Multi-target three-dimensional measurement device and method based on double-optical-comb femtosecond laser radar

Abstract

The invention discloses a multi-target three-dimensional measurement device and method based on a double-optical-comb femtosecond laser radar, and relates to the field of femtosecond laser measurement, and the device comprises a double-optical-comb laser source, a single-detector time-sharing switching receiving module, a beam splitting and optical switch module and a scanning galvanometer module which are connected in sequence, and further comprises a single-detector time-sharing switching receiving module, a beam splitting and optical switch module and a scanning galvanometer module which are connected in sequence. The signal control processing module is connected with the single-detector time-sharing switching receiving module, generates a reference pulse signal and a target pulse signal based on the above modules, carries out distance calculation according to the reference pulse signal and the target pulse signal of each target light path, determines a to-be-measured distance of a target object, and sends the to-be-measured distance to the single-detector time-sharing switching receiving module; and performing three-dimensional reconstruction on the target object according to the to-be-measured distance of the target object and the angle information of the scanning galvanometer, and generating a point cloud or a three-dimensional profile diagram of the target object in the current scene, so that the system implementation difficulty and the measurement error can be reduced.

Description

Technical Field

[0001] The present application relates to the field of femtosecond laser measurement, and particularly to a multi-target three-dimensional measurement device and method based on a dual-comb femtosecond lidar. Background Art

[0002] With the rapid development of automation, intelligent transportation, robotics, and scientific research, the demand for high-precision, high-speed, multi-target three-dimensional measurement and imaging technologies is increasing day by day.

[0003] Patent Publication No. CN102998676A discloses a dual-femtosecond laser frequency comb ranging system. The invention provides a dual-femtosecond laser frequency comb ranging system with high precision, large measurement range, no measurement dead zone, and capable of self-correcting the air refractive index. However, this system cannot perform three-dimensional scanning and multi-target simultaneous ranging detection.

[0004] Patent Publication No. CN221465826U discloses a method of pulse multiplexed time-division multiplexed two-photon imaging, which measures through different optical path lengths with different delay amounts. However, in this method, the signals of multiple channels are close in time, and echo signal superposition or overlap may occur, resulting in measurement errors or signal distortion. And more complex signal processing algorithms are required to distinguish and analyze the echo signals with different delays, increasing the computational burden.

[0005] The paper "Multi-target absolute distance measurement based on dual-femtosecond lasers with time-domain distinguishable features" published in the Journal of Scientific Instrumentation proposes a multi-target ranging scheme. In this scheme, a femtosecond laser source reaches multiple targets simultaneously through optical fiber beam splitting. The reference pulses of each path are distinguished by the optical intensity difference of the pulses, and the corresponding measurement pulses are matched, so as to realize the measurement of multiple paths of distances. Then, the multi-target absolute distance is calculated in real time through an intensity cross-correlation module and a Field Programmable Gate Array (FPGA) data processing unit. However, there are obvious deficiencies in this multi-path parallel measurement: on the one hand, the simultaneous transmission of multiple pulses is prone to crosstalk or partial overlap, and more complex signal separation and matching algorithms are required, increasing the difficulty of system implementation; on the other hand, the requirements for the configuration of the light source power, optical fiber, and detector are relatively high, and the overall cost and volume increase accordingly. Moreover, in the case of a large number of targets or long distances, the problems of signal-to-noise ratio reduction and measurement error amplification are more likely to occur. Summary of the Invention

[0006] The purpose of the present application is to provide a multi-target three-dimensional measurement device and method based on a dual-comb femtosecond lidar to solve the problems of large system implementation difficulty and large measurement error.

[0007] To achieve the above purpose, the present application provides the following solutions:

[0008] In a first aspect, the present application provides a multi-target three-dimensional measurement device based on a dual-comb femtosecond lidar. The multi-target three-dimensional measurement device based on a dual-comb femtosecond lidar includes: a dual-comb laser source, a single-detector time-division switching receiving module, a beam splitting and optical switch module, and a scanning galvanometer module that are connected in sequence, and a signal control and processing module connected to the single-detector time-division switching receiving module;

[0009] The dual-comb laser is configured to emit measurement signal pulses to a reference target in the single-detector time-division switching receiving module and a target optical path in the beam splitting and optical switch module; and is further configured to emit sampling signal pulses to a reference optical path and a measurement optical path in the single-detector time-division switching receiving module;

[0010] The single-detector time-division switching receiving module is configured to receive echo pulses of each target optical path according to a timing switching signal, so that the echo pulses and the sampling signal pulses undergo a sum-frequency reaction in the measurement optical path, and are photoelectrically detected by a first photodetector to generate target pulse signals, and input the target pulse signals into channel 1 of an analog-to-digital converter; the echo pulses are echo pulses of the measurement signal pulses; and is further configured to make the reflected pulses passing through the reference target and the sampling signal pulses undergo a sum-frequency reaction in the reference optical path, and are photoelectrically detected by a second photodetector to generate reference pulse signals, and input the reference pulse signals into channel 2 of the analog-to-digital converter;

[0011] The beam splitting and optical switch module is configured to split the measurement signal pulses into multiple pulses, emit them into the target optical paths, and control the opening and closing of optical switches on each target optical path according to a timing switching signal to achieve time-division multiplexing measurement of multiple targets or multiple channels;

[0012] The scanning galvanometer module is configured to, on each target optical path, use a scanning galvanometer to sample a to-be-measured target area of a target object in a two-dimensional or three-dimensional space according to a set scanning trajectory;

[0013] The signal control and processing module is configured to perform distance calculation based on the reference pulse signals and the target pulse signals of each target optical path to determine the to-be-measured distance of the target object, and perform three-dimensional reconstruction on the target object according to the to-be-measured distance of the target object and the angle information of the scanning galvanometer to generate a point cloud or a three-dimensional contour map of the target object in the current scene.

