Four-dimensional detection system of large detection field of view and high-precision streak tube imaging lidar

Abstract

The present invention belongs to the field of optoelectronic imaging technology. Aiming at the problem that the streak tube imaging lidar developed at present is difficult to meet the detection requirements of large field of view and high precision, a four-dimensional detection system for a large detection field of view and high-precision streak tube imaging lidar is provided, which includes a pulsed laser, a transmitting optical system, a delay system, a receiving optical system, a fiber optic image converter, a streak tube detector, a CCD camera and a signal processing system. Among them, the streak tube detector uses a large detection area streak tube with a single lens focusing system, realizing a large detection field of view and improving the range resolution in three directions. At the same time, it can image under the condition of the movement of the target object, meeting the requirements of large detection range and high-precision diagnosis.

Description

Technical Field

[0001] The present invention relates to a four-dimensional detection system of a streak tube imaging lidar with a large detection field of view and high precision, belonging to the technical field of optoelectronic imaging. Background Art

[0002] The streak tube imaging lidar can provide four-dimensional images of high-resolution range images (three-dimensional) and intensity images (one-dimensional), and its range information is determined by the time resolution of the streak tube, and is not easily affected by effects such as scattering. There is a very large demand in the military and aerospace fields, especially when the contrast of the target is small but there is a certain depth of field.

[0003] The detection range of the streak tube imaging lidar along the horizontal X direction is related to the distance between the lidar and the target and the divergence angle of the laser in the X direction; the range resolution along the horizontal X direction is positively correlated with the number of pixels in the slit direction of the streak tube; the detection range along the horizontal Y direction is related to the distance between the lidar and the target and the divergence angle of the laser in the Y direction; the range resolution along the horizontal Y direction is positively correlated with the laser repetition frequency and negatively correlated with the radar operating speed; the detection range along the Z direction is positively correlated with the full-screen time of the streak tube detector; the range resolution along the Z direction is positively correlated with the spatial resolution in the scanning direction of the streak tube photocathode and the length in the scanning direction; it can be seen that the larger the detection area of the streak tube, the higher the spatial resolution, and the larger the detection field of view under the same precision requirements.

[0004] At present, regarding the problem that it is difficult for streak tube imaging lidar to simultaneously achieve a large detection field of view and high detection accuracy, researchers at home and abroad have conducted a large number of studies, especially on improving the detection area and spatial resolution of the streak tube. Among them, for example, the ST-Y type streak image tube developed by PHOTEK Company in the UK adopts a curved photocathode, slit grid, curved fluorescent screen, and immersion lens focusing system structure, achieving a static spatial resolution of 50 lp / mm in the scanning direction. However, its effective detection range is relatively low, which is 35 mm × 5 mm, and the number of pixels in the scanning direction is 250. Another example is the N3831 streak image tube developed by Hamamatsu Corporation in Japan. Although it achieves a static spatial resolution higher than 35 lp / mm in the slit direction, the effective detection area of its photocathode is small, which is 25 mm × 15 mm, and the number of pixels in the slit direction is 875. Another example is the long-slit streak image tube developed by Xi'an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences. It adopts a spherical slit grid and immersion lens focusing system structure, achieving a static spatial resolution higher than 40 lp / mm in the scanning direction within an effective detection range of 30 mm × 5 mm. However, its static spatial resolution in the slit direction is relatively low, which is 25 lp / mm, and the number of pixels in the slit direction and the scanning direction are 750 and 200 respectively. Since almost all traditional streak tubes adopt immersion lenses, the cooperative focusing ability of each electrode is weak, resulting in a small detection area and low spatial resolution.

[0005] In summary, it is difficult for the currently developed streak tube imaging lidar to simultaneously achieve a large detection field of view and high detection accuracy, and it is difficult to meet the detection requirements of large field of view and high precision in the lidar field. Summary of the Invention

[0006] The purpose of the present invention is to address the problem that the currently developed streak tube imaging lidar is difficult to meet the detection requirements of large field of view and high precision, and to provide a four-dimensional detection system for a large detection area streak camera with a single lens focusing system for a large detection field of view and high precision streak tube imaging lidar, which can simultaneously achieve a large detection field of view and high precision and meet the detection requirements of large field of view and high precision.

[0007] The technical solution of the present invention is to provide a four-dimensional detection system for a large detection field of view and high precision streak tube imaging lidar, which is characterized in that it includes a pulsed laser, a transmitting optical system, a delay system, a receiving optical system, an optical fiber image transmitter, a streak tube detector, a CCD camera, and a signal processing system;

[0008] The pulsed laser is used to emit light pulses of the required wavelength;

[0009] The transmitting optical system is used to expand the light pulse in the transverse (X direction) and compress it in the scanning direction (Y direction), and then irradiate it onto the target surface;

[0010] The delay system is used to synchronize the operation of the pulsed laser, streak tube detector and CCD camera, and control the strobe gate width and delay time;

[0011] The receiving optical system is used to receive the echo signal reflected by the target surface;

