CN115295395B - Ionization source based on LIBS and SLRI - Google Patents

Abstract

The invention discloses an ionization source based on LIBS and SLRI. The ionization source consists of a controller, a LIBS subsystem, a SLRI subsystem, a timing controller and a sample cabin. The beneficial effect of the present invention is that the ionization source is based on the LIBS laser and the secondary laser resonance ionization SLRI. When realizing the primary ionization of LIBS, preliminary analysis of the composition and content of elements can be simultaneously realized; the isotopes corresponding to the elements obtained based on the first LIBS With prior knowledge of atomic energy levels, the resonance wavelength can be selected first during secondary resonance ionization. The four-channel SLRI optical path configuration enables tunable laser output from ultraviolet to infrared, which can meet the mass spectrometry measurement requirements of all isotope shifts and atomic ultra-fine structures.

Description

An ionization source based on LIBS and SLRI

Technical field

The invention relates to a mass spectrometry ionization source, in particular to an isotope mass spectrometry laser ionization source based on LIBS (Laser-induced breakdown spectroscopy) and secondary laser resonance ionization SLRI, which belongs to the field of photoelectric detection.

Background technique

Isotope mass spectrometry requires distinguishing isotopes of elements and requires extremely high resolution. It is the hotspot and the highest point in the field of mass spectrometry and belongs to the field of high-end mass spectrometry. Isotope mass spectrometry emerged with the development of nuclear science and industry. So far, isotope mass spectrometry analysis methods such as stable isotope mass spectrometry, isotope ratio mass spectrometry, accelerator mass spectrometry, static analysis mass spectrometry, thermal ionization mass spectrometry, and secondary ion mass spectrometry have emerged. It is worth noting that the development of laser technology has greatly enriched the varieties and rapidly improved the performance. A suitable laser source is an excellent mass spectrometry ionization source. Technologies that use lasers as mass spectrometry analysis and ionization methods are becoming increasingly abundant. Matrix assisted laser desorption ionization (Matrix assisted laserdesorption ionization) mass spectrometry, laser microprobe (Laser microprobe) mass spectrometry, laser resonance ionization (Laser resonance ionization) mass spectrometry, laser Lift-off inductively coupled plasma mass spectrometry (LA-ICP-MS) and other laser desorption mass spectrometry technologies.

Laser ionization multiple reflection time-of-flight mass spectrometry is a hot field in mass spectrometry technology. In atomic spectroscopy experiments, due to the selectivity of stimulated transitions of atomic energy levels, laser excitation for stimulated ionization not only improves the ionization efficiency, but also allows ionization at specific wavelengths. Specific elements or isotopes show great development prospects in the nuclear, chemical, and geological industries. For example, in nuclear physics research, it includes the accurate determination of atomic mass, determination of the binding energy and convergence curve of atomic nuclei, and determination of the half-life of radioactive isotopes. Precise measurement of isotope abundance and atomic weight, discovery of natural reactors, nuclear reaction mechanisms, and the relationship between short-lived particles generated by nuclear reactions and their mass. In nuclear science and industry, analysis of ultra-low abundance isotope impurities, burnup and nuclear fuel purity analysis (B, Pb, Sm, Y, Eu, Th). Currently, nuclear science and protection have put forward deeper requirements for the detection of radioactive elements and isotopes.

In response to the above needs, the present invention proposes an isotope mass spectrometry laser ionization source and method that utilizes LIBS laser primary ablation ionization and ultrafast multi-band OPO tuned secondary resonance ionization to meet the needs of high-precision isotope mass spectrometry analysis.

Contents of the invention

The purpose of the present invention is to provide an isotope mass spectrometry laser ionization source and ionization method to achieve efficient ionization of elements and their isotopes, and during ionization, use LIBS spectrum for simultaneous detection to initially obtain the elemental composition and content of the object to be measured.

The present invention is implemented as follows:

The isotope mass spectrometry laser ionization source proposed by the present invention is used to achieve high-efficiency ion resonance excitation required for high-precision isotope analysis, and at the same time meet the needs of optical mass spectrometry analysis; the ionization source is controlled by a controller, a LIBS subsystem, a SLRI subsystem, and a timing sequence. It is composed of instrument and sample cabin.

