CN109975828B

CN109975828B - Self-triggering gating laser imaging method

Info

Publication number: CN109975828B
Application number: CN201910340576.5A
Authority: CN
Inventors: 母一宁
Original assignee: Changchun University of Science and Technology
Current assignee: Changchun University of Science and Technology
Priority date: 2019-04-25
Filing date: 2019-04-25
Publication date: 2020-08-21
Anticipated expiration: 2039-04-25
Also published as: CN109975828A

Abstract

A self-triggering gating laser imaging method belongs to the technical field of laser active imaging detection. The self-triggering gating is characterized in that under a normal state, a pulse power supply adds 50-100V reverse voltage between an emergent end face electrode of a first-stage micro-channel plate and an incident end face electrode of a second-stage micro-channel plate, when an electron beam image emitted from the first-stage micro-channel plate is between two laser pulses in time, the electron beam image at the moment corresponds to a background noise light image actually, and the background noise light image is prevented by the reverse voltage; when an electron beam image emitted from the first-stage microchannel plate is in a laser pulse in time, electrons with a part of larger kinetic energy of the electron beam image reach a trigger signal bypass electrode and input trigger current to a trigger circuit, wherein the trigger current is larger than a preset current threshold value, so that the trigger circuit outputs a gating signal with the same duration as the laser pulse; and after receiving the gating signal, the pulse power supply instantaneously converts the output reverse voltage into a forward voltage of 200-250V, so that the electron beam image at the moment normally passes through the micropore array grid.

Description

Self-triggering gating laser imaging method

Technical Field

The invention relates to a self-triggering gating laser imaging method, and belongs to the technical field of laser active imaging detection.

Background

The existing distance gating laser active imaging detection technology is that a laser imaging light source emits infrared short pulse laser, the infrared short pulse laser is collimated and split into beams, and one beam of the beam illuminates a target and then is reflected by the target to form a detection image signal and is imaged on a gating camera; the other beam of illumination target is reflected by the target to become an external trigger source and is received by an external trigger device (such as APD) to be used as a delay reference pulse; determining the delay time of a synchronous control circuit according to the distance between a laser imaging light source and a target, determining the opening duration of a gating door according to the imaging detection depth of field, wherein at the gating moment, the detection image signal just enters a gating camera to be gated for imaging, and the gating door is closed at the rest time. The scheme effectively eliminates background stray light entering the gating camera during non-pulse imaging time, and improves the signal to noise ratio of imaging detection. The light splitting scheme adopted by the scheme only ensures that a part of laser is not used for imaging, the optical power of a detection image signal is reduced, and the improvement of the signal to noise ratio of imaging detection is not facilitated.

Disclosure of Invention

In order to further improve the signal-to-noise ratio of gated laser active imaging detection, an electric vacuum amplifying device is used as a main body, a part of an image signal which is subjected to primary amplification is used as a trigger signal to trigger the gate gating of a micropore array grid, the image signal which is subjected to primary amplification passes through the micropore array grid and is amplified again, and finally the image is imaged on a gating camera.

The self-triggering gating laser imaging method is characterized in that as shown in figure 1, infrared pulse laser irradiates a target and a background and then reflects, a generated optical detection image is incident into a self-triggering gating laser imaging device, focuses on a photocathode 3 through a glass window 1, excites to generate photoelectrons to form an electron beam image, and is incident into a primary microchannel plate 4 to enhance the image under the action of an external forward electric field; under a normal state, a pulse power supply adds 50-100V reverse voltage between an emergent end face electrode of a first-stage microchannel plate 4 and an incident end face electrode of a second-stage microchannel plate 6, when an electron beam image emitted from the first-stage microchannel plate 4 is between two laser pulses in time, the electron beam image at the moment corresponds to a background noise light image actually, even if the first-stage microchannel plate 4 is enhanced, the image is still weak and will be prevented by the reverse voltage, and perhaps the electron beam image at the moment is strong and falls on a trigger signal bypass electrode 11 of a micropore array grid 5 to generate current and serve as a trigger signal to flow to a trigger circuit; before a specific detection item is carried out, a current threshold value is preset for the trigger circuit according to the actual detection conditions of the target and the background, the current generated by the electron beam image corresponding to the background noise light image is smaller than the current threshold value, the trigger circuit does not output gating signals, and the background noise light image is completely prevented; when the electron beam image emitted from the first-stage microchannel plate 4 is in the laser pulse in terms of time, although the electron beam image is still under the reverse voltage at this time, a part of electrons constituting the electron beam image has large kinetic energy, reaches the trigger signal bypass electrode 11 and inputs a trigger current to the trigger circuit, the trigger current is greater than a preset current threshold value, and then the trigger circuit outputs a gating signal with the same duration as the laser pulse; after receiving the gating signal, the pulse power supply instantaneously converts the output reverse voltage into a forward voltage of 200-250V, so that the electron beam image at the moment normally passes through the micropore array grid 5, is amplified again by the secondary microchannel plate 6, is transmitted to the fluorescent screen 7 under the action of the forward high voltage, is restored into an optical image, and is coupled to the gating camera 9 by the optical fiber light cone 8.

A self-triggered-gated laser imaging apparatus useful for implementing the self-triggered-gated laser imaging method of the present invention is as follows.

