JPS6146774B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laser emission spectroscopic analysis method, and in particular, spectroscopic analysis of light emitted when a sample is irradiated with laser light, which is suitable for quantitative analysis of impurity elements in steel. This invention relates to improvements in laser emission spectroscopic analysis methods.

With the development of laser technology, attempts are being made to utilize it as an excitation source for spectroscopic analysis. This laser emission spectrometry basically converts light energy into thermal energy to evaporate and turn a solid sample into plasma, and the light emitted from the plasma is transmitted to the spectrometer using an appropriate light introduction system. death,
After separating spectra using a diffraction grating or the like, the content of the target element is determined by detecting the spectra using a photographic film, a photomultiplier tube, a photodiode, or the like.

As shown in FIG. 1, the optical system used for this laser emission spectroscopic analysis includes, for example, a laser emitting section 10 consisting of a ruby laser or the like that oscillates a laser beam with a wavelength of 0.69 μm;
A condenser lens 12 for condensing laser light emitted from zero and irradiating it onto the surface of the sample 14 placed at the focal position, and a converging lens for converging the light emitted from the surface of the sample 14 16 and a spectrometer 18 for spectroscopically analyzing the light converged by the converging lens 16, or in general, the ratio of the signal to the background (referred to as the SB ratio) is Therefore, as shown in FIG. 2, an auxiliary electrode 20 is placed between the condenser lens 12 and the sample 14 to collect the atoms emitted by laser irradiation. lead between the auxiliary electrodes 20 to discharge,
A device that is excited to an even higher energy state to obtain a stronger emission spectrum has been put into practical use.

However, in any case, in the conventional method, the sample 14 is placed accurately at the focal position of the condenser lens 12, and the optical axis of the spectrometer 18 is set at the laser irradiation position on the sample 14 or at the center between the electrodes of the auxiliary electrode 20. Part 2
It is necessary to adjust it to 0a. However, in actual analysis, the sample 14 is always
It is difficult to place the sample at a certain distance from the center due to the shape of the sample, etc. In particular, as in the case of the optical system shown in Figure 1, it is difficult to place the sample at a point where the optical axes of the laser system and spectrometer system coincide. It was not easy to set up.

The present invention was made in order to eliminate the above-mentioned conventional drawbacks, and provides a highly practical laser emission spectroscopic analysis method in which there is little change in emission spectrum intensity due to fluctuations in sample position, and sample setting is easy. The purpose is to

The present invention provides a laser emission spectrometry method for spectroscopically analyzing the light emitted when a sample is irradiated with laser light, in which the energy density at the sample surface is 2.0×10 ⁹ W/mm ² or more regardless of changes in the sample position. The sample is irradiated with an infrared pulsed laser beam so that the sample is irradiated with an infrared pulsed laser beam, and the light emitted from the sample is separated using a spectroscopic means arranged such that a direction perpendicular to the spectroscopic direction is parallel to the laser beam. In this way, the above objective has been achieved.

Further, the spectroscopic means and the photodetector for detecting the separated emission spectrum are arranged such that the centers of the spectroscopic means and the light receiving window of the photodetector in a direction perpendicular to the spectroscopic direction are the same as the focal point of the laser condensing lens. It is arranged so that it is in-plane.

The principle of the present invention will be explained below.

Generally, ruby laser light with a wavelength of 0.69 μm is often used as the laser light for laser emission spectrometry analysis. A method has been adopted in which the irradiation area is made into a pulse with a width of several nanoseconds and the irradiation area is brought into a high energy state before the thermal energy diffuses around the laser irradiation area.

The present inventors decided to perform such laser emission spectroscopic analysis using an infrared pulsed laser with even better heat transfer efficiency, and applied infrared pulsed laser light with a wavelength of 1.06 μm emitted by a Nd glass laser to the steel surface. irradiation and observed the emission spectrum. As a result, (1) an emission spectrum with a sufficiently excellent SB ratio can be obtained without using an auxiliary electrode, and (2) the intensity of the emission spectrum increases with the laser output, but eventually saturates as shown in Figure 3. tending to, (3)
It has been found that a linear relationship exists between the laser irradiation area on the sample surface and the minimum laser output Jmin at which the emission spectrum intensity reaches the saturation value, as shown in FIG. In addition, during the experiment,
The pulse width of the laser beam was set to 15 nsec, and the laser irradiation area was changed by moving the position of the condenser lens. From FIG. 4, it can be seen that a sufficiently good emission spectrum can be obtained if a power density of 2.0×10 ⁹ W/mm ² or more is obtained.

