Miniature laser-induced breakdown spectroscopy detection method and device

Abstract

The invention relates to the technical field of laser-induced breakdown spectroscopy, and discloses a miniature laser-induced breakdown spectroscopy detection method and device, and the method comprises the following steps: focusing pulse laser on the surface of a sample, and exciting the sample to be detected to generate high-temperature plasma; synchronously collecting optical signals of the plasma from different spatial orientations through a multi-channel optical input structure integrated on a chip; transmitting the optical signal collected by each channel to an on-chip light splitting element through a waveguide structure on the chip; performing light splitting on the optical signal of each channel by using an on-chip light splitting element; and processing the spectral signal of each channel, and reconstructing a final spectrum for elemental analysis. According to the invention, the deep ultraviolet transparent substrate and the waveguide are adopted, and chip-level vacuum / inert gas sealing is combined, so that the contact between a deep ultraviolet signal and the atmosphere is fundamentally cut off, and the ultra-low-loss transmission of a deep ultraviolet band signal is realized.

Description

Technical Field

[0001] This invention relates to the field of laser-induced breakdown spectroscopy technology, specifically to a miniature laser-induced breakdown spectroscopy detection method and device. Background Technology

[0002] Laser-induced breakdown spectroscopy (LIBS) is a versatile elemental analysis technique with advantages such as no sample pretreatment required and real-time rapid analysis. However, traditional LIBS systems generally employ a single-channel detection method, which has the following inherent drawbacks: Low signal acquisition efficiency and poor signal-to-noise ratio: The plasma signal excited by a single laser pulse has non-uniform and unstable spatiotemporal distribution. Single-channel detection can only capture a portion of the signal from a single perspective, resulting in limited information. It is also susceptible to plasma scintillation and laser energy fluctuations, leading to insufficient analytical sensitivity and accuracy. Severe deep ultraviolet signal transmission loss: When detecting key elements such as carbon (C), phosphorus (P), and sulfur (S), their characteristic spectral lines are located in the deep ultraviolet band (approximately 150nm~200nm). Traditional discrete optical systems have long optical paths, and the signal is easily absorbed by oxygen and water vapor in the air, causing a sharp attenuation of signal strength. Poor adaptability to long-range detection: In long-range or micro-area detection applications, the plasma signal is weak and divergent. The limited receiving angle of a single channel makes it difficult to efficiently collect the signal, resulting in decreased detection capability.

[0003] While existing technologies employ multiple detectors or fiber bundles for signal collection, these approaches fail to fundamentally address the issues of complex system structure, large size, high cost, and deep ultraviolet loss. On-chip integrated photonics technology offers new insights for miniaturization and performance improvement of LIBS systems. However, combining it with LIBS technology and effectively addressing the challenges of multi-channel synchronous detection and low-loss transmission of deep ultraviolet signals remains a pressing technical challenge. Therefore, this paper proposes a miniature laser-induced breakdown spectroscopy detection method and device to address the aforementioned problems. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] To address the shortcomings of existing technologies, this invention provides a miniature laser-induced breakdown spectroscopy detection method and device. Through multi-channel parallel detection and on-chip integration technology, it significantly improves signal acquisition efficiency and signal-to-noise ratio, and achieves low-loss transmission of deep ultraviolet signals, thereby enabling high-sensitivity and high-precision qualitative and quantitative elemental analysis.

[0006] (II) Technical Solution

[0007] To achieve the aforementioned goal of completing high-sensitivity and high-precision qualitative and quantitative elemental analysis, this invention provides the following technical solution: a miniature laser-induced breakdown spectroscopy detection method, comprising the following steps: Step 1: Focus a pulsed laser onto the sample surface to excite the sample to generate high-temperature plasma; Step 2: Multi-channel spatially resolved optical signal collection: At the input end of the chip, a microlens array is designed. Each microlens is responsible for collecting signals from different spatial azimuth angles of the plasma. Through the multi-channel optical input structure integrated on the chip, the optical signals of the plasma are collected synchronously from different spatial azimuths. Step 3: The optical signals collected from each channel are transmitted to an on-chip beam splitter through the waveguide structure on the chip; Step 4: Use the on-chip beam splitter to split the optical signals of each channel; Step 5: Synchronously detect the spectral signals of each channel after dispersion; Step 6: Process the spectral signals of each channel to reconstruct the final spectrum for elemental analysis.

