LIBS system based on dual-mode spectrum acquisition

Abstract

A LIBS system based on dual-mode spectrum acquisition, comprising a laser excitation apparatus (1), a first spectroscopic component, a second spectroscopic component, and a data processing device. The laser excitation apparatus (1) emits a laser beam towards a sample (3), so as to excite the sample (3) to generate plasma; the first spectroscopic component is used acquire a full spectrum signal obtained after the sample (3) has been excited and convert the full spectrum signal into a first digital signal; the second spectroscopic component is used to acquire a local spectrum signal of a target frequency band obtained after the sample (3) has been excited and convert the local spectrum signal into a second digital signal, the target frequency band being an acquisition frequency band determined on the basis of material properties of the sample; and the data processing device is used to obtain and fuse the first digital signal and the second digital signal and generate a spectrum acquisition result.

Description

LIBS system based on dual-mode spectral acquisition Technical Field

[0001] The present invention relates to the technical field of spectrum acquisition, and in particular to a LIBS system based on dual-mode spectrum acquisition. Background Art

[0002] Laser-induced breakdown spectroscopy (LIBS) is a plasma emission spectroscopy technique with advantages such as simultaneous multi-element measurement, simple sample pretreatment, fast analysis speed, and minimal sample damage. It is very suitable for full-element detection and is currently widely used in space exploration, environmental protection, industrial process monitoring, agriculture, food safety and other fields.

[0003] In some existing technologies, LIBS systems generally use fiber spectrometers or echelle grating spectrometers as their spectroscopic units. The detectors of this type of spectrometer are mainly CCD / CMOS array detectors. The advantages are high system integration and wide spectral band range. However, they are limited by the inherent characteristics of the detectors, spectroscopic optical paths, etc. For some trace or trace elements, the weak signals at the characteristic spectral lines collected are easily covered by noise, resulting in low spectral line intensity or even no response. The detection sensitivity of this spectroscopic unit is still relatively low and cannot meet the detection limit requirements of trace or trace elements.

[0004] Photomultiplier tubes (PMTs) use the photoelectric effect to convert extremely weak light signals into electrical signals. They offer advantages such as high sensitivity, high gain, and fast response, making them an important tool for weak-light detection. However, they can only collect signals in specific wavelength bands and cannot achieve full-spectrum detection.

[0005] Therefore, for the detection of trace or micro elements, since the content of trace or micro elements themselves is low or difficult to excite, the obtained spectral signal is very weak and easily covered by the noise signal, resulting in the existing LIBS system being unable to meet the detection sensitivity and accuracy requirements of trace or micro elements. Summary of the Invention

[0006] In view of this, the present invention provides a LIBS system based on dual-mode spectral acquisition, which can simultaneously achieve full-band spectral detection and high-sensitivity detection of key local bands.

[0007] In order to achieve the above objectives, the technical solution of the present invention provides a LIBS system based on dual-mode spectral acquisition, comprising:

[0008] a laser excitation device, wherein the laser excitation device emits a laser beam toward the sample to excite the sample to generate plasma;

[0009] a first spectroscopic component, configured to collect a full spectrum signal obtained after the sample is excited, and convert the full spectrum signal into a first digital signal;

[0010] a second spectroscopic component configured to collect a local spectral signal of a target frequency band obtained after the sample is excited, and convert the local spectral signal into a second digital signal, wherein the target frequency band is a collection frequency band determined according to the material properties of the sample;

[0011] A data processing device is used to acquire and fuse the first digital signal and the second digital signal, and generate a spectrum acquisition result.

[0012] In some embodiments, the first light splitting component includes:

[0013] a convex lens, wherein the convex lens is used to converge the plasma on the surface of the sample;

[0014] a spectrometer connected to the optical fiber and converting the plasma signal passing through the convex lens and the optical fiber into a spectral signal;

[0015] An optical fiber, one end of which is placed behind the convex lens, and the other end of which is connected to the spectrometer, and the plasma signal is transmitted to the spectrometer via the optical fiber.

[0016] In some embodiments, the spectrometer is an echelle spectrometer or a fiber spectrometer.

[0017] In some embodiments, the second light splitting component includes:

[0018] An optical filter, wherein the optical filter is used to filter an optical signal of a preset wavelength band;

[0019] a photomultiplier tube, which is disposed downstream of the filter and collects light waves in the target frequency band and converts the collected light waves into electrical signals;

[0020] An acquisition card is provided downstream of the photomultiplier tube and converts the electrical signal into a second digital signal.

