheral portion thereof is permeating-treated by applying, for example, paint. Since the other points are the same as those of the conventional example, description thereof will be omitted. The operation of the first embodiment will be described below. The laser light emitted from the laser oscillator 14 is focused by the condenser lens 12
Then, the surface of the sample 10 is focused and irradiated. The light excited and emitted by the laser light irradiation is spectroscoped by the condenser lens 42 of the light introduction system 18.
An image is formed on the incident slit 26 of 20 and is introduced into the spectroscope 20. At this time, only the light emitted from the peripheral portion of the plasma is introduced into the spectroscope 20 by the condenser lens 42, while the light emitted from the central portion of the plasma cannot pass through the central portion of the condenser lens 42, and Not introduced in 20. The light introduced into the spectroscope 20 is separated into a spectrum by the diffraction grating 22, the spectrum of a predetermined element is selected by the exit slit 30, and the spectrum intensity is converted into an electric signal by the photomultiplier tube 24. The electric signal is amplified, integrated and analog-digital converted by the signal processor 32, and sent to the computer 34. The calculator 34 has the value sent from the signal processor 32,
The element concentration in Sample 10 is calculated from the calibration curve prepared in advance. Next, a second embodiment of the present invention will be described in detail. As shown in FIG. 2, this second embodiment is the same as the first embodiment except that the light introducing system 18 is used in the laser emission spectrum analyzer.
Is composed of a slit 44, which is provided on the surface of the sample, for passing only the light emitted from the peripheral portion of the plasma excluding the light emitted from the plasma central portion, and a condenser lens 46. Since the other points are the same as those in the first embodiment, the description thereof will be omitted. According to this embodiment, the configuration is very simple and the present invention can be easily applied.

【The invention's effect】

As described above, according to the present invention, the plasma emission light is spatially separated to improve the S / B ratio, so that the analysis sensitivity is high, and sufficient sensitivity and accuracy can be obtained even in the analysis of trace components. It has an excellent effect that

[Brief description of drawings]

FIG. 1 is a first diagram of a laser emission spectroscopic analyzer according to the present invention.
FIG. 2 is an optical path diagram including a partial cross-sectional view showing the overall configuration of the embodiment, FIG. 2 is an optical path diagram including a partial cross-sectional view showing the configuration of a main part of a second embodiment of the present invention, and FIG. It is an optical-path figure which shows the structural example of the conventional laser emission spectroscopy analyzer including a partial cross section figure. 10 ... Sample, 14 ... Laser oscillator, 16 ... Plasma, 18 ... Light introducing system, 20 ... Spectroscope, 42 ... Condensing lens, 44 ... Slit.

Claims (2)

[Claims] 1. A laser emission spectroscopic analyzer that separates the light emitted when a sample is irradiated with laser light into a spectrum with a spectroscope and quantitatively analyzes the constituent elements from the spectral intensity of each element. A light selection system that selectively introduces only the light emitted from the peripheral part of the plasma formed on the sample surface, excluding the light emitted from the central part, into the spectroscope in the light introduction system that is introduced into the instrument. The laser emission spectrum analyzer according to claim 1, further comprising a condensing lens which is subjected to a transmission preventing treatment in a central portion and which is subjected to a transmitting treatment in a peripheral portion. 2. A laser emission spectroscopic analyzer that separates the light emitted when a sample is irradiated with laser light into a spectrum by a spectroscope and quantitatively analyzes the component elements from the spectral intensity of each element. A light selection system that selectively introduces only the light emitted from the peripheral part of the plasma formed on the sample surface, excluding the light emitted from the central part, into the spectroscope in the light introduction system that is introduced into the instrument. And a slit is provided as a laser emission spectrum analyzer.