Apparatus and method for testing light feedback characteristics of a microchannel plate image tube

Abstract

The application discloses a device and method for testing the light feedback characteristic of a low-light image intensifier image tube, which comprises a light source, a neutral filter box, an adjustable aperture diaphragm, an integrating sphere, an illuminometer, a contrast test target plate, a conjugate projection lens assembly, an image tube, an industrial camera, an image tube high-voltage power supply, a computer and a test dark box. The method tests the linearity of a certain fixed spatial frequency line under the corresponding MCP voltage of the image tube, and obtains the MCP voltage of the image tube at which the light feedback occurs according to the change of the contrast of the image tube with the MCP voltage. If the brightness gain corresponding to the voltage is higher than the required brightness gain, the image tube does not have the risk of light feedback, otherwise, the image tube has the risk of light feedback. Whether the image tube and the high-voltage power supply packaged as an image intensifier have the risk of light feedback is determined. The application realizes the accurate test of the light feedback characteristic of the low-light image tube, can avoid the circulation of the image tube with the risk of light feedback, and guarantees the imaging quality of the low-light image intensifier.

Description

Technical Field

[0001] This invention belongs to the field of low-light image intensifier technology. This invention discloses an apparatus and method for testing the light feedback characteristics of the image tube of a low-light image intensifier. Background Technology

[0002] The low-light image intensifier is the core of a low-light night vision instrument, and its performance determines the quality of the instrument. During the manufacturing process, the low-light image tube and the dedicated high-voltage power supply are manufactured and tested separately. Qualified low-light image tubes and the dedicated high-voltage power supply are then integrated and packaged together, and sealed in a plastic housing using silicone rubber to form a complete image intensifier. After the image intensifier is integrated and packaged, the brightness gain of the image intensifier is adjusted to meet the technical specifications by adjusting the MCP operating voltage of the dedicated high-voltage power supply.

[0003] The following is a schematic diagram of the common near-field low-light image tube (hereinafter referred to as image tube). Figure 2 As shown, the main components of the image intensifier for image enhancement include a cathode input window 81, a photocathode 82, a microchannel plate 83 (hereinafter referred to as MCP), a phosphor screen aluminum film 84, a phosphor screen powder layer 85, and an optical fiber output window 86. When a weak light image is incident on the image intensifier, it passes through the cathode input window 81 to reach the photocathode 82 and excites photoelectrons. The photoelectrons are multiplied by the microchannel plate 83 and then bombard the phosphor screen powder layer 85 to emit light. Finally, the light is output through the anode optical fiber output window 86, thereby enhancing the weak light image.

[0004] Optical feedback in a cathode ray tube refers to the phenomenon where electrons emitted from the photocathode are multiplied by the MCP (Mechanical Coefficient of Motion) and then pass through the aluminum film of the phosphor screen to excite the phosphor layer to emit light. The light emitted by the phosphor layer then passes through the aluminum film and MCP back to the photocathode, causing it to emit non-image-forming photoelectrons. These photoelectrons are then multiplied by the MCP again, further exciting the phosphor layer to emit light. The emitted light from the phosphor then passes through the aluminum film and MCP back to the cathode, and this cycle repeats, increasing in intensity with each iteration until a stable output brightness is achieved. This is optical feedback in a cathode ray tube. The presence of optical feedback reduces the contrast of the image intensifier, severely degrading its image quality. Therefore, optical feedback should be avoided when using an image intensifier.

