Sodium resonance fluorescence disturbance characteristic-based airborne marine foreign matter detection system and method

Abstract

The invention belongs to the technical field of optical sensing and magnetic field measurement, and provides an airborne marine foreign matter detection system and method based on sodium resonance fluorescence disturbance characteristics. The objective of the invention is to solve the bottleneck problems of low resolution, susceptibility to carrier interference, limited spatial resolution and the like in the existing marine foreign matter detection technology. The system comprises a femtosecond laser, a 589nm laser, a modulator, a light path assembly and a signal processing unit. The method comprises the following steps: starting a femtosecond laser to emit femtosecond pulse laser to control a light path; the 589nm laser emits resonance light which is subjected to filtering and frequency stabilization modulation to realize dual-frequency single-beam multiplexing for Na atomic polarization and frequency sweep detection; the femtosecond laser and the detection light are focused in a seawater area to generate Na atom ensemble through light path control; resonance fluorescence signals are generated through double-frequency light irradiation, and converted electric signals are collected; performing sweep-frequency measurement on the peak frequency of the fluorescence intensity to obtain Larmor resonance frequency, and calculating the magnetic field intensity. The device realizes long-distance and high-sensitivity ocean magnetic field detection, and is used for identifying and positioning airborne ocean foreign matters.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical sensing and magnetic field measurement, and proposes an airborne marine foreign object detection system and method based on sodium resonance fluorescence disturbance characteristics. BACKGROUND

[0002] Traditional marine foreign object detection technologies (such as sonar, towed magnetometer, etc.) have many limitations. Sonar detects underwater targets by emitting sound waves and receiving their reflected echoes, but cannot accurately distinguish target types, which can easily lead to misjudgment. Deep water detection also requires large acoustic arrays or deep tow equipment, which is complex to operate and costly, and is difficult to adapt to rapid dynamic monitoring requirements. Towed magnetometer detects underwater metal objects by measuring geomagnetic field anomalies, and measures the magnetic field at different spatial positions by towing a streamlined body with a ship. Its disadvantages are that the tow cable and ship body ferromagnetic material can easily introduce their own magnetic field interference; and the tow speed and sea current fluctuations can easily cause the tow body to be unstable, affecting data continuity. The above two traditional marine foreign object detection technologies need to rely on carrier platforms (ships or submarines), and it is difficult to achieve completely autonomous and remote measurement, and there are bottlenecks in terms of remoteness, concealment and multi-target recognition capability. Sodium laser guide star technology based on sodium resonance fluorescence disturbance characteristics is a remote geomagnetic field measurement method based on sodium atomic resonance fluorescence spectrum analysis, which mainly uses the naturally existing sodium layer in the atmosphere to measure the geomagnetic field, but cannot be directly used for magnetic field measurement in seawater. In summary, it is of great significance for marine resource exploration, shipwreck salvage and military reconnaissance to realize a marine foreign object detection system that can measure the magnetic field wirelessly at a long distance, with more accurate data, more stable transmission and flexible arrangement.

[0003] The present application aims to propose an airborne marine foreign object detection system based on sodium atomic resonance fluorescence, which is used for detecting underwater metal targets. Its method is based on quantum effect and laser-induced plasma technology, which measures the magnetic field by using the resonance fluorescence characteristics of sodium atoms. By irradiating the sea salt mist with high-energy pulsed laser, NaCl molecules can be ionized to produce plasma. During the cooling process of the plasma, excited-state sodium ions (Na + ) and electrons recombine to form ground-state sodium atoms (Na), and the Larmor precession of the electrons will shift with the change of the size and direction of the external magnetic field. When the frequency of the pump laser is resonant with the characteristic spectrum of sodium atoms, the photon energy is absorbed by the ground-state electrons and jumps to the excited state, and then randomly releases photons to return to the ground state through spontaneous emission. In the process of downward transition at high energy level, isotropic resonance fluorescence will be emitted. At this time, the magneto-optical resonance phenomenon is derived from the quantum characteristics of the characteristic spectrum of sodium atoms, and the transmission light intensity and the fluorescence signal show a complementary relationship. By measuring the intensity change of the fluorescence signal, the magnetic field disturbance characteristics of the underwater target can be accurately inverted, and non-contact high-precision detection can be realized.