[0014] Second aspect, the present application provides a multi-target three-dimensional measurement method based on a dual-comb femtosecond lidar. The multi-target three-dimensional measurement method based on the dual-comb femtosecond lidar applies the above-mentioned multi-target three-dimensional measurement device based on the dual-comb femtosecond lidar. The multi-target three-dimensional measurement method based on the dual-comb femtosecond lidar includes:

[0015] Using a dual-comb laser to emit measurement signal pulses to a reference target in a single-detector time-division switching receiving module and a target optical path in a beam splitting and optical switch module, and to emit sampling signal pulses to a reference optical path and a measurement optical path in the single-detector time-division switching receiving module;

[0016] Generating a target pulse signal according to the echo pulse returned by the measurement signal pulse via the target optical path and the sampling signal pulse on the measurement optical path;

[0017] Generating a reference pulse signal according to the reflected pulse reflected by the reference target and the sampling signal pulse;

[0018] Performing distance calculation according to the reference pulse signal and the target pulse signals of each target optical path to determine the distance to be measured of the target object;

[0019] Performing three-dimensional reconstruction on the target object according to the distance to be measured of the target object and the angle information of the scanning galvanometer to generate a point cloud or a three-dimensional contour map of the target object in the current scene.

[0020] According to the specific embodiments provided by the present application, the following technical effects are disclosed in the present application:

[0021] The present application only sets one photodetector for the echo pulses of multiple target optical paths, adopts a time-division switching method of a single detector, and sequentially receives the echo pulses of each target optical path, reducing the hardware complexity and cost. Each time the present application only receives the echo pulse of one target optical path, avoiding crosstalk or signal overlap caused by multiple echo pulses arriving at the photodetector simultaneously, reducing the measurement error, having a low implementation difficulty, and reducing the requirements for the light source power and the detector sensitivity, and reducing the complexity of the signal separation and matching algorithm, effectively improving the signal-to-noise ratio and accuracy of the measurement; based on the timing switching signal, the present application can dynamically select the reflection channels to be measured to adapt to different measurement requirements.

[0022] In addition, the present application also sets a reference optical path, performs distance calculation according to the reference pulse signal and the target pulse signals of each target optical path to determine the distance to be measured of the target object, and performs three-dimensional reconstruction on the target object according to the distance to be measured of the target object and the angle information of the scanning galvanometer to generate a point cloud or a three-dimensional contour map of the target object in the current scene. The present application can simultaneously measure the distance to be measured of the target object and the point cloud or the three-dimensional contour map of the target object in the current scene. Description of the Drawings

[0023] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the accompanying drawings required in the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0024] Figure 1 Schematic diagram of a multi-target three-dimensional measurement device based on a dual-comb femtosecond lidar provided by the present application;

[0025] Figure 2 Schematic diagram of the optical path of the reference pulse signal provided by the present application;

[0026] Figure 3 Schematic diagram of the optical path of the target pulse signal provided by the present application;

[0027] Figure 4 Control timing diagram provided by the present application;

[0028] Figure 5 Schematic diagram of the optical path of the sampling signal pulse provided by the present application;

[0029] Figure 6 Schematic diagram of the waveform that should theoretically be collected by the ADC at a certain moment provided by the present application;

[0030] Figure 7 Schematic diagram of the synchronous hardware architecture provided by the present application. Detailed implementation manners

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, rather than all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0032] To make the above objects, features, and advantages of the present application more obvious and understandable, the present application will be further described in detail below with reference to the accompanying drawings and specific implementation manners.

[0033] The present application provides a multi-target three-dimensional measurement device based on a dual-comb femtosecond lidar, including: a dual-comb laser source, a single-detector time-sharing switching receiving module, a beam splitting and optical switch module, and a scanning galvanometer module that are connected in sequence, and a signal control and processing module connected to the single-detector time-sharing switching receiving module.

[0034] The dual optical frequency comb laser is used to emit measurement signal pulses to the reference target in the single detector time-division switching receiving module and the target optical path in the beam splitting and optical switch module; it is also used to emit sampling signal pulses to the reference optical path and the measurement optical path in the single detector time-division switching receiving module.

[0035] In practical applications, the dual optical frequency comb laser source consists of two femtosecond lasers, which are respectively used as the local oscillator laser (Local Laser) and the signal laser (Signal Laser). Through phase-locking technology, stable signals are generated by the two femtosecond laser frequency combs, providing ranging capabilities with high resolution and high-speed sampling.

[0036] The single detector time-division switching receiving module is used to receive the echo pulses of each target optical path according to the timing switching signal, so that the echo pulses and the sampling signal pulses undergo sum-frequency reaction in the measurement optical path. The first photodetector performs photoelectric detection to generate target pulse signals, and inputs the target pulse signals into channel 1 of the analog-to-digital converter; the echo pulses are the echo pulses of the measurement signal pulses; it is also used to make the reflected pulses passing through the reference target and the sampling signal pulses undergo sum-frequency reaction in the reference optical path. The second photodetector performs photoelectric detection to generate reference pulse signals, and inputs the reference pulse signals into channel 2 of the analog-to-digital converter.

[0037] In practical applications, the single detector time-division switching receiving module: This application only sets 2 photodetectors (for reference light and multi-target light). The control system sequentially receives the return light of each target signal optical path according to the time-division switching method; the return light of each optical path undergoes sum-frequency reaction with the local oscillator laser through a periodically poled KTP (PPKTP) crystal, and after the clutter is filtered by a low-pass filter (Low Pass Filter, LPF), it is input into the photodetector, and an electrical signal is output to an analog-to-digital converter (Analog-to-digital converter, ADC).

[0038] The photodetector uses an avalanche photodiode (APD) to detect the envelope of the sum-frequency signal and output an analog signal to the analog-to-digital converter (ADC).

[0039] The beam splitting and optical switch module is used to split the measurement signal pulses into multiple pulses and emit them into the target optical paths, and control the opening and closing of the optical switches on each target optical path according to the timing switching signal to achieve time-division multiplexing measurement of multiple targets or multiple channels.

[0040] In practical applications, the beam splitting and optical switch module: The optical pulses output by the signal laser are distributed to multiple optical paths according to a preset ratio through a beam splitter (BS); high-speed optical switches are arranged on each optical path, and the control system opens or closes each liquid crystal beam shutter according to a predetermined timing signal, so as to realize time-division multiplexing measurement of multiple targets or multiple channels.

[0041] Furthermore, the high-speed optical switch is a liquid crystal beam shutter (LCBS), which can be quickly opened or closed according to the timing signal set by the control system, so as to sequentially select the echo signals of different optical paths in different time periods.

[0042] The scanning galvanometer module is used to sample the target area to be measured of the target object in two-dimensional or three-dimensional space according to a set scanning trajectory by using a scanning galvanometer on each target optical path.

[0043] In practical applications, the scanning galvanometer module: is configured in each signal optical path, uses a Galvanometers scanning galvanometer, and samples the target area to be measured point by point or line by line in two-dimensional or three-dimensional space according to a predetermined scanning trajectory.