By the way, in actual spectroscopic analysis, the laser output is kept constant and the setting position of the condenser lens is also fixed. Furthermore, when the auxiliary electrode is not used, the relationship between the sample and the spectrometer system is as shown in FIG. Therefore, in the conventional method, the relationship between the laser output and its irradiation area is at one point in the upper left region of the straight line in FIG. However, as is clear from FIG. 3, even if the laser output is constant, it is possible to obtain a sufficiently strong emission spectrum as long as the relationship with the irradiated area is to the upper left of the straight line in FIG. That is, if the spectrometer system allows,
It can be seen that it is not necessary to set the sample position very precisely.

The present invention has been made based on such knowledge.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a laser emission spectrometer employing a laser emission spectrometry method according to the present invention will be described in detail with reference to the drawings.

In this example, as shown in FIG.
A Nd glass laser light source 22 and a laser oscillator connected to the laser light source 22 for irradiating an infrared pulsed laser beam with an energy density of 2.0×10 ⁹ W/mm ² or more on the sample surface regardless of changes in the sample position. A laser emitting section 10 comprising a power source 24 and a power source 26 for a high speed switching element (not shown) incorporated in the laser beam 22, and a laser beam emitted from the laser light source 22 of the laser emitting section 10. A rectangular prism 28 for making the infrared pulsed laser beam incident on the sample 14 at a predetermined angle, a condensing lens 12 similar to the conventional one, and a sample arranged to face the laser beam in a predetermined direction. a planar diffraction circuit 32 disposed so that the longitudinal direction of the grating perpendicular to the diffraction direction (direction of arrow A) is parallel to the laser beam, for spectroscopically analyzing the light emitted from the surface of 14; It has a photodetector 34 such as a photomultiplier tube or a photodiode, which receives the emission spectrum separated by the planar diffraction circuit 32 and has a long light receiving window in a direction parallel to the laser beam. Planar diffraction grating 3
2 and the photodetector 34 are arranged such that the longitudinal center of the planar diffraction grating 32 and the longitudinal center of the light receiving window of the photodetector 34 are in the same plane as the focal point of the condenser lens 12. a spectrometer 30, and the spectrometer 3
It is composed of a photodetector control device 36 for controlling the photodetector 34 of No. 0, and a display section 38 for displaying the measurement results of the output of the photodetector control device 36.

The action will be explained below. First, the electric energy stored in the laser oscillator power supply 24 is transferred to the laser light source 24.
2, and converts it into light energy such that the energy density at the sample surface is 2.0×10 ⁹ W/mm ² or more regardless of changes in the sample position. At this time, when a predetermined amount of electrical energy is stored in the laser light source 22,
A pulse signal is sent from the laser oscillator power supply 24 to the high-speed switching element power supply 26, and the laser light source 2
A high-speed switching element in laser light source 22 is activated to release the electrical energy stored in laser light source 22 all at once.

The infrared pulsed laser beam thus obtained passes through the right-angle prism 28 and the condensing lens 12, and has an energy density of 2.0× on the sample surface.
It is focused on the surface of the sample 14 so that the power is 10 ⁹ W/mm ² or more. Then, the surface of the sample 14 is locally heated in a short time, turned into plasma, and further excited. At this time, the light emitted from the plasma is dispersed by a plane diffraction grating 32 inside the spectrometer 30. This dispersed light is detected by a photodetector 34,
It is converted into an electrical signal proportional to the spectral line intensity. This electrical signal is input to the display section 38 via the amplifier or photodetector control device 36, and the measurement results are displayed on the display section 38.

In this embodiment, the sample 14 is placed at the focal point of the condensing lens 12, and the sample is adjusted so that the plane diffraction grating 32 and the photodetector 34 satisfy the diffraction conditions for the spectral line of a specific wavelength emitted from the sample 14. If set, even if the sample 14 moves thereafter, the diffraction conditions will always be satisfied as shown in FIG.
As long as the emission spectrum does not appear outside the light receiving window, a sufficiently good emission spectrum can be obtained and stable spectroscopic analysis can be performed.

Incidentally, in the above embodiment, the laser emitting section 10
A right-angle prism 28 was placed between the laser light source 22 and the condensing lens 12, but when the Nd glass laser light source 22 of the laser emitting unit 10 is set in a predetermined irradiation direction with respect to the sample 14 from the beginning It is also possible to omit this rectangular prism 28.