[0004] The application is based on an airborne marine foreign matter detection system made of sodium atom resonance fluorescence disturbance characteristics, which can accurately identify underwater metal targets and realize remote high-precision detection. Compared with traditional marine foreign matter detection technology, the system does not need to rely on physical probe to contact the sea surface, effectively avoiding the magnetic field interference introduced by the ferromagnetic materials of the carrier such as ship or towed cable, and overcoming the shortcomings such as easy misjudgment of sonar and poor data continuity of towed magnetometer. The system carries advanced laser-induced plasma technology, which excites sodium atoms in sea salt fog on site without carrying external sodium source, significantly improving environmental adaptability and deployment flexibility. In addition, the system uses synchronous optical pumping and fluorescence magnetometry technology to realize non-contact magnetic field measurement without the intervention of radio frequency coil and contact sodium source. Through optimization of laser parameters and signal processing technology, the magnetic field sensitivity and anti-interference ability are significantly enhanced. This innovative technology not only meets the needs of remote, high-precision and covert detection in the fields of marine resource exploration, shipwreck salvage and military reconnaissance, but also provides a new solution for marine magnetic field and magnetic anomaly detection. SUMMARY

[0005] The application provides a high-sensitivity, non-contact and high-anti-interference airborne marine foreign matter detection system, which mainly solves the problems of low resolution, easy interference of carrier, limited spatial resolution and other bottleneck problems in the existing marine foreign matter detection technology.

[0006] In order to achieve the above purpose, the application adopts the following technical means:

[0007] The application provides an airborne marine foreign matter detection system based on sodium resonance fluorescence disturbance characteristics, comprising:

[0008] A laser emission and fluorescence receiving end is used for emitting laser and receiving sodium atom resonance fluorescence signal;

[0009] A seawater Na atom probe is used for exciting sodium atoms in sea salt fog by a femtosecond laser and a 589nm laser to form a ground state sodium atom ensemble;

[0010] A femtosecond laser is used for generating ultrafast laser pulses to induce plasma and excite sodium atoms;

[0011] A 589nm laser is used for emitting resonance light as detection light, and the frequency is adjusted to the Larmor precession frequency of sodium atom D2 line electron by a frequency-variable filter and a laser frequency stabilizer;

[0012] An AOM acousto-optic modulator is used for double-frequency single-beam multiplexing of pump light, one frequency band is used for sodium atom spin polarization, and the other frequency band is used for sweep detection light;

[0013] A quarter-wave plate is used for adjusting the laser polarization state to match the optical path requirement;

[0014] The laser emission system comprises a primary mirror group, a secondary mirror group and a large-aperture telescope, and is used for focusing femtosecond laser pulses and detection light to a seawater area.

[0015] The optically pumped magnetometer comprises an ultra-narrow bandpass filter and a CCD (Charge-Coupled Device) and is used for capturing and analyzing resonance fluorescence signals.

[0016] The digital acquisition and lock-in amplification module is used for processing fluorescence intensity signals and calculating magnetic field disturbance characteristics.

[0017] In the scheme, the laser emission system realizes aiming and locking on the seawater area through a two-degree-of-freedom rotating structure and a large-aperture telescope, and the laser emitter fixing base is adapted to an airborne platform.

[0018] In the scheme, the light paths of the femtosecond laser and the 589 nm laser are spatially arranged through the primary mirror group and the secondary mirror group, wherein the ultrafast laser pulse light path and the detection light path are angle-adjusted at a fast aspheric mirror, and finally focused on the same seawater area.

[0019] In the scheme, the AOM (Acousto-Optic Modulator) dynamically adjusts the sweep frequency of the detection light through the lock-in amplification technology, the sweep frequency range covers the sodium atom Larmor resonance frequency, and the magnetic field strength is inversely calculated through the fluorescence intensity peak, and the calculation formula is as follows:

[0020]

[0021] Wherein v is the Larmor resonance frequency, mu B is the Bohr magneton, g F is the Lande factor, B is the magnetic field strength, and h is the reduced Planck constant. The Bohr magneton mu B is the basic unit of the electron orbital magnetic moment in an atom, and the calculation formula is as follows Wherein e is the electron charge, m e is the electron mass. The Lande factor g F is a dimensionless quantity, which is used to describe the relationship between the magnetic moment and the angular momentum of an atom or particle, and reflects the proportion of spin and orbital motion to the magnetic moment.

