A laser isotope mass spectrometer

Abstract

This invention discloses a laser isotope mass spectrometer, which consists of a controller, a LIBS subsystem, an SLRI subsystem, a timing controller, an ion transport primary focusing module, and a TOF mass analyzer. The beneficial effects of this invention are that the combination of LIBS laser and secondary laser resonance ionization (SLRI) allows for simultaneous preliminary analysis of elemental composition and content during the first LIBS ionization; based on the prior knowledge of the isotopic atomic energy levels of elements obtained from the first LIBS ionization, the resonance wavelength can be preferentially selected during the secondary resonance ionization. The four-channel SLRI optical path configuration enables tunable laser output from ultraviolet to infrared, and the application of ion focusing mirrors and reflectors enables spatiotemporally synchronized focusing and high-resolution mass sensing.

Description

Technical Field

[0001] This invention relates to a mass spectrometer, and more particularly to a TOF isotope mass spectrometer based on LIBS (Laser-induced breakdown spectroscopy) and secondary laser resonance ionization (SLRI), belonging to the field of photoelectric detection. Background Technology

[0002] Isotope mass spectrometry requires distinguishing isotopes of elements and demands extremely high resolution, making it a hot topic and pinnacle in the field of mass spectrometry, belonging to the high-end mass spectrometry domain. Isotope mass spectrometry arose alongside the development of nuclear science and the nuclear industry. To date, various isotope mass spectrometry analysis methods have emerged, including stable isotope mass spectrometry, isotope ratio mass spectrometry, accelerator mass spectrometry, static analysis mass spectrometry, thermal ionization mass spectrometry, and secondary ion mass spectrometry. Notably, the development of laser technology has greatly enriched the variety of methods and rapidly improved performance. A suitable laser source is a high-performance mass spectrometry ionization source. The technology of using lasers as a mass spectrometry resolution and ionization method is becoming increasingly diverse, resulting in various laser resolution mass spectrometry techniques such as matrix-assisted laser desorption / ionization (LA-ICP-MS), laser microprobe mass spectrometry, laser resonance ionization mass spectrometry, and LA-ICP-MS.

[0003] Laser-induced multiple reflection time-of-flight mass spectrometry (LAMS), a hot topic in mass spectrometry, offers significant potential in atomic spectroscopy experiments. Due to the selectivity of stimulated transitions in atomic energy levels, laser excitation for stimulated ionization not only improves ionization efficiency but also allows for the ionization of specific elements or isotopes at specific wavelengths, demonstrating immense development prospects in the nuclear, chemical, and geological industries. In nuclear physics research, applications include the precise determination of atomic mass, the measurement of binding energy and convergence curves of atomic nuclei, and the determination of the half-life of radioactive isotopes. Precise measurements of isotopic abundance and atomic weight are crucial for discovering natural nuclear reactors, understanding nuclear reaction mechanisms, and the relationship between the mass of short-lived particles generated in nuclear reactions. In nuclear science and the nuclear industry, applications include the analysis of ultra-low abundance isotopic impurities, burnup analysis, and nuclear fuel purity analysis (B, Pb, Sm, Y, Eu, Th). Currently, nuclear science and protection place even deeper demands on the detection of radioactive elements and isotopes.

[0004] To address the above requirements, this invention proposes an isotope mass spectrometer that utilizes LIBS laser ablation ionization, ultrafast multi-band OPO tuned secondary resonance ionization, and W-shaped TOF mass spectrometry analysis to meet the needs of high-precision isotope analysis. Summary of the Invention

[0005] The purpose of this invention is to provide a laser isotope mass spectrometer that enables efficient ionization of elements and their isotopes. Simultaneously, LIBS spectroscopy is used for synchronous detection to initially obtain the elemental composition and content of the analyte, and then a TOF mass analyzer is used for precise quantification.

[0006] This invention is implemented as follows:

[0007] The laser isotope mass spectrometer proposed in this invention can simultaneously meet the needs of optical mass spectrometry analysis. The mass spectrometer consists of a controller, a LIBS subsystem, an SLRI subsystem, a timing controller, an ion transport primary focusing module, and a TOF mass analyzer.

[0008] The LIBS subsystem consists of a LIBS laser, a spectrometer, optical fiber, a LIBS focusing mirror, a total reflection mirror C, and a fiber coupler. It is used to perform primary ionization excitation on the sample to initially obtain its elemental composition and content. The LIBS laser is a semiconductor-pumped solid-state laser. The emitted LIBS laser travels along the emission optical axis, is reflected by the total reflection mirror C, and then redirects to the reflection axis. It is then focused by the LIBS focusing mirror through the upper window onto the sample in the sample chamber. The resulting high-temperature ablation and vaporization of the sample generates a primary ionized gas cloud. The plasma in the primary ionized gas cloud cools and transitions to a lower order. The emitted light travels upward along the principal optical axis through the upper window, is focused and coupled into the fiber surface by the fiber coupler, and then transmitted to the spectrometer, where it is converted into a LIBS spectral signal.

