CN203324186U - Laser induced breakdown spectroscopy system based on wavelength division multiplexing and time domain overlapping - Google Patents

Abstract

This patent discloses a laser-induced breakdown spectroscopy system based on wavelength division multiplexing and time-domain overlapping. A beam of laser pulses is divided into several beams of laser pulses with different wavelengths and different timings and combined. These laser pulses of different wavelengths sequentially excite the same point of the sample after a certain delay. Since laser pulses of different wavelengths have different excitation effects on different types of atoms, the wavelength division multiplexing LIBS method proposed in this patent can significantly improve the detection effect. At the same time, due to the delay and overlap of each laser pulse in the time domain, the previous The plasma induced by the laser pulse is injected into the next laser pulse when it is about to cool down, which can significantly improve the detection signal-to-noise ratio.

Description

Laser-induced breakdown spectroscopy system based on wavelength division multiplexing and time-domain overlapping

technical field

This patent relates to a laser spectrum detection method, in particular to a laser-induced breakdown spectroscopy (LIBS for short) system based on wavelength division multiplexing and time domain overlap.

Background technique

Laser-induced breakdown spectroscopy (LIBS) detection technology uses laser pulses emitted by a pulsed laser to focus on the sample through a focusing lens, and obtain high-energy laser pulses at the focal point to ablate, evaporate, excite and ionize the sample to form Plasma sparks with high temperature, high pressure, and high electron density radiate a spectrum containing characteristic spectral lines of atoms and ions, which can be used to detect the elemental composition of matter.

The traditional LIBS detection method uses a low-repetition-frequency single-pulse laser as the excitation source. During single-pulse LIBS detection, the shock wave generated on the surface of the sample target makes the excited plasma emission spectrum signal attenuated greatly, so the measured signal is weak. The signal-to-noise ratio is small. In addition, since the single-pulse laser has a single central wavelength, it only has high excitation efficiency for some elements, so it is impossible to obtain the elemental composition of the sample to be measured more comprehensively.

In order to improve the signal-to-noise ratio of LIBS detection and fully obtain the elemental composition of the sample to be tested, this patent proposes a LIBS system and detection method based on wavelength division multiplexing and time-domain overlapping. This method decomposes a beam of laser pulses into several beams Laser pulses with different wavelengths and different time sequences are combined, and these laser pulses with different wavelengths are sequentially overlapped with a certain time delay to excite the same point of the sample. Different frequency doubling crystals and OPOs can be selected to obtain a set of suitable WDM wavelength distributions λ ₁ , λ ₂ , λ ₃ ,..., λ _n-1 , λ _n (n represents the total number of WDM wavelengths), The element composition of the sample to be tested can be comprehensively obtained through LIBS spectral analysis excited by laser pulses with these wavelength distributions. At the same time, due to the delay and overlap of each laser pulse in the time domain, injecting the next laser pulse when the plasma induced by the previous laser pulse is about to cool down can significantly improve the detection signal-to-noise ratio.

Contents of the invention

The purpose of this patent is to provide a LIBS system based on wavelength division multiplexing and time-domain overlapping, which overcomes the shortcomings of traditional single-pulse LIBS, improves the signal-to-noise ratio of LIBS detection and comprehensively obtains the elemental composition of the sample to be tested.

As shown in Figure 1, the laser-induced breakdown spectroscopy system based on wavelength division multiplexing and time-domain overlapping includes proportional beam splitters, high-energy solid-state pulsed lasers, time-delayed optical components, optical delay lines, frequency-doubling crystals, or optical parametric oscillators Mirrors, full mirrors, half mirrors, dichroic mirrors, polychromatic mirrors, mirrors with holes, fiber optic ICCD spectrometers, computers and focusing lenses.

