Real-time high-response large-aperture laser space-time parameter measurement method and device

Abstract

The invention discloses a real-time high-response large-aperture laser space-time parameter measurement method and device, and relates to the field of light spot image processing and optical imaging calculation, and the method comprises the steps: carrying out the light splitting of incident light through a spectroscope, and dividing the incident light into transmission light and reflected light; the transmission light directly enters a diffuse transmission plate right behind the spectroscope, and then respectively enters a spectrograph, a light spot measurement camera and a photoelectric detector; the reflected light is reflected by the 45-degree reflector, is kept parallel to the light path of the transmitted light, enters the aberration-eliminating spherical mirror, and then enters the pointing measurement camera; detection information in the pointing measurement camera, the spectrograph and the light spot measurement camera is transmitted to the industrial personal computer, information in the photoelectric detector needs to be processed by the FPGA timer and then transmitted to the industrial personal computer, and the industrial personal computer processes and analyzes all gathered measurement information in real time. According to the invention, large-aperture laser detection has good real-time performance and responsivity.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of image processing and optical imaging calculation, and particularly relates to a real-time high-response large-aperture laser time-space parameter measurement method and device. BACKGROUND

[0002] With the wide application of high-energy laser technology in space laser communication, deep space exploration and industrial precision machining, the performance optimization of large-aperture laser devices puts forward higher requirements for the accurate measurement of laser parameters. Laser time-space parameters (including time waveform, spatial intensity distribution, wavefront phase, polarization state, etc.) are the core indicators for evaluating the performance of laser systems, and directly affect the energy transmission efficiency and optical element damage threshold. Traditional single-point or low-resolution measurement methods (such as mechanical scanning method, spectral interference method) cannot meet the comprehensive needs of large-aperture laser devices for high dynamic range, multi-parameter synchronous measurement and anti-interference ability. Therefore, developing a large-aperture laser time-space parameter measurement device with high precision and high integration has become a key bottleneck restricting the development of laser technology.

[0003] At present, the existing time division multiplexing system realizes multi-pulse separation measurement through electro-optical switch and polarization beam splitting, but the wedge angle error of the spatial separation unit will cause the introduction of optical path difference, and the aberration correction ability for large-aperture beams is limited. In addition, the single polarization characteristic limits the synchronous acquisition of polarization state parameters, which is difficult to meet the multi-dimensional characterization needs of complex laser field. Although the method based on the fusion of physical optics and computational imaging improves the signal-to-noise ratio, the reconstruction algorithm is sensitive to the initial aberration calibration, and the dynamic range is limited by the pixel density of the CCD detector. In a strong scattering environment, the wavefront reconstruction error caused by light field distortion can exceed 10%. The differential confocal-interference compound measurement technology realizes surface shape measurement through mechanical phase shifting, but the stability of the large-aperture system is insufficient due to the weight limitation of the reference mirror, and the drift amount introduced by thermal noise in ultra-long focal length measurement reaches λ / 20 (λ is the wavelength of incident light), which cannot meet the real-time requirements.

[0004] The existing system mostly adopts time-sharing multiplexing or light splitting and measurement scheme, which leads to the mutual restriction of time resolution and spatial resolution. Although the light-thermal / optical-electric compound device can synchronously acquire energy and distribution parameters, the diffraction effect introduced by the integrating sphere attenuator makes the wavefront measurement error of small-aperture laser reach λ / 5. In addition, the strong transient characteristics of high-energy laser require the detector to have ultrafast response and nonlinear suppression capability. The traditional CCD detector is prone to saturation and signal flooding in a strong light field due to the limitation of readout noise and dark current. In addition, the vibration, temperature fluctuation and air turbulence in the measurement environment will cause the accumulation of measurement error, and the device also needs to have the functions of active compensation and real-time calibration. SUMMARY

[0005] In order to make up for the deficiency of the current large aperture laser measurement system in the ability of fast response and real-time display of space-time parameter information, the application provides a real-time high-response large-aperture laser space-time parameter measurement method and device.