[0022] In the scheme, the laser emission system comprises a multi-laser beam fiber, which is used for synchronously transmitting femtosecond laser pulses and detection light to the primary mirror group and the secondary mirror group, wherein the primary mirror group adopts a double convex lens and a fast aspheric mirror, the secondary mirror group adopts a fast aspheric mirror, and the light beam is collimated and focused by adjusting the primary mirror group and the secondary mirror group.

[0023] In the scheme, the optically pumped magnetometer selectively captures sodium atom resonance fluorescence signals through a BF ultra-narrow band-pass filter, and converts optical signals into electrical signals through a CCD charge-coupled device to input a digital acquisition and phase-locked amplification module.

[0024] The application also provides an airborne marine foreign matter detection method, comprising the following steps:

[0025] a. Start the femtosecond laser and the 589nm laser, and transmit them to the laser emission system through an optical fiber;

[0026] b. After the detection light of the 589nm laser is adjusted by a gradual variable filter and a frequency stabilizer, the double-frequency single-beam multiplexing is realized through an AOM acousto-optic modulator;

[0027] c. The femtosecond laser pulse and the detection light are focused to the seawater area through a main mirror group and a secondary mirror group, to induce plasma and excite sodium atoms;

[0028] d. The sodium atom ensemble produces intensity changes related to magnetic field disturbance in the resonance fluorescence signals;

[0029] e. The fluorescence signals are captured through an ultra-narrow band-pass filter and a CCD charge-coupled device, and input into a digital acquisition and phase-locked amplification module;

[0030] f. The fluorescence intensity peak value of the swept-frequency detection light is used to inversely deduce the Larmor resonance frequency, and then the magnetic field strength is calculated.

[0031] The application solves multiple technical problems existing in the prior art marine magnetic field detection method through innovative technical means, and realizes efficient and accurate foreign matter detection.

[0032] 1. The application adopts the technical means of AOM acousto-optic modulator to realize double-frequency single-beam multiplexing, solves the technical problem of low efficiency and complex system caused by the need for independent light sources and modulators in the traditional marine magnetic field detection, and achieves the effects of simplifying the optical path structure and improving the detection efficiency.

[0033] The specific analysis is as follows:

[0034] In the traditional method, the pump light and the detection light usually need independent laser sources and modulation devices, which not only increases the system volume and cost, but also easily introduces interference between the light beams and reduces the detection accuracy. The application modulates the detection light emitted by the 589nm laser through the AOM acousto-optic modulator, so that two frequency bands are multiplexed in one light beam: one frequency band drives the sodium atom to occur resonance polarization, and the other frequency band sweeps around the Larmor resonance frequency to detect the magnetic field. This multiplexing design avoids the complexity of independent transmission of multiple light beams (such as Figure 3The optical path principle shown) reduces the number of optical elements, thereby simplifying the overall system structure. At the same time, the multiplexed light beams ensure that the pumping and probing processes are synchronized, eliminating timing control errors in traditional methods and improving probing efficiency. Ultimately, this approach makes the system more suitable for airborne environments, enhancing stability and practicality.

[0035] 2. The present application solves the technical problem of accurately focusing laser beams on the same seawater location under airborne conditions by using the technical means of rearranging and angle controlling the optical path with the primary mirror group and the secondary mirror group, achieving the effects of improving focusing accuracy and ensuring the effective formation of sodium atom ensembles.

[0036] Specific analysis as follows:

[0037] In airborne detection, aircraft vibration and movement easily lead to beam deviation, and traditional systems cannot guarantee that multiple laser beams (such as detection light and ultrafast laser pulses) are accurately focused on the same seawater area, affecting the generation of sodium atom ensembles and subsequent fluorescence detection. The present application controls the exit angles of the detection light and ultrafast laser pulse light paths through the reflection mechanism of the primary mirror group and the secondary mirror group (as shown in Figure 2 and Figure 3 ), with the light beams being reflected back to the outer ring fast aspheric mirror of the primary mirror group when first incident on the secondary mirror group, and then being reflected out at the same angle. By adjusting the distance between the primary mirror group and the secondary mirror group (10 and 11 in Figure 1 ), the exit angles of the two laser beams can be accurately calibrated so that they are ultimately focused on the same seawater location (26 in Figure 1 ). This reflective optical path design counteracts the effects of vibration in airborne environments, avoiding beam divergence or misalignment, thereby ensuring that the irradiated seawater area can stably generate salt fog and plasma, forming a uniform ground-state sodium atom ensemble (18 in Figure 1 ). Ultimately, this approach improves the reliability of magnetic field detection, providing a basic guarantee for foreign object identification.