Among them, the LIBS subsystem consists of a LIBS laser, a spectrometer, an optical fiber, a LIBS focusing mirror, a total reflection mirror, and a fiber coupling mirror. It is used to perform primary ionization excitation on the sample and initially obtain the elemental composition and content of the sample. The LIBS laser is a semiconductor-pumped solid-state laser. The LIBS laser it emits travels along the emission optical axis. After being reflected by the total reflection mirror, it turns to the reflex axis and is focused on the sample in the sample cabin through the upper window through the LIBS focusing mirror. , the high-temperature ablation produced strips off the gasified sample and generates primary ionized air masses. The plasma in the primary ionized air mass cools and transitions to a low level. The radiated light passes upward through the upper window along the main optical axis, is focused and coupled into the fiber surface through the fiber coupling mirror, and then transmitted into the spectrometer and converted into a LIBS spectrum signal.

The SLRI subsystem consists of the first OPO, the first ultrafast pump laser, the second ultrafast pump laser, the second OPO, solid laser, proportional beam splitter, twin dye laser A, total reflective mirror A, twin It consists of a dye laser B, a frequency doubling module, a total mirror B, a two-color film A, a two-color film B, a two-color film C, and an SLRI focusing lens; the SLRI subsystem uses multiple lasers to ionize the primary ionized air mass obtained by ionizing the sample of the LIBS subsystem. Selective secondary resonance excitation and ionization. The first ultrafast pump laser and the second ultrafast pump laser are the same solid laser. The lasers they emit pump the first OPO and the second OPO along the first ionization optical axis and the second ionization optical axis respectively. Road OPO. After being pumped, the first OPO retains the signal light part, which is the first SLRI laser. After being reflected by the dichroic plate, it travels upward along the main optical axis; the second OPO retains the idle frequency after being pumped. The light part is the second SLRI laser. After being reflected by the dichromatic film B, it travels upward along the main optical axis, then passes through the dichromatic film C, and then merges with the first SLRI laser. The laser light emitted by the solid-state laser passes through the proportional beam splitter and pumps the twin dye laser A along the third ionization optical axis to produce a laser with a tunable wavelength in the visible near-red band, which is the third SLRI laser. After reflection by the two-color plate A, It travels upward along the main optical axis, then passes through the dichromatic film B and the dichromatic film C, and then merges with the first and second SLRI lasers; the laser emitted by the solid laser is reflected by the proportional beam splitter and the total reflection mirror A, and then ionizes along the fourth path. The optical axis-pumped twin dye laser B produces a tunable laser in the visible and near-infrared bands that is multiplied by the frequency doubling module to produce a tunable laser in the ultraviolet band, which is the fourth SLRI laser. After being reflected by the total reflective mirror B, It travels upward along the main optical axis, then passes through the two-color film A, two-color film B and two-color film C, and then merges with the first, second and third SLRI lasers. The four-channel SLRI optical path configuration achieves tunable laser output from ultraviolet to infrared, which can meet the secondary laser resonance ionization mass spectrometry measurement of all isotope shifts and atomic ultra-fine structures. After the merged four-channel SLRI laser passes through the SLRI focusing lens and the lower window, it focuses on the primary ionized air mass obtained by ionizing the sample in the LIBS subsystem, and performs selective secondary resonance excitation and ionization.

There is a sample electrode in the sample cabin, and the sample is installed on the sample electrode. The sample electrode can apply a certain DC bias voltage to form a DC electric field between the sample electrode of the back-end mass spectrometer system to attract the ionized ions into the back-end mass spectrometer system for analysis. The sample chamber has a lower window and an upper window to facilitate the entry of ionizing lasers emitted by the LIBS subsystem and SLRI subsystem, and the passage of LIBS-induced plasma radiation light.

The timing controller is used to start and control the timing relationship between the LIBS laser, the spectrometer, the first ultrafast pump laser, the second ultrafast pump laser, and the solid-state laser.

The controller is used to turn on the timing controller and receive the LIBS spectrum data of the spectrometer for analysis. The controller is also used to tune the four SLRI output wavelengths of the first OPO, the second OPO, twin dye laser A, and twin dye laser B.