[0012] The fiber optic image converter is used to ratio-focus the echo signal to the streak tube detector;

[0013] The streak tube detector is used to convert the echo signal carrying high-speed time information into low-speed spatial information and output a streak image;

[0014] The CCD camera is used to collect the streak image output by the streak tube detector;

[0015] The signal processing system is used to restore and reconstruct the image collected by the CCD camera and give the three-dimensional distance information and one-dimensional intensity information of the target object;

[0016] Among them, the streak tube detector is a large-detection-area streak tube with a single-lens focusing system, including a photocathode, a focusing system, a scanning deflection system, an anode and a fluorescent screen; the photocathode is used to convert the echo signal ratio-focused by the fiber optic image converter into an electron image; the focusing system is used to focus the electron image emitted by the photocathode; the scanning deflection system is used to convert the time information of the electron image into spatial information; the anode is used to accelerate the electrons; the fluorescent screen is used to convert the electron image output by the anode into a visible optical image;

[0017] The photocathode is a spherical photocathode; the streak tube detector also includes a cylindrical electromagnetic focusing ring arranged at the rear end of the spherical photocathode, and the outer radius of the cylindrical electromagnetic focusing ring is equal to the maximum outer radius of the spherical photocathode;

[0018] The focusing system is a single-lens focusing system, including a first focusing electrode, a second focusing electrode and a third focusing electrode arranged in sequence along the electron propagation direction. The first focusing electrode, the second focusing electrode and the third focusing electrode are all cylindrical electrodes, and their inner radii, outer radii and axial lengths are equal;

[0019] The anode is a conical tube structure, with the small end being the electron entrance, and an anode hole is arranged at the electron entrance;

[0020] The fluorescent screen is a spherical fluorescent screen, and the radius of curvature of the spherical fluorescent screen is equal to the radius of the conical tube at the electron exit of the anode;

[0021] The photocathode, the first focusing electrode, the second focusing electrode and the third focusing electrode are sequentially connected by ceramic rings;

[0022] The anode is embedded within the focusing system, and the anode aperture is located at the electron exit of the second focusing electrode; the third focusing electrode is connected to the anode through a ceramic ring.

[0023] The deflection system is embedded within the anode. The electron inlet of the deflection system is close to the anode aperture, and the fluorescent screen is connected to the electron exit of the anode.

[0024] Furthermore, the potential difference between the first focusing electrode and the third focusing electrode is 0V, the potential difference between the first focusing electrode and the second focusing electrode is 3200V - 4000V; the potential difference between the photocathode and the first focusing electrode is 150V - 250V; the potential difference between the third focusing electrode and the anode is 14750V - 14850V.

[0025] Furthermore, the pulsed laser is a Nd:YAG solid pulsed laser, and the output optical pulse wavelength is 532nm; the emission optical system includes a first telescope and a shaping system arranged in sequence along the optical path, and the shaping system is an expanding and shaping system or a compressing and shaping system; the delay system is a delay trigger circuit; the receiving optical system includes a second telescope and an objective lens arranged in sequence along the optical path; the fiber optic image transmitter is a fiber optic faceplate or a variable magnification optical fiber taper.

[0026] Furthermore, the first telescope is a catadioptric telescope; the shaping system is an expanding and shaping system.

[0027] Furthermore, the light output port size of the variable magnification optical fiber taper is Φ50mm, and the light input port size is the same as the light pulse size output by the receiving optical system.

[0028] Furthermore, the CCD camera is a high frame rate CCD with a frame rate greater than 100Hz.

[0029] Furthermore, the deflection system includes two flat folding plates symmetrically placed up and down. The flat folding plate includes a parallel plate and a trapezoidal inclined plate. The parallel plate adopts a cuboid structure, and the trapezoidal inclined plate adopts a trapezoidal structure.

[0030] Furthermore, the streak tube detector also includes an MCP located inside the anode at the rear end of the scanning deflection system.

[0031] Or, the streak tube detector also includes a spherical structure fiber optic faceplate and an image intensifier. The spherical structure fiber optic faceplate is located at the rear end of the fluorescent screen and is concentric with the fluorescent screen, and the image intensifier is located at the rear end of the spherical structure fiber optic faceplate.

[0032] Furthermore, the radius of curvature of the photocathode is 58mm - 62mm, the spherical crown height is 11mm - 13mm, and the size of the cylindrical electromagnetic focusing ring along the optical axis length direction is 4mm - 6mm.

[0033] The inner radii of the first focusing electrode, the second focusing electrode, and the third focusing electrode are 35 mm to 45 mm, and the thickness is 0.5 mm; the dimension along the optical axis length direction is 20 mm to 25 mm; the spacing between the first focusing electrode, the second focusing electrode, and the third focusing electrode is 3 mm to 6 mm; the aspect ratios of the first focusing electrode, the second focusing electrode, and the third focusing electrode are all 0.28 to 0.30;

[0034] The spacing between the two parallel plates in the two flat folding plates placed symmetrically up and down in the scanning deflection system is 3 mm to 4 mm;

[0035] The outer radius of the small end of the anode is 5 mm to 6 mm, the outer radius of the large end is 40 mm to 50 mm, the thickness is 0.5 mm, and the dimension along the optical axis length direction is 80 mm to 82 mm; the outer radius of the anode hole is 5 mm to 6 mm, and the inner radius is 1.5 mm to 2.5 mm; the outer radius corresponding to the anode electron exit is 40 mm to 50 mm;

[0036] The curvature radius of the fluorescent screen is 40 mm to 50 mm, and the length along the optical axis direction is 40 mm to 50 mm.