[0038] 3. The present application solves the technical problem of the airborne system being difficult to stably aim at a specific seawater area in a dynamic environment by combining a large-aperture telescope and a two-degree-of-freedom rotation structure, achieving the effects of enhancing system mobility and expanding the detection range.

[0039] Specific analysis as follows:

[0040] Ocean foreign object detection needs to be scanned over a wide sea area, but the movement of the airborne platform (such as changes in flight altitude or wind direction) easily leads to aiming errors, and traditional fixed telescopes cannot adapt to dynamic environments. The present application mounts a large-aperture telescope (19 in Figure 1 ) and a two-degree-of-freedom rotation structure (20 in Figure 1 ) on the laser emitter fixed base,21), allowing the system to flexibly adjust the azimuth and pitch angles on the vehicle platform (such as Figure 1 This design enables the laser emission system to lock onto the seawater area to be measured in real time ( Figure 1 12), maintaining a stable beam incidence even during flight. The dual-degree-of-freedom rotational structure provides multi-axis adjustment, compensating for deviations caused by vehicle motion. The large-aperture telescope expands the field of view. Combined with the optical path focusing in step 3, this ensures efficient beam coverage of the target area. Ultimately, this approach enables the system to rapidly respond to detection needs in diverse maritime environments, enhancing the adaptability and coverage of airborne applications.

[0041] 4. The present invention adopts the technical means of dual-frequency multiplexing detection optical sweep measurement and phase-locked amplification module to quantitatively output signals, thereby solving the technical problem of weak signal intensity and susceptibility to noise interference in magnetic field detection, resulting in insufficient accuracy, and achieving the effect of improving magnetic field measurement accuracy and realizing real-time foreign object recognition.

[0042] The specific analysis is as follows:

[0043] In the marine environment, the sodium resonance fluorescence signal is easily attenuated by background light or seawater disturbance. Traditional methods have difficulty distinguishing effective signals, resulting in large errors in magnetic field inversion. The present invention uses dual-frequency single-beam multiplexed detection light to illuminate the sodium atomic ensemble, simultaneously promoting spin polarization and generating resonance fluorescence signals; through a wide-angle telescope ( Figure 1 17) to collect the signal, and with the help of BF ultra-narrow bandpass filter and CCD charge coupled device ( Figure 1 16 and 15) to filter out noise and extract pure fluorescence electrical signals. The frequency is further swept near the Larmor resonance frequency by the AOM acousto-optic modulator, and the fluorescence intensity is measured every time the frequency is modulated. Combined with the data acquisition and phase-locked amplification module ( Figure 1 15) quantitatively outputs the peak frequency of the signal, allowing precise calculation of the magnetic field strength. The frequency sweep process enhances the signal-to-noise ratio through continuous frequency modulation, while the lock-in amplifier module processes the data in real time, avoiding the lag inherent in traditional static measurements. Ultimately, this method ensures high-precision magnetic field detection, providing a reliable basis for the rapid identification of marine foreign objects (such as metal objects or mineral deposits).

[0044] In summary, through the synergistic effect of the above-mentioned technical means, the present invention has comprehensively solved the core problems of airborne marine foreign object detection, such as system complexity, low accuracy, and poor adaptability, and achieved efficient, stable and high-precision magnetic field detection effects, providing innovative solutions for marine safety monitoring and resource exploration. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 The figure is a general structural diagram of an airborne marine foreign object detection system based on the sodium resonance fluorescence disturbance characteristics according to the present invention.

[0046] Figure 2 Figure 1 is a schematic diagram of the basic structure of a laser emission system device in the device of the present application.

[0047] Figure 3 Figure 2 is a schematic diagram of the principle of light path focusing in the laser emission system device;

[0048] Figure 4 Figure 3 is a schematic diagram of the structure of a fast aspheric mirror.

