JPH01321340A - Laser double stage excitation emission analysis method and apparatus - Google Patents

Abstract

PURPOSE:To enable implementation of a quantitative analysis quickly with a high accuracy by irradiating a vapor cloud formed by a first laser pulse with a second laser pulse at a time interval of 10ns-10mus between the two laser pulses. CONSTITUTION:A trigger for a laser light emission is applied to a switching circuit 3' at a time of 10ns-10mus from an electric delay circuit 2. Laser pulses 5 and 5' emitted from first and second laser devices 4 and 4' by way of switching circuits 3 and 3' are condensed to an analysis sample 8 through reflecting mirrors 6 and 6' and condenser lenses 7 and 7'. Then, a high excitation plasma is formed at a position slightly biased to a plasma receiving side of a vapor cloud formed by a laser right 5. Light released from the plasma forms an image on a photoelectric surface of an image intensifier 16 through a lens 9 and a spectroscope 10 and a light intensity ratio of an atomic spectral line is determine by a photodiode array 17 and a signal processing section 18 and the concentration of an element to be analyzed is determined by a calibration curve and the results are displayed 20.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a laser emission analysis method, and relates to improvements in a laser two-stage excitation emission analysis method and apparatus for qualitative and quantitative analysis of substances with high accuracy and sensitivity. .

Problems to be Solved by Future Technologies and Inventions In recent years, with advances in laser technology, this technology is being incorporated into industry from multiple angles. In laser emission analysis, a device called a laser microprobe was developed in the 1960s, and it became possible to easily perform emission analysis of non-electrically conductive substances. This method vaporizes and excites the substance using a pulsed laser, and performs qualitative and quantitative analysis of the components using spark discharge. Furthermore, for the purpose of analyzing molten steel as it is, a method has been used in the past in which the surface of molten steel is irradiated with a giant pulse laser beam and the generated plasma light is photometered to analyze its components.

In addition to the atomic spectrum light emission, this method also generated strong white light emission, which had a negative impact on analytical accuracy. In order to suppress this influence, a method of delaying the photometry start time was proposed in JP-A-57-100623. Also, in order to increase the atomic spectrum light, Japanese Patent Application Laid-Open No. 58-76744
proposed a method to increase the energy density of laser light. As a matter of fact, it has been proposed in JP-A-56-114746 and JP-A-58-219440 to improve accuracy by controlling the mode of laser output and performing signal processing. However, these methods focus on technology that captures light from plasma;
It was not intended to increase the intensity of light emitted from plasma.

Therefore, we decided to put this laser emission spectrometry into practical use.
The applicant has already filed JP-A-62-85847 and JP-A-62-85847.
No. 188,919 proposed that if an analysis sample is evaporated and excited by multistage excitation of laser pulses, it is possible to emit light particularly strongly in the long wavelength component of 200 nm or more in the emission line spectrum of the target analysis element. However, the problem has been how to perform multistage laser excitation efficiently.

<Object of the Invention> The present invention relates to a laser two-stage excitation emission spectrometry method and apparatus that generates a stable atomic spectrum with strong emission intensity in order to perform highly accurate and accurate analysis in laser emission spectrometry. .

Means for Solving Problems> The present invention generates a vapor cloud on a substance with a first laser pulse, excites the vapor cloud with a second laser pulse, generates an atomic spectrum with high efficiency, and generates a high The object of the present invention is to provide an accurate two-stage laser excitation emission analysis method. The pulse width of the laser pulse is in the range of 2 to 50 ns, and the optical energy per laser pulse is 10 mJ to 1 J.
is used, and the time interval between firing of the first and second laser pulses is in the range of 10 ns to 10 μs. Sincerely,
Keep the analytical sample in an inert gas atmosphere. Furthermore, according to the present invention, the emission timing of the first laser pulse and the second laser pulse is controlled by an electronic circuit, and the first laser fist pulse is emitted by the lens through the laser light reflector or prism. A lens so that the light is focused on the material surface and the second laser pulse is irradiated to the plasma light receiving side of the vapor cloud formed by the first laser pulse through a laser light reflecting mirror or prism. The light is focused by As a result, a part of the substance is evaporated and excited, and the generated plasma light is guided to a spectrometer using a plasma light reflector, a lens, and/or an optical fiber, and is detected by a photodetector.
An object of the present invention is to provide a two-stage laser excitation emission spectrometer that measures components and amounts of components by measuring atomic spectrum intensity.