[0009] The SLRI subsystem consists of a first OPO, a first ultrafast pump laser, a second ultrafast pump laser, a second OPO, a solid-state laser, a proportional beam splitter, twin dye laser A, a total reflection mirror A, a twin dye laser B, a frequency doubling module, a total reflection mirror B, two-color filters A, B, and C, and an SLRI focusing lens. The SLRI subsystem uses multiple lasers to selectively resonate and ionize the primary ionized gas cloud obtained from the ionization of the sample by the LIBS subsystem. The first and second ultrafast pump lasers are identical solid-state lasers, and their emitted lasers pump the first and second OPOs along the first and second ionization optical axes, respectively. After being pumped, the first OPO retains the signal light portion, becoming the first SLRI laser. After being reflected by the dichroic plate C, it travels upward along the principal optical axis. After being pumped, the second OPO retains the idler light portion, becoming the second SLRI laser. After being reflected by the dichroic plate B, it travels upward along the principal optical axis, passes through the dichroic plate C, and then merges with the first SLRI laser. The laser emitted from the solid-state laser passes through a proportional beam splitter and pumps twin dye laser A along the third ionization axis, producing a tunable visible-near-infrared laser, the third SLRI laser. After reflection by dichroic mirror A, it travels upward along the principal axis, then passes through dichroic mirrors B and C, before merging with the first and second SLRI lasers. The laser emitted from the solid-state laser, after being reflected by a proportional beam splitter and total reflection mirror A, pumps twin dye laser B along the fourth ionization axis, producing a tunable visible-near-infrared laser. This tunable visible-near-infrared laser is then frequency-doubled by a frequency doubling module to produce a tunable ultraviolet laser, the fourth SLRI laser. After reflection by total reflection mirror B, it travels upward along the principal axis, then passes through dichroic mirrors A, B, and C, before merging with the first, second, and third SLRI lasers. This four-channel SLRI configuration enables tunable laser output from ultraviolet to infrared, satisfying the requirements for secondary laser resonance ionization mass spectrometry measurements of all isotope shifts and atomic hyperfine structures. After being combined, the four SLRI lasers are focused through the SLRI focusing lens and the lower window onto the primary ionized gas cloud obtained by the LIBS subsystem ionization of the sample, and then selectively resonantly excited and ionized.

[0010] The ion transport focusing module consists of a sample chamber, a sample inlet chamber, an ion funnel chamber, a quadrupole pre-bar chamber, a quadrupole chamber, an octupole chamber, DC power supply A, DC power supply B, a pulsed electric field controller, and molecular pumps A, B, C, D, and A. Molecular pump A is used to evacuate the sample inlet chamber; molecular pump B is used to evacuate the ion funnel chamber; molecular pump C is used to evacuate the quadrupole pre-bar chamber; molecular pump D is used to evacuate the quadrupole chamber; and molecular pump A is used to evacuate the octupole chamber. The sample chamber contains sample electrodes, on which the sample is mounted. The sample chamber has a lower window and an upper window to facilitate the entry of ionizing laser light emitted by the LIBS and SLRI subsystems, and the exit of LIBS-induced plasma radiation. The sample inlet chamber contains conical electrodes A and B, and an inlet orifice. The sample electrodes and the two conical electrodes form a three-electrode system. A DC power supply provides an accelerating electric field between the sample electrode and cone electrode A; a DC power supply B provides an accelerating electric field between cone electrode A and cone electrode B. The positive and negative voltages of DC power supply A are applied under pulsed electric field control. The application time is until the ions continuously ionized by the laser accumulate to a certain concentration. After being accelerated by the electric field of the three-electrode system, the ions enter the ion funnel cavity through the sample inlet. The ion funnel cavity contains a trap-shaped ion funnel for pre-focusing the incoming ions; the quadrupole pre-bar cavity contains a quadrupole pre-bar, the quadrupole cavity contains a quadrupole, and the octupole cavity contains an octupole; these three are connected in series for further focusing of the incoming ions.

[0011] The Time-of-Flight (TOF) mass analyzer consists of a molecular pump B, an ion focusing mirror A, a bottom ion reflector, a bottom electric field controller, a flight inlet, an orthogonal electric field controller, a repulsion electrode, a top electric field controller, a top ion reflector, an ion focusing mirror C, a cascaded MCP, a signal processing circuit, an ion focusing mirror D, and an ion focusing mirror B. Molecular pump B is used to evacuate the TOF mass analyzer. Ions exiting the octupole enter the TOF mass analyzer through the flight inlet. The orthogonal electric field controller applies an orthogonal electric field perpendicular to the incident ions at the repulsion electrode. After entering the TOF mass analyzer, the ions change their flight direction under the influence of the orthogonal electric field and fly along flight axis A. Simultaneously, ion focusing mirror A constrains the ion flight space, causing them to enter the bottom ion reflector. The bottom ion reflector is controlled by the bottom electric field controller, which applies an electric field consisting of two fields (deceleration / acceleration and reflection). Ions with higher kinetic energy enter the reflector first, followed by ions with lower kinetic energy. The former, due to its greater kinetic energy, penetrates deeper into the reflector than the latter, resulting in a longer residence time within the reflector. Appropriate selection of potential and size can compensate for the shorter flight time of high-energy ions in the field-free drift region by the longer residence time in the reflector. After being reflected by the bottom ion reflector, the ions turn towards flight axis B and, after being spatially constrained by ion focusing lens B, enter the top ion reflector. The top ion reflector is controlled by a top electric field controller; similarly, the electric field applied by the top electric field controller also consists of two electric fields (deceleration / acceleration and reflection). After being reflected by the top ion reflector, the ions turn towards flight axis C and, after being spatially constrained by ion focusing lens C, enter the bottom ion reflector. After being reflected again, they turn towards flight axis D and, after being spatially constrained by ion focusing lens D, enter the cascaded MCP. After being sensed by the cascaded MCP, an electrical signal is generated and sent to the signal processing circuit. The signal processing circuit extracts the flight time of different ions from the signal, converts the flight time into the ion's mass and charge value, and sends this data to the controller, thereby achieving accurate analysis of the sample's constituent elements and isotopes. In the TOF mass analyzer, flight axis A, flight axis B, flight axis C, and flight axis D form a W-shaped geometric configuration in space.

