CN112945936B - Liquid sample spectral measurement method and device based on laser plasma self-constraint - Google Patents
Liquid sample spectral measurement method and device based on laser plasma self-constraint Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/71—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light thermally excited
- G01N21/718—Laser microanalysis, i.e. with formation of sample plasma
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/01—Arrangements or apparatus for facilitating the optical investigation
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/01—Arrangements or apparatus for facilitating the optical investigation
- G01N2021/0106—General arrangement of respective parts
- G01N2021/0112—Apparatus in one mechanical, optical or electronic block
Abstract
The invention provides a liquid sample spectrum measuring method and a device based on laser plasma self-confinement, comprising the steps of forming jet flow by a liquid sample; a plurality of symmetrically distributed laser pulses with equal energy are radially focused on the liquid sample jet along the jet flow column to perform ablation, and laser self-confinement plasma which is spatially and symmetrically distributed is formed; and collecting and measuring the spectrum of the laser self-confinement plasma. The invention utilizes a plurality of laser pulses to simultaneously act on the symmetrically distributed plasmas formed by the liquid jet flow, can also inhibit the sputtering of the liquid, reduce the sample loss in the measuring process, avoid the pollution of an optical device and keep the consistency of the measuring conditions. The method can obviously improve the laser-induced breakdown spectroscopy signal intensity of elements in the liquid and the stability of multiple measurements, thereby achieving the purpose of improving the measurement precision and sensitivity.
Description
Technical Field
The invention relates to the technical field of laser spectroscopy, in particular to a liquid sample laser-induced breakdown spectroscopy measurement method and device based on laser plasma self-confinement.
Background
Heavy metal pollution in water is one of the important problems facing the current environmental management, and the ecological environment and the human life health are seriously threatened as the heavy metal pollution of the water is more and more serious. Common methods for detecting heavy metal elements in water bodies include inductively coupled plasma spectrometry (ICP), inductively coupled plasma mass spectrometry (ICP-MS), atomic Fluorescence Spectrometry (AFS), atomic Absorption Spectrometry (AAS), X-ray fluorescence spectrometry (XRF) and the like. When the methods are used for analyzing the content of heavy metal elements in a water body, a chemical reagent is needed to pretreat a sample, the operation process is complex, on one hand, great potential safety hazards exist for environment and instrument operation and maintenance personnel, on the other hand, the detection timeliness is not strong, and in-situ detection cannot be carried out, so that the development of an analysis technology for rapid, real-time and multi-element detection is urgently needed.
The Laser Induced Breakdown Spectroscopy (LIBS) technique is a technique in which high-energy laser pulses are focused on the surface of a sample to generate laser-induced plasma, and the sample is qualitatively and quantitatively analyzed by measuring a line spectrum emitted from the plasma. The technology has the advantages of rapidness, real-time performance, no need of sample preparation and the like, and is widely applied to detection of samples with different forms. However, when LIBS is directly used for liquid detection, severe sputtering may occur on the surface of the liquid surface due to the high-energy laser pulse acting on the liquid surface, contaminating the optical element, and thus causing the laser pulse energy acting on the liquid to decrease; meanwhile, shock waves generated by laser action can cause severe fluctuation of the liquid level, so that the power density of laser coupled on liquid is greatly changed, and therefore, the generated laser plasma is very unstable, the factors can cause low intensity and poor stability of a spectral signal when a liquid sample is measured by using a laser-induced breakdown spectroscopy technology, a quantitative measurement result with high precision and high sensitivity cannot be obtained, even long-time continuous measurement cannot be realized, and the problems of low detection signal, poor detection sensitivity and the like can be caused by short cooling time of the liquid plasma, so that the application of the LIBS technology in the field of liquid sample detection and analysis is greatly limited.
Therefore, it is an urgent need to solve the problems of the art to provide a method and an apparatus for measuring a liquid sample laser induced breakdown spectroscopy based on laser plasma self-confinement, which can prevent the laser power density change and the poor stability of the spectral signal caused by liquid sputtering and liquid surface fluctuation when a pulsed laser is directly applied to the liquid sample.