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

[0007] A real-time high-response large-aperture laser space-time parameter measurement method comprises the following steps:

[0008] S1: the incident light is split by a beam splitter into two beams of transmitted light and reflected light;

[0009] S2: the transmitted light is directly incident on a diffuse transmission plate behind the beam splitter, and then enters a spectrometer, a spot measurement camera and a photodetector respectively;

[0010] S3: the reflected light is first reflected by a 45° mirror and then enters an anastigmatic spherical mirror in parallel with the transmitted light path, and then is incident on a pointing measurement camera;

[0011] S4: the detection information in the pointing measurement camera, the spectrometer and the spot measurement camera is transmitted to an industrial computer, the information in the photodetector is processed by an FPGA timer and then transmitted to the industrial computer, and the industrial computer processes and analyzes all the measurement information.

[0012] The application also provides a real-time high-response large-aperture laser space-time parameter measurement device, comprising: a beam splitter for splitting incident laser into a transmitted light beam and a reflected light beam; a diffuse transmission plate located behind the beam splitter for the transmitted light beam to be incident and generate scattered light; a spectrometer, a spot measurement camera and a photodetector which sequentially receive the scattered light and output a spectrum signal, a spatial intensity signal and a time start signal respectively; a 45° mirror for turning the reflected light beam; an anastigmatic spherical mirror for focusing the reflected light beam; a pointing measurement camera located at the focal point of the anastigmatic spherical mirror and outputting a pointing deviation signal; an FPGA timer connected with the photodetector for converting the time start signal into a digital time signal; and an industrial computer which synchronously receives the spectrum signal, the spatial intensity signal, the pointing deviation signal and the digital time signal, completes real-time processing and outputs laser space-time parameters.

[0013] Further, the beam splitter, the 45° mirror and the anastigmatic spherical mirror all have an aperture diameter of ≥200mm.

[0014] Further, the diffuse transmission plate is made of high-temperature sintered microbead material, has a thickness of 1mm, a diameter of 170mm and is installed by flexible compression with a silicone pad at the edge.

[0015] Further, the pointing measurement camera has a pixel size of 5.5μm×5.5μm, the anastigmatic spherical mirror has a focal length of 1500mm, and the pointing test accuracy is ≤5μrad.

[0016] Further, the spectrometer is a micro fiber grating spectrometer, and the fiber input is coupled through an SMA905 interface.

[0017] Further, the photoelectric detector is directly connected with the FPGA timer through a coaxial cable, and the clock cycle of the FPGA timer is less than or equal to 10 ns.

[0018] Further, the spot measurement camera is located at 1.5 m behind the diffuse transmission plate, and is provided with a near-infrared lens and an adjustable attenuation sheet.

[0019] Further, the surface of the spectroscope and the 45-degree mirror is coated with a 1030 nm-1080 nm high reflection film, and the reflectivity is greater than or equal to 99.5%.

[0020] Further, the beam pointing test assembly, the near-field spot acquisition assembly, the spectral characteristic acquisition assembly and the time characteristic acquisition assembly are all installed on the same bearing assembly, and the height is adjustable.

[0021] Beneficial effects:

[0022] 1. The application can be used for measuring large-aperture laser light sources, and time characteristics, near-field spot characteristics, spectral characteristics and other parameters, and has the ability of fast response and real-time display of space-time parameter information.

[0023] 2. The application greatly improves the parameter analysis and calculation efficiency of the laser light source under the premise of ensuring the measurement accuracy of the large-aperture laser, so that the large-aperture laser detection has good real-time performance and response. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is a flow chart of a real-time high-response large-aperture laser space-time parameter measurement method of the application.

[0025] Figure 2 It is an optical path schematic diagram of a real-time high-response large-aperture laser space-time parameter measurement device of the application.

[0026] Figure 3 It is a schematic diagram of the internal structure of the light shielding cylinder.

