A fully solid-state ozone lidar system based on a solid-state tunable ultraviolet light source

Abstract

The invention discloses a full-solid-state ozone laser radar system based on a solid-state tunable ultraviolet light source, comprising a pump laser, a solid-state tunable ultraviolet laser module, a multi-wavelength laser beam expander, an emission coupling optical path, a receiving telescope, a follow-up optical path, an acquisition computer and a control unit. The solid-state tunable ultraviolet laser module realizes a tunable ultraviolet laser oscillation stage and an amplification stage. Under the laser pumping action of the pump laser, the differential absorption wavelength pair required by the full-solid-state ozone laser radar system is generated by electrically adjusting the cavity length. The cavity length is adjusted synchronously with the pump laser pulse, and the laser wavelength can be switched once for one or several pulses. The full solid-state of the ozone laser radar system can be realized, and the need for regular replacement of gas or dye consumables of a non-solid-state laser radar system is avoided. The stability of the laser radar system is increased, the volume is greatly reduced, and the system weight is reduced, so that the system is easier to be carried on an aircraft platform, a balloon or an airship platform and a satellite platform.

Description

Technical Field

[0001] The present invention relates to the technical field of laser radar, and in particular to an all-solid-state ozone laser radar system based on a solid-state tunable ultraviolet light source, which is used for detecting the ozone concentration profile in the troposphere region which is closely related to human life. Background Art

[0002] Lidar is an irreplaceable active optical remote sensing method for detecting atmospheric parameter profiles. It emits light waves as the system light source and has the characteristics of high temporal and spatial resolution. In recent decades, Lidar has developed rapidly, from the initial atmospheric density Lidar to various types of Lidar, including temperature Lidar, wind Lidar, atomic density Lidar, carbon dioxide Lidar, trace pollutant gas Lidar, etc.

[0003] At present, environmental issues are the focus of global governments, including haze pollution and ozone pollution. Excessive tropospheric ozone can cause poisoning, vision loss, skin diseases, cardiopulmonary failure, damage to human immune function, etc., which greatly threatens human health. To this end, we need to take effective countermeasures to control ozone pollution, among which the detection of tropospheric ozone is an indispensable part of the governance of environmental pollution. The Chinese government has increased its investment in this area, and the construction of ozone lidar has ushered in unprecedented opportunities. However, at present, the tropospheric ozone lidar mainly uses Raman light source as the differential absorption wavelength. Its main principle is to use the Raman frequency shift of gas on laser to generate Stokes laser. For example, the 266nm (or 262nm) laser after the quadrupling of YAG (or YLF) laser pumps the Raman tube of deuterium or hydrogen to generate the laser after Raman frequency shift, which forms the differential absorption wavelength pair required for detecting tropospheric ozone. For example, the wavelength pair with 266nm as pump light: 266nm / 289nm, 289nm / 316nm, or 289nm / 299nm, etc. Since gas is used as the working medium, on the one hand, the shape and divergence angle of the Raman laser generated by the gas are difficult to control; on the other hand, gas as a working substance requires a long working length and occupies a large space; furthermore, the gas working substance needs to be replaced regularly, which is not conducive to long-term stable operation and is not suitable for space platforms. These are the inherent defects of using gas Raman light as the system light source. It cannot meet the needs of long-term stable operation and airborne detection platforms. Summary of the invention

[0004] The purpose of the present invention is to use cerium-doped lithium calcium fluoroaluminate crystals to produce a tunable ultraviolet laser light source, and through cavity length adjustment, obtain the differential absorption laser light source wavelength pair required for detecting tropospheric ozone in the atmosphere, and combine the receiving part and the acquisition control part to realize an all-solid-state ozone detection lidar system to meet the needs of detecting tropospheric ozone profiles, realize the all-solid-state and miniaturization of the ozone lidar system, extend the system life, enhance the system stability, and further provide a technical basis for airborne and satellite-borne.

[0005] To solve the above problems, the present invention proposes a solid-state ozone laser radar system based on a solid-state tunable ultraviolet light source, which includes: a pump laser, a solid-state tunable ultraviolet laser module, a laser beam expander, a transmitting coupling optical path, a receiving telescope, a follow-up optical path, a collection computer and a control unit. Among them:

[0006] The pump laser generates short-wave ultraviolet 266nm (or 262nm) laser by quadruple frequency of YAG (or YLF) laser, which is used for pumping tunable ultraviolet laser.

[0007] The solid-state tunable ultraviolet laser module is based on a cerium-doped calcium lithium fluoroaluminate crystal to realize a tunable ultraviolet laser oscillation stage and an amplification stage. Under the laser pumping action of the pump laser, the cavity length is electrically adjusted to generate the differential absorption wavelength pair required by the all-solid-state ozone lidar system. The cavity length is adjusted synchronously with the pump laser pulse, and the laser wavelength can be switched once with one or several pulses.