Further, in the embodiment, a plane diffraction grating 32 is used as the spectroscopic means, and the plane diffraction grating 32
Although the longitudinal direction of the grating is parallel to the laser beam, the type of spectroscopic means is not limited to this. For example, a prism is used, and the prism is arranged so that the direction perpendicular to the direction of spectroscopy is It is also possible to arrange it parallel to the laser beam.

Further, in the above embodiment, a photodetector having a long photodetector in one direction is used,
Although the longitudinal direction of the light-receiving window was arranged to be parallel to the laser beam, the type of photodetector is not limited to this. For example, a photodetector having a circular light-receiving window may be used. It is also possible to arrange the circular light receiving window so that its diameter direction is parallel to the laser beam.

Furthermore, in the embodiment described above, the light emitted from the sample 14 is directly transmitted to the plane diffraction grating 3 of the spectrometer 30.
However, the arrangement of the light introduction system is not limited to this, and it is also possible to arrange lenses, reflectors, etc. around the sample 14 to efficiently guide the emission spectrum to the plane diffraction grating 32, etc. It is also possible to jump.

Furthermore, in the embodiment, the plane diffraction grating 3
Although one photodetector 2 and one photodetector 34 are arranged, it is also possible to provide a plurality of photodetectors 34 or a plurality of sets of planar diffraction gratings 32 and photodetectors 34. It is.

Although the present invention is applied to the analysis of steel in the above embodiment, the scope of application of the present invention is not limited thereto, and it is clear that the present invention can be similarly applied to the analysis of molten steel.

As described above, the present invention has excellent effects in that there is little change in emission spectrum intensity due to variation in sample position, sample setting is easy, and therefore practicality is high.

Using a laser emission spectrometer as described in the previous example, the infrared laser output was 10 J, the pulse width was 15 nsec (approximately 6.7 x 10 ⁸ W), and the lattice density was
Using a planar diffraction grating with 1200 lines/mm and a grating height of 100 mm, and a silicon photodiode with a receiving window height of 60 mm, we investigated the change in the 2714.4 Å iron line spectrum intensity due to vertical movement of the sample. , as shown in FIG. 7, and it was confirmed that an almost constant emission spectrum intensity could be obtained even if the focal point of the condenser lens was moved up and down by 2 cm.

[Brief explanation of the drawing]

Figure 1 is a front view showing an example of the arrangement of the optical system used in conventional laser emission spectroscopy;
The figure is also a perspective view showing another example of the arrangement of the optical system used in conventional laser emission spectroscopy;
Figure 3 is a diagram showing the relationship between the laser output and the intensity of the emission spectrum to explain the principle of the present invention, and Figure 4 is a diagram showing the relationship between the laser irradiation area on the sample surface and the spectrum intensity when the spectrum intensity reaches the saturation value. FIG. 5, a diagram showing the relationship between the minimum laser outputs reached, includes a partial block diagram showing the configuration of an embodiment of a laser emission spectrometer in which the laser emission spectrometry method according to the present invention is adopted. The front view and FIG. 6 are perspective views showing changes in the incident position on the plane diffraction grating and the photodetector as the sample position changes in the above embodiment;
Similarly, FIG. 7 is a diagram showing an example of the relationship between the moving distance of the sample from the focus of the condenser lens and the intensity of the emission spectrum. 10... Laser emitting section, 12... Condensing lens,
14...Sample, 22...Laser light source, 24...Laser oscillator power supply, 26...High speed switching element power supply, 30...Spectroscope, 32...Plane diffraction grating, 34...Photodetector.

Claims (1)

[Claims] 1. In a laser emission spectrometry method for spectroscopically analyzing the light emitted when a sample is irradiated with laser light, the energy density at the sample surface is 2.0×10 ⁹ W/mm regardless of changes in the sample position. So that it is ² or more,
While irradiating the sample with infrared pulsed laser light,
By separating the light emitted from the sample using a spectroscopic means arranged such that the direction perpendicular to the spectroscopic direction is parallel to the laser beam, changes in the emission spectrum intensity due to changes in the sample position are suppressed. A laser emission spectroscopic analysis method characterized by: 2. The spectroscopic means and the photodetector for detecting the separated emission spectrum are arranged such that the centers of the spectroscopic means and the light-receiving window of the photodetector in a direction perpendicular to the spectroscopic direction are on the same plane as the focal point of the laser condensing lens. The laser emission spectroscopic analysis method according to claim 1, wherein the laser emission spectroscopic analysis method is arranged so as to be located within the scope of the present invention.