[0027] Figure 4 It is an installation structure diagram of the diffuse transmission plate.

[0028] Figure 5 It is a counter time measurement principle diagram. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and not to limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0030] As shown in Figure 2 A real-time high-response large-aperture laser time-space parameter measuring device of the present application is mainly used for measuring the time parameter, near-field spot characteristics and spectral characteristics of a laser light source. The device has the ability of fast response and real-time display of time-space parameter information, and comprises a beam pointing test assembly, a near-field spot collection assembly, a spectral characteristic collection assembly and a bearing assembly 21. The beam pointing test assembly mainly consists of a beam splitter, a 45° mirror, a focusing system and a pointing measurement camera; the near-field spot collection assembly mainly consists of a diffuse transmission plate and a measurement camera; the time characteristic collection assembly mainly consists of a photodetector and an FPGA timer; and the spectral characteristic collection assembly mainly consists of a high-resolution spectrometer.

[0031] The beam splitter 11 is used for splitting the incident laser into a transmitted beam and a reflected beam; the diffuse transmission plate 12 is located directly behind the beam splitter and is used for the incident transmitted beam to generate scattered light; the spectrometer 13, the spot measurement camera 14 and the photodetector 15 receive the scattered light in sequence and output spectral signals, spatial intensity signals and time start signals, respectively; the 45° mirror 16 is used for turning the reflected beam; the aberration-corrected spherical mirror 17 is used for focusing the reflected beam; the pointing measurement camera 18 is located at the focal point of the aberration-corrected spherical mirror and outputs a pointing deviation signal; the FPGA timer 20 is connected with the photodetector and is used for converting the time start signal into a digital time signal; and the industrial computer 19 synchronously receives the spectral signals, the spatial intensity signals, the pointing deviation signal and the digital time signal, completes real-time processing and outputs laser time-space parameters.

[0032] The incident light is split by the beam splitter 11 into a transmitted beam and a reflected beam; the transmitted beam is directly incident on the diffuse transmission plate 12 located directly behind the beam splitter, and then enters the spectrometer 13, the spot measurement camera 14 and the photodetector 15, which is the transmitted light path; the reflected light is first reflected by the 45° mirror 16 and then enters the aberration-corrected spherical mirror 17 in parallel with the transmitted light path, and then is incident on the pointing measurement camera 18; the detection information in the pointing measurement camera 18, the spectrometer 13 and the spot measurement camera 14 is transmitted to the industrial computer 19, and the information in the photodetector 15 needs to be processed by the FPGA timer 20 before being transmitted to the industrial computer 19, and the industrial computer 19 processes and analyzes all the measurement information. All the device components are placed on the bearing assembly 21, and the height position is adjustable.

[0033] The light beam pointing test assembly is mainly used for testing light beam pointing stability. The principle is that parallel light emitted by a laser is focused by an optical system, and is received by a camera. The change of the laser pointing in the light process is calculated by the movement of the imaging position of the light spot centroid on the camera target surface. The test accuracy of the assembly is mainly related to the focal length of the imaging system, the camera pixel size and the optical quality of the focusing system. In actual measurement, since the intensity of the incident laser is not fixed, the power density of the light beam focused on the camera may be too large to cause the measurement camera to be saturated and even burned out. Therefore, an attenuation sheet is installed in front of the camera to ensure that the camera is not saturated by adjusting the attenuation sheet and the camera exposure time. The filter of the application is a long-wave pass filter. The filter is installed between the attenuation sheet and the camera, and its function is to filter out ambient stray light and beacon light.

[0034] Preferably, a high reflection film is coated for the 1030nm-1080nm waveband, so that the reflectivity in the waveband is ≥99.5%. In order to avoid the influence of stray light on measurement, all optical paths of the light beam pointing test assembly are designed as closed optical paths. The inside of the light shielding cylinder and the inside of the mirror holder are sandblasted and blackened as shown in Figure 3 , combined with the small blocking inside the light shielding cylinder, the influence of stray light can be effectively eliminated.