The isotope mass spectrometry laser ionization method proposed by the present invention includes the following steps:

(1)LIBS preliminary elemental analysis

The controller issues instructions to start the sequence controller. The timing controller controls to turn on the LIBS laser and turn on the spectrometer light receiving signal after a certain delay. The LIBS laser emitted by the LIBS laser is focused onto the sample, generating primary ionized air masses and simultaneously generating LIBS radiation. The radiated light is transmitted into the spectrometer and converted into a LIBS spectrum signal, which is received by the spectrometer. The spectrometer sends the LIBS spectrum signal to the controller, and the controller analyzes the elemental composition of the sample based on the spectrum signal.

(2)SLRI laser wavelength selection

The controller obtains the elemental composition of the sample based on the first step, and calculates the optimal set of resonance excitation wavelengths corresponding to the isotopes of these elements based on the isotope atomic spectral parameters. Then, the controller tunes the four SLRI output wavelengths, which include all wavelengths in the optimal excitation wavelength set. The timing controller controls to simultaneously turn on the first ultrafast pump laser, the second ultrafast pump laser, and the solid laser.

(3)SLRI secondary ionization

After the four SLRI lasers are merged, through the SLRI focusing lens and the lower window, they focus on the primary ionized air mass obtained by ionizing the sample in the LIBS subsystem, and perform selective secondary resonance excitation to make particles that are not fully ionized for the first time, especially isotopes. , obtain the second full ionization, and then, under the acceleration of the DC electric field between the sample electrode and the back-end mass spectrometry system injection electrode, enter the back-end mass spectrometry system for analysis along the injection axis.

The beneficial effect of the present invention is that the ionization source is based on the LIBS laser and the secondary laser resonance ionization SLRI. When realizing the primary ionization of LIBS, preliminary analysis of the composition and content of elements can be simultaneously realized; the isotopes corresponding to the elements obtained based on the first LIBS With prior knowledge of atomic energy levels, the resonance wavelength can be selected first during secondary resonance ionization. The four-channel SLRI optical path configuration enables tunable laser output from ultraviolet to infrared, which can meet the mass spectrometry measurement requirements of all isotope shifts and atomic ultra-fine structures.

Description of drawings

Figure 1 is a schematic structural diagram of the system of the present invention. In the figure: 1 - controller; 2 - LIBS laser; 3 - sample electrode; 4 - timing controller; 5 - first OPO; 6 - first Ultrafast pump laser; 7—the first ionization optical axis; 8—the second ultrafast pump laser; 9—the second ionization optical axis; 10—the second OPO; 11—the third Ionization optical axis; 12 - solid laser; 13 - fourth ionization optical axis; 14 - proportional beam splitter; 15 - twin dye laser A; 16 - total reflection mirror A; 17 - twin dye laser B; 18——Frequency doubling module; 19——Total reflective mirror B; 20——Double-color film A; 21-Double-color film B; 22-Double-color film C; 23—SLRI focusing lens; 24—Lower window; 25 ——sample cabin; 26——sample; 27——sampling axis; 28——primary ionized air mass; 29——upper window; 30——reflection axis; 31——LIBS focusing mirror; 32——emission optical axis ; 33 - Total reflective mirror C; 34 - LIBS subsystem; 35 - Fiber coupling mirror; 36 - Spectrometer; 37 - Main optical axis; 38 - Optical fiber; 39 - SLRI subsystem.

Note: OPO, optical parametric oscillator; SLRI, Secondary laser resonance ionization, referred to as SLRI.

Detailed ways

The specific implementation mode of the present invention is shown in Figure 1.

The isotope mass spectrometry laser ionization source proposed by the present invention is used to achieve high-efficiency ion resonance excitation required for high-precision isotope analysis, and at the same time meet the needs of optical mass spectrometry analysis; the ionization source is composed of a controller 1, a LIBS subsystem 34, and an SLRI subsystem 39 , timing controller 4, and sample cabin 25.

