A multi-longitudinal mode blue light ocean high spectral resolution lidar transmitter system

Abstract

The present invention discloses a multi-longitudinal mode blue light ocean high spectral resolution lidar transmitter system, comprising a narrow linewidth single longitudinal mode pulse laser, an adjustable polarization beam splitter, a parallel plane cavity optical parametric oscillator, an optical parametric amplifier, a laser frequency doubler, and a laser beam expander; the pulsed pump light emitted by the narrow linewidth single longitudinal mode pulse laser is divided into two beams of unequal energy by the adjustable polarization beam splitter; the low-energy pulsed pump light is injected into the parallel plane cavity optical parametric oscillator and converted into a fundamental frequency multi-longitudinal mode pulse signal light, which is simultaneously injected into the optical parametric amplifier together with the high-energy pulsed pump light to further increase the signal light energy; the laser frequency doubler then generates a multi-longitudinal mode blue light band detection laser, which is finally output to the laser beam expander to adjust the divergence angle and then injected into the target water body. The present invention can significantly reduce the dependence on seed lasers of special working bands and can also select a detection wavelength with better remote sensing measurement effect to construct a transmitter system.

Description

Technical Field

[0001] The present invention relates to the field of laser radar remote sensing measurement, and in particular to a multi-longitudinal mode blue light ocean high spectral resolution laser radar transmitter system. Background Art

[0002] LiDAR is an important tool for remote sensing of ocean optical parameters. Its laser transmitter emits a nanosecond pulsed laser beam at a specific frequency toward the water. Once inside the water, the laser continuously interacts with water molecules, colored soluble organic matter, phytoplankton, non-pigmented particles, and debris. The resulting backscattered, Mie-scattered, and Rayleigh-scattered signals are received by the LiDAR detection and acquisition system and converted into voltage signals for transmission to analog-to-digital converters. Signal processing and inversion yield the measured optical parameters of the water. High-spectral-resolution marine LiDAR (HSRL), based on a general radar structure, uses a spectral discriminator to separate the elastic and backscattered components of the seawater echo signal. This fundamentally overcomes the "one equation, two unknowns" limitation in the inversion process, significantly improving the accuracy of seawater optical property inversion.

[0003] Thanks to advances in single-longitudinal-mode semiconductor lasers and Nd:YAG laser technology, the HSRL architecture, which uses a seed-injected Nd:YAG laser as its core, in conjunction with an iodine molecular absorption cell and a Fabry-Perot interferometer or Michelson interferometer spectral discriminator, has been widely adopted both domestically and internationally. For example, Chinese patent publication CN114488199A discloses a semiconductor seed laser frequency-locking system for high-spectral-resolution lidar.

[0004] However, due to differences in the composition and concentration of water substances in different sea areas, the transmission attenuation characteristics of lasers in water also vary significantly. Considering the detection depth, it is generally believed that the optimal detection wavelengths for nearshore and offshore waters are distributed in the range of 520-580nm and 420-510nm, respectively. Due to the very limited output bands of currently stable and reliable commercial single-longitudinal-mode seed lasers, the detection wavelength of marine HSRL systems at home and abroad is concentrated at 532nm. This makes it difficult to select the appropriate detection wavelength for different marine water conditions to achieve remote sensing measurements of seawater optical parameters at greater depths. How to expand the construction of marine HSRLs in the blue light band and even a wider range to address the differences in seawater laser transmission attenuation is currently a key issue in the field of marine lidar remote sensing measurement. Summary of the Invention

[0005] To address the dependence of blue-light ocean HSRL transmitter systems on single-longitudinal-mode seed lasers in special operating bands, the present invention provides a multi-longitudinal-mode blue-light ocean high-spectral-resolution lidar transmitter system. This system optimizes the ocean HSRL detection wavelength based on the laser transmission attenuation characteristics of different water bodies, enriches the construction methods of blue-light ocean HSRLs, and enhances the universal application of HSRL technology in remote sensing measurements of ocean optical properties.