[0044] Furthermore, the scanning galvanometer module is a Galvanometers scanning galvanometer (Galvanometers1, Galvanometers2) and its driving circuit, which is used to change the beam emission angle and realize scanning measurement of the target object within a three-dimensional space range.

[0045] The signal control and processing module is used to perform distance calculation according to the reference pulse signal and the target pulse signals of each target optical path to determine the distance to be measured of the target object, and, according to the distance to be measured of the target object and the angle information of the scanning galvanometer, perform three-dimensional reconstruction of the target object to generate a point cloud or a three-dimensional contour map of the target object in the current scene.

[0046] In practical applications, the signal control and processing module: receives the digital signals output by an analog-to-digital converter (ADC), and uses hardware acceleration means such as FPGA+GPU to perform distance calculation and three-dimensional data reconstruction; combines the scanning galvanometer angle information and the ranging result, and converts the measured internal coordinates into real three-dimensional space coordinates through a geometric calibration algorithm to generate a point cloud or a three-dimensional contour map of the target scene.

[0047] Furthermore, a field programmable gate array (Field Programmable Gate Array, FPGA) is used to perform real-time preprocessing on high-speed sampled data and execute part of the initial operations of distance calculation.

[0048] The Graphics Processing Unit (GPU) is used to perform deep operations on massive data, real-time imaging, and visualization processing to achieve three-dimensional reconstruction.

[0049] Through the above structure, the present application realizes multi-target three-dimensional measurement. And due to the time-sharing switching method of a single detector, the hardware complexity and the risk of algorithm interference are reduced, and the signal-to-noise ratio and measurement accuracy of the measurement are improved.

[0050] In an exemplary embodiment, the single-detector time-sharing switching receiving module specifically includes: a measurement signal pulse optical path and a sampling signal pulse optical path.

[0051] Among them, the measurement signal pulse optical path includes a reference target optical path and the reference optical path; the reference target optical path includes a first collimator, a first half-wave plate, a first mirror, a first polarization beam splitter prism, a quarter-wave plate, and a reference target on the same optical path.

[0052] The measurement signal pulse is reflected by the reference target optical path into the reference optical path, and a sum-frequency reaction occurs with the sampling signal pulse in the reference optical path, and is photoelectrically detected by a second photodetector to generate a reference pulse signal.

[0053] The sampling signal pulse optical path includes a reflection optical path and a polarization optical path; the reflection optical path and the polarization optical path share a second collimator, a second half-wave plate, and a second polarization beam splitter prism; the reflection optical path further includes a second mirror and the measurement optical path; the polarization optical path further includes a third half-wave plate, a third polarization beam splitter prism, and the reference optical path.

[0054] After the sampling signal pulse is polarization-split by the second polarization beam splitter prism, one beam of the sampling signal pulse enters the second mirror and is reflected into the measurement optical path; the other beam of the sampling signal pulse enters the reference optical path after passing through the third half-wave plate and the third polarization beam splitter prism.

[0055] In an exemplary embodiment, the measurement optical path specifically includes: a first focusing lens, a first sum-frequency crystal, a first low-pass filter, and a first photodetector on the same optical path;

[0056] The reference optical path specifically includes: a second polarization beam splitter prism, a second focusing lens, a second sum-frequency crystal, a second low-pass filter, and a second photodetector on the same optical path.

[0057] In an exemplary embodiment, the beam splitting and optical switch module specifically includes: a beam splitter and multiple target optical paths;

[0058] The beam splitter divides the measurement signal pulse into multiple pulses and emits them into each target optical path;

[0059] The target optical path includes an optical fiber, a third collimator, an optical switch, and a target object on the same optical path; the optical switch is a liquid crystal beam shutter.

[0060] In an exemplary embodiment, the scanning galvanometer module is disposed between the optical switch and the target object; the scanning galvanometer module changes the beam exit angle to perform a scanning measurement on the target object.

[0061] In an exemplary embodiment, the signal control and processing module specifically includes: an FPGA and a GPU;

[0062] The FPGA is used to perform distance calculation according to the reference pulse signal and the target pulse signals of each target optical path;

[0063] The GPU is used to perform distance calculation according to the reference pulse signal and the target pulse signals of each target optical path.

[0064] This application adopts a single-detector structure at the target signal end that combines time-division multiplexing and a high-speed optical switch, and sequentially selects multiple target optical paths for ranging; thereby avoiding crosstalk or signal overlap caused by multiple pulses arriving at the detector at the same time, reducing the requirements for the light source power and the detector sensitivity, and reducing the complexity of the signal separation and matching algorithms, effectively improving the signal-to-noise ratio and accuracy of the measurement.

[0065] The technical solution of this application will be further elaborated below with specific examples.

[0066] In this embodiment, the dual-comb laser is composed of two femtosecond lasers, namely a local oscillator laser and a signal laser. Through phase-locking technology (locking the repetition frequency, carrier-envelope phase, etc.), a stable sum-frequency signal is generated after the sum-frequency of the two combs, providing high-resolution (micrometer to sub-millimeter level) and high-speed sampling ranging capabilities. The signal light is split by a beam splitter (50:50 BS) and distributed to different optical paths. Each optical path is equipped with a high-speed optical switch, namely a liquid crystal beam shutter (LCBS1, LCBS2), and the switch state is controlled by the control system according to a predetermined timing signal to achieve time-division multiplexing.

[0067] The scanning galvanometer module is installed in the signal comb path and is configured with Galvanometers scanning galvanometers (Galvanometers1, Galvanometers2). The scanning galvanometer scans the signal beam along a predetermined trajectory in a two-dimensional or three-dimensional space to achieve point-by-point or line-by-line sampling, which is suitable for the measurement of large-area or multi-target scenarios. The drive control board of the scanning galvanometer sends real-time scanning angle information to the FPGA for subsequent geometric calibration.

[0068] The measurement principle is as follows:

[0069] The repetition frequency and phase offset frequency of an existing commercial fiber femtosecond laser are locked to a rubidium atomic clock by the first femtosecond laser frequency comb (i.e., signal Laser) and the second femtosecond laser frequency comb (i.e., Local Laser) respectively. The repetition frequencies of the two are 100 MHz and 100.003 MHz, that is, 3k measurements can be performed per second. The ADC uses a 14-bit model ad9643 with a sampling rate of 250 MHz. The model of the scanning galvanometer is GVS212( / M), the model of the APD is ky-aprm-50M-S-1MM, the low-pass filter is 40 MHz, the model of the liquid crystal beam shutter is LCC1623( / M), and the accuracy of the three-dimensional measurement is in the micron level.