The two-stage excitation emission spectrometer of the present invention is characterized in that it uses a combination of a photomultiplier tube, an image pickup tube, or an image intensifier and a 7-otodiode array as a photodetector.

Effect〉 When the giant pulse laser beam is focused on a substance,
A part of the substance is evaporated and excited and becomes a plasma state. This plasma emits white light that is continuous in wavelengths due to the atomic spectrum of the elements constituting the substance, black body radiation, bremsstrahlung radiation, etc. Laser emission analysis is a method of analyzing these emitted lights by measuring the atomic spectra specific to the elements.

Atomic spectra are emitted when electrons are excited and transition from a higher energy level to a lower energy level. The wave number at that time is expressed by the following equation.

Here, smn: wave number of atomic spectrum, Tm: high energy level, Tn: low energy level, h blank constant, C: speed-of-light dust.

The radiation intensity Ir of this atomic spectrum is expressed by the following equation using the number Nm of atoms in a high level and the transition probability Amn for radiation.

Ir = NmnAmn hCνm n (21
Therefore, the atomic spectral intensity is proportional to the product of the number of atoms in the excited state and the transition probability. Therefore, to strengthen the atomic spectrum intensity, either increase the number of atoms in high energy levels, or
All you have to do is increase the transition probability. One way to increase the number of atoms in high energy levels is to evaporate and excite a large amount of material, but this does not change the amount of light emitted per unit volume of the plasma, and the spot diameter of the objective lens on the light receiving side increases. Considering that it is constant, it cannot be said that it is a very effective method.

Therefore, in the present invention, in order to increase the amount of light emitted per unit volume of plasma, the first laser pulse evaporates the substance and forms a vapor cloud. Furthermore, the plasma light receiving side of this vapor cloud is irradiated with a second laser pulse. By doing this, the second laser pulse uses energy only for excitation of the vapor cloud on the plasma light receiving side, thereby increasing the number of atoms in high energy levels and changing the atomic spectrum from the vapor cloud. This makes it possible to increase the atomic spectrum intensity by minimizing the amount of energy that is reabsorbed.

In this method, the first and second laser pulse widths are between 2 and 50
ns, and the light energy of one laser working pulse is 1.
Use one that is between 0 mJ and 1 J. This is because the peak output of the laser pulse needs to be 5x10W or more in order to increase the number of atoms in the high energy level.

Further, the time interval between the first laser pulse and the second laser pulse is set to 10 ns to 10 μs. This is because the transition probability differs depending on the atomic spectrum, and it is necessary to change the time interval between the first and second laser pulses depending on the type of element to be analyzed.

Further, by forming plasma on the sample surface by holding the analysis sample in an inert gas atmosphere, reactions caused by gases such as oxygen can be suppressed, and atoms can be excited efficiently. In particular, when plasma is formed in argon gas, the intensity of the emitted atomic spectrum increases due to effects such as the Penning ion effect.

The two-stage laser excitation emission spectrometer according to the present invention transmits a firing signal to each laser device by an electronic circuit in order to control the time interval between the first laser pulse and the second laser pulse.・Pulses pass through a laser beam reflection mirror made of a dielectric multilayer film or a prism made of quartz, etc., the first laser pulse is focused onto the material surface by a lens made of quartz, etc., and the second laser pulse is focused on a material surface using a lens made of quartz or the like. The light is focused by a mirror made of quartz or the like so that the plasma light receiving side of the vapor cloud formed by the first laser pulse is irradiated through a laser beam reflecting mirror made of a multilayer film or a prism made of quartz or the like. □The formed plasma light is efficiently excited and reflected by a plasma light reflecting mirror such as M,
Components and their amounts are measured by guiding them to a spectrometer through a lens made of quartz or an optical fiber made of quartz, etc., and measuring the light intensity of the atomic spectrum using a highly sensitive photodetector in the wavelength range where the atomic spectrum occurs. It is characterized by As a photodetector, use a photomultiplier tube or image pickup tube with a photocathode that is sensitive in the wavelength range of the generated atomic spectrum, or an image intensifier. If an image intensifier is used, a photodiode array is used. receives the light generated from the image intensifier. When using a photomultiplier tube as a spectrometer, a concave diffraction grating is used to analyze multiple elements simultaneously by placing the photomultiplier tube at each wavelength position of the target atomic spectral line on the Rowland circle. By using this method, analysis time can be shortened.