Among them, the LIBS subsystem 34 is composed of a LIBS laser 2, a spectrometer 36, an optical fiber 38, a LIBS focusing mirror 31, a total reflective mirror 33, and a fiber coupling mirror 35. It is used to perform primary ionization excitation on the sample 26 and initially obtain the sample. The elemental composition and content of 26. The LIBS laser 2 is a semiconductor pumped solid laser. The LIBS laser it emits (in this embodiment, the emission wavelength is 1064 nm, the repetition frequency is 300 Hz, and the pulse width is 400 ps) travels along the emission optical axis 32 and is reflected by the total reflective mirror 33 before turning to The reflection axis 30 is focused on the sample 26 in the sample chamber 25 through the upper window 29 through the LIBS focusing mirror 31, and the generated high-temperature ablation peels off the gasified sample and generates primary ionized air mass 28. The plasma in the primary ionized air mass 28 cools and transitions to a low level. The radiated light passes upward through the upper window 29 along the main optical axis 37, is focused and coupled into the end face of the optical fiber 38 through the fiber coupling mirror 35, and is then transmitted into the spectrometer 36 and converted into a LIBS spectrum. Signal.

SLRI subsystem 39 consists of the first OPO5, the first ultrafast pump laser 6, the second ultrafast pump laser 8, the second OPO10, the solid laser 12, the proportional beam splitter 14, the twin dye laser A 15, It consists of total mirror A 16, twin dye laser B 17, frequency doubling module 18, total mirror B 19, dichromatic film A 20, dichromatic film B 21, dichromatic film C 22, and SLRI focusing lens 23; the SLRI subsystem 39 adopts a multi-color film The laser ionizes the primary ionized air mass 28 obtained by ionizing the sample 26 by the LIBS subsystem 34 for selective secondary resonance excitation and ionization. The first ultrafast pump laser 6 and the second ultrafast pump laser 8 are the same solid laser, and the laser they emit (in this embodiment, the wavelength is 1064nm, the repetition frequency is 80MHz, and the pulse width is 15ps), respectively along the first The ionization optical axis 7 and the second ionization optical axis 9 pump the first OPO5 and the second OPO10. After being pumped, the first OPO5 retains the signal light part (the tunable wavelength range of this embodiment is 1400 to 2000nm, and the pulse width is 15ps), which is the first SLRI laser. After being reflected by the dichromatic film C22, The main optical axis 37 travels upward; after being pumped, the second OPO10 retains the idler frequency light part (the tunable wavelength range of this embodiment is 2200 to 4200nm, and the pulse width is 20ps), which is the second SLRI laser. After being reflected by the dichromatic piece B 21, it travels upward along the main optical axis 37, passes through the dichromatic piece C 22, and then merges with the first SLRI laser. The laser light emitted by the solid laser 12 (in this embodiment has a wavelength of 532 nm, a repetition frequency of 20 kHz, and a pulse width of 50 ps) passes through the proportional beam splitter 14 and pumps the twin dye laser A 15 along the third ionization optical axis 11 to generate a tunable wavelength It can be seen that the laser in the near-red band (the wavelength range of this embodiment is 450-850nm) is the third SLRI laser. After being reflected by the two-color film A 20, it travels upward along the main optical axis 37, and then passes through the two-color film B 21 and the two-color film A. After C 22, it merges with the first and second SLRI lasers; after the laser emitted by the solid laser 12 is reflected by the proportional beam splitter 14 and the total reflective mirror A 16, it pumps the twin dye laser B 17 (twin dye) along the fourth ionization optical axis 13 Laser A 15 and pump twin dye laser B 17 are dye lasers with the same parameters), and the generated tunable laser in the visible and near-infrared band is multiplied by the frequency doubling module 18 to produce an ultraviolet band (the wavelength range of this embodiment is 225-225 425nm) tunable laser, which is the fourth SLRI laser. After being reflected by the total mirror B 19, it travels upward along the main optical axis 37, and then passes through the bicolor film A 20, the bicolor film B 21 and the bicolor film C 22, and then The first, second and third SLRI laser paths converge. The four-channel SLRI optical path configuration realizes tunable laser output from ultraviolet to infrared (wavelength range 225-4200 nm in this embodiment), which can meet the secondary laser resonance ionization mass spectrometry measurement of all isotope shifts and atomic ultra-fine structures. After the merged four-channel SLRI laser passes through the SLRI focusing lens 23 and the lower window 24, it is focused on the primary ionized air mass 28 obtained by ionizing the sample 26 in the LIBS subsystem 34, and performs selective secondary resonance excitation and ionization.