[0008] Preferably, step 2, multi-channel spatially resolved optical signal collection, further includes: The plasma space region is divided into multiple sub-regions, and each microlens independently captures optical signals at a specific azimuth angle: The substrate selection is as follows: a 1mm thick wafer made of deep ultraviolet transparent material MgF2 or AlN with a transmittance of >90% in the 180nm wavelength band; Lens design: Asymmetrical layout, Channel 1 central region: diameter 200μm, focal length 1.0mm, optical axis perpendicular to the substrate for capturing core ion spectral lines of the plasma; Channel 2 transition region: diameter 150μm, focal length 1.5mm, optical axis tilted 15° for capturing the central region; Channel 3 edge region: diameter 100μm, focal length 2.0mm, optical axis tilted 30° for capturing atomic spectral lines in the outer low-temperature region.

[0009] Preferably, in step 3, the optical signals collected by each channel are transmitted to an on-chip beam splitter through the waveguide structure on the chip, which further includes the following steps: Step 301: Optical signal coupling and on-chip transmission, efficiently guiding the light focused by the microlens into the chip waveguide to reduce deep ultraviolet band loss: Tapered waveguide integration: Etching inverted tapered aluminum nitride waveguides at the focal point of each microlens: Input end: 50μm diameter matching lens spot; Output end: 5μm diameter compressing optical field; Taper angle: 2°, 10nm thick Al2O3 passivation layer deposited on the waveguide sidewall to suppress surface scattering; Step 302: Inert gas sealing: A transparent quartz cover plate is bonded to the surface of the microlens array, and the cavity is filled with high-purity argon gas to eliminate atmospheric absorption. A continuous relief structure is formed by ion beam etching, and the edge roughness is <10nm to reduce scattering. Step 303: Spatial channel mapping calibration, establishing the correspondence between the spatial orientation of the microlens and the electrical channel: Standard light source scanning: Using a mercury lamp as a point light source, the three-dimensional translation stage controls the position to record the response peak position of each microlens channel, generating a miniature laser-induced breakdown spectroscopy detection method and device "spatial coordinates-channel number" mapping matrix; Step 304: Data solidification: Write the mapping matrix into the chip's built-in EEPROM memory. When the system is working, this matrix is ​​directly called to assign spatial attributes to the data of each channel. Step 305: Online verification: Excite the standard sample and check whether the sample signal intensity in channel 1 is greater than 3 times that in channel 3.

[0010] Preferably, step 4, which uses the on-chip beam splitter to split the optical signals of each channel, further includes the following steps: Step 401: Multi-channel optical signal input to planar waveguide region: After mode conversion and equal-length transmission, each channel optical signal enters the common input planar waveguide region of AWG through its respective input waveguide at different preset incident angles; Step 402: Introduction of Optical Path Difference and Phase Modulation in the Arrayed Waveguide: The extended planar wavefront enters an arrayed waveguide region composed of numerous parallel waveguides. A fixed path length difference ΔL exists between adjacent waveguides in this region. ΔL is a key design parameter of the AWG, determining its free spectral range and dispersion capability. As the optical signal passes through these waveguides, a wavelength-dependent phase difference accumulates. Step 403: Interference focusing in the output planar waveguide: The waveguide optical signals carrying phase information diffract and interfere with each other again in the output planar waveguide; Step 404: Decoupling and output of wavelength-spatial channel information: An arrayed waveguide grating is placed on the focal plane of the output planar waveguide. All wavelengths from input channel 1 will be focused on a specific set of pixels of the detector; similarly, the spectrum from input channel 2 will be focused on another set of adjacent but independent pixels.

[0011] Preferably, step 5, synchronously detecting the spectral signals of each channel after spectral splitting, further includes: using a deep ultraviolet enhancement array waveguide grating integrated with an AWG monolith to perform global shutter exposure and synchronous data acquisition on the spectral signals of all channels after spectral splitting, ensuring that all data correspond to the plasma state at the same moment.

[0012] Preferably, step 6, processing the spectral signals of each channel to reconstruct the final spectrum for elemental analysis, further includes: performing adaptive weighted fusion processing based on the signal-to-noise ratio of each channel spectral signal or the intensity of a specific element spectral line to reconstruct the final high signal-to-noise ratio spectrum, and performing elemental analysis based on it.

[0013] Preferably, the adaptive weighted fusion process further includes the following steps: (a) Calculate the signal-to-noise ratio (SNR) of each channel at the target wavelength. i And element intensity factor I_i^{elem}; (b) According to the formula: ; α=1.5 (enhance high signal-to-noise ratio channels), β=0.8 (suppress outliers) Calculate the weights, and use the weights w i Weighted fusion spectrum; (c) Verify the constraint conditions for the radial distribution of plasma.