Embodiments Hereinafter, embodiments of the two-stage laser excitation emission spectrometry method of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the laser two-stage excitation emission analysis method and apparatus. First, the control unit 1 triggers the switching circuit 6 and the electrical delay circuit 2 to emit a laser beam. The switching circuit 3 sends a firing signal to the first laser device 4 and the first laser pulse 5 is fired. After receiving the trigger from the control section 1, the electrical delay circuit 2 waits 10 ns to 10 μs using an internal LC circuit, etc., and then triggers the switching circuit 6' to emit a laser beam, and the second laser device 4' A second laser pulse 5' is emitted from. Therefore, the time interval between the first and second laser pulses is between 10 ns and 10 μs.

The first laser pulse 5 is reflected by a laser light reflecting mirror 6 and focused onto an analysis sample 8 by a condensing lens 7 to form a vapor cloud. The second laser pulse 5' is reflected by a laser beam reflector 6' so as to irradiate the plasma light spectrometer from the vapor cloud at an angle of about 10 in the direction of the optical axis, and the second laser pulse 5' is reflected by a condensing lens 7'. The vapor cloud formed by the laser pulse No. 1 was focused at a position slightly biased toward the plasma light receiving side to form highly excited plasma.

The light emitted from this plasma is imaged by a lens 9 onto a slit 11 of a spectroscope 10.

The light imaged on the slit 11 is reflected by the cotmeter mirror 12 to the diffraction grating 16, and the diffraction grating 13 selects the wavelength of the atomic spectrum by diffraction of the light.
4, and a plane mirror 15 forms a wavelength-resolved image of the plasma on the photocathode of an image intensifier 16.

The image intensifier 16 converts light into electrons with a photocathode, multiplies the electrons with a microchannel plate, converts them into light again with a fluorescent surface, and measures an atomic spectrum with a photodiode array 17. Further, the image intensifier 16 can electrically control the photometry time by a gate circuit 19 to remove noise components, and the gate circuit 19 operates in synchronization with the emission timing of the second laser e-pulse. Because I set it like this,
The trigger from the switching circuit 6' was divided to cause the gate circuit 19 to receive the signal. Note that the gate circuit 19 can arbitrarily change the delay of the photometry start time and the photometry time width.

The signal output from the photodiode array 17 enters the signal processing section 18, which calculates the light intensity ratio of the atomic spectral lines, and displays the concentration of the analyte element on the display section 20 using a calibration curve prepared in advance using a standard sample. Output to .

During analysis, an inert gas such as argon is constantly injected into the case 21 from the inert gas inlet 22 at a flow rate of 301/min to maintain the optical path of the plasma light in an inert gas atmosphere. This prevents the plasma light intensity from attenuating due to the influence of oxygen and other factors. Also, during laser irradiation, an inert gas such as sialbone is blown into the plasma generation area at a flow rate of 101/min through the inert gas blowing pipe 26 to locally reduce the concentration of impurity gases such as oxygen, thereby suppressing the plasma light. Prevented strength from decreasing.

The data obtained by the apparatus shown in FIG. 1 is shown in FIG.

YAG laser devices with Q switches are used as the first and second laser devices, and YAG laser devices with Q switches are used as the first and second laser devices.
The firing times of the first and second laser pulses were controlled by triggering the Bockel cell of the G laser device. Therefore, the jitter was within Zns.

In FIGS. 2 and 6, the vertical axis represents relative light intensity, and the horizontal axis represents wavelength. The center wavelength was set to 380 nm, and a wavelength region of about 4.5 nm was photometered at once. FIG. 2 is an emission spectrum of a standard sample measured by setting the energy of the first laser pulse to 4.20 mJ/pulse without emitting the second laser pulse.

Recommendation Figure 3 shows the laser two-stage excitation emission spectrometer of the present invention, in which the energy of the first laser pulse is 340 mJ/pulse.
, the energy of the second laser pulse is 80 mJ
/ pulse so that the sum of the output power of the first and second laser pulses is 420 mJ, which is the same as the method shown in FIG. 2. Also, the time interval between the first and second laser pulses is 30
It was set to 0 ns.

In FIGS. 2 and 6, photometry was carried out 100 times each, then integrated and averaged.

As a result, the emission spectrum intensity shown in Figure 3 is higher than the second one.
It can be seen that the emission spectrum intensity is about 5 to 10 times greater than the intensity shown in the figure.

Table 1 below compares this using the S/B value and coefficient of variation.

The peak value of the relative light intensity at the wavelength of the Fe spectrum was designated as S, and the relative light intensity at the wavelength without the atomic spectrum was designated as B, and the S/B value was expressed. In addition, pack ground (
B) was set to 378.3 nm, and the Fe spectrum that appeared within the photometric wavelength was arbitrarily selected. Furthermore, the coefficient of variation of the Fe spectral line intensity when the measurements in FIGS. 2 and 6 were repeated 10 times each was compared.