[0049] BRIEF DESCRIPTION OF DRAWINGS

[0050] 1-laser emission and fluorescence receiving end; 2-seawater Na atom probe; 3-femtosecond laser; 4-589 nm laser; 5-gradual filter; 6-laser frequency stabilizer; 7-AOM acousto-optic modulator; 8-QWP quarter-wave plate; 9-laser emission system; 10-primary mirror group; 11-secondary mirror group; 12-seawater; 13-power supply driving control; 14-digital acquisition and lock-in amplification; 15-CCD charge-coupled device; 16-BF ultra-narrow band filter; 17-large-aperture telescope; 18-Na atom ensemble; 19-large-aperture telescope; 20-multi-laser beam optical fiber; 21-two-degree-of-freedom rotation structure; 22-laser emitter fixing base; 23-detection light path; 24-fast aspheric mirror; 25-ultrafast laser pulse light path; 26-seawater, 27-voice coil motor, 28-aspheric mirror. DETAILED DESCRIPTION

[0051] The embodiments of the present application will be described in detail below. Although the present application will be described and illustrated by referring to the specific embodiments, it is noted that the present application is not limited to these embodiments only. On the contrary, modifications or equivalent arrangements within the scope of the present application are contemplated.

[0052] In addition, in order to better illustrate the present application, numerous specific details are given in the following detailed description of the embodiments. Those skilled in the art will understand that the present application can be practiced without these specific details.

[0053] PRINCIPLE DESCRIPTION

[0054] Innovation point 1: improve the sensitivity and signal-to-noise ratio of the magnetic field detection. On the detection principle, based on the disturbance characteristics of sodium atom resonance fluorescence, the sodium atoms in the sea salt mist are excited by femtosecond laser-induced plasma technology, the double-frequency tunable laser is combined to realize the atom spin polarization, and the optical pumping magnetometer is used to capture the magnetic field disturbance signal caused by foreign matters in real time. Through the signal processing technology such as lock-in amplification space gradient calculation, the signal-to-noise ratio is significantly improved, the environmental background interference is effectively filtered out, the reliable extraction of the weak magnetic field disturbance signal is ensured, and the high-precision positioning of the underwater metal target is realized.

[0055] Innovation point 2: Reduce the magnetic field noise of the detection system and environmental interference. Optimize the system design, adopt remote non-contact detection method, avoid the interference of the carrier's own ferromagnetic material caused by the contact of the traditional physical probe to the measured area. At the same time, through the uniform plasma channel formed by the femtosecond filamentation technology, the influence of environmental turbulence on the detection light path is greatly reduced, and the stability and adaptability of the system are enhanced.

[0056] The system is based on the principle of sodium atomic resonance fluorescence measurement, adopts a picotesla level sensitive optical pumping magnetometer, and combines femtosecond laser induced plasma technology to realize non-contact high sensitivity marine magnetic field measurement. There is no introduction of traditional magnetic elements in the system, which avoids the generation of magnetic field noise. Through the optimization of laser parameters and signal processing technology, the system can work stably in complex marine environment and is not disturbed by environmental factors such as sea wave movement. The system is connected and communicated through the mode of optical fiber coupling on the airborne platform, which ensures the stability and reliability of data transmission.

[0057] The application provides an airborne marine foreign matter detection system based on sodium resonance fluorescence disturbance characteristics, which comprises:

[0058] A laser emission and fluorescence receiving end 1 is used for emitting laser and receiving sodium atomic resonance fluorescence signals;

[0059] A seawater Na atom probe 2 is excited by a femtosecond laser 3 and a 589nm laser 4 to excite sodium atoms in sea salt mist to form a ground state sodium atom ensemble 18;

[0060] The femtosecond laser 3 is used for generating ultrafast laser pulses to induce plasma and excite sodium atoms;

[0061] The 589nm laser 4 is used for emitting resonance light as detection light, and the frequency is adjusted to the Larmor precession frequency of the D2 line electron of sodium atom through a gradual variable filter 5 and a laser frequency stabilizer 6;

[0062] An AOM acousto-optic modulator 7 is used for double-frequency single-beam multiplexing of pump light, wherein one frequency band is used for sodium atom spin polarization, and the other frequency band is used for frequency sweeping detection light;

[0063] A quarter-wave plate 8 is used for adjusting the laser polarization state to match the light path requirement;

[0064] A laser emission system 9 comprises a main mirror group 10, a secondary mirror group 11 and a large-aperture telescope 19, and is used for focusing the femtosecond laser pulse and the detection light to the seawater area;

[0065] An optical pumping magnetometer comprises an ultra-narrow bandpass filter 16 and a CCD charge coupled device 15, and is used for capturing and analyzing the resonance fluorescence signals;

[0066] A digital acquisition and lock-in amplifier module 14 is used to process the fluorescence intensity signal and calculate the magnetic field perturbation characteristics.