[0012] The timing controller is used to start and control the timing relationship of the LIBS laser, spectrometer, first ultrafast pump laser, second ultrafast pump laser, and solid-state laser.

[0013] The controller is used to turn on the timing controller, receive LIBS spectral data from the spectrometer for analysis; to tune the four SLRI output wavelengths of the first OPO, the second OPO, twin dye laser A, and twin dye laser B; and to turn on the signal processing circuit and receive its data for isotope content analysis.

[0014] The laser isotope mass spectrometry analysis method proposed in this invention includes the following steps:

[0015] (1) Instrument initialization

[0016] Start molecular pumps A, B, C, D, A, and B until the sample injection chamber, ion funnel chamber, quadrupole pre-bar chamber, quadrupole chamber, octupole chamber, and TOF mass analyzer are close to a vacuum state. Turn on the pulse electric field controller, DC power supply B, bottom electric field controller, orthogonal electric field controller, and top electric field controller.

[0017] (2) Preliminary elemental analysis of LIBS

[0018] The controller issues a command to activate the timing controller. The timing controller activates the LIBS laser and, after a certain delay, activates the spectrometer's light receiving signal. The LIBS laser emitted by the LIBS laser is focused onto the sample, generating a primary ionized gas cloud and simultaneously producing LIBS radiation. This radiation is transmitted to the spectrometer, converted into a LIBS spectral signal, and received by the spectrometer. The spectrometer sends the LIBS spectral signal to the controller, which analyzes the elemental composition of the sample based on this signal.

[0019] (3) SLRI laser wavelength selection

[0020] Based on the elemental composition of the sample obtained in the first step, the controller calculates the optimal resonant excitation wavelength set corresponding to the isotopes of these elements according to the isotopic 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 simultaneously activates the first ultrafast pump laser, the second ultrafast pump laser, and the solid-state laser.

[0021] (4) SLRI secondary ionization

[0022] After the four SLRI lasers are combined, they are focused through the SLRI focusing lens and lower window onto the primary ionized gas cloud obtained from the LIBS subsystem's ionization of the sample. This allows for selective secondary resonance excitation, enabling particles, especially isotopes, that were not fully ionized in the first ionization to undergo a second, more complete ionization.

[0023] The pulsed electric field controller sends out control pulses, which instantaneously provide positive and negative voltages to DC power supply A, forming a pulsed accelerating electric field between the sample electrode and the conical electrode A. Under the acceleration of this electric field, the ions, which are fully ionized twice, enter the ion transport primary focusing module along the sample introduction axis.

[0024] (5) Ion transport initial focusing

[0025] Ions enter the ion transport initial focusing module, and after passing through the trap-shaped ion funnel, quadrupole pre-focusing bar, quadrupole, and octupole initial focusing bar, they enter the TOF mass analyzer through the flight port.

[0026] (6) W-shaped TOF quality analysis

[0027] After entering the TOF mass analyzer through the flight inlet, ions are first repelled by the repulsion poles, then focused by ion focusing lens A into the bottom ion reflector. Reflected by the bottom ion reflector and then focused by ion focusing lens B into the top ion reflector, they are reflected again by the top ion reflector and focused by ion focusing lens C into the bottom ion reflector. Finally, reflected by the bottom ion reflector and focused by the flight axis D into the cascaded MCP. After sensing by the cascaded MCP, the signal is sent to the signal processing circuit, which sends the ion mass and charge data to the controller. The controller calculates the elemental composition and isotopic content of the sample.

