JPH06241999A - Spectral analytical method by laser emission using two step excitation method - Google Patents

Abstract

PURPOSE:To provide the title device utilized in the element concentration analysis of a solid or molten metal. CONSTITUTION:In a laser emission spectral analyzer, a laser beam from a laser oscillator 1 is convergently emitted on a surface of a sample S, the luminous intensity from plasma 4 formed is measured by a spectroscope 7, and the concentration of a target element is analyzed, by a previously given calibration curve in an analyzer 8. A laser oscillator 9 for excitation is added to the laser emission spectral analyzer, and the laser beam EL for excitation thereof is emitted on the plasma 4 through a prism 10. Thus, in analyzing with the two step excitation method in which the plasma 4 is excited at two steps, the deflection intensity of the laser beam EL passed through the plasma 4 is measured by using a laser beam detector 12. The prism 10 is controlled according to the deflection intensity through an operation controller 14, thereby the positioning of the laser beam EL within the plasma is carried out, and the element analysis can be very accurately done.

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 using a two-step excitation method used for element concentration analysis of solid or molten metal.

[0002]

2. Description of the Related Art A laser emission spectroscopic method capable of in-situ analysis is used for elemental concentration analysis of solid or molten metal. In this analysis method, as shown in FIG. 4, the laser light SL from the laser oscillator 1 is focused and irradiated on the surface of the sample S through the prism 2 and the condenser lens 3, and is emitted from the generated plasma 4. The emitted light is introduced into the spectroscope 7 through the condensing lens 3, the half mirror 5, and the condensing lens 6, the emission intensity thereof is measured, and the concentration of the target element is determined by the analytical curve previously given in the analyzer 8. It is to be analyzed (see, for example, JP-A-63-18249).

In such a laser emission spectroscopic method, in order to further enhance the sensitivity, a two-stage excitation method has been developed in recent years (for example, "Analysis of P in steel by the two-stage laser excitation method (spring 1992). Proceedings of the Iron and Steel Institute of Japan Conference, CA
MP-ISIJ Vol.5, 1992-445) "). An example of this two-stage excitation method is shown in FIG. 5, in which an excitation laser oscillator 9 is added to a conventional laser emission spectroscopic analyzer, and the excitation laser light EL is passed through a prism 10 and a condenser lens 11. By irradiating the central portion of the plasma 4 of the sample S generated by the evaporation laser beam SL, the plasma 4 is to be excited in two stages.

[0004]

In general, electrons, multiply-charged ions, neutral atoms and the like are present at a high density in the center of plasma generated by laser light irradiation. The area emits continuous light over a wide wavelength range. This continuous light becomes a background in measuring the emission intensity of the target element, and due to its influence, the accuracy of analysis is reduced. On the other hand, the intensity of continuous light is low in the peripheral portion of the plasma because the density of electrons and multiply charged ions is low, and as shown in FIG. 6, the S / B ratio of the emission intensity of the target element is higher in the peripheral portion.

Therefore, if the excitation laser light is focused and irradiated at a predetermined position on the periphery of the plasma,
Higher sensitivity analysis becomes possible. Further, in order to obtain a high reproducibility of analysis, it is necessary to irradiate the excitation laser light to a fixed position in the plasma for each measurement, and in order to realize such a thing, the plasma of the excitation laser light It is essential to determine the exact transit location inside.

However, in the above-described conventional two-stage excitation method, the excitation laser light EL is irradiated only so as to be focused on the central portion of the plasma 4, and the accurate passage position in the plasma is measured. However, there was no means for accurately irradiating a predetermined position in the plasma 4. The present invention has been made to solve the problems of the above-described conventional techniques, and a laser using a two-stage excitation method that can determine and position an accurate passage position of excitation laser light in plasma. It is an object to provide an emission spectroscopic analysis method.

[0007]

According to the present invention, when positioning the laser light passing through the plasma in the plasma by the two-step excitation method in the laser emission spectroscopy, the temperature of the medium in the plasma changes. This is a laser emission spectroscopic analysis method using a two-step excitation method characterized in that the deflection intensity of laser light due to a change in the refractive index is measured, and the laser light is positioned according to the deflection intensity.

[0008]

[Operation] The present inventors have found the following as a result of repeated intensive research and experiments to solve the above problems. That is, when the sample is irradiated with the laser beam for evaporation, heat is released by photothermal conversion, whereby the plasma directly above the sample has a spatial heat distribution and the refractive index changes. It was found that when the exciting laser light passes through this plasma, the optical path of the laser light is deflected due to the difference in refractive index.