[0070] As Figure 1 shown, the multi-target three-dimensional measurement device based on a dual-comb femtosecond lidar proposed in this application includes a first femtosecond laser frequency comb signal Laser, a second femtosecond laser frequency comb Local Laser, polarizing beam splitters (PBS) 1, PBS2, PBS3, a half-wave plate λ / 2, a first photodetector APD1, a second photodetector APD2, an analog-to-digital converter ADC, and a signal control and processing module, focusing lenses Lens1, lens2, sum-frequency crystals PPKTP1, PPKTP2, mirrors Flat Mirror1, Flat Mirror2, collimators Col1, Col2, Col3, Col4, optical fibers (OF) 1, OF2, a beam splitter BS, target mirrors Mirror(Tar)1, Mirror(Tar)2, a reference target Mirror(Ref), liquid crystal beam shutters LCBS1, LCBS2, and scanning galvanometers Galvanometers1, Galvanometers2. Wherein, λ is the wavelength.

[0071] As Figure 2As shown, the echo pulse returned by the laser of the signal laser hitting the reference target undergoes a sum-frequency effect with the local oscillator laser and enters APD2, which is called the reference pulse signal. The first femtosecond laser frequency comb, the signal Laser, serves as the measurement signal source and emits measurement signal light pulses to Col1 for collimation. The polarization direction of the incident light is adjusted by a half-wave plate λ / 2 to control the distribution ratio of light in PB. Among them, compared with the incident pulse, the pulse reflected by the target object on the flat mirror Flat Mirror1 changes in the vertical height, and this mirror is lower than the incident light in height. At this time, the light passing through PBS1 is divided into two parts: reflected light and transmitted light. The reflected light passes through a λ / 4 wave plate, and the linearly polarized light is converted into circularly polarized light. When the circularly polarized light is reflected on the mirror, its rotation direction will reverse (left-handed becomes right-handed, right-handed becomes left-handed), but it still remains circularly polarized light. When the reflected circularly polarized light passes through the λ / 4 wave plate again, it will be converted back into linearly polarized light.

[0072] Since the rotation direction of the circularly polarized light has reversed, the direction of the outgoing linearly polarized light rotates 90° relative to the initial incident light and changes from reflection to transmission when passing through PBS. Subsequently, it passes through PBS2, is transmitted, passes through Lens2 and is focused on PPKTP2, causing the reflected pulse of the reference target to undergo a sum-frequency reaction with the local oscillator laser to generate a sum-frequency signal. After passing through LPF2, high-frequency clutter is filtered out to obtain the envelope of the sum-frequency signal. After passing through APD2, photoelectric detection is performed, and then it enters the 2nd channel of the ADC. This local oscillator laser is the sampling signal pulse.

[0073] As Figure 3As shown in the figure, the laser of the signal laser hits the target, and the returned echo pulse generates a sum-frequency effect with the local oscillator laser. It enters APD1, which is called the target pulse signal. The transmitted light of PBS1 passes through BS and is split into two equal parts at a ratio of 50:50. One half passes through OF1, is collimated by Col3, passes through the high-speed optical switch liquid crystal beam shutter LCBS1, passes through the scanning galvanometer Galvanometers1, and is scanned at a certain frequency. Then it passes through the target mirror Mirror(Tar)1 and returns along the original optical path. At this time, the high-speed optical switch, that is, the liquid crystal beam shutter LCBS1, has its switching state controlled by the control system according to the predetermined timing signal. When it is in the open state, light is allowed to pass through and return. The returned echo pulse is transmitted at PBS1, passes through the flat mirror Flat Mirror1, and is reflected at this time. The pulse reflected by the target on the flat mirror Flat Mirror1 has a change in the vertical height compared to the incident pulse, and this mirror is lower than the incident light in height. It passes through PBS3 and continues to be transmitted, enters Lens1, is focused on PPKTP1, generates a sum-frequency effect, has a sum-frequency reaction with the local oscillator laser, generates a sum-frequency signal, passes through LPF1 to filter out high-frequency clutter, obtains the envelope of the sum-frequency signal, passes through APD1 for photoelectric detection, and then enters channel 1 of the ADC. The light passing through BS is split into two equal parts at a ratio of 50:50, and the other half of the light passing through OF2 enters channel 1 of the ADC in the same way.

[0074] Furthermore, the beam splitter (BS) is a 50:50 beam splitter, or the beam splitting ratio can be adjusted according to measurement requirements; by adjusting the beam splitting ratio and the timing control of the optical switch, the number of optical paths can be flexibly increased or decreased to meet the requirements for different fields of view, different resolutions, or different measurement rates.

[0075] After the FPGA issues an enable signal, first, LCBS1 is turned on and LCBS2 is turned off to measure the distance to target 1. At this time, Galvanometers2 performs a scanning action for the subsequent positioning or pre-scanning of target 2, while the scanning galvanometer (Galvanometers1) of target 1 remains stable to reduce interference. After continuously measuring target 1 600 times and calculating the average value, it is switched to turn on LCBS2 and turn off LCBS1 to start measuring the distance to target 2. At this time, Galvanometers1 performs a scanning action to obtain the average value of 600 measurements of target 2 in the same way. By alternately enabling different optical valves and making the corresponding scanning galvanometers "remain stationary" or "act in advance", the interference of the galvanometer movement on the same target during the ranging process can be avoided, thereby improving the measurement accuracy and efficiency.

[0076] In this embodiment, target 1 is Mirror(Tar)1 and target 2 is Mirror(Tar)2.

[0077] The timing diagram is asFigure 4 As shown, after the system issues an enable signal (EN), the timer CNT1 starts timing first. Every 0.2 seconds, its count value is cleared and the counter CNT2 is triggered to flip between 0 and 1. When CNT2 is 0, LCBS1_EN is pulled high and LCBS2_EN remains low; when CNT2 is 1, LCBS2_EN is pulled high and LCBS1_EN is set low.

[0078] During the period when LCBS1_EN is at a high level, at the midpoint of its duration, Galvanometers2_EN is pulled high for one clock cycle; when LCBS2_EN is pulled high, similarly at the midpoint of its duration, Galvanometers1_EN is pulled high for one clock cycle. Here, "pulled high" means switching the signal from a low level to a high level, indicating the start of the corresponding light valve or scanning galvanometer. Through this alternating timing control and counting flip, the time-sharing measurement of two targets and the coordination of the corresponding galvanometer actions are achieved, thus avoiding interference with the galvanometer movement during the ranging process.