[0014] Preferably, the miniature laser-induced breakdown spectroscopy detection device includes a pulsed laser, a spectral analysis chip, a sealed housing, and a signal processing and controller; The pulsed laser is used to generate a laser beam to excite the plasma; the multi-channel on-chip integrated spectral analysis chip includes a substrate and a microlens array. The substrate is made of a deep ultraviolet transparent material, and multiple deep ultraviolet low-loss optical waveguide on-chip spectral splitting modules are integrated on the substrate. The microlens array, integrated on the substrate, is used to receive plasma optical signals from multiple spatial angles; multiple deep ultraviolet low-loss optical waveguides, integrated within the substrate, are used to transmit the optical signals; the on-chip spectral splitting module, integrated on the substrate and optically connected to the multiple optical waveguides, is used to split the optical signals of each channel; the output end of the on-chip spectral splitting module is coupled with an arrayed waveguide grating for synchronously detecting the spectral signals of each channel; The sealed housing is used to encapsulate at least the area containing the optical signal transmission path of the multi-channel on-chip integrated spectral analysis chip, and to provide a vacuum or inert gas environment for the area. The signal processing and controller is electrically connected to the arrayed waveguide grating and the pulsed laser, and is used to control laser emission, acquire spectral data, and execute the adaptive weighted fusion algorithm.

[0015] Preferably, the multi-channel optical input module is a microlens array, the on-chip spectral splitting module is a multi-input multi-output arrayed waveguide grating, and the substrate material is magnesium fluoride or calcium fluoride. Beneficial effects

[0016] Compared with the prior art, the present invention provides a miniature laser-induced breakdown spectroscopy detection method and device, which has the following beneficial effects: 1. This miniature laser-induced breakdown spectroscopy detection method and device can acquire multi-dimensional spatial-spectral information of plasma with a single excitation through multi-channel spatial diversity detection. It adopts an adaptive weighted fusion algorithm to intelligently integrate the signals of each channel, effectively suppressing random noise and significantly improving the signal-to-noise ratio. By using a deep ultraviolet transparent substrate and waveguide, combined with chip-level vacuum / inert gas sealing, the contact between the deep ultraviolet signal and the atmosphere is fundamentally cut off, realizing extremely low-loss transmission of deep ultraviolet signals and greatly improving the detection limits of elements such as C, P, and S.

[0017] 2. This miniature laser-induced breakdown spectroscopy detection method and device integrates the core optical path system onto a single chip, eliminating a large number of discrete optical components. This makes the device compact, robust, and stable, making it more suitable for field, online, and portable applications. The multi-channel receiver forms an equivalent large field of view. Combined with the potential of chip-level optical phased arrays, it is easy to capture weak plasma signals at long distances, improving the sensitivity and reliability of remote detection. Attached Figure Description

[0018] Figure 1 This is a three-dimensional schematic diagram of the present invention; Figure 2 This is a schematic diagram of the arrayed waveguide grating of the present invention; Figure 3 This is a flowchart of the miniature laser-induced breakdown spectroscopy detection method of the present invention.

[0019] In the figure: 1 Pulsed laser, 2 Spectral analysis chip, 201 Microlens array, 202 Substrate, 203 Arrayed waveguide grating, 204 Deep ultraviolet enhanced CCD detector, 3 Sealed housing, 4 Signal processing and controller. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Please see Figure 1-3 A miniature laser-induced breakdown spectroscopy detection method includes the following steps: Step 1: Focus a pulsed laser onto the sample surface to excite the sample to generate high-temperature plasma; Step 2: Multi-channel spatially resolved optical signal collection: At the input end of the chip, a microlens array is designed. Each microlens is responsible for collecting signals from different spatial azimuth angles of the plasma. Through the multi-channel optical input structure integrated on the chip, the optical signals of the plasma are collected synchronously from different spatial azimuths. Step 3: The optical signals collected from each channel are transmitted to an on-chip beam splitter through the waveguide structure on the chip; Step 4: Use the on-chip beam splitter to split the optical signals of each channel; Step 5: Synchronously detect the spectral signals of each channel after dispersion; Step 6: Process the spectral signals of each channel to reconstruct the final spectrum for elemental analysis.

[0022] An apparatus for implementing the above method includes: a pulsed laser 1, a multi-channel on-chip integrated spectral analysis chip 2, a sealed housing 3, and a signal processing and controller 4.

[0023] The laser emitted by pulsed laser 1 is focused by a lens and then irradiates the sample surface, generating plasma.