[0021] In some embodiments, the filters are connected to the photomultiplier tubes via optical fibers.

[0022] In some embodiments, the LIBS system further comprises:

[0023] A focusing mirror is provided between the laser excitation device and the sample, the focusing mirror and the laser excitation device are arranged radially symmetrically, and is used to focus the laser beam emitted by the laser excitation device.

[0024] In some embodiments, the laser excitation device is a Nd:YAG laser or a semiconductor laser.

[0025] In some embodiments, the data processing device is a computer, and the computer outputs the generated spectrum acquisition result in the form of a spectrum graph.

[0026] In some embodiments, the sample is a solid powder pellet, an alloy, or a liquid slurry.

[0027] The LIBS system based on dual-mode spectral acquisition provided by the present invention includes a laser excitation device, a first spectroscopic component, a second spectroscopic component and a data processing device; wherein, the laser excitation device emits a laser beam to a sample to excite the sample to generate plasma, the first spectroscopic component is used to collect the full spectrum signal obtained after the sample is excited, and convert the full spectrum signal into a first digital signal; the second spectroscopic component is used to collect the local spectrum signal of the target frequency band obtained after the sample is excited, and convert the local spectrum signal into a second digital signal, wherein the target frequency band is an acquisition frequency band determined according to the material properties of the sample; the data processing device is used to acquire and fuse the first digital signal and the second digital signal, and generate a spectral acquisition result.

[0028] This invention combines two acquisition methods to create a dual-mode LIBS system. One acquisition method uses a spectrometer to collect full-band spectral information, providing greater element detection flexibility. The other acquisition method uses a photomultiplier tube with a filter to detect trace elements. This system improves detection sensitivity, lowers detection limits, and expands its application range. Therefore, the invention can simultaneously achieve full-band spectral detection and high-sensitivity detection in key localized bands. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0030] FIG1 is a schematic structural diagram of a LIBS system based on dual-mode spectral acquisition provided by the present invention;

[0031] 2 to 5 are test result diagrams of the LIBS system provided by the present invention in one embodiment.

[0032] The corresponding relationship between the reference numerals and component names in FIG1 is as follows:

[0033] 1-Laser excitation device, 2-Focusing mirror, 3-Sample, 4-Convex lens, 5-Optical fiber, 6-Spectrometer;

[0034] 7-Computer, 8-Filter, 9-Photomultiplier tube, 10-Acquisition card. DETAILED DESCRIPTION

[0035] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0036] It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments may be combined with each other; and, based on the embodiments in this disclosure, all other embodiments obtained by persons of ordinary skill in the art without creative work are within the scope of protection of this disclosure.

[0037] It should be noted that various aspects of the embodiments within the scope of the appended claims are described below. It should be apparent that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is merely illustrative. Based on this disclosure, it should be understood by those skilled in the art that an aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects described herein can be used to implement an apparatus and / or practice a method. In addition, other structures and / or functionalities other than one or more of the aspects described herein can be used to implement this apparatus and / or practice this method.

[0038] In a specific embodiment, the technical solution of the present invention provides a LIBS system based on dual-mode spectral acquisition, including a laser excitation device 1, a first spectroscopic component, a second spectroscopic component and a data processing device; wherein, the laser excitation device 1 emits a laser beam to the sample 3 to excite the sample 3 to generate plasma, the first spectroscopic component is used to collect the full-band spectral signal obtained after the sample 3 is excited, and convert the full-band spectral signal into a first digital signal, the second spectroscopic component is used to collect the local spectral signal of the target frequency band obtained after the sample 3 is excited, and convert the local spectral signal into a second digital signal, the target frequency band is an acquisition frequency band determined according to the material properties of the sample 3, and the data processing device is used to acquire and fuse the first digital signal and the second digital signal, and generate a spectral acquisition result.

[0039] In this system, the first and second spectroscopic components share a laser excitation device 1. The channel containing the spectrometer 6 in the first spectroscopic component collects full-spectral information from the sample 3, while the channel containing the PMT (photomultiplier tube) 9 in the second spectroscopic component collects narrow-band spectral information. The data processing device can be a computer 7, which outputs the generated spectral acquisition results in the form of a spectrogram and is used for data processing and display. The sample 3 can be a solid, liquid, or gas.