[0079] To ensure the strict synchronization of each module (femtosecond laser, galvanometer control board, ADC, FPGA), this application uses a rubidium atomic clock as the global clock reference, and the synchronization hardware architecture is as Figure 7 shown.

[0080] The rubidium clock usually outputs two highly stable signals:

[0081] 10MHz reference frequency signal: Provides a highly stable reference with frequency locking for each module;

[0082] 1PPS (Pulse Per Second) pulse signal: Serves as the global time mark, providing an accurate time reference for data acquisition and correction.

[0083] These signals are amplified and evenly distributed to each acquisition and control unit through a dedicated clock distribution and synchronization module, ensuring that all modules can work based on a unified time reference.

[0084] 1. Synchronization of the femtosecond laser.

[0085] The femtosecond laser (including the signal laser and the local oscillator laser) uses the 10MHz signal output by the rubidium clock for frequency and phase locking to ensure the stability and repeatability of the output laser pulses; at the same time, it also receives the 1PPS pulse as a time mark inside to ensure consistency with other modules of the system in the time domain.

[0086] 2. Synchronization of the galvanometer control board and other acquisition modules.

[0087] The galvanometer control board, ADC, and FPGA all receive the 10MHz and 1PPS signals from the clock distribution module. Inside each module, a high-precision counter (driven by the rubidium clock signal) is used to generate the local time reference, and a timestamp is embedded during the data acquisition process based on this.

[0088] 3. The ADC and FPGA cooperate to embed timestamps.

[0089] The ADC module performs data sampling under the drive of an external synchronization signal. Although the ADC itself does not directly generate timestamps, its sampling operation is strictly triggered by the rubidium clock synchronization signal. After the FPGA in the system receives the ADC sampling data, it uses the high-precision counter synchronized by the rubidium clock inside to attach the current sampling moment as a timestamp to the data. In this way, all the sampling data obtained through the ADC carry accurate time information, providing a reliable time alignment basis for subsequent distance calculation and 3D reconstruction.

[0090] 4. Signal distribution and delay correction.

[0091] The clock distribution and synchronization module is not only responsible for evenly distributing the 10MHz and 1PPS signals of the rubidium clock, but during the transmission process, due to reasons such as cable length and buffer circuits, certain delays and jitters will occur. To solve this problem, a buffer and delay compensation circuit is designed inside this module, which can reduce the inconsistency of these transmission delays. Each module uses a real-time correction algorithm according to the pre-measured transmission delay parameters to perform delay compensation on the acquired data, so as to achieve a time alignment accuracy of the overall system reaching the microsecond level or even approaching the nanosecond level.

[0092] As Figure 5 shown, the second femtosecond laser frequency comb Local Laser serves as the sampling signal source, emits optical pulses to Col1 for collimation, adjusts the polarization direction of the incident light through a half-wave plate to control the distribution ratio of light in the PBS, and then passes through PBS2. At this time, reflection and transmission occur. The transmitted light passes through a λ / 2 wave plate, passes through PBS3, undergoes reflection, enters Lens1, enters PPKT1, the echo pulse undergoes a sum-frequency reaction with the local oscillator laser to generate a sum-frequency signal, passes through LPF1 to filter out high-frequency clutter, obtains the envelope of the sum-frequency signal, passes through APD1 for photoelectric detection, and then enters Channel 1 of the ADC; the reflected light passes through the mirror FlatMirror2, undergoes reflection, the light enters PBS2 and undergoes reflection and enters Lens2, undergoes a sum-frequency reaction with the signal laser to generate a sum-frequency signal, passes through LPF2 to filter out high-frequency clutter, obtains the envelope of the sum-frequency signal, passes through APD2 for photoelectric detection, and then enters Channel 2 of the ADC.

[0093] The ADC inputs the acquired data into the signal processing and control unit for distance calculation.

[0094] The signal processing control unit performs distance calculation by adopting a two - level data acceleration processing method of GPU + FPGA. The FPGA is used for real - time pre - processing of high - speed sampled data and performing part of the initial operations of distance calculation; the GPU is used for in - depth operation, real - time imaging and visualization processing of massive data to achieve high - frame - rate three - dimensional reconstruction.

[0095] After obtaining multi - target time - sharing echo data, this application introduces a filtering and fitting method based on time - division multiplexing and Levenberg–Marquardt (LM) least - squares fitting to improve the accuracy of echo peak detection and the stability of three - dimensional measurement.

[0096] The embodiment of this application provides a multi - target three - dimensional measurement method based on a dual - optical - comb femtosecond lidar. This method is executed by a computer device, which can be specifically executed alone by a computer device such as a terminal or a server, or jointly executed by a terminal and a server. In the embodiment of this application, this method includes the following steps.

[0097] S1: Use a dual - optical - comb laser to emit measurement signal pulses to the reference target in the single - detector time - sharing switching receiving module and the target optical path in the beam splitting and optical switch module, and emit sampling signal pulses to the reference optical path and the measurement optical path in the single - detector time - sharing switching receiving module.

[0098] S2: Generate a target pulse signal according to the echo pulse returned by the measurement signal pulse via the target optical path and the sampling signal pulse on the measurement optical path.

[0099] S3: Generate a reference pulse signal according to the reflected pulse reflected by the reference target and the sampling signal pulse.

[0100] S4: Perform distance calculation according to the reference pulse signal and the target pulse signals of each target optical path to determine the distance to be measured of the target object.

[0101] S5: Perform three - dimensional reconstruction on the target object according to the distance to be measured of the target object and the angle information of the scanning galvanometer, and generate a point cloud or a three - dimensional contour map of the target object in the current scene.

[0102] In an exemplary embodiment, S4 can be replaced by the following steps.

[0103] Combine the reference pulse signal and the target pulse signal to generate continuous sampling data.

[0104] Based on the timing switching signal, divide the continuous sampling data into time - domain segments of multiple channels.

[0105] Perform pre - processing on each time - domain segment to determine the preliminary position of the pulse peak.

[0106] For the echo pulses of each channel, a Gaussian pulse model is selected to establish a least - squares residual function.

[0107] Based on the least - squares residual function, taking the preliminary position of the pulse peak as the fitting initial value, using the LM fitting algorithm to fit the Gaussian pulse model and the continuous sampling data, and determining the distance to be measured of the target object.