Disclosure of Invention
In view of this, the invention provides a liquid sample spectrum measurement method and device based on laser plasma self-confinement, which can avoid technical difficulties such as liquid sputtering, laser power density change caused by fluctuation of a liquid surface, poor stability of a spectrum signal, nonuniform spatial distribution of laser plasma, and rapid cooling of plasma, which are caused when pulse laser directly acts on a liquid sample for measurement.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a liquid sample laser-induced breakdown spectroscopy measurement method based on laser plasma self-confinement, which comprises the following steps: the liquid sample forms a jet; a plurality of symmetrically distributed laser pulses with equal energy are radially focused on the liquid sample jet along the jet flow column to perform ablation, and laser self-confinement plasma which is spatially and symmetrically distributed is formed; and collecting and measuring the spectrum of the laser self-confinement plasma.
Preferably, the schlieren imaging is carried out on the laser self-restraint plasma expansion process formed by a plurality of equal-energy laser pulses.
Preferably, the liquid sample is withdrawn from the sample cell and a jet is generated that falls back into the sample cell, forming a circulating liquid stream.
The invention provides a liquid sample laser-induced breakdown spectroscopy measuring device based on laser plasma self-confinement, which comprises a laser pulse emitting device, a laser transmission and modulation light path, a liquid jet device and a spectrum analysis device, wherein the laser pulse emitting device is used for emitting laser pulses; wherein, the first and the second end of the pipe are connected with each other,
the liquid jet device is used for enabling the liquid sample to form a jet;
the laser pulse emitting device comprises a nanosecond pulse laser serving as a plasma excitation light source and generates a pulse laser beam;
the laser transmission and modulation light path is used for splitting the pulse laser beam into a plurality of equal-energy laser pulses which are symmetrically distributed relative to the jet flow, and the laser pulses are focused on the jet flow of the liquid sample along the radial direction of the jet flow column for ablation to form laser self-confinement plasma which is symmetrically distributed in space;
the spectrum analysis device is used for collecting and measuring the spectrum of the laser self-confinement plasma.
Preferably, the device further comprises a plasma expansion transient shadow imaging device for performing schlieren imaging on a laser self-confinement plasma expansion process formed by a plurality of beams of isoenergetic laser pulses, and the device comprises: a visible light pulse laser, a light filter and a CCD camera;
the light emitted by the visible light pulse laser passes through the laser self-confinement plasma region of the liquid jet and is collected by a CCD camera through an optical filter for schlieren imaging, and the CCD camera is connected to a computer.
Preferably, the liquid jet device comprises a peristaltic pump, a damper and a metal capillary tube; the peristaltic pump pumps a liquid sample out of the sample cell, the liquid sample enters the metal capillary through the silicone tube and the damper, and liquid jet flow with constant flow rate and hundred-micron-order diameter is formed at the spout of the metal capillary.
Preferably, the laser transmission and modulation optical path comprises a plurality of laser beam splitters, a plurality of reflectors and a plurality of focusing lenses which are arranged along the propagation direction of the pulse laser beam generated by the nanosecond pulse laser; wherein, the first and the second end of the pipe are connected with each other,
the laser beam splitters are used for splitting the pulse laser beam into a plurality of equal-energy laser pulses;
the reflector is used for changing the propagation direction of the multiple laser pulses with equal energy, so that the multiple laser pulses with equal energy are symmetrically distributed along the radial direction of the jet flow column;
the focusing lenses are respectively positioned on a plurality of equal-energy laser pulse light paths and focus the equal-energy laser pulses on the liquid sample jet flow for ablation.