[0006] A multi-longitudinal mode blue light ocean high spectral resolution lidar transmitter system, comprising a narrow linewidth single longitudinal mode pulse laser, an adjustable polarization beam splitter, a parallel plane cavity optical parametric oscillator, an optical parametric amplifier, a laser frequency doubler and a laser beam expander;

[0007] The pulse pump light emitted by the narrow-linewidth single-longitudinal-mode pulse laser is divided into two beams of unequal energy by an adjustable polarization beam splitter. The low-energy pulse pump light is injected into a parallel plane cavity optical parametric oscillator and converted into a fundamental frequency multi-longitudinal-mode pulse signal light. The fundamental frequency multi-longitudinal-mode pulse signal light and the high-energy pulse pump light are simultaneously injected into an optical parametric amplifier to further increase the signal light energy. The multi-longitudinal-mode blue light detection pulse laser for remote sensing measurement of ocean optical properties is then generated by a laser frequency multiplier. The laser is finally output to a laser beam expander to adjust the divergence angle and then injected into the target water body.

[0008] Furthermore, considering the factors that affect the attenuation characteristics of laser transmission in water (including pure water absorption, particulate backscattering, vertical distribution of chlorophyll content, etc.), for the target water body to be measured, the wavelength with the greatest detection depth advantage in the blue light band is selected as the detection wavelength, and a parallel plane cavity optical parametric oscillator and an optical parametric amplifier are used to generate a fundamental frequency multi-longitudinal mode pulse signal light that is harmonically related to the detection wavelength, and then converted into a multi-longitudinal mode blue light detection pulse laser by a laser frequency multiplier.

[0009] Furthermore, the parallel plane cavity optical parametric oscillator comprises an input cavity mirror, a nonlinear crystal and an output cavity mirror fixed on a displacement platform connected in sequence; the longitudinal mode spacing Δv of the fundamental frequency pulse signal light singal Determined by the optical length L of the resonant cavity, the longitudinal mode spacing of the signal light is adjusted by the displacement platform until the longitudinal mode spacing Δν of the multi-longitudinal mode blue light detection pulse laser after frequency doubling. mb The 180° backward Brillouin scattering frequency shift ν generated by the laser propagating in water B Match, expressed as:

[0010]

[0011] Where λ mb is the wavelength of the pulsed probe light, ν s is the speed of sound, S, T, and P are the salinity, temperature, and pressure of the target water body to be measured, respectively.

[0012] Furthermore, the adjustable polarization beam splitter includes a 532nm half-wave plate 1, a polarization beam splitter prism, and a 532nm half-wave plate 2 connected in sequence. The 532nm pulse pump light emitted by the narrow-linewidth single-longitudinal-mode pulse laser is divided into low-energy pulse pump light and high-energy pulse pump light after passing through the 532nm half-wave plate 1 and the polarization beam splitter prism; the low-energy pulse pump light is polarized by the 532nm half-wave plate 2 and then sent to the input end of the parallel plane cavity optical parametric oscillator. Furthermore, under the action of the low-energy pulse pump light, the parallel plane cavity optical parametric oscillator simultaneously emits a first fundamental frequency multi-longitudinal mode pulse signal light, a first idler light, and a first residual pump light; wherein, the wavelength λ of the first fundamental frequency multi-longitudinal mode pulse signal light is singal Determined according to the laser transmission attenuation characteristics of the water body to be measured;

[0013] The first idler light and the first residual pump light are reflected by the first dichroic mirror into the first light block for absorption, and the fundamental frequency multi-longitudinal mode pulse signal light is transmitted through the first dichroic mirror and then transmitted to the second dichroic mirror; the fundamental frequency multi-longitudinal mode pulse signal light and the high-energy pulse pump light are combined at the second dichroic mirror and then input into the optical parametric amplifier.

[0014] The optical parametric amplifier outputs a second fundamental frequency multi-longitudinal mode pulse signal light, a second idler light, and a second residual pump light after further energy amplification. The second idler light and the second residual pump light are reflected by the third dichroic mirror into the second light block for absorption, and the second fundamental frequency multi-longitudinal mode pulse signal light passes through the third dichroic mirror and is emitted into the laser frequency doubler.

[0015] The optical parametric amplifier can further enhance the energy of the pulse signal light under the combined action of the first fundamental frequency multi-longitudinal mode pulse signal light and the high-energy pulse pump light, and the amplified signal light is sent to the input end of the laser frequency multiplier.

[0016] The laser frequency doubler includes a half-wave plate and an LBO crystal. After being amplified by the optical parametric amplifier, the second fundamental frequency multi-longitudinal mode pulse signal light is polarized by the half-wave plate and then injected into the LBO crystal, while simultaneously emitting multi-longitudinal mode pulse detection light and residual signal light. The residual signal light is reflected by the fourth dichroic mirror into the third light block for absorption, and the multi-longitudinal mode pulse detection light is injected into the laser beam expander.