[0028] The beneficial effects of this invention are that the ionization source is based on a combination of LIBS laser and secondary laser resonant ionization (SLRI). During the first LIBS ionization, preliminary analysis of elemental composition and content can be simultaneously achieved. Based on the prior knowledge of the isotopic atomic energy levels corresponding to the elements obtained from the first LIBS ionization, the resonant wavelength can be preferentially selected during the secondary resonant ionization. The four-channel SLRI optical path configuration enables tunable laser output from ultraviolet to infrared, and the application of ion focusing mirrors and reflectors enables spatiotemporally synchronized focusing for high-resolution quality sensing. Attached Figure Description

[0029] Figure 1This is a schematic diagram of the system structure 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—First ionization axis; 8—Second ultrafast pump laser; 9—Second ionization axis; 10—Second OPO; 11—Third ionization axis; 12—Solid-state laser; 13—Fourth ionization 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 reflection mirror B; 20—Dichroic plate A; 21—Dichroic plate B; 22—Dichroic plate C; 23—SLRI focusing lens; 24—Lower window; 25—Sample chamber; 26—Sample; 27—Sample entry axis; 28—Primary ionized gas cloud; 29—Upper window; 30—Calibration axis; 31—LIBS focusing mirror; 32—Emission axis; 33—Total reflection mirror C; 34—LIBS subsystem; 35—Fiber optic coupler; 36—Spectrometer; 37—Main optical axis; 38—Fiber optic cable; 39—SLRI subsystem; 4 0 – DC power supply B; 41 – DC power supply A; 42 – Pulse electric field controller; 43 – Conical electrode A; 44 – Molecular pump A; 45 – Molecular pump B; 46 – Trap-shaped ion funnel; 47 – Ion funnel cavity; 48 – Molecular pump C; 49 – Quadrupole pre-barrel cavity; 50 – Molecular pump D; 51 – Molecular pump A; 52 – Conical electrode B; 53 – Sample inlet; 54 – Sample inlet cavity; 55 – Quadrupole pre-barrel; 56 – Quadrupole; 57 – Quadrupole cavity; 58 – Octupleole; 59 – Octupleole cavity; 60 – TOF mass analyzer; 6 1 – Flight axis A; 62 – Molecular pump B; 63 – Ion focusing mirror A; 64 – Bottom ion reflector; 65 – Bottom electric field controller; 66 – Flight inlet; 67 – Orthogonal electric field controller; 68 – Repulsion electrode; 69 – Top electric field controller; 70 – Top ion reflector; 71 – Flight axis C; 72 – Ion focusing mirror C; 73 – Cascaded MCP; 74 – Signal processing circuit; 75 – Ion transport primary focusing module; 76 – Ion focusing mirror D; 77 – Flight axis D; 78 – Flight axis B; 79 – Ion focusing mirror B.

[0030] Note: OPO, Optical Parametric Oscillator; SLRI, Secondary Laser Resonance Ionization; TOF, Time of Flight; MCP, Multi-channel Plate. Detailed Implementation

[0031] Specific embodiments of the present invention are as follows Figure 1 As shown.

[0032] The laser isotope mass spectrometer proposed in this invention can simultaneously meet the needs of optical mass spectrometry analysis. The mass spectrometer consists of a controller 1, a LIBS subsystem 34, an SLRI subsystem 39, a timing controller 4, an ion transport initial focusing module 75, and a TOF mass analyzer 60.

[0033] The LIBS subsystem 34 consists of a LIBS laser 2, a spectrometer 36, an optical fiber 38, a LIBS focusing mirror 31, a total reflection mirror C33, and an optical fiber coupler 35. It is used to perform primary ionization excitation on the sample 26 to initially obtain the elemental composition and content of the sample 26. The LIBS laser 2 is a semiconductor-pumped solid-state laser. The emitted LIBS laser (in this embodiment, the emission wavelength is 1064 nm, the repetition rate is 300 Hz, and the pulse width is 400 ps) travels along the emission optical axis 32. After being reflected by the total reflection mirror C33, it is redirected to the reflection axis 30 and focused onto the sample 26 in the sample chamber 25 through the upper window 29 by the LIBS focusing mirror 31. The resulting high-temperature ablation and vaporization of the sample generates a primary ionized gas cloud 28. The plasma in the primary ionized gas cloud 28 cools and transitions to a lower level. 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 by the fiber coupler 35, and then is transmitted into the spectrometer 36 and converted into a LIBS spectral signal.