[0067] In the above scheme, the laser emitting system 9 realizes the aiming and locking of the seawater area through the two-degree-of-freedom rotating structure 21 and the large-aperture telescope 19, and the laser emitter fixed base 22 is adapted to the airborne platform.

[0068] In the above scheme, the optical paths of the femtosecond laser 3 and the 589nm laser 4 are arranged in space through the main mirror group 10 and the secondary mirror group 11, wherein the ultrafast laser pulse optical path 25 and the detection light optical path 23 realize angle adjustment at the fast aspheric mirror 24, and finally focus on the same seawater area 26.

[0069] The basic principle of the fast aspheric mirror 24 is as follows: four voice coil motors 27 are used to drive the back surface of the aspheric mirror 28. With the millimeter-level stroke control and mutual cooperation of the four voice coil motors 27, the tilt angle of the aspheric mirror 28 can be quickly and accurately adjusted, thereby controlling the exit angle of the reflected light.

[0070] With the help of algorithms and the fast aspheric mirror 24, the exit angles of the femtosecond laser and the detection light are quickly and accurately controlled, and the intersection point of the two optical paths is accurately controlled to fall on the seawater 26 in the magnetic field area to be detected.

[0071] In the above scheme, the AOM acousto-optic modulator 7 dynamically adjusts the sweeping frequency of the detection light through the lock-in amplification technology, the sweeping range covers the sodium atom Larmor resonance frequency, and the magnetic field strength is inversely calculated through the fluorescence intensity peak, and the calculation formula is:

[0072]

[0073] Where v is the Larmor resonance frequency, μ B is the Bohr magneton, g F is the Lande factor, B is the magnetic field strength, and h is the reduced Planck constant. The Bohr magneton μ B is the basic unit of the electron orbital magnetic moment in the atom, and the calculation formula is Where e is the electron charge, m e is the electron mass. The Lande factor g F is a dimensionless quantity, which is used to describe the relationship between the magnetic moment and the angular momentum of an atom or particle, and reflects the proportion of spin and orbital motion to the magnetic moment.

[0074] In the scheme, the laser emission system 9 comprises a multi-laser beam fiber 20 for transmitting femtosecond laser pulses and probe light synchronously to the primary mirror group 10 and the secondary mirror group 11, wherein the primary mirror group adopts a double convex lens and a fast aspherical mirror, and the secondary mirror group adopts a fast aspherical mirror, and the beam collimation and focusing are realized by adjusting the primary mirror group and the secondary mirror group.

[0075] In the scheme, the optically pumped magnetometer selectively captures the sodium atom resonance fluorescence signal through the BF ultra-narrow bandpass filter 16, and converts the optical signal into an electrical signal through the CCD charge-coupled device 15 and inputs the digital acquisition and phase-locked amplification module 14.

[0076] The application also provides an airborne marine foreign matter detection method, comprising the following steps:

[0077] a. Start the femtosecond laser 3 and the 589nm laser 4, and transmit them to the laser emission system 9 through the optical fiber;

[0078] b. After the probe light of the 589nm laser 4 is adjusted through the gradual change filter 5 and the frequency stabilizer 6, the double-frequency single-beam multiplexing is realized through the AOM acousto-optic modulator 7;

[0079] c. The femtosecond laser pulses and the probe light are focused to the seawater area through the primary mirror group 10 and the secondary mirror group 11, and the plasma is induced and the sodium atoms are excited;

[0080] d. The sodium atom ensemble 18 generates intensity changes related to magnetic field disturbance in the resonance fluorescence signal;

[0081] e. The fluorescence signal is captured through the ultra-narrow bandpass filter 16 and the CCD charge-coupled device 15, and is input into the digital acquisition and phase-locked amplification module 14;

[0082] f. The fluorescence intensity peak value of the swept-frequency probe light is used to deduce the Larmor resonance frequency, and then the magnetic field strength is calculated.

[0083] Embodiment 1

[0084] Figure 1 It is a general structure diagram of an airborne marine foreign matter detection system based on the sodium resonance fluorescence disturbance characteristics. Figure 2 It is a basic structure schematic diagram of the laser emission system device 9 in the device. Figure 3 It is a principle diagram of the optical path in the laser emission system device 9.