[0005] The optical feedback of a cathode ray tube (CRT) is mainly related to its brightness gain, while the brightness gain of an image intensifier is primarily determined by the MCP electronic gain. The MCP electronic gain of the CRT is, in turn, determined by the MCP operating voltage. The MCP voltage has an exponential relationship with its electronic gain. A typical MCP voltage versus electronic gain curve is shown in the diagram below. Figure 3As shown, the higher the MCP voltage, the higher the electronic gain of the MCP, and the higher the brightness gain of the image intensifier tube. However, the image intensifier tube is also more prone to optical feedback. Therefore, if a certain model of image intensifier requires a high brightness gain, its image intensifier tube's MCP operating voltage must also be higher, and the risk of optical feedback is also higher. However, currently there is no clear testing method for whether an image intensifier tube has optical feedback at its corresponding brightness gain. If the presence of optical feedback at the corresponding brightness gain of the image intensifier tube can be tested before the image intensifier tube and dedicated high-voltage power supply are integrated into the package, then image intensifier tubes with optical feedback can be prevented from being used in subsequent projects. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide an apparatus and method for testing the optical feedback characteristics of a low-light image intensifier tube. By testing the modulation index of a fixed spatial frequency line at the corresponding MCP voltage of the tube, the MCP voltage at which optical feedback occurs is obtained based on the change of the tube contrast with the MCP voltage. If the brightness gain corresponding to this MCP voltage is higher than the required brightness gain, then the tube does not have the risk of optical feedback; otherwise, optical feedback exists. This allows for the determination of whether there is a risk of optical feedback after the tube and high-voltage power supply are packaged together as an image intensifier.

[0007] The technical solution for realizing the present invention is as follows:

[0008] An apparatus for testing the optical feedback characteristics of a low-light image intensifier tube includes a light source, a neutral density filter box, an adjustable aperture stop, an integrating sphere, an illuminance meter, a contrast test target, a conjugate projection lens assembly, the image tube, an industrial camera, a high-voltage power supply for the image tube, a computer, and a dark chamber. The light source, neutral density filter box, adjustable aperture stop, integrating sphere, contrast test target, conjugate projection lens assembly, image tube, and industrial camera are arranged coaxially along the direction of light propagation; the contrast test target, conjugate projection lens assembly, image tube, and industrial camera are all housed within the dark chamber.

[0009] The light output from the integrating sphere is controlled within the range of 2–4 × 10⁻⁶ after measurement by the illuminance meter. -3 The contrast test target plate includes six 15 lp / mm grayscale test values, each 2 mm in length.

[0010] The working principle of the device of the present invention is as follows:

[0011] The light emitted from the light source is attenuated by a neutral density filter and an adjustable aperture stop before entering the integrating sphere. The integrating sphere outputs uniform diffused light, which illuminates a contrast test target. The image of the target is then projected onto the cathode surface of the image tube via a conjugate projection lens and finally output through the anode output window. This image is captured by an industrial camera, and its modulation is calculated. The image tube is powered by a high-voltage power supply, and the MCP voltage of the image tube is adjusted by regulating the MCP output voltage of the high-voltage power supply. A lux meter detects the illuminance output from the integrating sphere in real time, and the illuminance can be adjusted by regulating the adjustable aperture stop. The modulation test values ​​of the image tube at different MCP voltages can be obtained by adjusting the MCP voltage of the high voltage power supply of the image tube. The MCP voltage at which the contrast of the image tube decreases as the MCP voltage increases is the optical feedback voltage of the image tube. If the brightness gain of the image tube at this MCP voltage is higher than the gain requirement of the image intensifier, then the image tube can meet the selection requirements; if the brightness gain of the image tube at this MCP voltage is lower than the brightness gain value of the image intensifier, then the image tube cannot be used for this type of image intensifier.

[0012] A method for testing the light feedback characteristics of a low-light image intensifier tube includes: testing the light feedback characteristics of the image tube at an input illuminance of 2–4 × 10⁻⁶. -3 Under lx conditions, a 15 lp / mm resolution target plate is projected onto the photocathode of the image tube through a 1X conjugate optical lens, and the target plate image output from the anode fiber output window is acquired by a CCD camera after the target plate lines are imaged through the image tube. Finally, the modulation index of the target plate lines is calculated using image analysis and processing software. The grayscale test value of the target plate lines is calculated according to the following formula to obtain the corresponding modulation index value T of the line.

[0013]

[0014] In the formula: I max I is the average of the maximum grayscale values ​​of the target plate lines during testing. min This represents the average of the minimum grayscale values ​​for the target plate lines.

[0015] The contrast of the image tube can be obtained by adjusting the MCP operating voltage. In the normal operating range of the image tube, its contrast does not change with the change of the MCP voltage. When the MCP of the image tube is increased to the voltage at which it exhibits optical feedback, its contrast decreases. The MCP voltage at this time can be determined as the optical feedback voltage of the image tube.