As shown in fig. 1, a glass window 1 is plugged at one end of an insulating shell 2, a photocathode 3, a primary microchannel plate 4, a micropore array grid 5 and a secondary microchannel plate 6 are sequentially embedded in the insulating shell 2 from the end, a fluorescent screen 7 is plugged at the other end of the insulating shell 2, and a fiber optic cone 8 and a gating camera 9 are sequentially connected to the light emitting side of the fluorescent screen 7; the micropore array grid 5 has the structural characteristics that: as shown in fig. 2, micron-sized through holes 10 are densely distributed in a circular thin plate-shaped glass substrate along the axial direction, all the through holes 10 are parallel and form an angle of 7-15 degrees with the axis of the glass substrate, and a metal film is plated on the top surface of the glass substrate to serve as a trigger signal bypass electrode 11; the bottom surface of the micropore array grid 5 is contacted with the incident end surface of the secondary microchannel plate 6; the trigger signal bypass electrode 11 is in contact with a trigger signal input end of the power generation circuit, a gating signal output end of the trigger circuit is respectively connected with respective gating signal input ends of a pulse power supply and a control circuit, two electrode ends of the pulse power supply are respectively connected with an emergent end face electrode of the first-stage microchannel plate 4 and an incident end face electrode of the second-stage microchannel plate 6, and 50-100V reverse voltage or 200-250V forward voltage is added between the two electrodes; the driving signal output end of the control circuit is connected with the electronic shutter of the gating camera 9.

The invention has the technical effects that the invention utilizes laser to detect a part of image signal energy as a trigger signal, and simultaneously, the invention particularly provides an electric control gating device, namely a micropore array grid 5, wherein when receiving the trigger signal reaching threshold current, a trigger circuit sends a gating signal to a pulse power supply, and the pulse power supply controls the gating device to be switched on and off in a mode of changing voltage direction, so that the invention is called self-triggering. The reverse voltage is controlled within the range of 50-100V, so that no more than 40% of the energy of the electron beam image is bypassed to be used as a trigger signal, the electron beam image is subjected to primary enhancement before, and a reserved part of the electron beam image is subjected to a secondary gain process. This gating approach also has the side effect that the dynamic effect of gating is improved, since the gating process is done in a very centralized fashion.

Drawings

Fig. 1 is a schematic diagram of a gated imaging process of a self-triggered gated laser imaging method of the present invention, and is also a schematic diagram of a self-triggered gated laser imaging device structure which is helpful for implementing the present invention, and the diagram is taken as an abstract figure at the same time. Fig. 2 is an enlarged partial cross-sectional view of a gate structure of a micro-pore array in a self-triggered gated laser imaging device that is useful for implementing the present invention.

Detailed Description

An unnecessary feature of the self-triggering gating laser imaging method of the present invention is that the electronic shutter of the gating camera 9 is normally closed, a part of the gating signal output by the trigger circuit is transmitted to the control circuit, and is output to the gating camera 9 as a driving signal after time-delay processing, so as to drive the electronic shutter to open, and the optical image is captured by the gating camera 9. Therefore, the invention realizes secondary gating by using the electronic shutter in the gating camera 9, and further improves the signal-to-noise ratio of the laser detection image signal.

In addition, the invention sets the following four working voltages, namely the voltage V between the photocathode 3 and the primary microchannel plate 4₁Is 200V; the voltage V at two ends of the first-stage micro-channel plate 4 and the second-stage micro-channel plate 6₂、V₃All are 800-1000V; voltage V between the secondary microchannel plate 6 and the screen 7 conducting film₄Is 2000-4000V.

Claims

1. A self-triggering gating laser imaging method is characterized in that infrared pulse laser irradiates a target and a background and then reflects, a generated optical detection image is incident into a self-triggering gating laser imaging device, focuses on a photoelectric cathode through a glass window, excites to generate photoelectrons to form an electron beam image, and is incident into a primary microchannel plate to enhance the image under the action of an externally applied forward electric field; under a normal state, a pulse power supply adds 50-100V reverse voltage between an emergent end face electrode of a first-stage microchannel plate and an incident end face electrode of a second-stage microchannel plate, when an electron beam image emitted from the first-stage microchannel plate is between two laser pulses in time, the electron beam image at the moment corresponds to a background noise light image actually, even if the first-stage microchannel plate is enhanced, the electron beam image is still weak and is prevented by the reverse voltage, and perhaps the electron beam image at the moment is strong and falls on a trigger signal bypass electrode of a micropore array grid to generate current and serve as a trigger signal to flow to a trigger circuit; before a specific detection item is carried out, a current threshold value is preset for the trigger circuit according to the actual detection conditions of the target and the background, the current generated by the electron beam image corresponding to the background noise light image is smaller than the current threshold value, the trigger circuit does not output gating signals, and the background noise light image is completely prevented; when an electron beam image emitted from the first-stage microchannel plate is in laser pulse in time, although the electron beam image is still under reverse voltage at the time, part of electrons forming the electron beam image has larger kinetic energy, reaches a trigger signal bypass electrode and inputs trigger current to the trigger circuit, wherein the trigger current is larger than a preset current threshold value, and then the trigger circuit outputs a gating signal with the same duration as the laser pulse; and after receiving the gating signal, the pulse power supply instantaneously converts the output reverse voltage into a forward voltage of 200-250V, so that the electron beam image at the moment normally passes through the micropore array grid, is amplified again by the secondary microchannel plate, is transmitted to the fluorescent screen under the action of the forward high voltage, is restored into an optical image, and is coupled to the gating camera by the optical fiber light cone.

2. The self-triggering gating laser imaging method as claimed in claim 1, wherein the electronic shutter of the gating camera is closed in a normal state, a part of the gating signal output by the trigger circuit is transmitted to the control circuit, and is output to the gating camera as a driving signal after delay processing, so as to drive the electronic shutter to be opened, and the optical image is captured by the gating camera.

3. The self-triggered-gate laser imaging method as claimed in claim 1, wherein a voltage V between the photocathode and the primary microchannel plate₁Is 200V; the voltage V at two ends of the first-stage micro-channel plate and the second-stage micro-channel plate₂、V₃All are 800-1000V; voltage V between secondary microchannel plate and fluorescent screen₄Is 2000-4000V.