[0085] Referring to the drawings, a specific implementation method of an airborne marine foreign matter detection system based on the sodium resonance fluorescence disturbance characteristics is provided, comprising the following steps:

[0086] Step 1: Start the femtosecond laser 3 to emit a beam of femtosecond pulse laser, and control and adjust the optical path through the fiber-optic beam emitter 9.

[0087] Step 2: The power drive control 13 controls the 589 nm laser 4 to emit a beam of probe light in the positive direction of the Z-axis. The probe light passes through the gradual filter 5 to make the frequency spectrum close to the Larmor precession frequency of the Na atom D2 line electron, and then enters the AOM acousto-optic modulator 7 after further frequency stabilization by the frequency stabilizer 6 to modulate the pump light, thereby realizing the detection light and pump light dual-frequency single-beam multiplexing. One frequency band in the modulated light beam is responsible for pushing the Na atom to resonate and polarize, and the other frequency band is the probe light that continuously sweeps the frequency near the Larmor precession frequency, which is responsible for detecting the size of the Larmor precession frequency and then inferring the size of the magnetic field.

[0088] Step 3: The dual-frequency multiplexed detection light passes through the quarter-wave plate 8 and is injected into the laser emission system 9, and the ultrafast laser pulse light path 25 is simultaneously rearranged on the spatial light path. The detection light 23 and the ultrafast laser pulse light path 25 respectively pass through different inner ring main reflector groups 10 of fast aspherical mirrors 24 without changing the propagation direction, but when they first enter the reflector group of the secondary reflector group, the light beam is reflected at a certain angle, which is just reflected back to the outer ring fast aspherical mirror 24 of the main reflector group 20, and then reflected at the same angle, so that the ultrafast laser pulse light and the detection light are respectively emitted at a certain angle. By controlling the distance between the main reflector group 10 and the secondary reflector group 11, the exit angle of the two light paths can be accurately controlled, and finally the two lasers are focused on the same position of the seawater 26.

[0089] Step 4: Operate the mechanical structure of the laser emitter 9. The laser emitter 9 can be carried on different carrier platforms through the laser emitter fixed base 22. Through the large-aperture telescope 19 carried by the emitter and the two-degree-of-freedom rotating structure 21, the measured seawater area can be aimed and locked. The combined laser emitted by the laser emission system 9 passes through the main reflector group 10 and the secondary reflector group 11 and enters the specified area of the seawater 12, and the light beam can cause the irradiated area of the seawater to produce salt fog and ionize the plasma, which is quickly excited and cooled to produce a ground-state Na atom ensemble 18. Among them, the seawater 12 and the Na atom ensemble 18 partly constitute the seawater Na atom probe 2 part of the entire Na atom resonance fluorescence magnetic measurement system.

[0090] Step 5: By irradiation of the dual-frequency single-beam multiplexed detection light, the Na atom is spin-polarized and emits a certain intensity of resonance fluorescence signal, and the signal size is related to one of the frequencies in the detection light multiplexing frequency. The wide-angle telescope 17 can collect the fluorescence signal at a long distance. With the help of the BF ultra-narrow bandpass filter 16 and the CCD charge-coupled device 15, the fluorescence signal can be collected and analyzed. Figure 1As shown, we will successfully get the Na atomic resonance fluorescence signal containing the remote magnetic field information.

[0091] Step 6: The resonance fluorescence signal is input to the data acquisition and phase-locked amplification module 15, which quantitatively outputs the fluorescence intensity signal. With the help of the AOM acousto-optic modulator 7, a frequency band of the detection light can be swept within a narrow bandwidth near the Larmor resonance frequency. Each frequency modulation corresponds to one intensity measurement of the fluorescence signal. The frequency at the peak of the fluorescence intensity obtained by sweeping is the Larmor resonance frequency v of the Na atom under the influence of the magnetic field.

[0092] The formula is as follows:

[0093]

[0094] The scalar value of the magnetic field size is calculated, where μ B is the Bohr magneton, g F is the Lande factor, and B is the magnetic field strength.