FIG. 7 shows the relationship between the distance from the center of the plasma (the irradiation center of the evaporation laser) and the deflection intensity. If the deflection intensity of the laser light is measured based on this relationship characteristic, the laser from the center of the plasma will be measured. The distance of light can be easily known. Therefore, according to the present invention, by measuring the deflection intensity of the laser beam and positioning the laser beam in the plasma according to the deflection intensity, it is possible to always analyze the target element with high accuracy. It is possible.

[0010]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. The same members as those in the conventional example are designated by the same reference numerals and the description thereof will be omitted. In FIG. 1, reference numeral 12 is a laser light detector such as a four-division photodiode for detecting the excitation laser light EL that has passed through the plasma 4 from the excitation laser oscillator 9, and 13 is the laser light detector 12 Is a preamplifier for amplifying the detection signal of, and 14 is an arithmetic and control unit.

The four-division photodiode used as the laser light detector 12 is composed of four-division photodiode elements a, b, c and d as shown in FIG. Further, the arithmetic control device 14 outputs a signal for controlling the irradiation position of the excitation laser light EL based on the arithmetic result, and controls the angle of the prism 10. The arithmetic and control unit 14 is provided with a function of adjusting the irradiation timing of the laser oscillator (for evaporation) 1 and the excitation laser oscillator 9.

Then, the surface of the sample S is irradiated with the laser light SL for evaporation from the laser oscillator 1 to generate the plasma 4, and after a predetermined time, the laser oscillator EL for excitation is irradiated with the laser light EL for excitation. Excitation laser light passing through the plasma 4
The intensity of EL is measured by the laser light detector 12. Now, when the excitation laser light EL irradiates the central portion of the plasma 4 for measurement, the temperature distribution on the left and right of the central portion of the plasma 4 has symmetry with respect to the traveling direction of the laser light, so that no deflection occurs. . Therefore, the irradiation position of the excitation laser light EL is adjusted by controlling the angle of the prism 10 so that the sum of the intensities of the left and right photodiode elements a and c, b and d of the laser light detector 12 becomes equal. Of. Further, when it is desired to perform measurement at a specific position in the peripheral portion of the plasma 4, in the four photodiode elements a, b, c, d, the sum of the intensities of the left elements a and c and the intensities of the right elements b and d. The position of the excitation laser light EL may be adjusted so that the sum ratio, that is, the deflection intensity, becomes a predetermined value.

Pulse energy 2 as laser SL for evaporation
The method of the present invention was applied to the analysis of Mn element in steel by using a YAG laser of J and a YAG laser having a pulse energy of 250 mJ as the excitation laser EL. At this time, a four-division photodiode was used as the laser light detector 12. The results are shown in Fig. 3. As is clear from this figure, the analysis accuracy of the method of the present invention is within about 1%, which is improved compared to the accuracy of about 5% of the conventional method.

In the above embodiment, the laser light detector 12 is described as a four-division photodiode, but the present invention is not limited to this. For example, a photodiode array or a knife edge is partially used. A means for cutting the laser light and then measuring the intensity with a photodiode can be used.

[0015]

As described above, according to the two-stage excitation laser emission spectroscopic analysis method of the present invention, the passage position of the excitation laser in the plasma can be accurately determined. It is possible to improve the analysis accuracy of the target element and also improve the repetition accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram showing an outline of an embodiment of the present invention.

FIG. 2 is a schematic diagram showing an example of a laser light detector used in the present invention.

FIG. 3 is a characteristic diagram showing changes in analysis results of the method of the present invention and the conventional method in comparison.

FIG. 4 is a block diagram showing an outline of a conventional example of laser emission spectroscopy.

FIG. 5 is a block diagram partially showing an outline of a conventional example of a two-stage excitation laser emission spectral analysis method.

FIG. 6 is a characteristic diagram showing the relationship between the distance from the plasma center and the S / B ratio in the two-stage excitation laser emission spectroscopy.

FIG. 7 is a characteristic diagram showing the relationship between the distance from the plasma center and the deflection intensity.

[Explanation of symbols]

 1 laser oscillator (for evaporation) 4 plasma 7 spectroscope 8 analyzer 9 laser oscillator for excitation 12 laser light detector 13 preamplifier 14 arithmetic control device S sample SL laser light (laser light for evaporation) EL laser light for excitation

Claims (1)

[Claims] 1. When the laser light passing through the plasma by the two-step excitation method is positioned in the plasma in the laser emission spectroscopy, the deflection of the laser light due to the change in the refractive index of the medium in the plasma due to the temperature change. Measure the strength,
A laser emission spectroscopic analysis method using a two-step excitation method, characterized in that the laser light is positioned according to the deflection intensity.