Preferably, the laser beam splitter adopts a polarization beam splitter; the nanosecond pulse laser comprises a nanosecond pulse laser, a half-wave plate and a first polarization beam splitter are sequentially arranged in the propagation direction of a pulse laser beam generated by the nanosecond pulse laser, the first polarization beam splitter divides the pulse laser beam into a first light path and a second light path, and the first light path and the second light path are vertically propagated;
the light path I is provided with a half-wave plate and a polarization beam splitter II along the transmission direction, and the polarization beam splitter II divides the light path I into a light path III and a light path IV; the light path IV is focused on the liquid sample jet flow through the focusing lens, the light path III is focused on the liquid sample jet flow through the two reflectors and the focusing lens in sequence, and the focused light path III and the focused light path IV are perpendicular to each other in the cross section direction of the liquid sample jet flow;
the second light path is provided with a half-wave plate and a third polarization beam splitter along the transmission direction, and the third polarization beam splitter divides the light path into a fifth light path and a sixth light path; the light path six is focused on the liquid sample jet flow through the focusing lens, the light path five is focused on the liquid sample jet flow through the two reflectors and the focusing lens in sequence, and the focused light path five and the focused light path six are perpendicular to each other in the cross section direction of the liquid sample jet flow.
Preferably, the spectrum analysis device comprises a spectrum collection lens group, an optical fiber and a spectrometer; the spectrometer spectrum collection lens group collects the spectrum of the laser self-confinement plasma and transmits the spectrum to the spectrometer through the optical fiber; the spectrometer is connected to a computer.
Preferably, the device further comprises a digital delay signal generator, wherein the digital delay signal generator is connected with the pulse laser, the visible light pulse laser and the CCD camera and controls the triggering of the pulse laser, the visible light pulse laser and the CCD camera.
Through the technical scheme, compared with the prior art, the invention has the beneficial effects that:
the invention utilizes four laser pulses to excite liquid jet flow to form symmetrically distributed plasmas, and forms a plasma self-restraint method through the spatial interaction of four plasma shock waves, so that stable laser plasmas with more uniform central areas and longer duration are generated. The method can achieve the purpose of improving the signal intensity of the laser-induced breakdown spectroscopy measurement of the elements in the liquid and the stability of the multiple measurements, and further improve the measurement precision and sensitivity, which is very important for the application of the laser-induced breakdown spectroscopy technology in the fields of sewage field detection, industrial production process monitoring, salt lake resource investigation and the like, such as real-time analysis of the elements in the liquid, and the like.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts;
fig. 1 is a schematic diagram of a liquid sample spectrum measurement optical path based on laser plasma self-confinement provided in an embodiment of the present invention;
fig. 2 is a schematic diagram of a laser-induced breakdown spectroscopy measurement apparatus for a liquid sample based on laser plasma self-confinement, according to an embodiment of the present invention;
FIG. 3 is a diagram illustrating transient shadow imaging of plasma expansion under the action of a single-sided laser pulse according to an embodiment of the present invention;
FIG. 4 is a diagram illustrating transient shadow imaging of plasma shock expansion under the simultaneous action of two pulses according to an embodiment of the present invention;
FIG. 5 is a calibration curve diagram of Cr content measured by a single-sided laser pulse according to an embodiment of the present invention;
fig. 6 is a calibration curve diagram of the Cr content measured by the double-sided laser pulse according to the embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
In one aspect, the present embodiment discloses a liquid sample spectrum measurement method based on laser plasma 20 self-confinement, which includes the following steps: the liquid sample forms a jet; a plurality of symmetrically distributed laser pulses with equal energy are focused on the liquid sample jet along the radial direction of the jet flow column for ablation to form laser self-confinement plasma 20 which is spatially and symmetrically distributed; the spectrum of the laser self-confined plasma 20 is collected and measured. The method effectively improves the stability of experimental measurements due to the spatial confinement of the plasma 20 by the plurality of laser pulses.
In a specific embodiment, the laser self-confinement plasma 20 formed by a plurality of equal-energy laser pulses is subjected to schlieren imaging during the expansion process, so that the liquid jet and the plasma 20 form are observed to judge the space confinement effect of the four laser pulses on the liquid jet.
In a specific embodiment, the liquid sample is withdrawn from the sample cell 21 and a jet is generated that falls back into the sample cell 21, forming a circulating liquid stream. The method changes the liquid from static state to dynamic state, the dynamic liquid jet flow is refreshed continuously, so that the laser can be focused on the refreshed liquid jet flow every time, and meanwhile, the fluctuation and sputtering of the liquid can be reduced, thereby improving the repeatability and stability of experimental measurement.