Claims

1. An airborne marine foreign object detection system based on sodium resonance fluorescence disturbance characteristics, characterized in that: include: A laser emitting and fluorescence receiving end (1) is used for emitting laser light and receiving a sodium atom resonance fluorescence signal; The seawater Na atom probe (2) is composed of a femtosecond laser (3) and a 589nm laser (4) that jointly excite the sodium atoms in the sea salt spray to form a ground state sodium atom ensemble (18); Femtosecond laser (3), used to generate ultrafast laser pulses to induce plasma and excite sodium atoms; A 589 nm laser (4) is used to emit resonant light as a probe light, the frequency of which is adjusted to the Larmor precession frequency of the sodium atom D2 line electrons via a gradient filter (5) and a laser frequency stabilizer (6); AOM acousto-optic modulator (7), used for dual-frequency single-beam multiplexing of pump light, wherein one frequency band is used for spin polarization of sodium atoms and the other frequency band is swept-frequency detection light; A quarter wave plate (8) is used to adjust the polarization state of the laser to match the optical path requirements; A laser emission system (9) includes a primary reflector group (10), a secondary reflector group (11) and a large-aperture telescope (19), and is used to focus femtosecond laser pulses and detection light onto a seawater area; An optically pumped magnetometer, comprising an ultra-narrow bandpass filter (16) and a CCD charge-coupled device (15), for capturing and analyzing resonance fluorescence signals; The digital acquisition and phase-locked amplification module (14) is used to process the fluorescence intensity signal and calculate the magnetic field disturbance characteristics.

2. The system according to claim 1, wherein: The laser emission system (9) achieves aiming and locking of the seawater area through a dual-freedom rotation structure (21) and a large-aperture telescope (19), and the laser emitter fixed base (22) is adapted to the airborne platform.

3. The system according to claim 1, wherein: The optical paths of the femtosecond laser (3) and the 589nm laser (4) are spatially arranged through a primary reflector group (10) and a secondary reflector group (11), wherein the ultrafast laser pulse optical path (25) and the detection light optical path (23) are angle-adjusted at a fast aspheric reflector (24) and are ultimately focused on the same seawater area (26).

4. The system according to claim 1, wherein: The AOM acousto-optic modulator (7) dynamically adjusts the sweep frequency of the detection light through the phase-locked amplification technology. The sweep frequency range covers the Larmor resonance frequency of the sodium atom, and the magnetic field intensity is inferred from the peak value of the fluorescence intensity. The calculation formula is: Where v is the Larmor resonance frequency, is the Bohr magneton, g F is the Lande factor, B is the magnetic field strength, is the reduced Planck constant, where e is the electron charge, m e The mass of the electron.

5. The system according to claim 1, wherein: The laser emission system (9) comprises a multi-laser beam optical fiber (20) for synchronously transmitting femtosecond laser pulses and detection light to a primary reflector group (10) and a secondary reflector group (11), wherein the center of the primary reflector group (10) adopts a double-sided convex lens, the outer ring adopts a fast aspheric reflector (24), and the secondary reflector group (11) adopts a fast aspheric reflector (24), and light beam collimation and focusing are achieved through the primary reflector group (10) and the secondary reflector group (11).

6. The system according to claim 1, wherein: The optical pump magnetometer selectively captures the sodium atom resonance fluorescence signal through a BF ultra-narrow bandpass filter (16), and converts the optical signal into an electrical signal through a CCD charge coupled device (15) and inputs it into a digital acquisition and phase-locked amplification module (14).

7. An airborne marine foreign object detection method based on the system according to any one of claims 1 to 6, characterized in that: The following steps are involved: a. Start the femtosecond laser (3) and the 589nm laser (4), and transmit them to the laser emission system (9) via optical fiber; b. The detection light of the 589nm laser (4) is adjusted by the gradient filter (5) and the frequency stabilizer (6), and then the dual-frequency single-beam multiplexing is achieved through the AOM acousto-optic modulator (7); c. The femtosecond laser pulse and the probe light are focused onto the seawater region via the primary reflector group (10) and the secondary reflector group (11), inducing plasma and exciting sodium atoms; d. The sodium atom ensemble (18) produces intensity changes in the resonance fluorescence signal that are related to magnetic field perturbations; e. The fluorescence signal is captured by an ultra-narrow bandpass filter (16) and a CCD charge-coupled device (15), and input into a digital acquisition and lock-in amplifier module (14); f. The Larmor resonance frequency is inferred from the peak fluorescence intensity of the swept-frequency detection light, and the magnetic field strength is calculated.

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