[0108] In an exemplary embodiment, based on the least - squares residual function, taking the preliminary position of the pulse peak as the fitting initial value, using the LM fitting algorithm to fit the Gaussian pulse model and the continuous sampling data, and determining the distance to be measured of the target object, specifically including:

[0109] Using To determine the distance to be measured of the target object; where \(L\) is the distance to be measured of the target object; \(c\) is the speed of light in vacuum; is the refractive index of air; is the repetition frequency of the signal laser; is the target pulse peak time of the target pulse signal; is the reference pulse peak time of the reference pulse signal; is the reference pulse peak time of the reference pulse signal in the next cycle.

[0110] In an exemplary embodiment, S5 can be replaced by the following steps.

[0111] Through geometric calibration, establish a corresponding relationship between the distance to be measured of the target object and the angle information of the scanning galvanometer and the real - space coordinates.

[0112] According to the corresponding relationship, perform three - dimensional reconstruction on the target object to generate a point cloud or a three - dimensional contour map of the target object in the current scene.

[0113] In practical applications, geometric calibration is completed through the following steps:

[0114] 1) Place a reference target or a corner reflector at a position with known accurate coordinates.

[0115] Furthermore, at least 5 - 10 calibration points are selected within the measured area. It is required that the calibration points are evenly distributed at the edges, center, and corners of the area to ensure coverage of the entire measurement area.

[0116] Use a high - precision measuring instrument to pre - determine the real coordinates of each calibration point.

[0117] 2) Execute the conventional measurement process of this system for each reference point to obtain the internal coordinates of the system.

[0118] Furthermore, this application also includes information such as the angle and distance of the scanning galvanometer.

[0119] Using the system's own measurement process, repeat the measurement of each reference point (for example, take the average of 600 times), and collect the distance data R obtained by laser ranging and the angle information θ collected by the scanning galvanometer, so as to form the internal coordinate data.

[0120] 3) Establish an error model and perform non-linear fitting and correction on parameters such as scanning angle and ranging.

[0121]

[0122]

[0123] Among them, θ represents the angle information collected by the scanning galvanometer, and R is the distance information obtained by laser ranging.

[0124] The internal coordinates measured by the system are set as and the true coordinates are Then the model can be expressed as:

[0125]

[0126]

[0127]

[0128] Among them: are the scanning scale factors of each axis (reflecting the conversion ratio from internal measurement data (including angle information) to true coordinates); , , are the zero-drift compensation amounts of each axis; is a function describing the non-linear error, expressed by a quadratic or higher-order polynomial (for example ).

[0129] 4) Obtain the mapping relationship between the scanning galvanometer angle and the true space coordinates, as well as calibration parameters such as zero drift and scale factor.

[0130] Furthermore, using the preliminary measurement data, the initial values of each scale factor and zero drift are obtained by simple linear regression.

[0131] For example, perform regression on the x-axis data: .

[0132] can be regarded as the preliminary estimate. Similarly, process the y and z axes.

[0133] Using the Levenberg–Marquardt (LM) algorithm, perform nonlinear least squares fitting on all the calibration point data to solve for the unknown calibration parameters in the above error model.

[0134] Define the residual for each calibration point i: .

[0135] : The "residual" of the i-th calibration point.

[0136] : The "true coordinates" of the i-th calibration point.

[0137] : The "model predicted coordinates" of the i-th calibration point.

[0138] i: Represents the number of the calibration point.

[0139] The goal is to minimize the sum of the squared residuals: .

[0140] By iteratively updating the parameters until the residuals converge or reach the preset number of iterations, obtain the optimal set of calibration parameters .

[0141] 5) Fix the calibration parameters into the system software to ensure the three-dimensional measurement accuracy of unknown targets.

[0142] In practical applications, after obtaining the time-division multiplexed echo data of multiple targets, introduce the filtering and fitting method based on time-division multiplexing and Levenberg–Marquardt (LM) least squares fitting through the following steps to improve the echo peak detection accuracy and three-dimensional measurement stability.

[0143] Step 1: Time-domain slicing and data rearrangement: According to the timing information of the high-speed optical switch (LCBS), divide the continuous sampling data output by the analog-to-digital converter (ADC) into independent time-domain segments of multiple channels; if a certain target channel is not enabled or has no significant echo, directly discard the corresponding data; leave a protection interval near the optical switch switching boundary to avoid switching interference samples.

[0144] 1.1: Timing marking.

[0145] In the FPGA, read the open / close control signal of the high-speed optical switch (LCBS) in real time; map this timing information to the ADC sampling clock index.

[0146] For example: If the LCBS connects to "Target 1" in the time period from t = 0 s to 0.2 s, then the corresponding ADC sample range from N1_begin to N1_end is the data range of the echo of Target 1.

[0147] 1.2: Data Slicing.

[0148] Slice the continuous sampled data output by the ADC into multiple segments according to the selected target timing range as described above , where i represents the target number.

[0149] If a certain target channel is not enabled or has no significant echo, directly discard the corresponding data segment during slicing to save processing resources.

[0150] 1.3: Guard Interval.

[0151] Interference will be generated during the moment of optical switch switching. To avoid the influence of this interference on subsequent fitting, the present invention leaves several sampling points (such as 10 - 50 sampling points) near the switching boundary of the target channel not to participate in the subsequent fitting operation.

[0152] Step 2: Filtering and Preprocessing: Perform wavelet denoising on each time-domain segment and perform baseline correction; use moving average in the denoised result to maintain the continuity of the pulse envelope; obtain the preliminary position of the pulse peak through threshold detection.

[0153] 2.1: Wavelet Denoising.

[0154] Perform discrete wavelet decomposition (such as Daubechies order 4, decomposed to 5 layers) on the channel data after each slice; set the coefficients with small attenuation amplitudes in the high-frequency subbands, and then perform inverse transformation to remove high-frequency random noise; the reconstructed time-domain signal is denoted as , and the intensity of its high-frequency spikes or random noise is significantly reduced.

[0155] 2.2: Baseline Correction and Simple Smoothing.

[0156] Introduce baseline estimation in : Take the mean value of the interval without echo before and after as the baseline value, and subtract it as a whole; the remaining signal can be further subjected to moving average to ensure the overall smoothness of the pulse envelope.

[0157] 2.3: Threshold Detection and Coarse Peak Positioning.

[0158] Set a threshold (such as 20% of the global maximum value) on the filtering result to detect the approximate interval of the pulse peak; quickly fit the points within the threshold interval with a quadratic polynomial to obtain the preliminary "peak position" , "amplitude" , "pulse width" as the initial value for subsequent LM iteration.