The invention provides a liquid sample laser-induced breakdown spectroscopy measuring device based on laser plasma 20 self-restraint, which comprises a laser pulse emitting device, a laser transmission and modulation light path, a liquid jet device and a spectral analysis device; wherein the content of the first and second substances,
the liquid jet device is used for enabling the liquid sample to form a jet;
the laser pulse emitting device includes a nanosecond pulse laser 1 as an excitation light source of the plasma 20, and generates a pulse laser beam 2;
the laser transmission and modulation light path is used for splitting the pulse laser beam 2 into a plurality of equal-energy laser pulses which are symmetrically distributed relative to the jet flow, and the laser pulses are focused on the liquid sample jet flow along the radial direction of the jet flow column for ablation to form laser self-confinement plasma 20 which is symmetrically distributed in space;
the spectral analysis device is used for collecting and measuring the spectrum of the laser self-confinement plasma 20.
In this embodiment, the nanosecond pulse laser 1 may be a Q-switched nanosecond pulse laser 1.
In a specific embodiment, the plasma 20 expansion transient shadow imaging device is further included, and is used for performing schlieren imaging on a laser self-confinement plasma 20 expansion process formed by a plurality of equal-energy laser pulses, and the device comprises: a visible light pulse laser 8, a filter 15, and a CCD camera 14;
In this embodiment, the visible light pulse laser 8 is connected to the digital delay signal generator 11, and light emitted from the visible light pulse laser 8 is collected by the CCD camera 14 through the plasma 20 region of the liquid jet and the optical filter 15, so as to perform schlieren imaging on the plasma expansion process formed by a plurality of laser beams.
In a particular embodiment, the liquid jet device comprises a peristaltic pump 16, a damper 19 and a metal capillary tube 18; the peristaltic pump 16 pumps the liquid sample out of the sample cell 21, the liquid sample enters the metal capillary 18 through the silicone tube 17 and the damper 19, and liquid jet flow with constant flow rate and hundred-micron-order diameter is formed at the spout of the metal capillary 18. The peristaltic pump 16 pumps the liquid sample out of the sample cell 21, the liquid sample enters the metal capillary 18 through the silicone tube 17 and the damper 19, and a liquid jet flow with constant flow rate and hundreds of microns in diameter is formed at a spout of the metal capillary 18.
In a specific embodiment, the laser transmission and modulation optical path includes a plurality of laser beam splitters, a plurality of reflectors 5 and a plurality of focusing lenses 6 arranged along the propagation direction of the pulse laser beam 2 generated by the nanosecond pulse laser 1; wherein, the first and the second end of the pipe are connected with each other,
the laser beam splitters are used for splitting the pulse laser beam 2 into a plurality of equal-energy laser pulses;
the reflector 5 is used for changing the propagation direction of the multiple equal-energy laser pulses so that the multiple equal-energy laser pulses are symmetrically distributed along the radial direction of the jet flow column;
the focusing lenses 6 are respectively positioned on a plurality of equal-energy laser pulse light paths and focus the equal-energy laser pulses on the liquid sample jet flow for ablation.
In a specific embodiment, the laser beam splitter adopts a polarization beam splitter; the pulse laser beam 2 generated by the nanosecond pulse laser 1 is sequentially provided with a half-wave plate 3 and a first polarization beam splitter 41 in the transmission direction, the first polarization beam splitter 41 divides the pulse laser beam 2 into a first light path and a second light path, and the first light path and the second light path are mutually vertically transmitted;
the half-wave plate 3 and the polarization beam splitter plate II 42 are arranged on the light path I along the transmission direction, and the polarization beam splitter plate II 42 divides the light path I into a light path III and a light path IV; the light path IV is focused on the liquid sample jet flow through the focusing lens 6, the light path III is focused on the liquid sample jet flow through the two reflectors 5 and the focusing lens 6 in sequence, and the focused light path III and the focused light path IV are perpendicular to each other in the cross section direction of the liquid sample jet flow;
the half-wave plate 3 and the polarization beam splitter plate III 43 are arranged on the light path II along the transmission direction, and the polarization beam splitter plate III 43 divides the light path into a light path five and a light path six; the light path six is focused on the liquid sample jet flow through the focusing lens 6, the light path five is focused on the liquid sample jet flow through the two reflectors 5 and the focusing lens 6 in sequence, and the focused light path five and the focused light path six are perpendicular to each other in the cross section direction of the liquid sample jet flow.