[0040] In order to better focus the laser beam, the LIBS system also includes a focusing mirror 2, which is arranged between the laser excitation device 1 and the sample. The focusing mirror 2 is radially symmetrical with the laser excitation device 1 and is used to focus the laser beam emitted by the laser excitation device 1.

[0041] The laser excitation device 1 is a Nd:YAG laser or a semiconductor laser, which is used to emit a laser beam to excite the sample 3 to generate plasma. Two lasers can also be used as needed. By setting the excitation delay time between the two lasers, the plasma signal can be enhanced by several to ten times at the same laser energy.

[0042] In some embodiments, the first spectroscopic component includes a convex lens 4, a spectrometer 6, and an optical fiber 5. The convex lens 4 is used to collect the full spectrum signal from the plasma generated by the sample 3. The convex lens 4 is a quartz lens, which can achieve full spectrum signal collection. The spectrometer 6 is disposed downstream of the convex lens 4 and receives the full spectrum signal collected by the convex lens 4. One end of the optical fiber 5 is connected to the convex lens 4, and the other end is connected to the spectrometer 6. The full spectrum signal is transmitted to the spectrometer 6 via the optical fiber 5, which has high transmittance. The spectrometer 6 is a medium-step grating spectrometer or a fiber spectrometer, which is used to collect the optical signal transmitted by the optical fiber 5.

[0043] In some embodiments, the second spectroscopic assembly includes a filter 8, a photomultiplier tube 9, and an acquisition card 10. The filter 8 is used to filter optical signals within a preset wavelength band. The filter 8 determines the half-bandwidth specification of the central wavelength based on the element to be measured. The photomultiplier tube 9 is disposed downstream of the filter 8 and collects light waves within the target frequency band and converts the collected light waves into electrical signals. The electrical signals collected by the photomultiplier tube 9 can be converted into digital quantities, namely, the intensities of the spectral lines. The acquisition card 10 is disposed downstream of the photomultiplier tube 9 and converts the electrical signals into a second digital signal.

[0044] It should be understood that the downstream mentioned in this article refers to the transmission direction of the signal. For example, if the acquisition card is set downstream of the photomultiplier tube, it means that the signal from the photoelectric signal tube enters the acquisition card.

[0045] The optical filters 8 can be arranged in one or more groups. When there are multiple groups of optical filters, each of the optical filters 8 is connected to the photomultiplier tube 9 via an optical fiber 5. The photomultiplier tube 9 is a photoelectric detection device that can convert extremely weak optical signals into electrical signals and amplify them. It has the characteristics of high spectral detection sensitivity, fast spectral acquisition speed, high gain, and good linearity. It can detect optical signals in the range of approximately 1 μm to 100 nm, but its response range is narrow and can only measure one piece of information at a time, that is, the number of channels is 1. If the detection band is wide, the spectrum needs to be scanned point by point, which greatly reduces the spectrum acquisition speed. Therefore, this characteristic of the photomultiplier tube 9 can be used in combination with a specific bandwidth filter 8 to obtain weak spectral signals within a narrow band, that is, spectral signals around the characteristic spectral lines of trace or trace elements, thereby meeting the detection needs of trace or trace elements.

[0046] In the above-mentioned specific embodiment, the LIBS system based on dual-mode spectral acquisition provided by the present invention includes a laser excitation device 1, a first spectroscopic component, a second spectroscopic component and a data processing device; wherein, the laser excitation device 1 emits a laser beam to the sample 3 to excite the sample 3 to generate plasma, and the first spectroscopic component is used to collect the full spectrum signal obtained after the sample 3 is excited, and convert the full spectrum signal into a first digital signal; the second spectroscopic component is used to collect the local spectrum signal of the target frequency band obtained after the sample 3 is excited, and convert the local spectrum signal into a second digital signal, wherein the target frequency band is an acquisition frequency band determined according to the material properties of the sample 3; the data processing device is used to acquire and fuse the first digital signal and the second digital signal, and generate a spectrum acquisition result.

[0047] In the system, it is necessary to ensure that the laser beam is perpendicular to the sample surface. There are two structural forms according to the spectrum collection optical path. One is that the spectrum collection optical path is coaxial with the laser optical path, so that the focusing mirror 2, convex lens 4, optical fiber 5, filter 8, etc. are all in the direction of the laser beam; the other is that the spectrum collection optical path is perpendicular to the laser optical path, and the plasma spectrum is collected from the side. The distribution of the components is shown in Figure 1.