[0034] The SLRI subsystem 39 consists of a first OPO5, a first ultrafast pump laser 6, a second ultrafast pump laser 8, a second OPO10, a solid-state laser 12, a proportional beam splitter 14, a twin dye laser A 15, a total reflection mirror A 16, a twin dye laser B 17, a frequency doubling module 18, a total reflection mirror B 19, a dichroic plate A 20, a dichroic plate B 21, a dichroic plate C 22, and an SLRI focusing lens 23. The SLRI subsystem 39 uses multiple lasers to selectively excite and ionize the primary ionized gas cloud 28 obtained from the ionization of sample 26 by the LIBS subsystem 34. The first ultrafast pump laser 6 and the second ultrafast pump laser 8 are identical solid-state lasers. The lasers they emit (wavelength 1064nm, repetition rate 80MHz, pulse width 15ps in this embodiment) pump the first OPO5 and the second OPO10 along the first ionization optical axis 7 and the second ionization optical axis 9, respectively. After being pumped, the first OPO5 retains the signal light portion (in this embodiment, its tunable wavelength range is 1400 to 2000 nm, and its pulse width is 15 ps), which is the first SLRI laser. After being reflected by the dichroic plate C22, it travels upward along the main optical axis 37. After being pumped, the second OPO10 retains the idler light portion (in this embodiment, its tunable wavelength range is 2200 to 4200 nm, and its pulse width is 20 ps), which is the second SLRI laser. After being reflected by the dichroic plate B21, it travels upward along the main optical axis 37, passes through the dichroic plate C22, and then merges with the first SLRI laser. The laser emitted by solid-state laser 12 (in this embodiment, wavelength 532nm, repetition rate 20kHz, pulse width 50ps) passes through proportional beam splitter 14 and pumps twin dye laser A 15 along the third ionization optical axis 11, generating a wavelength-tunable visible near-infrared laser (wavelength range 450-850nm in this embodiment), which is the third SLRI laser. After being reflected by dichroic plate A 20, it travels upward along the principal optical axis 37, then passes through dichroic plates B 21 and C 22, and merges with the first and second SLRI lasers. The laser emitted by solid-state laser 12 passes through proportional beam splitter 14 and the full... After reflection by mirror A 16, the twin dye laser B 17 (which uses the same parameters as twin dye laser A 15) is pumped along the fourth ionization optical axis 13. The resulting tunable visible and near-infrared laser is frequency-doubled by frequency-doubler module 18 to produce a tunable ultraviolet laser (wavelength range 225-425nm in this embodiment), which is the fourth SLRI laser. After reflection by total reflection mirror B 19, it travels upward along the main optical axis 37, then passes through dichroic plates A 20, B 21, and C 22, before merging with the first, second, and third SLRI lasers. This four-channel SLRI optical path configuration enables tunable laser output from ultraviolet to infrared (wavelength range 225-4200nm in this embodiment), which can meet the requirements of secondary laser resonance ionization mass spectrometry measurements of all isotope shifts and atomic hyperfine structures.After the four SLRI lasers are combined, they are focused on the primary ionized gas cloud 28 obtained by ionizing sample 26 by LIBS subsystem 34 through SLRI focusing lens 23 and lower window 24, and selective secondary resonance excitation and ionization are performed.

[0035] The ion transport initial focusing module 75 consists of a sample chamber 25, a sample inlet chamber 54, an ion funnel chamber 47, a quadrupole pre-bar chamber 49, a quadrupole chamber 57, an octupole chamber 59, a DC power supply A 41, a DC power supply B 40, a pulsed electric field controller 42, a molecular pump A 44, a molecular pump B 45, a molecular pump C 48, a molecular pump D 50, and a molecular pump A 51. Molecular pump A 44 is used to evacuate the sample inlet chamber 25; molecular pump B 45 is used to evacuate the ion funnel chamber 47; molecular pump C 48 is used to evacuate the quadrupole pre-bar chamber 49; molecular pump D 50 is used to evacuate the quadrupole chamber 57; and molecular pump A 51 is used to evacuate the octupole chamber 59. The sample chamber 25 contains a sample electrode 3, on which a sample 26 is mounted. The sample chamber 25 has a lower window 24 and an upper window 29 to facilitate the entry of ionizing lasers emitted by the LIBS subsystem 34 and the SLRI subsystem 39, and the exit of LIBS-induced plasma radiation. The sample inlet chamber 54 contains a conical electrode A 43, a conical electrode B 52, and an inlet port 53. The sample electrode 3 and the two conical electrodes form a three-electrode system. A DC power supply A 41 provides an accelerating electric field between the sample electrode 3 and the conical electrode A 43; a DC power supply B 40 provides an accelerating electric field between the conical electrode A 43 and the conical electrode B 52. The positive and negative voltages of the DC power supply A 41 are applied by a pulsed electric field controller 42. The application time is until the ions continuously ionized by the laser accumulate to a certain concentration. After being accelerated by the electric field of the three-electrode system, the ions enter the ion funnel chamber 47 through the inlet port 53. The ion funnel cavity 47 contains a trap-shaped ion funnel 46 for pre-focusing incoming ions; the quadrupole pre-rod cavity 49 contains a quadrupole pre-rod 55; the quadrupole cavity 57 contains a quadrupole 56; and the octupole cavity 59 contains an octupole 58. These three are connected in series to further focus incoming ions.