In this embodiment, the nanosecond pulse laser 1 is connected to the digital delay signal generator 11, and the digital delay signal generator 11 provides an external trigger signal to the nanosecond pulse laser 1 to control the operation of the pulse laser. The pulse laser beam 2 emitted by the nanosecond pulse laser 1 is divided into four laser beams with equal energy through a light splitting path consisting of a half-wave plate 3 and a polarization light splitting plate, and then laser pulses are focused on liquid jet flow from four directions through a reflector 5 and a focusing lens 6 respectively to form self-constrained plasma 20 which is spatially symmetrically distributed.
In a specific embodiment, the spectrum analysis device comprises a spectrum collection lens group 7, an optical fiber 9 and a spectrometer 10; the spectrometer 10 spectrum collection lens group 7 collects the spectrum of the laser self-confined plasma 20 and transmits the spectrum to the spectrometer 10 through the optical fiber 9; the spectrometer 10 is connected to a computer 12.
In this embodiment, the spectrum of the laser plasma 20 enters the spectrometer 10 through the spectrum collecting lens and the optical fiber 9, and the spectrometer 10 is connected to the digital delay signal generator 11 and the computer 12, and is used to control the delay time collected by the spectrometer 10, store and process the spectral data, and analyze the characteristic spectrum through the spectrometer 10 and the computer 12.
In a specific embodiment, the digital delay signal generator 11 is connected to the pulse laser, the visible light pulse laser 8 and the CCD camera 14, and controls the triggering of the pulse laser, the visible light pulse laser 8 and the CCD camera 14.
The specific implementation principle of this embodiment is as follows:
the liquid sample is pumped from a sample cell 21 to a metal capillary tube 18 through a silicone tube 17 in a peristaltic pump 16, and liquid jet flow with constant flow rate is formed at a nozzle of the metal capillary tube 18; laser pulses emitted by the nanosecond pulse laser 1 are divided into four beams of laser with equal energy after passing through a laser beam splitting device, and are symmetrically focused on the liquid jet flow from four directions through a focusing lens 6, so that plasmas are formed on four side surfaces of the liquid column. The four symmetrically distributed plasma shock waves can be mutually balanced, the space self-restraint effect of plasma expansion is realized, and then a plasma which is more stable and longer in duration than the traditional single-side laser beam excitation is formed. The plasma emission spectrum is collected by the spectrum collection lens group 7, enters the optical fiber 9, and is transmitted to the spectrometer 10 for analysis and measurement. In addition, the device is also provided with a plasma plume transient imaging device consisting of a visible light pulse laser 8 and a CCD camera 14, and can perform schlieren imaging on the plasma expansion process formed by four beams of laser.
The first actual measurement example: plasma uniformity and stability enhancement using symmetrically distributed laser beams
Fig. 3 shows a plasma shock wave generated when a single laser pulse acts on a liquid at any time, and fig. 4 shows a plasma shock wave generated when two 1064nm nanosecond laser pulses act on a liquid at any time. It can be seen that when a single nanosecond pulse laser beam acts on liquid, the shock wave at one side of the laser incidence direction is strong, and the plasma shock wave also expands towards one side of the liquid, and the shock wave at the side is obviously reduced compared with the shock wave at the laser incidence side due to the blocking of the liquid. When the liquid sample laser-induced breakdown spectroscopy measurement device and method based on laser plasma self-restraint are used, as the two plasma shock waves are mutually extruded, a larger and more stable plasma region is formed on the liquid surface compared with a single-beam pulse plasma, and the dynamic behavior of the liquid is restrained by the mutual extrusion of the plasmas, so that the sputtering is reduced; two beams of plasmas are extruded, and a local transient high-pressure environment can be formed near a target sample, so that the temperature and the density of the plasmas are maintained in a high state, the cooling time of the plasmas is delayed, and the plasmas generated by the method are more stable.