[0017] The laser frequency doubler converts the fundamental frequency multi-longitudinal mode pulse signal light into a blue light band multi-longitudinal mode pulse detection laser with the best transmission attenuation characteristics in the water body to be measured by adjusting the temperature control and the nonlinear crystal angle, and sends the detection laser to the laser beam expander.

[0018] Blue band multi-longitudinal mode pulse detection laser λ mb and fundamental frequency multi-longitudinal mode pulse signal light λ singal There is a harmonic relationship, and the longitudinal mode spacing Δv mbProportional to the ratio of the speed of light to the optical length of the parallel plane cavity optical parametric oscillator resonant cavity, the combination of the parallel plane cavity optical parametric oscillator and the laser frequency doubler helps to alleviate the damage of short-wavelength ultraviolet pump light to optical components, improve the stability of the lidar transmitter system, and achieve high-energy detection laser output.

[0019] The laser beam expander can adjust the divergence angle of the multi-longitudinal mode pulse detection laser in the blue light band.

[0020] The key to the operation of this invention lies in the ability of the detection laser longitudinal mode spacing to match the Brillouin scattering frequency offset spacing generated by the interaction between the detection laser and water molecules. When the laser radar backscattering angle is 180°, the Brillouin scattering frequency offset is related to the temperature, salinity, and pressure of the water. Under typical marine conditions, the Brillouin scattering frequency offset generated by a 400-500nm wavelength laser is in the 8-10GHz range. To achieve separation of the elastic scattering signal from the Brillouin scattering signal, the detection laser longitudinal mode spacing emitted by the laser radar transmitter system should be between 16-20GHz.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The multi-longitudinal-mode blue-light ocean HSRL transmitter system of the present invention combines a parallel plane cavity optical parametric oscillator with a laser frequency doubler to match the longitudinal mode spacing of the multi-longitudinal-mode detection laser in the blue light band with the back Brillouin scattering frequency offset spacing generated by the detection laser transmitting in water. This eliminates the need for seed-injected optical parametric oscillator technology, avoids the dependence of the ocean HSRL system on seed lasers in special working bands, and promotes the localization and cost-effectiveness of ocean HSRL.

[0023] 2. The multi-longitudinal-mode blue-light ocean HSRL transmitter system of the present invention can optimize the detection wavelength in the blue light band and even a larger range according to the transmission attenuation coefficient of the laser in water, targeting the differences in the material composition and concentration of water bodies in different sea areas. It can output a multi-longitudinal-mode pulsed detection laser with a fixed wavelength, which helps to achieve remote sensing measurement of ocean optical characteristic parameters over a large range and at a large depth, significantly improve the environmental adaptability of ocean HSRL, and enrich the means of constructing ocean HSRL. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of a multi-longitudinal mode blue light ocean high spectral resolution lidar transmitter system according to the present invention;

[0025] Figure 2 Schematic diagram of the device for detecting a wavelength of 443 nm according to the present invention;

[0026] Figure 3Schematic diagram of the principle of matching the backward Brillouin scattering and elastic scattering signals generated by the propagation of multi-longitudinal mode pulse detection light in water with the free spectral range of the interference spectrum discriminator to achieve the spectral separation effect. DETAILED DESCRIPTION

[0027] The present invention will be described in further detail below with reference to the accompanying drawings and examples. It should be noted that the following examples are intended to facilitate understanding of the present invention and do not have any limiting effect on the present invention.

[0028] like Figure 1 As shown, a multi-longitudinal mode blue light ocean high spectral resolution lidar transmitter system includes a narrow linewidth single longitudinal mode pulse laser 1, an adjustable polarization beam splitter 2, a parallel plane cavity optical parametric oscillator 3, an optical parametric amplifier 4, a laser frequency doubler 5, a laser beam expander 6 and necessary optical lenses.

[0029] A narrow-linewidth single-longitudinal-mode pulsed pump light of 532 nm is emitted from a narrow-linewidth single-longitudinal-mode pulsed laser 1, which is divided into two beams of pulsed pump light with different energies by an adjustable polarization beam splitter 2. The low-energy pulsed pump light is incident on a parallel plane cavity optical parametric oscillator 3 to generate a fundamental frequency multi-longitudinal-mode pulsed signal light. The signal light and the high-energy pulsed pump light are simultaneously incident on an optical parametric amplifier 4, where the signal light energy is further increased and then incident on a laser frequency multiplier 5 to generate a multi-longitudinal-mode blue light band detection laser for detecting the optical properties of the ocean. The laser beam expander 6 then adjusts the divergence angle and then injects the laser light toward the water body.