[0008] The laser beam expander adopts an achromatic beam expander, which can be a reflective beam expander or a transmissive beam expander. It can work with several wavelengths of lasers working with the all-solid-state laser radar at the same time and have the same magnification, so as to change the laser divergence angle so that its divergence angle meets the field of view angle requirement of the receiving telescope.

[0009] The emission coupling optical path comprises an optical path turning reflector and an emission reflector driven by a motor, and is used to emit the laser light beam expanded by the laser beam expander into the atmosphere of the target object to be detected.

[0010] The receiving telescope is used to receive the backscattered echo signal after the laser interacts with the atmosphere, and the backscattered echo signal includes Mie scattering and Rayleigh scattering signals. The receiving telescope type can be a transmission telescope and a reflection telescope, and the received echo signal is transmitted by space coupling or fiber coupling.

[0011] The subsequent optical path includes a collimating lens, a dichroic mirror, a filter, a converging lens and a photomultiplier tube, which are used to extract effective echo signals from the echo signals received by the receiving telescope and convert them into electrical signals for collection by the collection device. A detector is used internally to realize time-space multiplexing detection of multiple wavelengths.

[0012] The acquisition computer contains a signal acquisition device, a storage hard disk and a data processing and analysis module. It is used to collect and record the electrical signal as a digital signal and store it on the storage hard disk of the acquisition computer. The data analysis module analyzes and processes the collected echo signal to obtain the ozone concentration profile.

[0013] The control unit includes a system operation timing control part and a system component action control part. The system operation timing control part is used to coordinate various components in the system, coordinate the pump laser, solid-state tunable ultraviolet laser module, emission coupling optical path and the acquisition computer in the laser radar system to work in sequence; the system component action control part is used to control the beam emission antenna and scanning unit in the emission coupling unit.

[0014] The advantages and positive effects of the present invention compared with the prior art are:

[0015] The all-solid-state ozone lidar system based on a solid-state tunable ultraviolet light source can realize the all-solid-state ozone lidar system, avoid the need to regularly replace the gas or dye consumables of the non-solid-state lidar system, and increase the stability of the lidar system. In addition, it can greatly reduce the size of the ozone lidar system, reduce the system weight, avoid regular maintenance, liberate staff, and enable the system to achieve fully automated operation, making the system easier to carry on aircraft platforms, balloons or airship platforms and satellite platforms. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0017] Figure 1 This is the schematic diagram of the all-solid-state ozone lidar system based on a solid-state tunable ultraviolet light source;

[0018] Figure 2 This is a diagram of the internal composition of a tunable laser light source;

[0019] Figure 3 It is the subsequent optical path diagram of the system. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0021] An embodiment of the present invention provides an all-solid-state ozone lidar system based on a solid-state tunable ultraviolet light source, which is used to detect the concentration profile of ozone in the atmosphere. The all-solid-state ozone lidar system includes: a pump laser 1, a solid-state tunable ultraviolet laser module 2 based on a crystal of cerium-doped lithium calcium fluoroaluminate, a multi-wavelength laser beam expander 3, an emission coupling optical path 4, a signal receiving telescope 5, a follow-up optical path 6, an acquisition computer 7, and a control unit 8.

[0022] The pump laser 1 is composed of a Nd:YAG or Nd:YLF laser with a quadruple frequency function, which is used to output a 266nm laser or a 262nm laser as a pump light source for the all-solid-state lidar system. The working pulse frequency of the pump laser 1 is not limited and can be from 10Hz to several kHz. The single pulse energy is also not limited and can be selected according to the actual application scenario, ranging from a few millijoules to tens of millijoules. When the near-ground power supply capacity is sufficient, a flash lamp pumped type laser can be selected; for space platform applications, a diode pumped type laser is preferably selected.

[0023] The core component of the tunable ultraviolet laser module 2 is a crystal of cerium-doped calcium lithium fluoroaluminate. Under the laser pumping action output by the pump laser, the crystal component can output ultraviolet laser in a spectral range (280-320nm), and the required laser wavelength can be selected by setting the cavity length.

[0024] The multi-wavelength laser beam expander 3 is used to improve the beam divergence angle of the laser output by the tunable ultraviolet laser module 2 to meet the system reception requirements, and also to reduce the power density of the beam and reduce the damage threshold requirements for the optical devices in the emission coupling optical path. The multi-wavelength laser beam expander 3 needs to be able to meet the requirements of multi-wavelength applications, and can use a reflective beam expander or an achromatic transmission beam expander, and the specific structure type is not limited.