[0037] Furthermore, the curvature radius of the photocathode is 60 mm, the spherical crown height is 12 mm, and the dimension of the cylindrical electromagnetic focusing ring along the optical axis length direction is 5 mm; the outer radius of the cylindrical electromagnetic focusing ring is 35.5 mm;

[0038] The inner radii of the first focusing electrode, the second focusing electrode, and the third focusing electrode are 40 mm; the dimension along the optical axis length direction is 23.5 mm; the spacing between the first focusing electrode, the second focusing electrode, and the third focusing electrode is 4.5 mm;

[0039] The spacing between the two parallel plates in the two flat folding plates placed symmetrically up and down in the scanning deflection system is 3.5 mm;

[0040] The outer radius of the small end of the anode is 5.5 mm, the outer radius of the large end is 45.5 mm, the dimension along the optical axis length direction is 81 mm; the outer radius of the anode hole is 5.5 mm, and the inner radius is 2 mm; the outer radius corresponding to the anode electron exit is 45 mm;

[0041] The curvature radius of the fluorescent screen is 45 mm, and the length along the optical axis direction is 45 mm.

[0042] The beneficial effects of the present invention are:

[0043] 1. The four-dimensional detection system of the lidar of the present invention adopts a large detection area streak tube structure with a single-lens focusing system, realizing a large detection field of view and improving the distance resolution in three directions; at the same time, it can perform imaging under the condition of the movement of the target object, meeting the requirements of large detection range and high-precision diagnosis.

[0044] Through theoretical analysis, when the imaging lidar operates in the single-slit mode:

[0045] In the present invention, at a detection distance of 5 km, the following detection ranges and precisions can be achieved in three directions respectively:

[0046] In the X direction: the detection range is 349 m, and the detection precision is 174.5 mm;

[0047] In the Y direction: the detection range is 87 m, and the detection precision is 11.1 mm;

[0048] In the Z direction (depth of field direction): the detection range is 99.9 mm, and the detection precision is 333 nm.

[0049] When the imaging lidar operates in the multi-slit mode:

[0050] In the present invention, at a detection distance of 5 km, the following detection ranges and precisions can be achieved in three directions respectively:

[0051] In the X direction: the detection range is 349 m, and the detection precision is 9.2 mm;

[0052] In the Y direction: the detection range is 87 m, and the detection precision is 11.1 mm;

[0053] In the Z direction (depth of field direction): the detection range is 99.9 mm, and the detection precision is 17.53 nm.

[0054] 2. The streak tube detector of the present invention is a streak tube with a large detection area having a single-lens focusing system. The effective imaging area of its photocathode is Φ50 mm, and the static spatial resolution is higher than 40 lp / mm; in the dynamic scanning mode, when the full-screen scanning time is 0.66 ns, the time resolution is better than 60 ps, and the spatial resolutions in the scanning direction and the slit direction are both higher than 10 lp / mm.

[0055] 3. The lidar detection system of the present invention can operate either in the single-slit mode or in the multi-slit mode. When operating in the multi-slit mode, the photocathode can accommodate at least 19 slits.

[0056] 4. The structure of the streak tube detector of the present invention is simple, easy to assemble, and has strong voltage adjustability.

[0057] The focusing system of the present invention adopts a single-lens focusing system with strong focusing ability. Among them, the potential difference between the first focusing electrode and the third focusing electrode is 0 V. Therefore, by only adjusting the voltages of the first focusing electrode and the second focusing electrode, good adjustment of the intersection point and the focusing point can be achieved. Description of the Drawings

[0058] Figure 1 Schematic diagram of a four-dimensional detection system of a large detection field of view and high-precision streak tube imaging lidar in an embodiment of the present invention;

[0059] Figure 2 Schematic diagram of a large detection area streak tube with an internal enhancement type and a single-lens focusing system in an embodiment of the present invention;

[0060] Figure 3 Schematic diagram of a large detection area streak tube with an external enhancement type and a single-lens focusing system in an embodiment of the present invention;

[0061] Figure 4 Schematic diagram of a transmitting optical system in an embodiment of the present invention;

[0062] Figure 5 Schematic diagram of a receiving optical system in an embodiment of the present invention;

[0063] Figure 6 Illustration of direction (coordinate) description.

[0064] Figure 7 Simulation illustration of the multi-slit working mode of the streak tube detector.