The second actual measurement example: method for improving element detection sensitivity and measurement stability in liquid by using symmetrically distributed laser beams
When the laser-induced breakdown spectroscopy is used for detecting liquid, a pulse laser with the repetition frequency of 10Hz is used in the experiment, when the 10Hz pulse laser acts on the liquid, the problems of low spectral signal intensity, poor stability and the like can be caused due to the fluctuation and sputtering of the liquid, the accuracy and the sensitivity of a measuring result are poor, and the requirement on quantitative detection of metal elements in an aqueous solution can not be met. The method changes liquid from static state to dynamic state by a peristaltic pump, the method continuously refreshes the dynamic liquid jet, so that laser can focus on the refreshed liquid jet at each time, and fluctuation and sputtering of the liquid can be reduced, thereby improving repeatability and stability of experimental measurement. In the experiment, the self-prepared sodium chromate solution is quantitatively detected by a method of combining liquid jet flow and four laser pulses, and meanwhile, shadow imaging is carried out on liquid plasma to observe the expansion process of plasma shock waves.
In the experiment, 532nm pulse laser is used as an imaging shadow light source, and a DG-645 digital delay signal generator is used for simultaneously controlling the triggering of a 1064nm Nd. FIG. 5 is a calibration curve of Cr element content measurement in liquid by using single-sided laser pulse, and FIG. 6 is a calibration curve of Cr element content measurement in liquid by using the laser plasma self-constrained liquid sample laser-induced breakdown spectroscopy measurement apparatus and method. It can be seen from fig. 5 and 6 that the correlation coefficient of the calibration curve measured by the laser beam with symmetrical distribution proposed by the method reaches 0.993, which is significantly improved compared with the correlation coefficient of 0.985 obtained by single-side laser pulse excitation, so that the accuracy of quantitative measurement results can be improved, the Relative Standard Deviation (RSD) of spectral line signals is also significantly reduced, and the signal intensity of the double-side laser pulse action is 40% higher compared with the single-side laser pulse action under the condition of equal total laser energy, and by combining the improvement of the two aspects, the detection limit of elements in the liquid obtained by using the method is lower than the direct action of the conventional single-side laser beam and the liquid nozzle, which shows that the intensity and stability of the spectral signal can be effectively improved by using the proposed method, and higher detection sensitivity can be obtained.
The method and the device for measuring the liquid sample spectrum based on laser plasma self-confinement provided by the invention are described in detail, the principle and the implementation mode of the invention are explained by applying specific examples, and the description of the examples is only used for helping to understand the method and the core idea of the invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed, and in summary, the content of the present specification should not be construed as a limitation to the present invention.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (10)
1. A liquid sample laser-induced breakdown spectroscopy measurement method based on laser plasma self-confinement is characterized by comprising the following steps: the liquid sample forms a jet; a plurality of symmetrically distributed laser pulses with equal energy are focused on the liquid sample jet along the radial direction of the jet flow column for ablation to form laser self-confinement plasma which is spatially and symmetrically distributed; and collecting and measuring the spectrum of the laser self-confinement plasma.
2. The laser-induced breakdown spectroscopy measurement method for the liquid sample based on the laser plasma self-confinement according to claim 1, wherein the schlieren imaging is performed on the laser self-confinement plasma expansion process formed by a plurality of equal-energy laser pulses.
3. The laser-induced breakdown spectroscopy measurement method and apparatus for liquid samples based on laser plasma self-confinement according to claim 1, wherein the liquid sample is drawn from the sample cell and the jet stream is generated and falls back to the sample cell to form a circulating liquid stream.
4. A liquid sample laser-induced breakdown spectroscopy measuring device based on laser plasma self-confinement is characterized by comprising a laser pulse emitting device, a laser transmission and modulation light path, a liquid jet device and a spectral analysis device; wherein the content of the first and second substances,
the liquid jet device is used for enabling the liquid sample to form a jet;
the laser pulse emitting device comprises a nanosecond pulse laser serving as a plasma excitation light source and generates a pulse laser beam;
the laser transmission and modulation light path is used for splitting the pulse laser beam into a plurality of equal-energy laser pulses which are symmetrically distributed relative to the jet flow, and the laser pulses are radially focused on the liquid sample jet flow along the jet flow column to be ablated so as to form laser self-confinement plasma which is symmetrically distributed in space;
the spectrum analysis device is used for collecting and measuring the spectrum of the laser self-confinement plasma.