[0030] In the present invention, the system parameters of the multi-longitudinal mode blue light ocean HSRL transmitter need to be determined by first optimizing the detection laser wavelength according to the transmission attenuation coefficient of lasers of different wavelengths in the water body to be measured, and calculating the backward Brillouin scattering frequency offset generated by the interaction between the detection wavelength laser and water molecules. This helps to realize the remote sensing measurement of the optical characteristic parameters of the water body to be measured at great depths.

[0031] The adjustable polarization splitter 2 includes a 532nm half-wave plate 2-1, a polarization splitting prism 2-2 and a 532nm half-wave plate 2-3. By rotating the 532nm half-wave plate 2-1, the energy ratio of the two beams of pulsed light can be adjusted. The low-energy pulse pump light is input into the parallel plane cavity optical parametric oscillator 3 after the polarization state is adjusted by the 532nm half-wave plate 2-3, and the high-energy pulse pump light is input into the optical parametric amplifier 4.

[0032] The parallel plane cavity optical parametric oscillator 3 outputs a fundamental frequency multi-longitudinal mode pulse signal light that is harmonically related to the blue light band detection laser. The central wavelength of the signal light can be adjusted by changing the KTP crystal cutting angle, the angle at which the KTP is placed in the resonant cavity, and the coating parameters of the input and output cavity mirrors. The longitudinal mode spacing of the signal light can be adjusted by changing the resonant cavity length through a displacement platform.

[0033] In the parallel-plane cavity optical parametric oscillator (OPO) 3, low-energy pulsed pump light helps suppress excessive broadening of the signal light spectrum caused by the high intracavity gain, improving the spectral separation of radar echo signals. The use of a parallel-plane cavity reduces the optical length of the oscillator resonator, helping to match the longitudinal mode spacing of the probe laser to the backward Brillouin scattering frequency shift.

[0034] The optical parametric amplifier 4 can further enhance the signal light energy generated by the parallel plane cavity optical parametric oscillator 3, and contribute to the remote sensing measurement of optical characteristic parameters of ocean water bodies at greater depths.

[0035] The laser frequency doubler 5 can frequency double the fundamental frequency multi-longitudinal mode pulse signal light into a blue light band detection laser used for remote sensing measurement of ocean optical properties, and input the blue light band detection laser into the laser beam expander 6.

[0036] The laser beam expander 6 is used to improve the divergence angle of the detection laser.

[0037] like Figure 2 As shown below, taking the detection laser wavelength of 443nm as an example, a multi-longitudinal-mode blue-light ocean high-spectral-resolution lidar transmitter system is introduced. Specifically, the narrow-linewidth single-longitudinal-mode pulse laser 1 uses a 532nm narrow-linewidth single-longitudinal-mode pulse laser, the parallel-plane cavity optical parametric oscillator 3 uses an 886nm parallel-plane cavity KTP optical parametric oscillator, the optical parametric amplifier 4 uses an 886nm KTP optical parametric amplifier, the laser frequency doubler 5 uses an 886nm LBO laser frequency doubler, and the laser beam expander 6 uses a 443nm laser beam expander.

[0038] Narrow linewidth single longitudinal mode pulse laser 1, outputting 532nm high energy single longitudinal mode linearly polarized pulse light as pump light. A self-built seed-injected Nd:YAG pulse laser can be used, or commercial 532nm narrow linewidth single longitudinal mode pulse laser products such as the Nimma series of China Leibao Optoelectronics Technology Co., Ltd., the Powerlite series of Continuum Corporation of the United States, and the YG series of Quantel Corporation of France can be used.

[0039] The adjustable polarization beam splitter 2 includes a 532nm half-wave plate 2-1, a polarization beam splitter prism 2-2, and a 532nm half-wave plate 2-3 connected in sequence. The pump light output by the narrow-linewidth single-longitudinal-mode pulse laser 1 is divided into low-energy pulse pump light and high-energy pulse pump light after passing through the 532nm half-wave plate 2-1 and the polarization beam splitter prism 2-2. The low-energy pulse pump light is polarized by the 532nm half-wave plate 2-3 and then output to the parallel plane cavity optical parametric oscillator 3.