[0024] The multi-channel on-chip integrated spectral analysis chip 2 receives plasma optical signals through a microlens array 201 at its input end. Each lens in the microlens array 201 is preset with a different pointing angle, pointing at different regions such as the center and edge of the plasma to achieve spatial diversity. The collected optical signal immediately enters a deep ultraviolet low-loss waveguide prepared on a magnesium fluoride MgF2 substrate 202. The entire spectral analysis chip 2 is encapsulated by a sealed shell 3, which is filled with high-purity nitrogen gas to ensure that the deep ultraviolet light is not absorbed during transmission.

[0025] The optical signal is transmitted via a waveguide to a miniature bandpass filter integrated on chip 2 to filter out stray light outside the target band. Subsequently, the light from each channel is guided to an on-chip multi-input multi-output array waveguide grating 203. This array waveguide grating 203 has N input channels and M output channels, which can independently split and output the light from each input channel. The spectrum after splitting is synchronously received by a deep ultraviolet enhanced CCD detector 204.

[0026] The signal processing and controller 4 controls the entire process and runs an adaptive weighted fusion algorithm. This algorithm first evaluates the signal-to-noise ratio (SNRi) of each channel's spectrum, then assigns a weight coefficient wi to each channel, which is positively correlated with SNRi. Finally, the final fused spectrum is obtained using the weighted summation formula S_final=Σwi*Si, which is used for accurate elemental analysis.

[0027] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0028] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A miniature laser-induced breakdown spectroscopy detection method, characterized in that, Includes the following steps: Step 1: Focus a pulsed laser onto the sample surface to excite the sample to generate high-temperature plasma; Step 2: Multi-channel spatially resolved optical signal collection: At the input end of the chip, a microlens array is designed. Each microlens is responsible for collecting signals from different spatial azimuth angles of the plasma. Through the multi-channel optical input structure integrated on the chip, the optical signals of the plasma are collected synchronously from different spatial azimuths. Step 3: The optical signals collected from each channel are transmitted to an on-chip beam splitter through the waveguide structure on the chip; Step 4: Use the on-chip beam splitter to split the optical signals of each channel; Step 5: Synchronously detect the spectral signals of each channel after dispersion; Step 6: Process the spectral signals of each channel to reconstruct the final spectrum for elemental analysis.

2. The miniature laser-induced breakdown spectroscopy detection method according to claim 1, characterized in that: Step 2, multi-channel spatially resolved optical signal collection, specifically includes: The plasma space region is divided into multiple sub-regions, and each microlens independently captures optical signals at a specific azimuth angle: The substrate selection is as follows: a 1mm thick wafer made of deep ultraviolet transparent material MgF2 or AlN with a transmittance of >90% in the 180nm wavelength band; Lens design: Asymmetrical layout, Channel 1 central region: diameter 200μm, focal length 1.0mm, optical axis perpendicular to the substrate for capturing core ion spectral lines of the plasma; Channel 2 transition region: diameter 150μm, focal length 1.5mm, optical axis tilted 15° for capturing the central region; Channel 3 edge region: diameter 100μm, focal length 2.0mm, optical axis tilted 30° for capturing atomic spectral lines in the outer low-temperature region.

3. The miniature laser-induced breakdown spectroscopy detection method according to claim 1, characterized in that: In step 3, the optical signals collected from each channel are transmitted to an on-chip beam splitter through the waveguide structure on the chip. Specifically, this also includes the following steps: Step 301: Optical signal coupling and on-chip transmission, efficiently guiding the light focused by the microlens into the chip waveguide to reduce deep ultraviolet band loss: Tapered waveguide integration: Etching an inverted tapered aluminum nitride waveguide at the focal point of each microlens: Input end: 50μm diameter matching lens spot; Output: 5μm diameter compressed optical field; Cone angle: 2°, waveguide sidewalls are deposited with a 10nm thick Al2O3 passivation layer to suppress surface scattering; Step 302: Inert gas sealing: A transparent quartz cover plate is bonded to the surface of the microlens array, and the cavity is filled with high-purity argon gas to eliminate atmospheric absorption. A continuous relief structure is formed by ion beam etching, and the edge roughness is <10nm to reduce scattering. Step 303: Spatial channel mapping calibration, establishing the correspondence between the spatial orientation of the microlens and the electrical channel: Standard light source scanning: Using a mercury lamp as a point light source, the three-dimensional translation stage controls the position to record the response peak position of each microlens channel, generating a miniature laser-induced breakdown spectroscopy detection method and device "spatial coordinates-channel number" mapping matrix; Step 304: Data solidification: Write the mapping matrix into the chip's built-in EEPROM memory. When the system is working, this matrix is ​​directly called to assign spatial attributes to the data of each channel. Step 305: Online verification: Excite the standard sample and check whether the sample signal intensity in channel 1 is greater than 3 times that in channel 3.