A beam of nanosecond-level pulsed laser with a wavelength of _λ1 is emitted by a high-energy solid-state pulsed laser 2, and is divided into two paths through a 1 to n-1 ratio beam splitter 1, and the wavelength transmitted through a 1 to n-1 ratio beam splitter 1 is λ ₁ The first laser pulse, which accounts for one nth of the total energy of the laser, passes through the polychromatic mirror B20 and first reaches the focusing lens 19. After being focused, it passes through the small hole in the center of the perforated mirror 18 and reaches the surface of the sample target 16. The sample The target is induced by laser pulses to generate plasma; the LIBS signal induced by laser pulses is reflected by the perforated mirror 18, and the lens 17 is focused on the end face of the fiber optic probe attached to the fiber ICCD spectrometer 14, and the fiber ICCD spectrometer 14 will accept the wavelength The LIBS signal data generated by the laser induction of _λ1 is transmitted to the computer 15;

The laser pulse reflected by the 1 to n-1 ratio beam splitter 1 with a wavelength of _λ1 accounting for n/n-1 of the total energy of the laser enters the first group of delay optical components 3 and passes through the first group of frequency doubling crystals or optical The parametric oscillator 6 is converted into a laser pulse with a wavelength of _λ2 , which is divided into two paths of reflection and transmission through an n-2 to 1 ratio beam splitter 9, wherein the wavelength obtained by reflection is λ2 _and the energy is one of n of the total amount of laser light The second laser pulse is reflected by the polychromatic mirror A12 and the polychromatic mirror B20 and is focused by the lens 19. The focused laser pulse passes through the small hole in the center of the perforated mirror 8 and reaches the surface of the sample target 16. The sample target passes through The laser pulse induces plasma; the LIBS signal induced by the laser pulse is reflected by the perforated mirror 18, and the lens 17 is focused on the end face of the optical fiber probe attached to the optical fiber ICCD spectrometer 14 _. The LIBS signal data induced by the laser is transmitted to the computer 15; at this time, because the laser pulse has passed the time delay τ, it is ensured that the sample target is injected into the second laser pulse when the plasma induced by the first laser pulse is about to cool down;

The wavelength transmitted by the n-2 to 1 ratio beam splitter ₉ is the laser pulse whose energy is n-2 of the n/n of the total amount of laser light, and passes through the second group of time-delay optical components 3 and passes through the second group of frequency doubling crystals or The optical parametric oscillator 6 is converted into a laser pulse with a wavelength of _λ3 , and the _proportional beam splitter divides it into reflection and transmission. It is used to induce the sample target to generate LIBS signals, and the transmitted light part is converted into a laser pulse with a wavelength of _λ4 by the third group of time-delay optical components 3 and passed through the third group of frequency-doubling crystals or optical parametric oscillators 6, and then split again To excite the sample target; work in this way until the system completes the conversion of laser pulses with a wavelength of λ _n-2 , which is converted by the n-2 group of delay optical components 3 and the n-2 group of frequency doubling crystals or optical parametric oscillators 6 The laser pulse with a wavelength of λ _n-1 is divided into two paths by the half mirror 11, the reflected path is used to excite the sample to provide the LIBS signal corresponding to the laser with a wavelength of λ _n-1 , and the transmitted path is group n-1 The delay optical component 3 and the n-1th group of frequency-doubling crystals or optical parametric oscillators 6 are processed into laser pulses with a wavelength of λ _n , which are used to induce the sample target to generate -LIBS signals after being reflected by the total reflection mirror 10; thus, The system obtains a set of laser pulses with wavelengths λ ₁ , λ ₂ , λ ₃ ,..., λ _n-1 , λ _n for inducing LIBS signals from the sample target, where n is the wavelength division multiplexing selected by the system The total number of wavelengths.

The time-delay optical assembly 3 is composed of an incident reflector 3.1, a prism 3.2 and an exit reflector 3.3, and all the n-1 prisms 3.2 in the n-1 groups of time-delay optical assemblies 3 are installed on the same bracket 5 On the only optical delay line 4, the optical delay line 4 finely adjusts the distance between the triangular mirror 3.2 and the incident reflector 3.1 and exit reflector 3.3 in all time-delay optical components 3, so as to achieve the same effect on all adjacent laser pulses by changing the optical path delay.

The LIBS signal induced by n laser pulses with n wavelengths is reflected by the hole mirror, and the lens is focused on the end face of the fiber optic probe attached to the fiber optic ICCD spectrometer. The fiber optic probe is installed on the fiber optic bracket, which can be easily adjusted for accurate focus. The software on the computer connected to the optical fiber ICCD spectrometer can accurately control the opening and closing time of the ICCD, and can collect and store the LIBS signals induced by n laser pulses with n wavelengths to determine the composition of the sample target. accurate analysis.