[0040] The parallel plane cavity optical parametric oscillator 3 utilizes an 886nm parallel plane cavity KTP optical parametric oscillator, comprising a sequentially connected input cavity mirror 3-1, a KTP crystal 3-2, and an output cavity mirror 3-3 fixed on a displacement platform. Under the action of low-energy pulsed pump light, it simultaneously emits 886nm multi-longitudinal mode pulsed signal light, idler light, and residual pump light. The idler light and residual pump light are reflected by a first dichroic mirror 7 and absorbed by a first light block 8. The 886nm multi-longitudinal mode pulsed signal light passes through the first dichroic mirror 7 and is transmitted to a second dichroic mirror 11 via an 886nm reflector 9. Calculations show that under normal water conditions, the backward Brillouin scattering frequency shift generated by the interaction between 443nm laser light and water molecules is above 9GHz, indicating that the physical length of the 886nm parallel plane cavity resonator is approximately 9-10mm. By varying the spacing between the input cavity mirror 3-1 and the output cavity mirror 3-3 via the displacement platform, the longitudinal mode spacing of the signal light can be adjusted, thereby achieving excellent spectral separation of the echo signal.

[0041] The 886nm multi-longitudinal mode pulse signal light and the high-energy pulse pump light after passing through the 532nm reflector 10 are combined at the second dichroic mirror 11, and input into the KTP optical parametric amplifier after passing through the 532&886nm reflector 12. At the same time, the 886nm multi-longitudinal mode pulse signal light, idler light and residual pump light with further energy amplification are emitted. The idler light and the residual pump light are reflected by the third dichroic mirror 13 into the second light block 14 for absorption. The amplified 886nm multi-longitudinal mode pulse signal light passes through the third dichroic mirror 13 and is incident on the laser frequency doubler 5.

[0042] The laser frequency doubler 5 adopts an 886nm LBO laser frequency doubler, including an 886nm half-wave plate 5-1 and an LBO crystal 5-2. The multi-longitudinal mode pulse signal light is polarized by the 886nm half-wave plate 5-1 and then injected into the LBO crystal 5-2. At the same time, 443nm multi-longitudinal mode pulse detection light and residual signal light are emitted. The residual signal light is reflected by the fourth dichroic mirror 15 into the third light block 16 for absorption, and the 443nm multi-longitudinal mode pulse detection light is injected into the 443nm laser beam expander 6 after passing through the 443nm reflector 17.

[0043] The 443nm laser beam expander 6 can improve the divergence angle of the 443nm multi-longitudinal mode pulse detection light, and after being emitted therefrom, it can be injected into the water body for detection.

[0044] Figure 3This is a schematic diagram of the principle of matching the backward Brillouin scattering and elastic scattering signals generated by multi-longitudinal mode pulse detection light propagating in water with the free spectral range of the interference spectrum discriminator to achieve spectral separation. The frequency of the elastically scattered echo signal light is consistent with that of the multi-longitudinal mode pulse detection light, and the frequency interval of the backward Brillouin scattering echo signal light and the multi-longitudinal mode pulse detection light is the same, but the center frequency is offset and distributed on both sides of the longitudinal mode of the detection light. When the longitudinal mode interval of the multi-longitudinal mode pulse detection light and the free spectral range of the interference spectrum discriminator are equal to the backward Brillouin scattering frequency interval, the elastically scattered echo signal light can be completely located at the lowest transmittance of the interference spectrum discriminator, and the Brillouin scattering signal can be completely located at the highest transmittance of the interference spectrum discriminator, thereby achieving the purpose of spectral separation.

[0045] The embodiments described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A multi-longitudinal mode blue light ocean high spectral resolution lidar transmitter system, characterized in that: It comprises a narrow linewidth single longitudinal mode pulse laser (1), an adjustable polarization beam splitter (2), a parallel plane cavity optical parametric oscillator (3), an optical parametric amplifier (4), a laser frequency doubler (5) and a laser beam expander (6); The pulse pump light emitted by the narrow-linewidth single-longitudinal-mode pulse laser (1) is divided into two beams with different energies by an adjustable polarization beam splitter (2); the low-energy pulse pump light is injected into a parallel plane cavity optical parametric oscillator (3) to be converted into a fundamental frequency multi-longitudinal-mode pulse signal light, and the fundamental frequency multi-longitudinal-mode pulse signal light and the high-energy pulse pump light are simultaneously injected into an optical parametric amplifier (4) to further increase the signal light energy; the multi-longitudinal-mode blue light detection pulse laser for remote sensing measurement of ocean optical properties is then generated by a laser frequency multiplier (5), and finally output to a laser beam expander (6) to adjust the divergence angle and then be injected into a target water body.