[0048] Thus, the present invention combines two acquisition methods to propose a dual-mode LIBS system. One acquisition method uses a spectrometer 6 to collect full-band spectral information, providing greater element detection flexibility. The other acquisition method uses a photomultiplier tube 9 with a filter 8 to detect trace or micro-element concentrations. This system can improve detection sensitivity, lower detection limits, and expand its application range. This solves the problem of existing LIBS systems being unable to simultaneously achieve full-band spectral detection and high-sensitivity detection in key localized bands.

[0049] The following takes a specific embodiment as an example to briefly describe the specific implementation process of the LIBS system based on dual-mode spectral acquisition provided by the present invention.

[0050] The LIBS system is used for elemental detection of phosphate rock flotation products. The eight elements routinely detected are P, Mg, Fe, Al, Ca, Si, K, and Na, with concentrations ranging from 0.5% to 50%. The common characteristic lines of these eight elements cover a spectral range of 200 to 800 nm. Regarding the concentration of the trace element Cr, the national standard GB22549-2017 requires that the Cr content in the product be less than or equal to 30 mg / kg. The Cr content in the ore pulp is below 0.1%, an extremely low level. The spectrometer-based acquisition method cannot detect the characteristic peak at 267.7 nm in the Cr characteristic spectrum, as shown in Figure 2 and Table 1:

[0051] Table 1

[0052]

[0053] The intensity values ​​collected by the spectrometer in Table 1 are all background noise, and the element cannot be modeled due to the lack of response at the characteristic spectral line. The linear fit of the Cr intensity obtained by the photomultiplier tube acquisition method is not ideal, as shown in Table 1 and Figure 3. Data obtained using either acquisition method cannot be used to model the Cr element and calculate an accurate concentration value.

[0054] In this embodiment, a LIBS system based on dual-mode spectral acquisition includes a laser, a focusing lens, a convex lens, an optical fiber, a filter, a photomultiplier tube, an acquisition card, a spectrometer, and a computer. The specific implementation scheme is as follows: a focusing lens is provided in front of the 1064nm pump laser, which is radially symmetrical with the laser and is used to focus the laser beam; the experimental sample is provided in front of the lens, where the sample can be an alloy, a powder tablet, or a slurry. In this embodiment, phosphate ore slurry is used. The laser beam hits the surface of the slurry column, and laser ablation generates plasma; two spectral acquisition channels are provided on one side of the sample, one of which is a convex lens, an optical fiber, and a three-channel optical fiber spectrometer. The spectrometers selected are AvaSpec-DUAL (spectral range 207-430nm) and AvaSpec-ULS2048CL-EV0 (spectral range 555-783nm). The optical fiber collects the plasma light passing through the convex lens and transmits it to the connected spectrometer. The spectrometer converts the light signal into visible spectral information, collects spectral data in the 207-783nm band, and collects the spectrum for analysis by computer display. The other path is a convex lens, a filter, an optical fiber, a photomultiplier tube, and an acquisition card. According to the measurement requirements of the trace element Cr in phosphate rock, the filter in this embodiment adopts a filter with a center wavelength of 267.7nm and a half-bandwidth of 0.5nm according to the common characteristic spectrum line of Cr at 267.7nm. The photomultiplier tube selects a Japanese Hamamatsu R928 28mm diameter side-type photomultiplier tube. The optical fiber collects the narrow band light passing through the convex lens and the filter and transmits it to the photomultiplier tube. The photomultiplier tube converts the light signal into an electrical signal, which is then converted into a digital signal by the acquisition card and analyzed by computer display. The numerical value collected by the photomultiplier tube is fitted to the full spectrum data wavelength 267.7nm and the Gaussian peak at the half-bandwidth 0.5nm collected by the spectrometer, thereby obtaining a complete full spectrum spectrum data including the response of the trace element Cr, as shown in Figure 4. The concentrations of the desired elements were calculated using full spectrum spectral data modeling, as shown in Figure 5.

[0055] From the above embodiments, it can be seen that the LIBS system based on dual-mode spectral acquisition provided by the present invention has the following technical effects:

[0056] 1. The LIBS system of the present invention has a simple structure, including a laser excitation module, a two-channel spectrum acquisition module, and a computer. Fewer modules are required, making system construction and debugging easier.