[0159] ​Step 3: Establishment of LM fitting model: For the echo pulses of each channel, select the Gaussian pulse model and establish the least squares residual function.

[0160] 3.1: Pulse model.

[0161] For a single echo pulse, the following shape model function can be selected where ; is a way of writing a mathematical formula, and the expression represents a function y with respect to time t and parameter θ i of i y i represents the i-th observed value, θ i represents the model parameter, and t represents the model time parameter.

[0162] is the peak position, is the amplitude, is the pulse width, is the offset, because the sampled pulse generally has a non-zero DC voltage offset.

[0163] Since this is a Gaussian function model here, therefore, represents the initial value calculation implemented in the FPGA, and A i is the amplitude of the echo fitting of the i-th channel solved by the LM algorithm in the GPU.

[0164] Implement data slicing, wavelet transform, and threshold detection in the FPGA; upload the initial value to the GPU; the GPU then performs matrix operations for LM iteration.

[0165] 3.2: Residual function.

[0166] Record the measured data after filtering as , and the corresponding sampling time is ; define the residual , and the sum of squares of this residual is the least squares fitting objective function for fitting the echo of the i-th channel.

[0167] Step 4: Use LM iteration to solve: Based on the preliminary peak positioning result described above as the fitting initial value, input the pulse model required for fitting and the sampling data into the LM algorithm together.

[0168] Use FPGA+GPU collaboration to implement data slicing, wavelet transform, and threshold detection in the FPGA; input the initial value Upload the GPU; the GPU then performs matrix operations for LM iteration, which can quickly and parallelly process multi-channel data; the GPU is used for deep operations, real-time imaging, and visualization processing of massive data to achieve high-frame-rate three-dimensional reconstruction.

[0169] Step 5: Multi-frame averaging and distance calculation: Collect several groups of echo data for the same target through multiple repeated samplings; finally, perform weighted averaging on the distance results obtained from multiple measurements for each channel to eliminate accidental noise points, obtain a more stable target distance value, and combine the galvanometer angle to achieve high-precision three-dimensional reconstruction of multiple targets.

[0170] 5.1: Multi-frame measurement and outlier removal.

[0171] As Figure 6 shown, it is the waveform that the ADC should theoretically collect at a certain moment. Obtain envelope 1 (a group with relatively high intensity), which is the peak moment of the reference pulse , obtain envelope 2 (a group with relatively low intensity), which is the peak moment of the target pulse , and the peak moment of the reference pulse in the next cycle . Input the signal processing control unit for distance calculation, and substitute it into the following formula to calculate the distance L to be measured:

[0172]

[0173] where c is the speed of light in a vacuum, represents the refractive index of air, represents the repetition frequency of the signal laser, and these are all known quantities measured in advance.

[0174] For each target (channel), usually M repeated samplings (such as 600 times, etc.) are performed, so as to obtain the distance values calculated from M groups of LM fitting results ; weighted averaging is used to eliminate accidental noise points, and the average of the remaining values is , obtaining a more stable distance value estimate.

[0175] Geometric calibration: Place a standard target and position multiple standard corner reflectors at different orientations within the system's field of view at known precise coordinates. Ensure that these calibration points are reasonably distributed to cover all angular / distance segments of the system's measurement range. Measure the calibration points, collect the echo or interference data of these points using the system's regular measurement process, and obtain their values in the system's internal coordinates. Establish an error model, considering various errors: the difference between the galvanometer scanning angle and the actual spatial angle, the deviation of the beam exit position, the tilt of the detector installation angle, the non-linearity of the dual optical frequency comb beat frequency, etc. When mapping the "system measurement value" to the "true spatial coordinate" using a mathematical model, a series of parameters to be estimated are added (such as the scanning scale factor, offset, zero drift, etc.). Solve for the calibration parameters. Given the "true coordinates" (obtained from the measurement tool of the calibration target) and the "system observation values", use methods such as non-linear fitting to solve for the optimal set of system parameters. Substitute the obtained correction parameters into the system and re-measure the calibration points to check whether the deviation is within the acceptable range. If the deviation is still large, re-correct the parameters or improve the error model until the desired accuracy is achieved.

[0176] Apply to measurement: Fix the above parameters in the system software. When measuring any unknown target, the position (x, y, z) of the target object in the true three-dimensional coordinates can be calculated in real-time based on the original data such as the galvanometer angle and optical path. Calibrate and fuse multi-channel and multi-angle data to output a 3D point cloud.

[0177] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0178] In this article, specific examples are used to elaborate on the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and its core idea of this application; at the same time, for those of ordinary skill in the art, according to the idea of this application, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be construed as a limitation to this application.

Claims

1. A multi-target three-dimensional measurement device based on dual-comb femtosecond laser radar, characterized in that: The multi-target three-dimensional measurement device based on dual-comb femtosecond laser radar comprises: a dual-comb laser source, a single detector time-sharing switching receiving module, a beam splitting and optical switch module and a scanning galvanometer module connected in sequence, and a signal control processing module connected to the single detector time-sharing switching receiving module; The dual optical comb laser is used to transmit measurement signal pulses to the reference target in the single detector time-sharing switching receiving module and the target optical path in the beam splitting and optical switch module; and is also used to transmit sampling signal pulses to the reference optical path and the measurement optical path in the single detector time-sharing switching receiving module; The single detector time-sharing switching receiving module is used to receive the echo pulses of each target optical path according to the timing switching signal, so that the echo pulse and the sampling signal pulse generate a sum frequency reaction in the measuring optical path, and the first photodetector performs photoelectric detection to generate a target pulse signal, and the target pulse signal is input into channel 1 of the analog-to-digital converter; the echo pulse is the echo pulse of the measuring signal pulse; and it is also used to make the reflected pulse through the reference target and the sampling signal pulse generate a sum frequency reaction in the reference optical path, and the second photodetector performs photoelectric detection to generate a reference pulse signal, and the reference pulse signal is input into channel 2 of the analog-to-digital converter; The beam splitting and optical switch module is used to split the measurement signal pulse into multiple pulses, transmit them to the target optical path, and control the opening and closing of the optical switch on each target optical path according to the timing switching signal, so as to realize time-division multiplexing measurement of multiple targets or multiple channels; The scanning galvanometer module is used to sample the target area to be measured of the target object in two-dimensional or three-dimensional space according to a set scanning trajectory using a scanning galvanometer on each target optical path; The signal control processing module is used to perform distance calculation based on the reference pulse signal and the target pulse signal of each target optical path to determine the distance of the target object to be measured, and to perform three-dimensional reconstruction of the target object based on the distance of the target object to be measured and the angle information of the scanning galvanometer to generate a point cloud or a three-dimensional contour map of the target object in the current scene.