[0016] The beneficial effects of this invention are:

[0017] This invention enables accurate testing of the optical feedback characteristics of low-light image tubes (LSIs). By testing the contrast of a corresponding resolution target plate at different MCP voltages, the MCP voltage at which optical feedback occurs in the LSI can be accurately determined. This MCP voltage is then used as the optical feedback voltage of the LSI, thereby determining whether the LSI meets the requirements of the corresponding image intensifier. Firstly, this invention allows for accurate determination of whether optical feedback exists in the brightness gain of the LSI before its integration and packaging with a dedicated high-voltage power supply, preventing LSIs with optical feedback from being selected. Secondly, the optical feedback voltage of the LSI can be used as the selection criterion for image intensifiers with different gain requirements, avoiding the selection of LSIs that exhibit optical feedback and ensuring the imaging quality of the LSI image intensifier. Attached Figure Description

[0018] Figure 1 Schematic diagram of the optical feedback characteristics testing device for the image tube in a low-light image intensifier. Figure 1 In the middle: 1-Light source, 2-Neutral filter box, 3-Adjustable aperture stop, 4-Integrating sphere, 5-Luminometer, 6-Contrast test target plate, 7-Conjugate projection lens assembly, 8-Image tube, 9-Industrial camera, 10-Image tube high voltage power supply, 11-Computer, 12-Test dark box.

[0019] Figure 2 : Schematic diagram of the tube's structure Figure 2 In the middle: 81-Cathode input window, 82-Photocathode, 83-Microchannel plate, 84-Aluminum film for fluorescent screen, 85-Powder layer for fluorescent screen, 86-Fiber optic output window.

[0020] Figure 3 Typical MCP voltage vs. electron gain curves: Schematic diagram

[0021] Figure 4 Schematic diagram of the contrast test target plate.

[0022] Figure 5 : Schematic diagram of grayscale test results for contrast target plate lines. Detailed Implementation

[0023] The apparatus for testing the light feedback characteristics of the image tube in the image intensifier of the present invention is as follows: Figure 1As shown, the light emitted from light source 1 is attenuated by neutral density filter box 2 and adjustable aperture stop 3 before entering integrating sphere 4. Uniform diffused light is output through the integrating sphere. The light output from the integrating sphere illuminates contrast test target plate 6, and the target plate image is projected onto the cathode surface of image tube 8 through conjugate projection lens 7 and finally output through the anode output window. The image is then acquired by industrial camera 9, and its modulation is calculated. Image tube 8 is powered by high-voltage power supply 10, and the modulation test value of the image tube at different MCP voltages can be obtained by adjusting the MCP voltage value of the high-voltage power supply 10. The MCP voltage at which the contrast of the image tube decreases as the MCP voltage increases is the light feedback voltage of the image tube. If the brightness gain of the image tube at this MCP voltage is higher than the gain requirement of the image intensifier, then the image tube meets the selection requirements; if the brightness gain of the image tube at this MCP voltage is lower than the brightness gain value of the image intensifier, then the image tube cannot be used for this type of image intensifier.

[0024] Methods for testing the optical feedback characteristics of the image tube in a low-light image intensifier include:

[0025] (1) The light emitted from light source 1 is attenuated by neutral density filter box 2 and adjustable aperture stop 3 before entering integrating sphere 4. Adjusting the adjustable aperture stop 3 ensures that the uniformly diffused light output from the integrating sphere is within an illuminance range of 2 to 4 × 10⁻⁶ lux. -3 lx.

[0026] (2) The contrast test target plate 6 consists of 6 high contrast target plates with a length of 2mm and a height of 15lp / mm.

[0027] (3) In order to measure the contrast of the image tube under different MCP voltages, the high voltage power supply 10 of the image tube supplies power to the image tube 8. The brightness gain of the image tube can be adjusted by adjusting the MCP voltage value of the high voltage power supply 10 of the image tube.

[0028] (4) The target plate 6 is focused onto the input surface of the image tube 8 through the conjugate lens 7, and the output target plate image after the target plate 6 is projected onto the image tube 8 through the conjugate lens 7 is adjusted to the best clear state by adjusting the focal length of the industrial camera 9.