Since laser pulses of different wavelengths have different excitation effects on different types of atoms, different frequency doubling crystals and OPOs can be selected to obtain a set of suitable wavelength division multiplexing wavelength distributions λ ₁ , λ ₂ , λ ₃ ,..., λ _{n- 1.} λ _n (n represents the total number of wavelengths of wavelength division multiplexing), the elemental composition of the sample to be measured can be comprehensively obtained through LIBS spectral analysis excited by laser pulses with these wavelength distributions.

The wavelength division multiplexing LIBS method proposed in this patent can significantly improve the detection effect. At the same time, due to the delay and overlap of each laser pulse in the time domain, the plasma induced by the previous laser pulse is injected into the next laser when it is about to cool down. Pulse, can detect significantly signal-to-noise ratio.

Description of drawings

Figures 1 and 2 are schematic diagrams of this patent, in which: 1——1 to n-1 ratio beam splitter; 2——high-energy solid-state pulsed laser; 3——delay optical components; 3.1——incident mirror; 3.2—prism; 3.3—exit reflector; 4—optical delay line; 5—bracket; 6—frequency doubling crystal (or optical parametric oscillator OPO); Half mirror; 9—n-2 to 1 ratio beam splitter; 10—full mirror B; 11—dichromatic mirror A; 12—polychromatic mirror A; 13—fiber support; 14—optical fiber ICCD spectrometer; 15—computer; 16—sample target; 17—lens; 18—mirror with hole; 19—focusing lens; 20—polychromatic mirror B.

Note: n represents the total number of wavelengths for wavelength division multiplexing, and ICCD represents an enhanced charge-coupled device. τ represents the time delay between adjacent laser pulses.

Detailed ways

The principle of this patent is shown in Figures 1 and 2. In this specific embodiment, n=4 is selected, that is, the total number of wavelengths for wavelength division multiplexing is 4.

A beam of nanosecond-level pulsed laser light with a wavelength of λ ₁ =1064nm is emitted by a high-energy solid-state pulsed laser 2, and is divided into two paths through a 1:3 ratio beam splitter 1:

The wavelength that passes through the 1:3 ratio beam splitter 1 is λ _1. The first laser pulse (accounting for a quarter of the total energy of the laser) passes through the polychromatic mirror B20 and first reaches the focusing lens 19, which is focused and passes through the perforated reflector The small hole in the center of 18 reaches the surface of the sample target 16, requiring the distance from the surface of the sample target 16 to the focusing lens 19 to be equal to the focal length of the focusing lens 19 (that is, in focus) to induce plasma;

The laser pulse (accounting for three-quarters of the total laser energy) reflected by the 1:3 ratio beam splitter 1 enters the first group of time-delay optical components 3. 3.3 composition, all the triangular prisms 3.2 of each group of time-delay optical components 3 are installed on the optical delay line 4 through the same bracket 5, and each group of triangular prisms 3.2 and the incident mirror 3.1 can be finely adjusted through the optical delay line 4 at the same time. The distance of the mirror 3.3 achieves the purpose of changing the optical path and realizing time delay. After the laser pulse passes through the first group of time-delay optical components 3, it is converted into a laser pulse with a wavelength of λ through the first group of frequency doubling crystal (or optical parametric oscillator OPO) 6, which is reflected by a 2: ₁ ratio beam splitter 9 And transmission: wherein the second laser pulse obtained by reflection (the energy becomes 1/4 of the total amount of laser light, and the wavelength is λ ₂ ), is reflected by the polychromatic mirror A12, and then reflected by the polychromatic mirror B20, and the first A laser pulse similarly arrives at the focusing lens 19, is focused and passes through the small hole at the center of the perforated reflector 18, and arrives at the surface of the sample target 16. Because of the time delay, the laser pulse with a wavelength of λ ₂ The first laser pulse with a wavelength of _λ1 arrives late, and the delay τ between the two pulses can be precisely adjusted by adjusting the optical delay line 4 (as shown in Figure 2), that is, a certain overlap is generated in the time domain, so that the first laser pulse Inject the second pulse when the pulse-induced plasma is about to cool;