[0065] Reference numerals in the figure are: 1 - pulsed laser, 2 - transmitting optical system, 21 - first telescope, 22 - shaping system, 3 - delay system, 4 - receiving optical system, 41 - second telescope, 42 - objective lens, 5 - fiber optic image converter, 6 - streak tube detector, 61 - photocathode, 611 - cylindrical electromagnetic focusing ring, 62 - focusing system, 621 - first focusing electrode, 622 - second focusing electrode, 623 - third focusing electrode, 63 - scanning deflection system, 631 - parallel plate, 632 - trapezoidal inclined plate, 64 - anode, 641 - anode hole, 65 - fluorescent screen, 66 - MCP, 67 - spherical structured fiber optic panel, 68 - image intensifier, 7 - CCD camera, 8 - signal processing system. Detailed implementation manners

[0066] To make the above objects, features and advantages of the present invention more obvious and understandable, the following detailed description of the specific implementation manners of the present invention is made in conjunction with the accompanying drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0067] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention may be practiced in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0068] Secondly, as used herein, an "embodiment" or "embodiments" refers to specific features, structures, or characteristics that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments.

[0069] Furthermore, the present invention is described in detail in conjunction with schematic diagrams. When describing the embodiments of the present invention in detail, for the sake of convenience in explanation, the cross-sectional views showing the device structure will be enlarged locally out of the general proportion, and the schematic diagrams are only examples and should not limit the scope of protection of the present invention herein. In addition, in actual production, three-dimensional spatial dimensions including length, width, and depth should be included.

[0070] Meanwhile, in the description of the present invention, it should be noted that the orientation or positional relationship indicated by terms such as "front, rear, inner, and outer" is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the present invention. In addition, the terms "first or second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0071] Unless otherwise clearly defined and limited in the present invention, the terms "mounted, connected, and coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection. Similarly, it can be a mechanical connection, an electrical connection, or a direct connection, or can be indirectly connected through an intermediate medium, or can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0072] The structure of a four-dimensional detection system of a large detection field of view and high-precision streak tube imaging lidar in this embodiment is shown in Figure 1 , and includes a pulsed laser 1, a transmitting optical system 2, a delay system 3, a receiving optical system 4, an optical fiber image intensifier 5, a streak tube detector 6, a CCD camera 7, and a signal processing system 8.

[0073] The pulsed laser 1 is used to emit light pulses of the required wavelength, and a Nd:YAG solid pulsed laser with an output light pulse wavelength of 532 nm can be used. In other embodiments, other types of pulsed lasers can also be used, such as carbon dioxide lasers, laser diode arrays, etc.

[0074] The emission optical system 2 is used to expand the light pulse in the transverse direction (X direction) and compress it in the scanning direction (Y direction), and then irradiate it onto the target surface. As Figure 4 shown, it can be the first telescope 21 and the shaping system 22 arranged in sequence along the optical path. The shaping system 22 can be an expanding and shaping system or a compressing and shaping system. In this embodiment, an expanding and shaping system is adopted, and the first telescope 21 is a catadioptric telescope.

[0075] The delay system 3 is used to control the simultaneous operation of the pulsed laser 1, the streak tube detector 6, and the CCD camera 7, and to control the strobe gate width and the delay time. Generally, a delay trigger circuit is selected as the delay system.

[0076] The receiving optical system 4 is used to receive the echo signal reflected by the target surface. As Figure 5 shown, the receiving optical system 4 in this embodiment includes a second telescope 41 and an objective lens 42 arranged in sequence along the optical path.

[0077] The fiber optic image converter 5 is used to ratio-focus the echo signal to the streak tube detector 6. A fiber optic faceplate or a ratio light cone can be used. When it is a ratio light cone, the light output port size of the ratio light cone is Φ50mm, and the light input port size is the same as the light pulse size output by the receiving optical system 4.