[0035] Preferably, in the light beam pointing test assembly, the sizes of the optical lenses such as the beam splitter, the 45° mirror and the focusing system are designed to be more than 1.2 times the clear aperture. The design size of the beam splitter is about , the design size of the 45° mirror is about , and the edge blocking width of the mounting mirror holder of the beam splitter and the 45° mirror is about 5mm. The actual clear aperture is about 235mm-240mm. The focusing system is designed by simulation with a 200mm diameter light beam. The actual clear aperture is greater than 200mm. Therefore, the effective clear aperture of all components in the light beam pointing test assembly is greater than 200mm.

[0036] The light beam pointing measurement accuracy is mainly related to the focal length in the light beam pointing test assembly and the pixel size of the camera. The parameters of the GT2050 camera used in the application are as follows. The pixel size is , and the design focal length of the focusing system is 1500mm. Therefore, the test accuracy is:

[0037] ;

[0038] The test accuracy meets the requirement of the light beam pointing test accuracy ≤5μrad.

[0039] The near-field light spot collection assembly is mainly used for measuring light spot diameter and other parameters. In the application, the assembly mainly comprises a diffuse transmission plate, a measuring camera, a near-infrared lens, a filter, an attenuation sheet and other components. The approximately Lambertian distribution of scattered light obtained after the laser is incident through the diffuse transmission plate is received and imaged by the measuring camera, and then the light beam diameter and other parameters are calculated. In order to improve the measurement accuracy, the measuring camera is placed about 1.5 m behind the diffuse transmission plate. Since the diffuse transmission plate has a certain thickness, the spot diameter is expanded to a certain extent when the laser exits through the diffuse transmission body, and this expansion can be eliminated by calibrating the diffuse transmission plate.

[0040] In the application, a material produced by using a high-temperature sintering process is used as the diffuse transmission plate. The process is to use micro-bead particles for high-temperature sintering, so the material of this type has the characteristics of high hardness and uniform and stable scattering, and can effectively reduce the thickness of the diffuse transmission plate. However, this type of material has high hardness, and the disadvantage is also very obvious, that is, the material is generally brittle and needs to be designed to prevent damage. Therefore, in the application, the diffuse transmission plate is installed in a flexible material transition manner, and the structure is as shown in Figure 4 The diffuse transmission plate has a design diameter of 170 mm and a thickness of 1 mm. The diffuse transmission plate and the diffuse transmission plate mounting frame use a 1 mm thick silica gel pad as a transition material. The pressure of the metal mounting frame is reduced through the silica gel material and then acts on the diffuse transmission plate. On the premise of ensuring that the diffuse transmission plate does not shake, direct contact between the diffuse transmission plate and the metal mounting frame is avoided, and damage to the diffuse transmission screen due to uneven pressure, stress mutation and other factors during installation is avoided.

[0041] The time characteristic collection assembly is mainly used for measuring parameters such as light source starting time and continuous light emission time. The assembly mainly comprises a photodetector and an FPGA signal collection and measurement timer circuit. The counter time measurement method is also called electronic counting method or pulse filling method, which is the most basic and convenient time interval measurement technology, and the measurement principle is as shown in Figure 5 The measurement device first uses a high-frequency stable clock pulse to fill the time interval to be measured, Figure 5 wherein Start is a start counting flag signal, Stop is a stop counting flag signal, Gate is the phase difference between the rising edges of the start and stop signals, that is, the time interval to be measured t, and Clk is a counting pulse with a period of T. t1 and t2 are the phase difference (small time interval) between the rising edges of the Start and Stop signals and the rising edges of the next counting pulse.