[0036] The TOF mass analyzer 60 consists of a molecular pump B 62, an ion focusing mirror A 63, a bottom ion reflector 64, a bottom electric field controller 65, a flight port 66, an orthogonal electric field controller 67, a repulsion electrode 68, a top electric field controller 69, a top ion reflector 70, an ion focusing mirror C 72, a cascaded MCP 73, a signal processing circuit 74, an ion focusing mirror D 76, and an ion focusing mirror B 79. The molecular pump B 62 is used to evacuate the TOF mass analyzer 60 into a vacuum; ions exiting the octupole 58 enter the TOF mass analyzer 60 through the flight port 66. An orthogonal electric field controller 67 applies an orthogonal electric field perpendicular to the incident ions at the repulsion electrode 68. After entering the TOF mass analyzer 60, the ions change their flight direction under the influence of the orthogonal electric field and fly along the flight axis 61. Simultaneously, the ion focusing mirror 63 constrains the flight space of the ions, causing them to enter the bottom ion reflector 64. The bottom ion reflector 64 is controlled by a bottom electric field controller 65, which applies an electric field consisting of two fields (deceleration / acceleration and reflection). Ions with higher kinetic energy enter the reflector first, followed by ions with lower kinetic energy. The former, due to their higher kinetic energy, enters the reflector more deeply than the latter, resulting in a longer residence time in the reflector. By appropriately selecting the potential and size, the problem of short flight time of high-energy ions in the field-free drift region can be compensated by a longer residence time in the reflector. After being reflected by the bottom ion reflector 64, the ions are directed to fly along the flight axis B 78 and enter the top ion reflector 70 after being spatially constrained by the ion focusing mirror B 79. The top ion reflector 70 is controlled by the top electric field controller 69. Similarly, the electric field applied by the top electric field controller 69 is also composed of two electric fields (deceleration / acceleration and reflection). After being reflected by the top ion reflector 70, the ions are redirected to flight axis C 71 and, after being spatially constrained by ion focusing mirror C 72, enter the bottom ion reflector 64. After being reflected again, they are redirected to flight axis D 77 and, after being spatially constrained by ion focusing mirror D 76, enter the cascaded MCP 73. After being sensed by the cascaded MCP 73, an electrical signal is generated and sent to the signal processing circuit 74. The signal processing circuit 74 extracts the flight time of different ions from the signal, converts the flight time into the mass and charge values ​​of the ions, and sends these data to the controller 1, thereby achieving accurate analysis of the constituent elements and isotopes of sample 26. In the TOF mass analyzer 60, flight axes A 61, B 78, C 71, and D 77 form a W-shaped geometric configuration in space.

[0037] The timing controller 4 is used to start and control the timing relationship of LIBS laser 2, spectrometer 36, first ultrafast pump laser 6, second ultrafast pump laser 8, and solid-state laser 12.

[0038] The controller 1 is used to turn on the timing controller 4, receive LIBS spectral data from the spectrometer 36 for analysis; to tune the four SLRI output wavelengths of the first OPO5, the second OPO10, the twin dye laser A 15, and the twin dye laser B 17; and to turn on the signal processing circuit 74 and receive its data for isotope content analysis.

[0039] The laser isotope mass spectrometry analysis method proposed in this invention includes the following steps:

[0040] (1) Instrument initialization

[0041] Start molecular pumps A (44), B (45), C (48), D (50), A (51), and B (62) until the sample injection chamber (54), ion funnel chamber (47), quadrupole pre-bar chamber (49), quadrupole chamber (57), octupole chamber (59), and TOF mass analyzer (60) are close to a vacuum state. Turn on pulse electric field controller (42), DC power supply B (40), bottom electric field controller (65), orthogonal electric field controller (67), and top electric field controller (69).

[0042] (2) Preliminary elemental analysis of LIBS

[0043] Controller 1 issues a command to activate timing controller 4. Timing controller 4 controls the activation of LIBS laser 2 and, after a certain delay (10 microseconds in this embodiment), activates spectrometer 36 to receive the signal. The LIBS laser emitted by LIBS laser 2 is focused onto sample 26, generating a primary ionized gas cloud 28 and simultaneously producing LIBS radiation. This radiation is transmitted into spectrometer 36, converted into a LIBS spectral signal, and received by spectrometer 36. Spectrometer 36 sends the LIBS spectral signal to controller 1, which analyzes the elemental composition of sample 26 based on this spectral signal.

[0044] (3) SLRI laser wavelength selection

[0045] Based on the elemental composition of sample 26 obtained in the first step, controller 1 calculates the optimal resonant excitation wavelength set corresponding to the isotopes of these elements according to the isotopic atomic spectral parameters. Then, controller 1 tunes the four SLRI output wavelengths, which include all wavelengths in the optimal excitation wavelength set. Timing controller 4 controls the simultaneous activation of the first ultrafast pump laser 6, the second ultrafast pump laser 8, and the solid-state laser 12.

[0046] (4) SLRI secondary ionization

[0047] After the four SLRI lasers are combined, they are focused on the primary ionized gas cloud 28 obtained by ionizing sample 26 through SLRI focusing lens 23 and lower window 24 by LIBS subsystem 34, and selective secondary resonance excitation is performed, so that the particles that were not fully ionized in the first ionization, especially isotopes, are fully ionized in the second ionization.

[0048] The pulse electric field controller 42 sends out control pulses to provide the positive and negative voltages of the DC power supply A 41 instantaneously, forming a pulse acceleration electric field between the sample electrode 3 and the conical electrode A 43. Under the acceleration of this electric field, the ions that have been fully ionized twice enter the ion transport primary focusing module 75 along the sample introduction axis 27.

[0049] (5) Ion transport initial focusing

[0050] Ions enter the ion transport initial focusing module 75, and after being initially focused by the trap-shaped ion funnel 46, the quadrupole pre-focusing rod 55, the quadrupole 56, and the octupole 58, they enter the TOF mass analyzer 60 through the flight inlet 66.