[0078] The streak tube detector 6 is used to convert the high-speed time information of the echo signal into low-speed spatial information. In this embodiment, a large detection area streak image tube structure with a single lens focusing system is adopted. Refer to Figure 2 and Figure 3 , where Figure 2 is a schematic diagram of an internally intensified large detection area streak tube with a single lens focusing system, Figure 3 is a schematic diagram of an externally intensified large detection area streak tube with a single lens focusing system. From Figure 2 and Figure 3It can be seen that the streak tube detector 6 includes a photocathode 61, a focusing system 62, a scanning deflection system 63, an anode 64, and a fluorescent screen 65. The photocathode 61 includes a spherical photocathode, and a cylindrical electromagnetic focusing ring 611 is provided at the rear end close to the spherical photocathode. The outer radius of the cylindrical electromagnetic focusing ring 611 is equal to the maximum outer radius of the spherical photocathode. The focusing system 62 is a single-lens focusing system composed of three cylindrical electrodes. The three cylindrical electrodes can be sequentially defined as a first focusing electrode 621, a second focusing electrode 622, and a third focusing electrode 623 along the electron propagation direction. The inner radius, outer radius, and axial length of the three cylindrical electrodes are all equal. The photocathode 61 is connected to the single-lens focusing system through a ceramic ring. Specifically, the cylindrical electromagnetic focusing ring 611 is connected to the first focusing electrode 621 through a ceramic ring. The first focusing electrode 621, the second focusing electrode 622, and the third focusing electrode 623 in the focusing system 62 are sequentially connected through ceramic rings. The scanning deflection system 63 has a flat-folded structure and includes two flat-folded plates symmetrically arranged up and down. The flat-folded plate includes a parallel plate 631 and a trapezoidal inclined plate 632. The parallel plate 631 adopts a thin-sheet cuboid structure, and the trapezoidal inclined plate 632 adopts a trapezoidal structure. The anode 64 has a conical tube structure, with the small end being the electron inlet, and an anode hole 641 is provided at the electron inlet; the fluorescent screen 65 is a spherical fluorescent screen, and the radius of curvature of the spherical fluorescent screen is equal to the radius of curvature of the conical tube at the electron outlet of the anode 64. The anode 64 is connected to the third focusing electrode 623 through a ceramic ring; the anode 64 is embedded in the focusing system 62, and the anode hole 641 is located at the electron outlet of the second focusing electrode 622; the deflection system 63 is embedded in the anode 64, the electron inlet of the deflection system 63 is close to the anode hole 641, and the fluorescent screen 65 is connected to the electron outlet of the anode 64. Figure 2 It is an internally intensified large-detection-area streak tube with a single-lens focusing system. Therefore, an MCP 66 is also provided in the equipotential region inside the anode 64 at the rear end of the deflection system 63 for multiplying electron signals. Figure 3It is an externally enhanced streak tube with a single-lens focusing system and a large detection area. Therefore, a spherical fiber optic faceplate 67 and an image intensifier 68 are sequentially provided at the rear end of the fluorescent screen 65. The spherical fiber optic faceplate 67 is concentric with the fluorescent screen 65, and the image intensifier 68 is located at the rear end of the spherical fiber optic faceplate 67 for enhancing visible light signals. In this embodiment, the potential difference between the first focusing electrode 621 and the third focusing electrode 623 is 0V, and the potential difference between the first focusing electrode 621 and the second focusing electrode 622 is 3200V - 4000V. The potential difference between the photocathode 61 and the first focusing electrode 621 is 150V - 250V. The potential difference between the third focusing electrode 623 and the anode 64 is 14750V - 14850V. The radius of curvature of the spherical photocathode is 58mm - 62mm, and 60mm can be selected; the height of the spherical crown is 11mm - 13mm, and 12mm can be selected; the size of the cylindrical electromagnetic focusing ring 611 along the optical axis length direction is 4mm - 6mm, and 5mm can be selected. The outer radius of the cylindrical electromagnetic focusing ring 611 is 35.5mm. The inner radii of the first focusing electrode 621, the second focusing electrode 622, and the third focusing electrode 623 are 35mm - 45mm, and 40mm can be selected. The thickness is 0.5mm, and the size along the optical axis length direction is 20mm - 25mm, and 23.5mm can be selected; the distance between the first focusing electrode 621, the second focusing electrode 622, and the third focusing electrode 623 is 3mm - 6mm, and 4.5mm can be selected; the aspect ratios of the first focusing electrode 621, the second focusing electrode 622, and the third focusing electrode 623 are all 0.28 - 0.30. The distance between the two parallel plates 631 of the two flat folding plates symmetrically placed up and down in the scanning deflection system 63 is 3mm - 4mm, and 3.5mm can be selected. The outer radius of the small end of the anode 64 is 5mm - 6mm, and 5.5mm can be selected; the outer radius of the large end is 40mm - 50mm, and 45.5mm can be selected; the thickness is 0.5mm, and the size along the optical axis length direction is 80mm - 82mm, and 81mm can be selected; the outer radius of the anode hole 641 is preferably 5mm - 6mm, and 5.5mm can be selected, and the inner radius is 1.5mm - 2.5mm, and 2mm can be selected. The outer radius corresponding to the anode electron exit is 40mm - 50mm, and 45mm can be selected. The radius of curvature of the spherical fluorescent screen 65 is 40mm - 50mm, and 45mm can be selected; the length along the optical axis direction is 40mm - 50mm, and 45mm can be selected.

[0079] The CCD camera 7 is used to record the streak image output by the streak tube detector 6. In this embodiment, a high frame rate CCD can be selected; such as a frame rate greater than 100Hz.

[0080] The signal processing system 8 is used to restore and reconstruct the images collected by the CCD camera 7 to give the three-dimensional distance information and one-dimensional intensity information of the target object.

[0081] The lidar detection system of the present invention can operate in both a single-slit mode and a multi-slit mode. When operating in the multi-slit mode, at least 19 slits can be accommodated on the photocathode, such as Figure 7 , which is a simulation diagram of the multi-slit operating mode of the streak tube detector.