[0042] Under a fixed measurement clock period, the number of bits of the counter determines the maximum range of time measurement. Assuming that the clock period of the measurement pulse is T, and the number of times recorded by the counter within a given time interval is N, the rough time measurement result can be represented as:

[0043] ;

[0044] However, the real value t of the time interval to be measured is:

[0045] ;

[0046] Therefore, the measurement error of the coarse time measurement method is :

[0047] ;

[0048] In order to improve the accuracy of the time measurement method, on the other hand, it is necessary to reduce the measurement error of the coarse time measurement method. In the digital TDC system based on FPGA, it is common to use a high-resolution TDC architecture to further subdivide the small time intervals t1 and t2, so as to further calculate the uncertainty of the start and end times, that is, to realize a fine time measurement module.

[0049] The spectral characteristic acquisition component is mainly used for measuring the working wavelength of the light source, and this function can be accurately detected by a high-resolution spectrometer. Considering the measurement accuracy, volume and weight of the spectrometer, in order to reduce the volume of the spectral measurement module and optimize the overall integration quality of the system, the present application selects a miniature fiber grating spectrometer as the core measurement module of the spectral characteristic acquisition component. Unlike traditional large spectrophotometers, the miniature fiber grating spectrometer uses folding light path, fiber transmission, array detector and other technologies, and is small in size, fast in detection, easy to use, and very suitable for online, in-situ, portable and other application fields. The miniature fiber grating spectrometer covers the spectral measurement scheme from deep ultraviolet to visible to near infrared, and can be used for measurement of absorbance, reflectivity, transmittance, fluorescence and Raman spectrum.

[0050] The light enters the spectrometer through the fiber and needs to be coupled by a connector. The connector usually uses an SMA905 interface, and an FC interface can also be selected for configuration. The slit is the entrance aperture of the light into the interior of the spectrometer. The optical resolution of the spectrometer is related to the slit width. The narrower the slit, the higher the optical resolution, and the wider the slit, the higher the light flux, and the lower the acquisition time.

[0051] As shown in Figure 1 , a real-time high-response large-aperture laser space-time parameter measurement method of the present application includes the following steps:

[0052] S1: the incident light is split by the beam splitter 11 into two beams of transmitted light and reflected light;

[0053] S2: the transmitted light is directly incident on the diffuse transmission plate 12 behind the spectroscope 11, and then enters the spectrometer 13, the light spot measurement camera 14 and the photodetector 15, which is the transmitted light path;

[0054] S3: the reflected light is first reflected by the 45° mirror 16 and then enters the anastigmatic spherical mirror 17, and then is incident on the pointing measurement camera 18;

[0055] S4: the detection information in the pointing measurement camera 18, the spectrometer 13 and the light spot measurement camera 14 is transmitted to the industrial computer 19, and the information in the photodetector 15 needs to be processed by the FPGA timer 20 and then transmitted to the industrial computer 19, and the industrial computer 19 processes and analyzes all the measurement information.

[0056] Specifically, in S2, the transmitted light is incident on the diffuse transmission plate behind the spectroscope, and becomes scattered light with approximate Lambertian distribution, the diffuse transmission plate adopts the flexible material transition installation mode shown in the figure. Figure 4

[0057] Specifically, in S3, the reflected light is incident on the focusing system through the 45° mirror and finally imaged in the pointing measurement camera, the 45° mirror is mainly used to change the direction of the light path, so that the device structure is more compact, thereby reducing the volume and weight of the device. The beam pointing test assembly mainly consists of a spectroscope, a 45° mirror, a focusing system, a pointing measurement camera, a filter, an attenuator, a lens holder, a light-tight barrel and the like. The main design indexes are as follows: 1) working wavelength range: 1030nm-1080nm; 2) effective light aperture: ≥200mm; 3) beam pointing test precision: ≤5μrad.

[0058] S5: the detection information in the beam pointing test assembly, the near-field light spot acquisition assembly and the spectral characteristic acquisition assembly is transmitted to the industrial computer, and the detection information of the photodetector in the time characteristic acquisition assembly needs to be processed by the FPGA timer and then transmitted to the industrial computer, and finally all the detection data are processed and analyzed in real time by the industrial computer, and then the time characteristic, the near-field light spot characteristic and the spectral characteristic of the incident laser source and the like are obtained.