There is a sample electrode 3 in the sample compartment 25, and a sample 26 is installed on the sample electrode 3. A certain DC bias voltage can be applied to the sample electrode 3 to form a DC electric field between the sample electrode 3 and the injection electrode of the back-end mass spectrometry system to attract the ionized ions into the back-end mass spectrometry system for analysis. The sample cabin 25 has a lower window 24 and an upper window 29 to facilitate the entry of the ionizing laser emitted by the LIBS subsystem 34 and the SLRI subsystem 39 and the passage of the LIBS-induced plasma radiation light.

The timing controller 4 is used to start and control the timing relationship between the LIBS laser 2, the spectrometer 36, the first ultrafast pump laser 6, the second ultrafast pump laser 8, and the solid-state laser 12.

The controller 1 is used to turn on the timing controller 4 and receive the LIBS spectrum data of the spectrometer 36 for analysis. The controller 1 is also used to tune the four SLRI output wavelengths of the first OPO5, the second OPO10, twin dye laser A 15, and twin dye laser B 17.

The isotope mass spectrometry laser ionization method proposed by the present invention includes the following steps:

(1)LIBS preliminary elemental analysis

Controller 1 issues an instruction to start sequence controller 4. The timing controller 4 controls to turn on the LIBS laser 2, and after a certain delay (10 microseconds in this embodiment), turns on the spectrometer 36 to expose and receive signals. The LIBS laser emitted by the LIBS laser 2 is focused on the sample 26 to generate primary ionized air mass 28 and at the same time generate LIBS radiation. The radiated light is transmitted into the spectrometer 36 and converted into a LIBS spectrum signal, which is received by the spectrometer 36 . The spectrometer 36 sends the LIBS spectrum signal to the controller 1, and the controller 1 analyzes the elemental composition of the sample 26 based on the spectrum signal.

(2)SLRI laser wavelength selection

The controller 1 obtains the elemental composition of the sample 26 according to the first step, and calculates the optimal set of resonance excitation wavelengths corresponding to the isotopes of these elements based on the isotope atomic spectrum parameters. Then, controller 1 tunes four SLRI output wavelengths, and the output wavelengths include all wavelengths in the optimal excitation wavelength set. The timing controller 4 controls the first ultrafast pump laser 6, the second ultrafast pump laser 8, and the solid-state laser 12 to be turned on at the same time.

(3)SLRI secondary ionization

After the four SLRI lasers are merged, they are focused on the primary ionized air mass 28 obtained by ionizing the sample 26 by the LIBS subsystem 34 through the SLRI focusing lens 23 and the lower window 24, and perform selective secondary resonance excitation, so that the first ionization is insufficient. The particles, especially the isotopes, are fully ionized for the second time, and then, under the acceleration of the DC electric field between the sample electrode 3 and the injection electrode of the back-end mass spectrometry system, they enter the back-end mass spectrometry system for analysis along the injection axis 27.

Claims (1)