[0082] The specific working process of the large detection field of view, high-precision streak tube imaging lidar four-dimensional detection system in this embodiment is as follows: The pulsed laser 1 emits pulsed optical signals with a wavelength of 532 nm. After passing through the emission optical system 2 for pulse shaping, that is, it is broadened into a fan-shaped light beam in the azimuth direction (transverse, X direction), and compressed in the horizontal direction perpendicular to the azimuth direction (scanning direction, Y direction). Then it irradiates the surface of the detection target. The echo signal reflected by the target enters the receiving optical system 4 and is focused through the fiber optic image intensifier 5. The slits on the photocathode of the streak tube detector 6 receive the light pulses and convert them into photoelectrons. The photoelectrons entering the streak tube detector 6 at different times are scanned to different positions on the fluorescent screen, reflecting the distance information and depth of field information of the target. The CCD camera 7 is used to collect and record the streak image on the fluorescent screen of the streak tube detector 6, and read it out to the signal processing system 8. The signal processing system 8 restores and reconstructs the image, and performs noise processing and target extraction algorithms to obtain the distance information and intensity information on a "slice" (i.e., two-dimensional) of the target. As the lidar system operates, the laser emits multiple pulsed lights, which are reflected by the target and received by the streak tube. The echo signals of multiple reflections are fused, and finally a three-dimensional distance image and intensity image of the target are obtained.

[0083] The distance resolution, depth of field and other indicators of the above large detection field of view, high-precision streak tube imaging lidar four-dimensional detection system are evaluated through the following process.

[0084] Assume that the imaging lidar is carried on a civilian mapping aircraft platform. The aircraft running speed is v = 80 km / h. When operating in the single-slit mode, and the distance to the detection target is H = 5 km, the repetition frequency f of the laser pulse laser = 200 Hz, the beam expansion angle 2α in the X direction is 2°, and the divergence angle 2β of the laser pulse in the Y direction is 0.1°. Then: When the imaging lidar operates in the single-slit mode:

[0085] First, calculate the line spot length L of the imaging lidar irradiating the detection target x as:

[0086] L x = 2H·tanα = 349 m

[0087] Secondly, determine the number M of horizontal lines on the photocathode of the streak tube:

[0088] The spatial resolution of the single-lens focusing system streak tube photocathode reaches 40 lp / mm within the 50-mm-long photocathode range, that is, the number of horizontal line pairs M on the streak tube photocathode is:

[0089] M = 50 mm × 40 lp / mm = 2000;

[0090] Again, determine the distance resolution X of the imaging lidar in the X direction min It is:

[0091] X min = L x / M = 0.1745 m;

[0092] Again, determine the line spot length L of the imaging lidar irradiating the detection target y It is:

[0093] L y = 2H · tanβ = 87 m;

[0094] After that, determine the distance resolution Y of the imaging lidar in the Y direction min , which is divided into two cases:

[0095] a) When v ≥ f laser · L y At this time, the linear light spots do not overlap during the pushbroom imaging process. At this time, the minimum resolvable distance for detection imaging in the Y direction is Y min = L y = 87 m;

[0096] b) When v ≤ f laser · L y At this time, the linear light spots overlap during the pushbroom imaging process. At this time, for the image obtained by image fusion and stitching, the minimum resolvable distance along the Y axis is: Y min = v / f laser = 0.111 m;

[0097] Finally, determine that the distance resolution of the streak tube imaging lidar in the Z direction is: Z min = (T screen · c / 2) / N, where T screen is the full-screen time of the streak tube detector, and N is the number of vertical line pairs on the fluorescent screen of the streak tube detector. For the single-lens focusing system streak tube, in its dynamic scanning mode (the full-screen scanning time is 666 ps), the dynamic spatial resolution is greater than 10 lp / mm within the 30-mm range in the vertical direction, that is, the effective length in the vertical direction is 30 mm, then N = 300, and the distance resolution of the streak tube imaging lidar in the Z direction is: Z min = (T screen·c / 2) / N = 0.333 mm, the depth of field H of the streak tube imaging lidar screen = 99.9 mm, where c is the speed of light;

[0098] The imaging lidar operates in a multi-slit mode:

[0099] First, calculate the line spot length L of the imaging lidar illuminating the detection target x as:

[0100] L x = 2H·tanα = 349 m

[0101] Second, determine the number of horizontal lines M on the photocathode of the streak tube:

[0102] The spatial resolution of the photocathode of the single-lens focusing system streak tube reaches 40 lp / mm within a 50-mm-long photocathode, that is, the number of horizontal lines M on the photocathode of the streak tube is:

[0103] M = 19×50 mm×40 lp / mm = 38000;

[0104] Third, determine the range resolution X of the imaging lidar in the X direction min as:

[0105] X min = L x / M = 9.2 mm;

[0106] Third, determine the line spot length L of the imaging lidar illuminating the detection target y as:

[0107] L y = 2H·tanβ = 87 m;

[0108] After that, determine the range resolution Y of the imaging lidar in the Y direction min , which is divided into two cases:

[0109] a) When v ≥ f laser ·L y , the linear light spots do not overlap during the pushbroom imaging process. At this time, the minimum resolvable distance for detection imaging in the Y direction is Y min = L y = 87 m;