[0057] 2. The present invention uses a photomultiplier tube in combination with a filter to collect plasma information, which can realize the collection of weak spectral signals in a narrow band.

[0058] 3. The present invention can be configured with multiple sets of photomultiplier tubes and filters to obtain weak spectral signals in multiple narrow bands.

[0059] 4. The present invention adopts two spectral acquisition methods and fuses two sets of spectral data to meet the detection needs of all elements, especially the detection needs of trace or trace elements, improve the detection sensitivity of the entire system, and reduce the detection limit.

[0060] 5. The LIBS system described in the present invention can detect both high- and low-content elements and has a wider range of applications.

[0061] In the present invention, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The term "plurality" refers to two or more, unless expressly limited otherwise. Terms such as "installed," "connected," "connected," and "fixed" should be interpreted broadly. For example, "connected" can mean a fixed connection, a detachable connection, or an integral connection; "connected" can mean a direct connection or an indirect connection through an intermediary. Those skilled in the art will understand the specific meanings of these terms in the present invention based on specific circumstances.

[0062] In the description of the present invention, it should be understood that the directions or positional relationships indicated by terms such as "up", "down", "left", "right", "front" and "back" are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or unit referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limiting the present invention.

[0063] Throughout this specification, terms such as "one embodiment," "some embodiments," and "specific embodiments" mean that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0064] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A LIBS system based on dual-mode spectral acquisition, characterized in that: include: A laser excitation device (1), wherein the laser excitation device (1) emits a laser beam toward a sample (3) to excite the sample (3) to generate plasma; a first spectroscopic component, the first spectroscopic component being used to collect a full spectrum signal obtained after the sample (3) is excited, and convert the full spectrum signal into a first digital signal; a second spectroscopic component, the second spectroscopic component being used to collect a local spectral signal of a target frequency band obtained after the sample (3) is excited, and convert the local spectral signal into a second digital signal, the target frequency band being a collection frequency band determined according to the material properties of the sample (3); A data processing device is used to acquire and fuse the first digital signal and the second digital signal, and generate a spectrum acquisition result.

2. The LIBS system based on dual-mode spectral acquisition according to claim 1, characterized in that: The first light splitting component comprises: A convex lens (4), the convex lens (4) being used to collect the plasma beam excited by the sample (3); An optical fiber (5), one end of which is connected to the convex lens (4) and is used to collect the plasma beam; A spectrometer (6), the spectrometer (6) is connected to the other end of the spectrometer (6), the optical fiber (5) transmits the collected plasma light beam to the spectrometer (6), and the spectrometer is used to analyze the input plasma light beam.

3. The LIBS system based on dual-mode spectral acquisition according to claim 2, characterized in that: The spectrometer (6) is an echelle grating spectrometer or a fiber optic spectrometer.

4. The LIBS system based on dual-mode spectral acquisition according to claim 1, characterized in that: The second light splitting component comprises: An optical filter (8), the optical filter (8) being used to filter an optical signal of a preset wavelength band; A photomultiplier tube (9), which is arranged downstream of the optical filter (8) and collects light waves in the target frequency band and converts the collected spectrum intensity into a current signal; An acquisition card (10), the acquisition card (10) being arranged downstream of the photomultiplier tube (9), the acquisition card being connected to the photomultiplier tube via a cable, and converting the electrical signal into a second digital signal.

5. The LIBS system based on dual-mode spectral acquisition according to claim 4, characterized in that: The optical filter (8) is connected to the photomultiplier tube (9) via an optical fiber (5).

6. The LIBS system based on dual-mode spectral acquisition according to any one of claims 1 to 5, characterized in that: The LIBS system further comprises: A focusing mirror (2), wherein the focusing mirror (2) is arranged between the laser excitation device (1) and the sample, the focusing mirror (2) and the laser excitation device (1) are arranged radially symmetrically, and are used to focus the laser beam emitted by the laser excitation device (1).

7. The LIBS system based on dual-mode spectral acquisition according to any one of claims 1 to 5, characterized in that: The laser excitation device (1) is a pulse laser.

8. The LIBS system based on dual-mode spectral acquisition according to any one of claims 1 to 5, characterized in that: The data processing device is a computer (7), and the computer (7) outputs the generated spectrum acquisition result in the form of a spectrum graph.

9. The LIBS system based on dual-mode spectral acquisition according to any one of claims 1 to 5, characterized in that: The sample (3) may be a solid, liquid or gas sample.

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