Results 1: The laser two-stage excitation emission analysis according to the present invention has a higher S/B ratio than the conventional laser-stage excitation method.
It can be seen that the value has been improved by about 6.7 to 7.8 times, and the coefficient of variation has been improved by about 2.4 times.

<Effects of the present invention> According to the present invention, all elements contained in metals in a solid or molten state and having emission spectrum lines in the visible and ultraviolet regions, especially light elements, which have been considered difficult to use with conventional methods, can be used. Quantitative analysis can be performed with high precision and quickly even at low content rates. In addition, analysis was considered difficult due to the low intensity of emission spectral lines in the visible region, but it is now possible to increase the intensity of emission spectral lines in the visible region by performing two-step laser excitation. The generated plasma light is guided to a spectrometer using an optical fiber, which has the excellent effect of allowing highly accurate quantitative analysis even in the visible region.

The embodiments of the present invention are as follows.

■ A first laser pulse from a first laser oscillator is focused on a substance to be analyzed to form a vapor cloud in part of the substance, and before this vapor cloud disappears, a second laser pulse is focused on the substance to be analyzed. In a method for analyzing the components of the substance to be analyzed by concentrating the light on a cloud and analyzing the generated plasma light using a spectroscopic analysis method, a second laser pulse is transmitted from the first laser pulse axis to a plasma receiving spectrometer. The vapor cloud formed by the first laser pulse is irradiated with the first and second laser pulses at a position slightly shifted in that direction along the optical axis with a time interval of 1On3 to 10μs. A two-stage laser excitation emission analysis method.

■ The irradiation axes of the first and second lasers V (Russ) are parallel to each other, or have an angle of 0 to 9 in the direction of the optical axis to the plasma light receiver. The method described in paragraph 1.

■ The pulse width of the first and second laser pulses is 2 to 50
ns, the light energy of one laser pulse is 10m
J to 1J, the method according to claim 1.

■ The plasma light generation part and the optical path are maintained in an inert gas atmosphere, and the timing of emitting the first laser pulse and the second laser pulse to the irradiated object is counted by an electronic circuit, The plasma light generated in the two stages is guided to a spectrometer using a reflecting mirror, lens, and/or optical fiber, and the atomic spectrum intensity is measured using a photodetector to measure p, components, and component amounts. A laser two-stage excitation emission spectrometer according to the first claim.

(2) The device according to item 4 of the patent scope, characterized in that a photomultiplier tube, an image pickup tube, or a combination of an image intensifier and a photodiode array is used as a photodetector.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing an example of the laser two-stage excitation emission spectrometry method and apparatus, Figure 2 is a Fe emission spectrum diagram measured by the laser two-stage excitation emission analysis method, and Figure 6 is the laser two-stage excitation emission analysis method. It is a Fe emission spectrum diagram measured in . Patent applicant: Osaka Sanso Kogyo Co., Ltd. (4 others)

Claims (2)

[Claims] (1) A first laser pulse from a first laser oscillator is focused on a substance to be analyzed, a part of the substance is turned into a vapor cloud in an inert gas atmosphere, and before this vapor cloud disappears, a second laser pulse is In the method, the second laser pulse is focused on the vapor cloud, the generated plasma light is analyzed by spectrometry, and the component of the substance to be analyzed is analyzed. the first and second laser pulses relative to the vapor cloud formed by the first laser pulse at a position slightly offset in that direction along the optical axis from the pulse axis to the plasma receiver spectrometer; A two-stage laser excitation emission analysis method characterized by irradiation at a time interval of 10 ns to 10 μs. (2) A spectroscopic analyzer, a first laser oscillator, and a second laser oscillator connected to an electrical delay device are fixed, and an optical path changer is installed near the emission port of the first laser oscillator as necessary. Fix the prism and/or dielectric multilayer mirror,
A prism and/or dielectric multilayer for changing the optical path as necessary near the exit of the second laser oscillator so that the second laser pulse is irradiated at a position shifted from the first laser pulse. A case that fixes the film mirror and covers the plasma light generation part and the optical path, an inert gas inlet and outlet is provided in the case, and an electronic device that controls the timing of emission of the first laser pulse and the second laser pulse. A two-stage laser excitation emission spectrometer consisting of a circuit, reflected light, a lens, and/or an optical fiber for guiding the plasma light generated in the two stages to a spectroscopic analyzer.