[0110] b) When v ≤ f laser ·L y , the linear light spots overlap during the pushbroom imaging process. At this time, for the image obtained by image fusion and stitching, the minimum resolvable distance along the Y-axis is: Y min = v / f laser = 0.111 m;

[0111] In addition, the range resolution of the streak tube imaging lidar along the Z direction is: Z min =(T screen ·c / 2) / N, where T screen is the full-screen time of the streak tube detector, and N is the number of vertical lines on the phosphor screen of the streak tube detector. For the single-lens focusing system streak tube, in the dynamic scanning mode (the full-screen scanning time is 666 ps), the dynamic spatial resolution is greater than 10 lp / mm within the range of 30 mm in the vertical direction, that is, the effective length in the numerical direction is 30 mm, then N = 5700, and the range resolution of the streak tube imaging lidar along the Z direction is: Z min =(T screen ·c / 2) / N = 17.53 nm, and the depth of field H screen of the streak tube imaging lidar is 99.9 mm.

Claims

1. A four-dimensional detection system for a large detection field of view and high-precision streak tube imaging lidar, characterized in that: It includes a pulsed laser (1), a transmitting optical system (2), a time delay system (3), a receiving optical system (4), an optical fiber image converter (5), a streak tube detector (6), a CCD camera (7), and a signal processing system (8); The pulsed laser (1) is used to emit optical pulses of the required wavelength; The transmitting optical system (2) is used to expand the optical pulse in the X direction and compress it in the Y direction, and then irradiate it onto the target surface; The time delay system (3) is used to synchronize the pulsed laser (1), the streak tube detector (6), and the CCD camera (7) to work simultaneously, and control the strobe gate width and delay time; The receiving optical system (4) is used to receive the echo signal reflected by the target surface; The optical fiber image converter (5) is used to ratio-focus the echo signal onto the streak tube detector (6); The streak tube detector (6) is used to convert the echo signal carrying high-speed time information into low-speed spatial information and output a streak image; The CCD camera (7) is used to collect the streak image output by the streak tube detector (6); The signal processing system (8) is used to restore and reconstruct the image collected by the CCD camera (7) and give the three-dimensional distance information and one-dimensional intensity information of the target object; Among them, the streak tube detector (6) is a large-detection-area streak tube with a single-lens focusing system, including a photocathode (61), a focusing system (62), a scanning deflection system (63), an anode (64), and a fluorescent screen (65); the photocathode (61) is used to convert the echo signal ratio-focused by the optical fiber image converter (5) into an electron image; the focusing system (62) is used to focus the electron image emitted by the photocathode (61); the scanning deflection system (63) is used to convert the time information of the electron image into spatial information; the anode (64) is used to accelerate the electrons; the fluorescent screen (65) is used to convert the electron image output by the anode (64) into a visible optical image; The photocathode (61) is a spherical photocathode; the streak tube detector (6) also includes a cylindrical electromagnetic focusing ring (611) arranged at the rear end of the spherical photocathode, and the outer radius of the cylindrical electromagnetic focusing ring (611) is equal to the maximum outer radius of the spherical photocathode; The focusing system (62) is a single-lens focusing system, including a first focusing electrode (621), a second focusing electrode (622), and a third focusing electrode (623) arranged in sequence along the electron propagation direction. The first focusing electrode (621), the second focusing electrode (622), and the third focusing electrode (623) are all cylindrical electrodes, and their inner radii, outer radii, and axial lengths are equal; The anode (64) is a conical tube structure, with the small end being the electron entrance, and an anode hole (641) is arranged at the electron entrance; The fluorescent screen (65) is a spherical fluorescent screen, and the radius of curvature of the spherical fluorescent screen is equal to the radius of the conical tube at the electron exit of the anode (64); The photocathode (61), the first focusing electrode (621), the second focusing electrode (622), and the third focusing electrode (623) are sequentially connected through ceramic rings; The anode (64) is embedded within the focusing system (62), and the anode aperture (641) is located at the electron exit of the second focusing electrode (622); the third focusing electrode (623) is connected to the anode (64) through a ceramic ring; The deflection system (63) is embedded within the anode (64). The electron entrance of the deflection system (63) is close to the anode aperture (641), and the fluorescent screen (65) is connected to the electron exit of the anode (64).

2. The four-dimensional detection system of a large detection field of view and high-precision streak tube imaging lidar according to claim 1, wherein: The potential difference between the first focusing electrode (621) and the third focusing electrode (623) is 0V, and the potential difference between the first focusing electrode (621) and the second focusing electrode (622) is 3200V - 4000V; the potential difference between the photocathode (61) and the first focusing electrode (621) is 150V - 250V; the potential difference between the third focusing electrode (623) and the anode (64) is 14750V - 14850V.