[0051] (6) W-shaped TOF quality analysis

[0052] After entering the TOF mass analyzer 60 through the flight inlet 66, the ions are first repelled and their direction changed by the repulsion electrode 68. Then, they are focused by the ion focusing mirror A 63 into the bottom ion reflector 64. Reflected by the bottom ion reflector 64, they are focused by the ion focusing mirror B 79 into the top ion reflector 70. Reflected by the top ion reflector 70, they are focused by the ion focusing mirror C 72 and re-enter the bottom ion reflector 64. Finally, reflected by the bottom ion reflector 64, they are focused by the flight axis D 77 into the cascaded MCP 73. After sensing by the cascaded MCP 73, the signal is sent to the signal processing circuit 74, which sends the ion mass and charge data to the controller 1. The controller 1 calculates the content of the constituent elements and isotopes of the sample 26.

Claims

1. A laser isotope mass spectrometer, comprising a controller (1), a LIBS subsystem (34), an SLRI subsystem (39), a timing controller (4), an ion transport initial focusing module (75), and a TOF mass analyzer (60); characterized in that: The LIBS subsystem (34) consists of a LIBS laser (2), a spectrometer (36), an optical fiber (38), a LIBS focusing mirror (31), a total reflection mirror C (33), and an optical fiber coupler (35). It is used to perform primary ionization excitation on the sample (26) to obtain the elemental composition and content of the sample (26). The LIBS laser (2) is a semiconductor-pumped solid-state laser. The LIBS laser emitted by the laser travels along the emission optical axis (32), and after being reflected by the total reflection mirror C (33), it is redirected to the reflection point. The optical axis (30) passes through the LIBS focusing lens (31) through the upper window (29) and is focused onto the sample (26) in the sample chamber (25). The high temperature generated ablation and vaporization of the sample produces a primary ionized gas cloud (28). The plasma in the primary ionized gas cloud (28) cools and transitions to a lower level. The radiation 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 coupler (35), and then transmitted into the spectrometer (36) and converted into a LIBS spectral signal. The SLRI subsystem (39) consists of a first OPO (5), a first ultrafast pump laser (6), a second ultrafast pump laser (8), a second OPO (10), a solid-state laser (12), a proportional beam splitter (14), twin dye laser A (15), a total reflection mirror A (16), twin dye laser B (17), a frequency doubling module (18), a total reflection mirror B (19), a two-color plate A (20), a two-color plate B (21), a two-color plate C (22), and an SLRI focusing lens (23). The SLRI subsystem (39) uses multiple lasers to selectively excite and ionize the primary ionized gas cloud (28) obtained by ionizing the sample (26) from the LIBS subsystem (34). The first ultrafast pump laser (6) and the second ultrafast pump laser (8) are the same solid-state lasers. The lasers they emit pump the first OPO (5) and the second OPO (10) along the first ionization optical axis (7) and the second ionization optical axis (9), respectively. After being pumped, the first OPO (5) retains the signal light portion, which becomes the first SLRI laser. After being reflected by the dichroic plate C (22), it travels upward along the principal optical axis (37). After being pumped, the second OPO (10) retains the idler light portion, which becomes the second SLRI laser. After being reflected by the dichroic plate B (21), it travels upward along the principal optical axis (37), passes through the dichroic plate C (22), and then merges with the first SLRI laser. The laser emitted by the device (12) passes through the proportional beam splitter (14) and pumps the twin dye laser A (15) along the third ionization optical axis (11), generating a tunable visible and near-infrared laser with a wavelength range of 450-850nm, which is the third SLRI laser. After being reflected by the dichroic plate A (20), it travels upward along the main optical axis (37), and then passes through the dichroic plate B (21) and dichroic plate C (22) before merging with the first and second SLRI lasers. The laser emitted by the solid-state laser (12) is reflected by the proportional beam splitter (14) and the total reflection mirror A (16), and then pumps the twin dye laser B (17) along the fourth ionization optical axis (13), generating a tunable visible and near-infrared laser, which is frequency-doubled by the frequency doubling module (18). Afterwards, a tunable ultraviolet laser is generated, which is the fourth SLRI laser. After being reflected by the total reflection mirror B (19), it travels upward along the main optical axis (37), and then passes through the two-color plate A (20), two-color plate B (21) and two-color plate C (22) before merging with the first, second and third SLRI lasers. The optical path configuration of the four SLRIs realizes the tunable laser output from ultraviolet to infrared, which can meet the secondary laser resonance ionization mass spectrometry measurement of all isotope shifts and atomic hyperfine structures. After merging, the four SLRI lasers are focused on the primary ionized gas cloud (28) obtained by ionizing the sample (26) by the LIBS subsystem (34) through the SLRI focusing lens (23) and the lower window (24) for selective secondary resonance excitation and ionization. The ion transport pre-focusing module (75) consists of a sample chamber (25), an injection chamber (54), an ion funnel chamber (47), a quadrupole pre-bar chamber (49), a quadrupole chamber (57), an octupole chamber (59), a DC power supply A (41), a DC power supply B (40), a pulsed electric field controller (42), a molecular pump A (44), a molecular pump B (45), a molecular pump C (48), a molecular pump D (50), and a molecular pump A (51); among them, molecular pump A (44) is used to evacuate the injection chamber (54); molecular pump B (45) is used to evacuate the injection chamber (54); and molecular pump B (46) is used to evacuate the injection chamber (54). 