[0059] The above is only a preferred embodiment of the present application, and is not used to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.​

Claims

1. A method for measuring the spatiotemporal parameters of a real-time, high-response, large-aperture laser, characterized in that, Includes the following steps: S1: The incident light is split by the beam splitter into two beams: transmitted light and reflected light. S2: The transmitted light is directly incident on the diffuse transmission plate directly behind the beam splitter, and then enters the spectrometer, the spot measurement camera and the photodetector respectively; S3: The reflected light is first reflected by the 45° reflecting mirror and then enters the aberration-correcting spherical mirror in parallel with the transmitted light path, and then enters the pointing measuring camera; S4: Transmits the detection information from the pointing measurement camera, spectrometer, and spot measurement camera to the industrial control computer. The information from the photodetector needs to be processed by the FPGA timer before being transmitted to the industrial control computer. The industrial control computer processes and analyzes all the imported measurement information.

2. A real-time, high-response, large-aperture laser spatiotemporal parameter measurement device, characterized in that, include: A beam splitter is used to separate the incident laser beam into a transmitted beam and a reflected beam; a diffuser plate is located directly behind the beam splitter to allow the transmitted beam to enter and generate scattered light; a spectrometer, a spot measurement camera, and a photodetector sequentially receive the scattered light and output spectral signals, spatial intensity signals, and time start signals, respectively; a 45° reflecting mirror is used to refract the reflected beam; and an aberration-correcting spherical mirror is used to focus the reflected beam. A pointing measurement camera, located at the focal point of the aberration-correcting spherical mirror, outputs a pointing offset signal; an FPGA timer, connected to a photodetector, is used to convert the time start signal into a digital time signal; an industrial control computer synchronously receives spectral signals, spatial intensity signals, pointing offset signals, and digital time signals, performs real-time processing, and outputs laser spatiotemporal parameters.

3. The real-time high-response large-aperture laser spatiotemporal parameter measurement device according to claim 1, characterized in that, The apertures of the beam splitter, 45° reflector, and aberration-correcting spherical mirror are all ≥200mm.

4. The real-time high-response large-aperture laser spatiotemporal parameter measurement device according to claim 1, characterized in that, The diffused light plate is made of high-temperature sintered microsphere material, with a thickness of 1mm and a diameter of 170mm. The edges are flexibly pressed and installed using silicone pads.

5. The real-time high-response large-aperture laser spatiotemporal parameter measurement device according to claim 1, characterized in that, The pointing measurement camera has a pixel size of 5.5μm×5.5μm, an aberration-correcting spherical mirror with a focal length of 1500mm, and a pointing test accuracy of ≤5μrad.

6. The real-time high-response large-aperture laser spatiotemporal parameter measurement device according to claim 1, characterized in that, The spectrometer is a miniature fiber optic grating spectrometer, with fiber optic input coupled via an SMA905 interface.

7. The real-time high-response large-aperture laser spatiotemporal parameter measurement device according to claim 1, characterized in that, The photodetector and the FPGA timer are directly connected by a coaxial cable, and the FPGA timer clock period is ≤10ns.

8. The real-time high-response large-aperture laser spatiotemporal parameter measurement device according to claim 1, characterized in that, The spot measurement camera is located 1.5m directly behind the diffuse transmission plate and is equipped with a near-infrared lens and an adjustable attenuator.

9. The real-time high-response large-aperture laser spatiotemporal parameter measurement device according to claim 1, characterized in that, The surfaces of the beam splitter and the 45° mirror are coated with a 1030nm-1080nm high-reflectivity film with a reflectivity ≥99.5%.

10. A real-time high-response large-aperture laser spatiotemporal parameter measurement device according to claim 1, characterized in that, The beam pointing test component, near-field spot acquisition component, spectral characteristic acquisition component, and time characteristic acquisition component are all mounted on the same support component, and the height is adjustable.

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