4. The miniature laser-induced breakdown spectroscopy detection method according to claim 1, characterized in that: Step 4, which uses the on-chip beam splitter to split the optical signals of each channel, further includes the following steps: Step 401: Multi-channel optical signal input to planar waveguide region: After mode conversion and equal-length transmission, each channel optical signal enters the common input planar waveguide region of AWG through its respective input waveguide at different preset incident angles; Step 402: Introduction of Optical Path Difference and Phase Modulation in the Arrayed Waveguide: The extended planar wavefront enters an arrayed waveguide region composed of numerous parallel waveguides. A fixed path length difference ΔL exists between adjacent waveguides in this region. ΔL is a key design parameter of the AWG, determining its free spectral range and dispersion capability. As the optical signal passes through these waveguides, a wavelength-dependent phase difference accumulates. Step 403: Interference focusing in the output planar waveguide: The waveguide optical signals carrying phase information diffract and interfere with each other again in the output planar waveguide; Step 404: Decoupling and output of wavelength-spatial channel information: An arrayed waveguide grating (203) is placed on the focal plane of the output planar waveguide, and all wavelengths from input channel 1 are focused on a specific set of pixels of the detector; similarly, the spectrum from input channel 2 is focused on another set of adjacent but independent pixels.

5. The miniature laser-induced breakdown spectroscopy detection method according to claim 1, characterized in that: Step 5, synchronously detecting the spectral signals of each channel after spectral splitting, specifically includes: using a deep ultraviolet enhancement array waveguide grating (203) integrated with an AWG monolith to perform global shutter exposure and synchronous data acquisition on the spectral signals of all channels after spectral splitting, ensuring that all data correspond to the plasma state at the same moment.

6. The miniature laser-induced breakdown spectroscopy detection method according to claim 1, characterized in that: Step 6, which processes the spectral signals of each channel to reconstruct the final spectrum for elemental analysis, further includes: performing adaptive weighted fusion processing based on the signal-to-noise ratio of each channel spectral signal or the intensity of a specific element spectral line to reconstruct the final high signal-to-noise ratio spectrum, and performing elemental analysis based on it.

7. The miniature laser-induced breakdown spectroscopy detection method according to claim 6, characterized in that: The adaptive weighted fusion process further includes the following steps: (a) Calculate the signal-to-noise ratio (SNR) of each channel at the target wavelength. i And element intensity factor I_i^{elem}; (b) According to the formula: ； α=1.5 (enhance high signal-to-noise ratio channels), β=0.8 (suppress outliers) Calculate the weights, and use the weights w i Weighted fusion spectrum; (c) Verify the constraint conditions for the radial distribution of plasma.

8. A miniature laser-induced breakdown spectroscopy detection device, comprising the apparatus used in the miniature laser-induced breakdown spectroscopy detection method according to any one of claims 1-7, characterized in that: The miniature laser-induced breakdown spectroscopy detection device includes a pulsed laser (1), a multi-channel on-chip integrated spectral analysis chip (2), a sealed housing (3), and a signal processing and controller (4). The pulsed laser (1) is used to generate a laser beam that excites the plasma; The multi-channel on-chip integrated spectral analysis chip (2) includes: a substrate (202) and a microlens array (201). The substrate (202) is made of a deep ultraviolet transparent material, and multiple deep ultraviolet low-loss optical waveguides and on-chip spectral splitting modules are integrated on the substrate (202); The microlens array (201), integrated on the substrate (202), is used to receive plasma optical signals from multiple spatial angles; multiple deep ultraviolet low-loss optical waveguides, integrated within the substrate (202), are used to transmit the optical signals; the on-chip spectral splitting module, integrated on the substrate (202), is optically connected to the multiple optical waveguides and is used to split the optical signals of each channel; the output end of the on-chip spectral splitting module is coupled with an arrayed waveguide grating (203) for synchronously detecting the spectral signals of each channel; The sealed housing (3) is used to encapsulate at least the area containing the optical signal transmission path of the multi-channel on-chip integrated spectral analysis chip (2) and to provide a vacuum or inert gas environment for the area; The signal processing and controller (4) is electrically connected to the arrayed waveguide grating (203) and the pulsed laser, and is used to control laser emission, acquire spectral data and execute the adaptive weighted fusion algorithm.

9. A miniature laser-induced breakdown spectroscopy detection device according to claim 8, characterized in that: The multi-channel optical input module is a microlens array, the on-chip spectral splitting module is a multi-input multi-output arrayed waveguide grating (NxMAWG), and the substrate (202) is made of magnesium fluoride (MgF2) or calcium fluoride.

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