[0029] (5) The target plate image output by the image tube 8 is acquired by the industrial camera 9 and then processed by the software of the computer 11 for image acquisition and analysis. The corresponding test diagram of the target plate image is shown below. Figure 4 As shown, the grayscale test values ​​of the target plate lines are as follows: Figure 5 As shown, the grayscale value obtained from the test is calculated according to the modulation calculation formula (1) to obtain the corresponding modulation value T;

[0030]

[0031] In the formula: I maxThe average of the 15% maximum values ​​selected from the test grayscale values ​​among the six target lines with a resolution of 15 lp / mm is I. min The average value of the minimum 18% of the grayscale values ​​selected from the test grayscale values ​​of the 6 target plate lines.

[0032] (6) In order to measure the contrast of the image tube 8 under different MCP voltages, the brightness gain of the image tube 8 is adjusted by adjusting the MCP voltage value of the high voltage power supply 10 of the image tube to obtain the modulation value of the image tube 8 under different voltages. When the MCP voltage is adjusted from low to high within the normal operating range of the image tube, its image contrast remains unchanged. When the MCP voltage is increased to its optical feedback voltage, its image contrast decreases. The MCP voltage at this time can be used to determine the optical feedback voltage of the image tube.

Claims

1. A method of testing the light feedback characteristics of an image tube of a low light level image intensifier, characterized by, The light feedback characteristic of the image tube of the low-light-level image intensifier is tested by using a testing device, and the testing device comprises the following steps: (1) The light emitted by the light source passes through the neutral filter box and the adjustable aperture diaphragm, and then enters the integrating sphere, and the adjustable aperture diaphragm is adjusted to make the uniform diffuse light output from the integrating sphere; (2) The brightness gain of the image tube is adjusted by adjusting the MCP voltage value of the image tube high-voltage power supply; (3) The target plate is focused on the input surface of the image tube through the conjugate lens, and the focus of the industrial camera is adjusted to make the output target plate image of the image tube through the conjugate lens clear; (4) The image of the output target plate of the image tube collected by the industrial camera is analyzed and calculated by the software of the computer, the gray value obtained by the test is calculated according to the modulation formula (1), and the corresponding modulation value T is obtained; （1） wherein: I max I is the average of the 6 strip 15 lp / mm resolution 6 strip target plate line between the test gray value selected 15% maximum value, I min I is the average of the 6 strip 15 lp / mm resolution 6 strip target plate line between the test gray value selected 15% maximum value, I (5) The contrast of the image tube under different MCP voltages is measured, the brightness gain of the image tube is adjusted by adjusting the MCP voltage value of the image tube high-voltage power supply, and the modulation value of the image tube under different voltages is obtained, when the MCP voltage is adjusted from low to high in the normal working range of the image tube, the image contrast remains unchanged, when the MCP voltage is increased to the light feedback voltage, the image contrast decreases, and the MCP voltage at this time is determined as the light feedback voltage of the image tube; The testing device comprises a light source, a neutral filter box, an adjustable aperture diaphragm, an integrating sphere, an illuminometer, a contrast test target plate, a conjugate projection lens assembly, an image tube, an industrial camera, an image tube high-voltage power supply, a computer and a test dark box; Along the direction of the light emitted by the light source, the light source, the neutral filter box, the adjustable aperture diaphragm, the integrating sphere, the contrast test target plate, the conjugate projection lens assembly, the image tube and the industrial camera are arranged in sequence on the same optical axis; The contrast test target plate, the conjugate projection lens assembly, the image tube and the industrial camera are arranged in the test dark box; The light emitted by the light source passes through the neutral filter box and the adjustable aperture diaphragm, and then enters the integrating sphere, and the diffuse light is output from the integrating sphere; The light output from the integrating sphere irradiates the contrast test target plate, and the image of the target plate is projected to the cathode surface of the image tube through the conjugate projection lens and finally output through the anode output window; The industrial camera collects the image of the target plate, and the computer is connected with the industrial camera, and is used for receiving the image of the target plate collected by the industrial camera and calculating the modulation of the lines of the target plate, The image tube high-voltage power supply adjusts the MCP voltage value of the image tube by adjusting the MCP output voltage, and obtains the modulation test value of the image tube under different MCP voltages; The light output in the integrating sphere was controlled in the range 2-4 x 10 -3 lx after measurement by the luxmeter. The contrast test target plate comprises six 15lp / mm gray scale test values with a length of 2mm.

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