2. The multi-longitudinal mode blue light ocean high spectral resolution lidar transmitter system according to claim 1 is characterized in that: Taking into account the factors that affect the attenuation characteristics of laser transmission in water, a wavelength with the greatest detection depth advantage is selected within the blue light band as the detection wavelength for the target water body to be measured, and a fundamental frequency multi-longitudinal mode pulse signal light having a harmonic relationship with the detection wavelength is generated through a parallel plane cavity optical parametric oscillator (3) and an optical parametric amplifier (4), and then converted into a multi-longitudinal mode blue light detection pulse laser through a laser frequency multiplier (5).

3. The multi-longitudinal mode blue light ocean high spectral resolution lidar transmitter system according to claim 1 is characterized in that: The parallel plane cavity optical parametric oscillator (3) comprises an input cavity mirror, a nonlinear crystal and an output cavity mirror fixed on a displacement platform connected in sequence; the longitudinal mode spacing Δν of the fundamental frequency pulse signal light singal Determined by the optical length L of the resonant cavity, the longitudinal mode spacing of the signal light is adjusted by the displacement platform until the longitudinal mode spacing Δv of the multi-longitudinal mode blue light detection pulse laser after frequency doubling. mb The 180° backward Brillouin scattering frequency shift v generated by the laser propagating in water B Match, expressed as: Where λ mb is the wavelength of the pulsed probe light, v s is the speed of sound, S, T, and P are the salinity, temperature, and pressure of the target water body to be measured, respectively.

4. The multi-longitudinal mode blue light ocean high spectral resolution lidar transmitter system according to claim 1 is characterized in that: The adjustable polarization beam splitter (2) comprises a 532nm half-wave plate 1, a polarization beam splitting prism, and a 532nm half-wave plate 2 connected in sequence. The 532nm pulse pump light emitted by the narrow linewidth single longitudinal mode pulse laser (1) is split into low-energy pulse pump light and high-energy pulse pump light after passing through the 532nm half-wave plate 1 and the polarization beam splitting prism. The low energy pulse pump light is polarized by a 532 nm half-wave plate 2 and then sent to the input end of a parallel plane cavity optical parametric oscillator (3).

5. The multi-longitudinal mode blue light ocean high spectral resolution lidar transmitter system according to claim 4 is characterized in that: Under the action of low-energy pulse pump light, the parallel plane cavity optical parametric oscillator (3) simultaneously emits a first fundamental frequency multi-longitudinal mode pulse signal light, a first idler frequency light and a first residual pump light; wherein the wavelength λ of the first fundamental frequency multi-longitudinal mode pulse signal light is singal Determined according to the laser transmission attenuation characteristics of the water body to be measured; The first idle frequency light and the first residual pump light are reflected by the first dichroic mirror (7) into the first light block (8) for absorption, and the first fundamental frequency multi-longitudinal mode pulse signal light is transmitted through the first dichroic mirror (7) and then transmitted to the second dichroic mirror (11); the first fundamental frequency multi-longitudinal mode pulse signal light and the high energy pulse pump light are combined at the second dichroic mirror (11) and then input into the optical parametric amplifier (4).

6. The multi-longitudinal mode blue light ocean high spectral resolution lidar transmitter system according to claim 5 is characterized in that: The optical parametric amplifier (4) emits a second fundamental frequency multi-longitudinal mode pulse signal light, a second idler light, and a second residual pump light after further energy amplification; wherein the second idler light and the second residual pump light are reflected by a third dichroic mirror (13) into a second light block (14) for absorption, and the second fundamental frequency multi-longitudinal mode pulse signal light passes through the third dichroic mirror (13) and is then emitted into a laser frequency multiplier (5).

7. The multi-longitudinal mode blue light ocean high spectral resolution lidar transmitter system according to claim 1 is characterized in that: The laser frequency multiplier (5) comprises a half-wave plate and an LBO crystal. After being amplified by the optical parametric amplifier (4), the second fundamental frequency multi-longitudinal mode pulse signal light is polarized by the half-wave plate and then injected into the LBO crystal, while emitting multi-longitudinal mode pulse detection light and residual signal light. The remaining signal light is reflected by the fourth dichroic mirror (15) into the third light block (16) for absorption, and the multi-longitudinal mode pulse detection light is injected into the laser beam expander (6).

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