1. An ionization source based on LIBS and SLRI, consisting of a controller (1), a LIBS subsystem (34), a SLRI subsystem (39), a timing controller (4), and a sample cabin (25); characterized by: : The LIBS subsystem (34) consists of a LIBS laser (2), a spectrometer (36), an optical fiber (38), a LIBS focusing mirror (31), a total reflective mirror (33), and a fiber coupling mirror (35). (26) performs the same amount of primary ionization excitation to initially obtain the elemental composition and content of the sample (26); the LIBS laser (2) is a semiconductor pumped solid laser, and the LIBS laser it emits travels along the emission optical axis (32). After reflection by the total mirror C (33), it turns to the reflection axis (30), passes through the upper window (29) through the LIBS focusing mirror (31) and focuses on the sample (26) in the sample cabin (25), resulting in High-temperature ablation strips off the gasified sample and generates a primary ionized air mass (28); the plasma in the primary ionized air mass (28) cools and transitions to a low level, and the radiated light passes upward along the main optical axis (37) through the upper window (29) , is focused and coupled into the end face of the optical fiber (38) through the fiber coupling mirror (35), and then transmitted into the spectrometer (36) and converted into a LIBS spectrum signal; The SLRI subsystem (39) consists of the first OPO (5), the first ultrafast pump laser (6), the second ultrafast pump laser (8), the second OPO (10), the solid laser ( 12), proportional beam splitter (14), twin dye laser A (15), total reflective mirror A (16), twin dye laser B (17), frequency doubling module (18), total reflective mirror B (19), two-color It consists of chip A (20), two-color chip B (21), two-color chip C (22), and an SLRI focusing lens (23); the SLRI subsystem (39) uses multiple lasers to ionize the LIBS subsystem (34) to the sample (26) The obtained primary ionized air mass (28) is subjected to selective secondary resonance excitation and ionization; the first ultrafast pump laser (6) and the second ultrafast pump laser (8) are the same solid laser, and they emit The laser pumps the first OPO (5) and the second OPO (10) along the first ionization optical axis (7) and the second ionization optical axis (9) respectively; the first OPO (5) is pumped After pumping, the signal light part is retained, which is the first SLRI laser. After being reflected by the dichroic plate C (22), it travels upward along the main optical axis (37); the second OPO (10) retains the free signal after being pumped. The frequency light part is the second SLRI laser. After being reflected by the double-color piece B (21), it travels upward along the main optical axis (37), then passes through the double-color piece C (22), and then merges with the first SLRI laser; The laser light emitted by the solid laser (12) passes through the proportional beam splitter (14), pumps the twin dye laser A (15) along the third ionization optical axis (11), and generates laser light with a tunable wavelength in the visible near-red band, which is the third The three-channel SLRI laser, after being reflected by the two-color piece A (20), travels upward along the main optical axis (37), and then passes through the two-color piece B (21) and the two-color piece C (22), and then connects with the first and second-line SLRI lasers. Convergence; after the laser light emitted by the solid laser (12) is reflected by the proportional beam splitter (14) and the total reflection mirror A (16), the twin dye laser B (17) is pumped along the fourth ionization optical axis (13), and the resulting After the tuned laser in the visible and near-infrared bands is doubled by the frequency doubling module (18), a tunable laser in the ultraviolet segment is generated, which is the fourth SLRI laser. After being reflected by the total reflective mirror B (19), it is reflected along the main optical axis (37 ) travels upward, and then passes through the two-color plate A (20), the two-color plate B (21) and the two-color plate C (22), and then merges with the first, second and third SLRI lasers; the optical path configuration of the four-way SLRI realizes ultraviolet to infrared The tunable laser output can meet the secondary laser resonance ionization mass spectrometry measurement of all isotope shifts and atomic ultra-fine structures; the combined four SLRI lasers are focused on LIBS after passing through the SLRI focusing lens (23) and the lower window (24) The primary ionized air mass (28) obtained by the subsystem (34) ionizing the sample (26) performs selective secondary resonance excitation and ionization; There is a sample electrode (3) in the sample cabin (25), and a sample (26) is installed on the sample electrode (3). A certain DC bias voltage can be applied to the sample electrode (3) to form a gap between the sample electrode (3) and the injection electrode of the back-end mass spectrometer system. DC electric field to attract ionized ions into the back-end mass spectrometer system for analysis; the sample cabin (25) has a lower window (24) and an upper window (29) to facilitate the emission of the LIBS subsystem (34) and the SLRI subsystem (39) The ionizing laser enters, and the LIBS-induced plasma radiation light passes out; The timing controller (4) is used to turn on and control the LIBS laser (2), the spectrometer (36), the first ultrafast pump laser (6), the second ultrafast pump laser (8), and the solid-state laser (12 ) timing relationship of startup; The controller (1) is used to turn on the timing controller (4) and receive the LIBS spectrum data of the spectrometer (36) for analysis; the controller (1) is also used to tune the first OPO (5) and the second OPO (10 ), the four-channel SLRI output wavelengths of twin dye laser A (15) and twin dye laser B (17).