The energy of the laser pulse generated by the transmission of the 2:1 ratio beam splitter 9 is 1/2 of the total energy of the laser. Oscillator OPO) 6 is transformed into the laser pulse that wavelength is λ ₃ , through half-mirror 8 reflection and transmission: wherein the 3rd laser pulse (energy becomes 1/4th of laser total amount by reflection, wavelength is λ ₃ ), reflected by the dichroic mirror A11, transmitted by the polychromatic mirror A12, and then reflected by the polychromatic mirror B20, similar to the second laser pulse, arrives at the focusing lens 19, is focused and passes through the center of the reflective mirror 18 with a hole reach the surface of the sample target 16, because of the time delay, the laser pulse with a wavelength of λ ₃ arrives later than the second laser pulse with a wavelength of λ ₂ , because the system uses a support 5 to hold all the delayed laser pulses The triangular prism 3.2 in the optical assembly 3 is all installed and fixed on an optical delay line 4 and due to the symmetry of the optical path structure, it realizes the same time delay τ (as shown in Figure 2) to all adjacent laser pulses, similarly making the first The plasma induced by the two laser pulses is injected into the third laser pulse when it is about to cool down;

The laser pulse generated by the transmission of the half mirror 8 has an energy of 1/4 of the total energy of the laser. After being delayed by the third group of time delay components 3, it passes through the third group of frequency doubling crystals (or optical parameter oscillation Device OPO) 6 is transformed into the laser pulse that wavelength is λ ₄ , is reflected by total reflection mirror A7 and total reflection mirror B10, is transmitted through dichroic mirror A11 and polychromatic mirror A12, after the reflection of polychromatic mirror B20 again, and the third The laser pulse similarly arrives at the focusing lens 19, is focused and passes through the small hole at the center of the perforated reflector 18, and arrives at the surface of the sample target 16, because the time delay τ has passed, so the laser pulse with a wavelength of λ ₄ is shorter than the wavelength The third laser pulse with λ ₃ arrives late, causing a certain overlap in the time domain, and the fourth pulse arrives just when the plasma induced by the third laser pulse is about to cool down.

The LIBS signal induced by multiple laser pulses with multiple wavelengths is reflected by the perforated mirror 18, and the lens 17 is focused on the end face of the fiber optic probe attached to the fiber optic ICCD spectrometer 14. The fiber optic probe is installed on the fiber optic bracket 13 for convenient adjustment. for accurate focus. The software on the computer 15 connected to the optical fiber ICCD spectrometer 14 can accurately control the opening and closing time of the ICCD, and can collect and store the LIBS signals induced by multiple laser pulses with multiple wavelengths to form the sample target 16 accurate analysis of elements.

Since laser pulses of different wavelengths have different excitation effects on different types of atoms, different frequency doubling crystals and OPOs can be selected to obtain a set of suitable wavelength division multiplexing wavelength distributions λ ₁ , λ ₂ , λ ₃ ,..., λ _{n- 1.} λ _n (n represents the total number of wavelengths of wavelength division multiplexing), the elemental composition of the sample to be measured can be comprehensively obtained through LIBS spectral analysis excited by laser pulses with these wavelength distributions.

The wavelength division multiplexing LIBS method proposed in this patent can significantly improve the detection effect. At the same time, due to the delay and overlap of each laser pulse in the time domain, the plasma induced by the previous laser pulse is injected into the next laser when it is about to cool down. Pulse, can detect significantly signal-to-noise ratio.

Claims (2)

1. one kind based on wavelength-division multiplex and the overlapping Laser-induced Breakdown Spectroscopy system of time domain, it comprises ratio spectroscope, high-energy solid pulse laser, time delay optical module, optical delay line, frequency-doubling crystal or optical parametric oscillator, total reflective mirror, half-reflecting half mirror, dichroic mirror, Multicolour mirror, catoptron with holes, optical fiber ICCD spectrometer, computing machine and condenser lens, it is characterized in that:

Sending a branch of wavelength by high-energy solid pulse laser (2) is λ ₁Nanosecond pulse laser, be divided into two-way through 1 than n-1 ratio spectroscope (1), seeing through 1 is λ than the wavelength of n-1 ratio spectroscope (1) ₁Account for first laser pulse of the n of laser gross energy/mono-through Multicolour mirror B(20) at first arrive condenser lens (19), pass the aperture at catoptron with holes (18) center after line focus, arrive sample target (16) surface, the sample target is induced the generation plasma through laser pulse; Laser pulse is induced the LIBS signal of generation, and through catoptron with holes (18) reflection, lens (17) focus on the subsidiary fibre-optical probe end face of optical fiber ICCD spectrometer (14), and what optical fiber ICCD spectrometer (14) will be accepted is λ by wavelength ₁The LIBS signal data that produces of induced with laser be sent to computing machine (15);

Through 1, than the wavelength of n-1 ratio spectroscope (1) reflection, be λ ₁The laser pulse that accounts for the n/n-1 of laser gross energy enter first group of time delay optical module (3) and see through first group of frequency-doubling crystal or optical parametric oscillator (6) to change wavelength into be λ ₂Laser pulse, through n-2 than 1 ratio spectroscope (9) be divided into the reflection and the transmission two-way, the wavelength wherein obtained by reflection is λ ₂Second laser pulse of one of n that energy is the laser total amount is by Multicolour mirror A(12) and Multicolour mirror B(20) by lens (19), focused on after reflection, laser pulse after focusing is through the aperture at catoptron with holes (8) center, arrive sample target (16) surface, the sample target is induced the generation plasma through laser pulse; Laser pulse is induced the LIBS signal of generation, and through catoptron with holes (18) reflection, lens (17) focus on the subsidiary fibre-optical probe end face of optical fiber ICCD spectrometer (14), and what optical fiber ICCD spectrometer (14) will be accepted is λ by wavelength ₂The LIBS signal data that produces of induced with laser be sent to computing machine (15); Now because laser pulse has passed through time delay τ, guarantee that the sample target induces the plasma of generation to be about to when cooling be injected into second laser pulse at first laser pulse;

Through n-2, than the wavelength of 1 ratio spectroscope (9) transmission, be λ ₂The laser pulse of n/n-2 that energy is the laser total amount through second group of time delay optical module (3) and see through second group of frequency-doubling crystal or optical parametric oscillator (6) to change wavelength into be λ ₃Laser pulse, the ratio spectroscope is divided into reflection and transmission two-way, and the wavelength wherein obtained by reflection is λ ₃The 3rd laser pulse of one of n that energy is the laser total amount be for inducing the sample target to produce the LIBS signal, the transmitted light part by the 3rd group of time delay optical module (3) and see through the 3rd group of frequency-doubling crystal or optical parametric oscillator (6) to change wavelength into be λ ₄Laser pulse and light splitting again; By mode work like this until system completes wavelength is λ _N-2Laser pulse conversion, being converted to wavelength through n-2 group time delay optical module (3) and n-2 group frequency-doubling crystal or optical parametric oscillator (6) is λ _N-1Laser pulse be divided into two tunnels through half-reflecting half mirror (11), a road of reflection is for to provide by wavelength be λ _N-1The LIBS signal of generation that laser is induced, it is λ that a route n-1 group time delay optical module (3) of transmission and n-1 group frequency-doubling crystal or optical parametric oscillator (6) are treated to wavelength _nLaser pulse, be used for inducing sample target generation-LIBS signal after total reflective mirror (10) reflection; Like this, system has obtained one group and has been respectively λ for the wavelength of inducing the sample target to produce the LIBS signal ₁, λ ₂, λ ₃..., λ _N-1, λ _nLaser pulse, wherein n is the total number of wavelength-division multiplex wavelength that system is selected.

2. according to claim 1 a kind of based on wavelength-division multiplex and the overlapping Laser-induced Breakdown Spectroscopy system of time domain, it is characterized in that: described time delay optical module (3) is by incidence reflection mirror (3.1), prism (3.2) and outgoing catoptron (3.3) form, n-1 prism (3.2) in all n-1 group time delay optical modules (3) all passes through same support (5) and is arranged on unique optical delay line (4), the distance of prism (3.2) and incidence reflection mirror (3.1) and outgoing catoptron (3.3) in all time delay optical modules of the meticulous adjusting of optical delay line (4) (3), come to realize the identical time delay of all adjacent laser pulses by changing light path.

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