[0025] The emission coupling optical path 4 is used to emit the laser beam expanded by the multi-wavelength laser beam expander 3 into the atmosphere of the target object to be detected. The emission coupling optical path 4 is mainly composed of a plurality of total reflection mirrors that change the position and direction of the beam. The beam pointing adjustment of the last emission mirror is driven by a motor, and the angle of the mirror in at least two dimensions can be controlled by application instructions, so that the two-dimensional adjustment of the emission beam pointing can be achieved.

[0026] The receiving telescope 5 is used to receive the backscattered echo signal after the laser emitted by the transmitting coupling optical path 4 interacts with the atmosphere, and the backscattered echo signal includes Mie scattering and Rayleigh scattering signals. The receiving telescope can be described as a transmission telescope and a reflection telescope, and the received echo signal is transmitted to the subsequent optical path 6 by space coupling or fiber coupling.

[0027] The subsequent optical path 6 includes a collimating lens, a dichroic mirror, a filter, a converging lens and a photomultiplier tube, which are used to extract effective echo signals from the echo signals received by the receiving telescope 5 and convert them into electrical signals for collection by the collection device. The collimating lens uses an ultraviolet band achromatic lens to collimate the multiple wavelength echo signals of the telescope 5 into quasi-parallel beams; the dichroic mirror is used to separate the collimated multiple band parallel beams into multiple single wavelength beams; the filter is used to extract the effective echo signals from the multiple single wavelength beams and suppress the sky background signals outside the band. If the filter is selected as a filter, a filter is set for each path; the converging lens is used to converge and reduce the echo signals passing through the filter to a target surface suitable for detection by the photomultiplier tube; the photomultiplier tube converts the weak light signal into an electrical signal through a photoelectric sensing material, and the internal photomultiplier amplifier stage amplifies the electrical signal.

[0028] The acquisition computer 7 contains a signal acquisition device, a storage hard disk and a data processing and analysis module. The acquisition device is an acquisition card or a photon counting card, which is used to collect and record electrical signals as digital signals and store them on the storage hard disk of the acquisition computer; the data analysis module is used to analyze and process the collected echo signals to obtain the ozone concentration profile.

[0029] The control unit 8 includes a system operation timing control part and a system component motion control part. The system operation timing control part is used to coordinate the various components in the system to work in sequence, and coordinate the various components pump laser 1, solid-state tunable ultraviolet laser module 2, emission coupling optical path 4 and the acquisition computer 7; the system component motion control part is used to control the light beam emission antenna and scanning unit in the emission coupling optical path 4.

[0030] like Figure 2As shown, it is a diagram of a tunable ultraviolet laser module, which includes an input window 101, a polarizer 102, a laser beam expander 103, a first reflector 104, a beam splitter 105, a first cerium-doped calcium lithium fluoroaluminate crystal 106, a dispersion prism 107, a second reflector 108, an output coupling mirror 109, a third reflector 110, a fourth reflector 111, a fifth reflector 112, a second cerium-doped calcium lithium fluoroaluminate crystal 113, a third cerium-doped calcium lithium fluoroaluminate crystal 114 and a sixth reflector 115. The laser output from the pump laser 1 is input into the tunable ultraviolet laser module through the input window 101, and the corresponding polarized laser is selected by the polarizer 102, and then the laser divergence angle and beam power density are improved through the laser beam expander 103. The first reflector 104 and the beam splitter 105 change the direction of the light beam to input the pump laser into the cerium-doped calcium lithium fluoroaluminate crystal 106 to generate the required ultraviolet wide-spectrum laser. The first cerium-doped calcium lithium fluoroaluminate crystal 106, the dispersion prism 107, the second reflector 108 and the output coupling mirror 109 constitute a resonant cavity to complete the oscillation amplification of the laser. The position of the second reflector 108 can be electrically changed to change the length of the resonant cavity, thereby dynamically selecting the required laser wavelength. In the all-solid-state ozone laser radar system described in the present invention, we can set three wavelengths (defined as wavelength A, wavelength B and wavelength C) to time-sharing switch output or two wavelengths (defined as wavelength A and wavelength B) to time-sharing switch output. The output coupling mirror 109 is a partial reflector, and the transmitted output light is the ultraviolet laser required for the laser radar. The output ultraviolet laser enters and exits the second cerium-doped calcium lithium fluoroaluminate crystal 113 and the third cerium-doped calcium lithium fluoroaluminate crystal 114 through the third reflector 110 and the fifth reflector 112. Under the joint action of another part of the pump laser reflected by the fourth reflector 111 and input into the second cerium-doped calcium lithium fluoroaluminate crystal 113 and the third cerium-doped calcium lithium fluoroaluminate crystal 114, the required two-stage amplification of the ultraviolet laser is achieved.