5. The laser-induced breakdown spectroscopy measurement device for the liquid sample based on laser plasma self-confinement according to claim 4, further comprising a plasma expansion transient shadow imaging device for performing schlieren imaging on the laser self-confinement plasma expansion process formed by a plurality of laser pulses with equal energy, comprising: a visible light pulse laser, a light filter and a CCD camera;
the light emitted by the visible light pulse laser passes through the laser self-confinement plasma area of the liquid jet and is collected by a CCD camera through an optical filter for schlieren imaging, and the CCD camera is connected to a computer.
6. The laser-plasma-self-confinement-based liquid sample laser-induced breakdown spectroscopy measurement device according to claim 4, wherein the liquid jet device comprises a peristaltic pump, a damper and a metal capillary; the peristaltic pump pumps a liquid sample out of the sample cell, the liquid sample enters the metal capillary through the silicone tube and the damper, and liquid jet flow with constant flow rate and hundred-micron-order diameter is formed at a spout of the metal capillary.
7. The laser plasma self-confinement based liquid sample laser-induced breakdown spectroscopy measurement device according to claim 4, wherein the laser transmission and modulation optical path comprises a plurality of laser beam splitters, a plurality of reflectors and a plurality of focusing lenses arranged along the propagation direction of the pulse laser beam generated by the nanosecond pulse laser; wherein the content of the first and second substances,
the laser beam splitters are used for splitting the pulse laser beam into a plurality of equal-energy laser pulses;
the reflector is used for changing the propagation direction of the multiple equal-energy laser pulses to ensure that the multiple equal-energy laser pulses are symmetrically distributed along the radial direction of the jet flow column;
the focusing lenses are respectively positioned on a plurality of equal-energy laser pulse light paths and focus the equal-energy laser pulses on the liquid sample jet flow for ablation.
8. The laser-plasma-self-confinement-based liquid sample laser-induced breakdown spectroscopy measurement device according to claim 7, wherein the laser beam splitter adopts a polarization beam splitter; the nanosecond pulse laser comprises a nanosecond pulse laser, a half-wave plate and a first polarization beam splitter are sequentially arranged in the propagation direction of a pulse laser beam generated by the nanosecond pulse laser, the first polarization beam splitter divides the pulse laser beam into a first light path and a second light path, and the first light path and the second light path are vertically propagated;
the light path I is provided with a half-wave plate and a polarization beam splitter II along the transmission direction, and the polarization beam splitter II divides the light path I into a light path III and a light path IV; the light path four is focused on the liquid sample jet flow through the focusing lens, the light path three is focused on the liquid sample jet flow through the two reflectors and the focusing lens in sequence, and the focused light path three and the focused light path four are perpendicular to each other in the cross section direction of the liquid sample jet flow;
the second light path is provided with a half-wave plate and a third polarization beam splitter along the transmission direction, and the third polarization beam splitter divides the light path into a fifth light path and a sixth light path; the light path six is focused on the liquid sample jet flow through the focusing lens, the light path five is focused on the liquid sample jet flow through the two reflectors and the focusing lens in sequence, and the focused light path five and the focused light path six are perpendicular to each other in the cross section direction of the liquid sample jet flow.
9. The laser plasma self-confinement based liquid sample laser-induced breakdown spectroscopy device of claim 1, wherein the spectral analysis device comprises a spectrum collection lens group, an optical fiber and a spectrometer; the spectrometer spectrum collection lens group collects the spectrum of the laser self-confinement plasma and transmits the spectrum to the spectrometer through the optical fiber; the spectrometer is connected to a computer.
10. The laser plasma self-confinement based liquid sample laser-induced breakdown spectroscopy measurement device according to claim 5, further comprising a digital time-delay signal generator, wherein the digital time-delay signal generator is connected with the pulse laser, the visible light pulse laser and the CCD camera, and controls the triggering of the pulse laser, the visible light pulse laser and the CCD camera.
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