2. The multi-target three-dimensional measurement device based on dual-comb femtosecond laser radar according to claim 1 is characterized in that: The single detector time-sharing switching receiving module specifically includes: a measurement signal pulse optical path and a sampling signal pulse optical path; Wherein, the measurement signal pulse optical path includes a reference target optical path and the reference optical path; the reference target optical path includes a first collimator, a first half-wave plate, a first reflector, a first polarization beam splitter prism, a quarter-wave plate and a reference target in the same optical path; The measurement signal pulse is reflected from the reference target optical path into the reference optical path, generates a sum frequency reaction with the sampling signal pulse in the reference optical path, and is photoelectrically detected by a second photodetector to generate a reference pulse signal; The sampling signal pulse optical path includes a reflection optical path and a polarization optical path; the reflection optical path and the polarization optical path share a second collimator, a second half-wave plate and a second polarization beam splitter prism; the reflection optical path also includes a second reflector and the measurement optical path; the polarization optical path also includes a third half-wave plate, a third polarization beam splitter prism and the reference optical path; After the sampling signal pulse is polarized and split by the second polarization beam splitter prism, one sampling signal pulse enters the second reflector and is reflected to the measurement optical path; the other sampling signal pulse enters the reference optical path after passing through the third half-wave plate and the third polarization beam splitter prism.

3. The multi-target three-dimensional measurement device based on dual-comb femtosecond laser radar according to claim 2 is characterized in that: The measuring optical path specifically includes: a first focusing lens, a first sum frequency crystal, a first low pass filter and a first photodetector in the same optical path; The reference optical path specifically includes: a second polarization beam splitter prism, a second focusing lens, a second sum frequency crystal, a second low-pass filter and a second photodetector in the same optical path.

4. The multi-target three-dimensional measurement device based on dual-comb femtosecond laser radar according to claim 1 is characterized in that: The beam splitting and optical switch module specifically includes: a beam splitter and a plurality of target optical paths; The beam splitter divides the measurement signal pulse into multiple pulses and emits them into each target optical path; The target optical path includes an optical fiber, a third collimator, an optical switch and a target object in the same optical path; the optical switch is a liquid crystal light beam shutter.

5. The multi-target three-dimensional measurement device based on dual-comb femtosecond laser radar according to claim 4 is characterized in that: The scanning galvanometer module is arranged between the optical switch and the target object; the scanning galvanometer module changes the light beam emission angle to scan and measure the target object.

6. The multi-target three-dimensional measurement device based on dual-comb femtosecond laser radar according to claim 1 is characterized in that: The signal control processing module specifically includes: FPGA and GPU; The FPUGA is used to perform distance calculation based on the reference pulse signal and the target pulse signal of each target optical path; The GPU is used to perform distance calculation according to the reference pulse signal and the target pulse signal of each target optical path.

7. A multi-target three-dimensional measurement method based on dual-comb femtosecond laser radar, characterized in that: The multi-target three-dimensional measurement method based on the dual-comb femtosecond laser radar is applied to the multi-target three-dimensional measurement device based on the dual-comb femtosecond laser radar according to any one of claims 1 to 6, and the multi-target three-dimensional measurement method based on the dual-comb femtosecond laser radar includes: Using a dual optical comb laser to transmit measurement signal pulses to a reference target in a single detector time-sharing switching receiving module and a target optical path in a beam splitting and optical switch module, and to transmit sampling signal pulses to a reference optical path and a measurement optical path in the single detector time-sharing switching receiving module; Generate a target pulse signal according to the echo pulse returned by the measurement signal pulse via the target optical path and the sampling signal pulse on the measurement optical path; generating a reference pulse signal according to the reflected pulse through the reference target and the sampling signal pulse; Perform distance calculation based on the reference pulse signal and the target pulse signal of each target optical path to determine the distance to be measured of the target object; According to the distance to be measured of the target object and the angle information of the scanning galvanometer, the target object is three-dimensionally reconstructed to generate a point cloud or a three-dimensional contour map of the target object in the current scene.

8. The multi-target three-dimensional measurement method based on dual-comb femtosecond laser radar according to claim 7 is characterized in that: The method further comprises: performing distance calculation according to the reference pulse signal and the target pulse signal of each target optical path to determine the distance to be measured of the target object; specifically, the method comprises: Combining the reference pulse signal and the target pulse signal to generate continuous sampling data; Based on the timing switching signal, the continuous sampling data is divided into time domain segments of multiple channels; Preprocessing each of the time domain segments to determine a preliminary position of a pulse peak; For the echo pulse of each channel, a Gaussian pulse model is selected and a least square residual function is established; Based on the least squares residual function, the preliminary position of the pulse peak is used as the initial fitting value, and the Gaussian pulse model and the continuous sampling data are fitted using the LM fitting algorithm to determine the distance of the target object to be measured.

9. The multi-target three-dimensional measurement method based on dual-comb femtosecond laser radar according to claim 8 is characterized in that: Based on the least squares residual function, the preliminary position of the pulse peak is used as the initial value of fitting, and the Gaussian pulse model and the continuous sampling data are fitted using the LM fitting algorithm to determine the distance of the target object to be measured, specifically including: use Determine the distance of the target object to be measured; where L is the distance of the target object to be measured; c is the speed of light in a vacuum; is the refractive index of air; is the repetition frequency of the signal laser; is the target pulse peak moment of the target pulse signal; is the reference pulse peak moment of the reference pulse signal; It is the reference pulse peak moment of the reference pulse signal in the next cycle.

10. The multi-target three-dimensional measurement method based on dual-comb femtosecond laser radar according to claim 7, characterized in that: According to the distance to be measured of the target object and the angle information of the scanning galvanometer, the target object is reconstructed in three dimensions to generate a point cloud or a three-dimensional contour map of the target object in the current scene, specifically including: By geometric calibration, a correspondence is established between the distance to be measured of the target object and the angle information of the scanning galvanometer and the real space coordinates; The target object is three-dimensionally reconstructed according to the corresponding relationship to generate a point cloud or a three-dimensional contour map of the target object in the current scene.

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