[0031] like Figure 3As shown, it is the subsequent optical path diagram of the all-solid-state ozone laser radar system, including a collimating lens 201, a first dichroic mirror 202, a first filter 203, a second dichroic mirror 204, a third dichroic mirror 205, a second filter 206, a fourth dichroic mirror 207, a seventh reflector 208, a third filter 209, an eighth reflector 210, a converging lens 211, and a detector 212. The collimating lens 201 is an achromatic lens, which can be applied to a wavelength of 266-320nm, and collimates the echo signal received by the telescope into a quasi-parallel beam. The first dichroic mirror 202 is used to separate the backscattered signals (corresponding to wavelength A light signal, wavelength B light signal and wavelength C light signal) of different wavelengths of laser emitted by the all-solid-state ozone laser radar system after the interaction with the atmosphere. As described above, different wavelengths of laser are realized by adjusting the cavity length of the tunable ultraviolet laser. The first dichroic mirror 202 realizes the reflection of wavelength A light signal and wavelength B light signal, and the transmission of wavelength C light signal. The third dichroic mirror 205 reflects the wavelength A light signal and transmits the wavelength B light signal. The seventh reflector 208 reflects the wavelength B light signal. The first filter 203 transmits the wavelength C light signal, and all the background light or other wavelength light outside the band is highly suppressed. The second filter 206 transmits the wavelength A light signal, and all the background light or other wavelength light outside the band is highly suppressed. The third filter 209 transmits the wavelength B light signal, and all the background light or other wavelength light outside the band is highly suppressed. The eighth reflector 210 highly reflects the wavelength B light signal. The fourth dichroic mirror 207 highly reflects the wavelength A light signal and transmits the wavelength B light signal. The second dichroic mirror 204 reflects the wavelength A light signal and the wavelength B light signal, and transmits the wavelength C light signal. The converging lens 211 is an achromatic lens, and its parameters can be the same as those of the collimating lens 201. The detector 212 is a detector with sensitive response in the ultraviolet band, which is used to convert the echo light signal into an electrical signal, and amplify it for collection by the collection device.

Claims

1. A fully solid-state ozone laser radar system based on a solid-state tunable ultraviolet light source, characterized in that: It includes a pump laser, a solid-state tunable ultraviolet laser module, a multi-wavelength laser beam expander, an emission coupling optical path, a receiving telescope, a follow-up optical path, a collection computer and a control unit, wherein: The pump laser is based on the quadrupled frequency of a YAG or YLF laser to generate a short-wave ultraviolet 266nm or 262nm laser, which is used to pump a tunable ultraviolet laser; The solid-state tunable ultraviolet laser module is based on a cerium-doped calcium lithium fluoroaluminate crystal to realize a tunable ultraviolet laser oscillation stage and an amplification stage. Under the laser pumping action of the pump laser, the cavity length is electrically adjusted to generate the differential absorption wavelength pair required by the all-solid-state ozone laser radar system. The cavity length is adjusted synchronously with the pump laser pulse, and the laser wavelength is switched once for one or several pulses. The multi-wavelength laser beam expander adopts an achromatic beam expander, which can be a reflective beam expander or a transmissive beam expander, and can simultaneously work with several wavelength lasers working with the all-solid-state ozone laser radar system, have the same magnification, and achieve the change of the laser divergence angle so that its divergence angle meets the field of view angle requirement of the receiving telescope; The emission coupling optical path comprises an optical path turning reflector and an emission reflector driven by a motor, which is used to emit the laser beam expanded by the laser beam expander into the atmosphere of the target object to be detected; The receiving telescope is used to receive the backscattered echo signal after the interaction between the laser and the atmosphere. The backscattered echo signal includes Mie scattering and Rayleigh scattering signals. The receiving telescope type can be a transmission telescope and a reflection telescope. The received echo signal is transmitted by space coupling or fiber coupling. The subsequent optical path includes a collimating lens, a dichroic mirror, a filter, a converging lens and a photomultiplier tube, which are used to extract effective echo signals from the echo signals received by the receiving telescope and convert them into electrical signals for collection by the collection device. A detector is used internally to realize spatiotemporal multiplexing detection of multiple wavelengths; The acquisition computer contains a signal acquisition device, a storage hard disk and a data processing and analysis module, which is used to collect and record the electrical signals as digital signals and store them on the storage hard disk of the acquisition computer. The data processing and analysis module analyzes and processes the collected echo signals to obtain the ozone concentration profile; The control unit includes a system operation timing control part and a system component action control part. The system operation timing control part is used to coordinate the various components in the system, and coordinate the pump laser, solid-state tunable ultraviolet laser module, emission coupling optical path and the acquisition computer in the laser radar system to work in sequence; the system component action control part is used to control the beam emitting antenna and scanning unit in the emission coupling unit.

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