3. The four-dimensional detection system of a large detection field of view and high-precision streak tube imaging lidar according to claim 1 or 2, characterized in that: The pulsed laser (1) is a Nd:YAG solid pulsed laser, and the output optical pulse wavelength is 532nm; the emission optical system (2) includes a first telescope (21) and a shaping system (22) arranged in sequence along the optical path, and the shaping system (22) is an expanding and shaping system or a compressing and shaping system; the delay system (3) is a delay trigger circuit; The receiving optical system (4) includes a second telescope (41) and an objective lens (42) arranged in sequence along the optical path; the fiber optic image converter (5) is a fiber optic faceplate or a variable ratio fiber optic taper.

4. The four-dimensional detection system of a large detection field of view and high-precision streak tube imaging lidar according to claim 3, wherein: The first telescope (21) is a catadioptric telescope; the shaping system (22) is an expanding and shaping system.

5. The four-dimensional detection system of a large detection field of view and high-precision streak tube imaging lidar according to claim 4, characterized in that: The exit port size of the variable ratio fiber optic taper is Φ50mm, and the entrance port size is the same as the size of the optical pulse emitted by the receiving optical system (4).

6. The four-dimensional detection system of a large detection field of view and high-precision streak tube imaging lidar according to claim 5, characterized in that: The CCD camera (7) is a high frame rate CCD with a frame rate greater than 100Hz.

7. The four-dimensional detection system of a large detection field of view and high-precision streak tube imaging lidar according to claim 6, characterized in that: The deflection system (63) includes two flat folding plates symmetrically placed above and below. The flat folding plate includes a parallel plate (631) and a trapezoidal inclined plate (632). The parallel plate (631) has a cuboid structure, and the trapezoidal inclined plate (632) has a trapezoidal structure.

8. The large detection field of view, high-precision streak tube imaging lidar four-dimensional detection system according to claim 7, characterized in that: The streak tube detector (6) further includes an MCP (66) located in the equipotential region inside the anode (64) at the rear end of the scanning deflection system (63); Or, the streak tube detector (6) further includes a spherical fiber optic faceplate (67) and an image intensifier (68). The spherical fiber optic faceplate (67) is located at the rear end of the fluorescent screen (65) and is concentric with the fluorescent screen (65), and the image intensifier (68) is located at the rear end of the spherical fiber optic faceplate (67).

9. The large detection field of view, high-precision streak tube imaging lidar four-dimensional detection system according to claim 8, characterized in that: The radius of curvature of the photocathode (61) is 58mm - 62mm, the height of the spherical crown is 11mm - 13mm, and the dimension of the cylindrical electromagnetic focusing ring (611) along the optical axis length direction is 4mm - 6mm; The inner radii of the first focusing electrode (621), the second focusing electrode (622), and the third focusing electrode (623) are 35 mm to 45 mm, and the thickness is 0.5 mm; the dimension along the optical axis length direction is 20 mm to 25 mm; the spacing between the first focusing electrode (621), the second focusing electrode (622), and the third focusing electrode (623) is 3 mm to 6 mm; the aspect ratios of the first focusing electrode (621), the second focusing electrode (622), and the third focusing electrode (623) are all 0.28 to 0.30; The spacing between the two parallel plates (631) in the two flat folding plates placed symmetrically up and down in the scanning deflection system (63) is 3 mm to 4 mm; The outer radius of the small end of the anode (64) is 5 mm to 6 mm, the outer radius of the large end is 40 mm to 50 mm, the thickness is 0.5 mm, and the dimension along the optical axis length direction is 80 mm to 82 mm; the outer radius of the anode hole (641) is 5 mm to 6 mm, and the inner radius is 1.5 mm to 2.5 mm; the outer radius corresponding to the electron exit of the anode (64) is 40 mm to 50 mm; The curvature radius of the fluorescent screen (65) is 40 mm to 50 mm, and the length along the optical axis direction is 40 mm to 50 mm.

10. The four-dimensional detection system of a large detection field of view and high-precision streak tube imaging lidar according to claim 9, characterized in that: The curvature radius of the photocathode (61) is 60 mm, the height of the spherical crown is 12 mm, and the dimension of the cylindrical electromagnetic focusing ring (611) along the optical axis length direction is 5 mm; the outer radius of the cylindrical electromagnetic focusing ring (611) is 35.5 mm; The inner radius of the first focusing electrode (621), the second focusing electrode (622), and the third focusing electrode (623) is 40 mm; the dimension along the optical axis length direction is 23.5 mm; the spacing between the first focusing electrode (621), the second focusing electrode (622), and the third focusing electrode (623) is 4.5 mm; The spacing between the two parallel plates (631) in the two flat folding plates placed symmetrically up and down in the scanning deflection system (63) is 3.5 mm; The outer radius of the small end of the anode (64) is 5.5 mm, the outer radius of the large end is 45.5 mm, and the dimension along the optical axis length direction is 81 mm; the outer radius of the anode hole (641) is 5.5 mm, and the inner radius is 2 mm; the outer radius corresponding to the electron exit of the anode (64) is 45 mm; The curvature radius of the fluorescent screen (65) is 45 mm, and the length along the optical axis direction is 45 mm.

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