45) is used to evacuate the ion funnel cavity (47); molecular pump C (48) is used to evacuate the quadrupole pre-bar cavity (49); molecular pump D (50) is used to evacuate the quadrupole cavity (57); molecular pump A (51) is used to evacuate the octupole cavity (59); the sample chamber (25) contains a sample electrode (3), and a sample (26) is mounted on the sample electrode (3); the sample chamber (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). Ionizing laser light enters and LIBS-induced plasma radiation light exits; the sample inlet cavity (54) contains conical electrode A (43), conical electrode B (52), and sample inlet (53); the sample electrode (3) and the two conical electrodes form a three-electrode system, and DC power supply A (41) provides the accelerating electric field between the sample electrode (3) and conical electrode A (43); DC power supply B (40) provides the accelerating electric field between conical electrode A (43) and conical electrode B (52); the positive and negative voltages of DC power supply A (41) are controlled by the pulsed electric field. The laser (42) is applied for a period of time until the ions continuously ionized by the laser accumulate to a certain concentration. After being accelerated by the electric field of the three-electrode system, the ions enter the ion funnel cavity (47) through the sample inlet (53). The ion funnel cavity (47) contains a trap-shaped ion funnel (46) for pre-focusing the incoming ions. The quadrupole pre-rod cavity (49) contains a quadrupole pre-rod (55), the quadrupole cavity (57) contains a quadrupole (56), and the octupole cavity (59) contains an octupole (58). The three are connected in series to further focus the incoming ions. The TOF mass analyzer (60) consists of a molecular pump B (62), an ion focusing mirror A (63), a bottom ion reflector (64), a bottom electric field controller (65), a flight port (66), an orthogonal electric field controller (67), a repulsion electrode (68), a top electric field controller (69), a top ion reflector (70), an ion focusing mirror C (72), a cascaded MCP (73), a signal processing circuit (74), an ion focusing mirror D (76), and an ion focusing mirror B (79). The molecular pump B (62) is used to evacuate the TOF mass analyzer (60); ions from the octupole (58) enter the TOF mass analyzer (60) through the flight port (66); the orthogonal electric field controller B (67) is used to evacuate the TOF mass analyzer (60). The electric field controller (67) applies an orthogonal electric field perpendicular to the incident ions at the repulsion electrode (68). After the ions enter the TOF mass analyzer (60), they change their flight direction under the action of the orthogonal electric field and fly along the flight axis (61). At the same time, the ion focusing mirror (63) constrains the space in which the ions fly, causing them to enter the bottom ion reflector (64). The bottom ion reflector (64) is controlled by the bottom electric field controller (65). The electric field applied by the bottom electric field controller (65) consists of a deceleration / acceleration electric field and a reflection electric field. Ions with higher kinetic energy enter the reflector first, followed by ions with lower kinetic energy. The former enter the reflector deeper than the latter due to their higher kinetic energy. This results in a longer residence time in the reflector; with appropriate selection of potential and size, the problem of short flight time of high-energy ions in the field-free drift region can be compensated by the longer residence time in the reflector; after being reflected by the bottom ion reflector (64), the ions turn to the flight axis B (78) and fly, and after being spatially constrained by the ion focusing mirror B (79), they enter the top ion reflector (70); the top ion reflector (70) is controlled by the top electric field controller (69), and the electric field applied by the top electric field controller (69) is also composed of a deceleration / acceleration electric field and a reflection electric field; after being reflected by the top ion reflector (70), the ions turn to the flight axis C (71) and fly, and after being spatially constrained by the ion focusing mirror C (72), they enter the top ion reflector (70). After entering the bottom ion reflector (64) and being reflected again, the ion turns to the flight axis (77) and flies. After being spatially constrained by the ion focusing mirror (76), it enters the cascaded MCP (73). After being sensed by the cascaded MCP (73), an electrical signal is generated and sent to the signal processing circuit (74). The signal processing circuit (74) extracts the flight time of different ions from the signal, converts the flight time into the mass and charge value of the ions, and sends these data to the controller (1), thereby realizing the accurate analysis of the constituent elements and isotopes of the sample (26). In the TOF mass analyzer (60), the flight axis A (61), flight axis B (78), flight axis C (71), and flight axis D (77) form a W geometric configuration in space. The timing controller (4) is used to turn on and control the timing relationship of the LIBS laser (2), spectrometer (36), first ultrafast pump laser (6), second ultrafast pump laser (8), and solid-state laser (12). The controller (1) is used to turn on the timing controller (4), receive LIBS spectral data from the spectrometer (36) for analysis; to tune the four SLRI output wavelengths of the first OPO (5), the second OPO (10), twin dye laser A (15), and twin dye laser B (17); and to turn on the signal processing circuit (74) and receive its data for isotope content analysis.

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