A non-coherent high-speed mid-infrared imaging method based on frequency up-conversion

Abstract

This invention discloses an incoherent high-speed mid-infrared imaging method based on frequency upconversion. It utilizes a cavity blackbody radiation source or thermal radiation from the target itself to generate 3-5 μm broadband incoherent mid-infrared image information. Unlike coherent optical imaging, which requires phase stability, this method employs a quasi-phase-matching design using a lithium niobate nonlinear crystal to upconvert the incoherent mid-infrared light to the visible / near-infrared band. An image intensifier enhances the weak upconverted light signal, improving the receiving capability of subsequent detectors. A high-frame-rate CMOS camera receives the upconverted image and acquires high-speed time-series images. This invention requires no active illumination or cryogenic cooling, enabling enhanced detection and high-speed imaging of weak incoherent mid-infrared signals at room temperature. It is suitable for monitoring transient thermal events such as arc discharge, combustion diagnostics, and high-temperature plasma evolution.

Description

Technical Field

[0001] This invention belongs to the field of infrared photoelectric imaging technology, specifically relating to an incoherent high-speed mid-infrared imaging method based on frequency upconversion, which is particularly suitable for high-speed monitoring and early warning of transient thermal events such as arc discharge and combustion diagnosis. Background Technology

[0002] Mid-infrared (3-5μm) thermal imaging is of great value in industrial monitoring and fault early warning, especially suitable for capturing the thermal evolution of microsecond-level transient events such as electric arcs and combustion. However, traditional mid-infrared detectors based on semiconductor detectors such as InSb and HgCdTe require cryogenic cooling to suppress dark current, which not only makes the system complex and expensive, but also limits its readout bandwidth, making it difficult to achieve high frame rate imaging while maintaining high sensitivity. Therefore, it cannot meet the complete capture requirements of microsecond-level transient processes.

[0003] Infrared imaging technology based on nonlinear frequency upconversion offers a new approach to solving the aforementioned problems: by performing a sum-frequency interaction between the mid-infrared signal and the pump light in a nonlinear crystal, visible light is generated, enabling high-speed, high-sensitivity imaging at room temperature using mature silicon-based detectors. However, existing research largely relies on active illumination or synchronous pump modulation, making it difficult to adapt to incoherent thermal radiation imaging in passive scenarios, thus limiting its deployment capabilities in remote, open environments. Furthermore, in practical applications, the system is often affected by noise interference from pump fluctuations, temperature drift, and background radiation, affecting imaging stability and leading to image quality degradation during long-term observation. In addition, optimizing gating parameters to capture weak precursor signals under high-speed acquisition and quantitatively assessing the impact of system drift on imaging remain challenging areas where a systematic solution is lacking in current technology. Summary of the Invention

[0004] This invention proposes an incoherent high-speed mid-infrared imaging method based on frequency upconversion. It achieves efficient upconversion of 3-5μm broadband incoherent mid-infrared scenes through a chirped periodically polarized nonlinear crystal, and simultaneously increases the imaging frame rate to 100kHz by means of fast dynamic gating, thereby realizing high frame rate and high stability imaging in passive incoherent scenes.

[0005] The technical solution for achieving this invention is: a high-speed mid-infrared imaging method based on frequency up-conversion, comprising the following steps:

[0006] S1. Construct a passive incoherent mid-infrared upconversion high-speed imaging system.

[0007] The passive incoherent mid-infrared upconversion high-speed imaging system includes a cavity blackbody radiation source, a first filter, a first lens, a first dichroic mirror, a semiconductor laser, a half-wave plate, a mirror, a nonlinear crystal, a second dichroic mirror, a second lens, a filter assembly, an image intensifier, a detector, and a beam attenuator.

[0008] A cavity blackbody radiation source, a first filter, a first lens, a first dichroic mirror, a nonlinear crystal second dichroic mirror, a second lens, a filter assembly, an image intensifier, and a detector are arranged sequentially along the first optical axis; a semiconductor laser, a half-wave plate, and a reflector are arranged along the second optical axis; a beam attenuator is fixed next to the second dichroic mirror.

[0009] The temperature of the cavity blackbody radiation source is adjusted to generate passive broadband incoherent mid-infrared radiation. After the stray light is filtered out by the first filter, it becomes signal light. The first lens is adjusted so that the signal light is focused onto the first dichroic mirror.

[0010] The power of the semiconductor laser is adjusted to emit pump light. The polarization state of the pump light is adjusted by a half-wave plate to obtain polarized pump light. The pump light is then sent to a mirror, which is a silver-plated mirror, to reflect the polarized pump light to the first dichroic mirror.

[0011] The first dichroic mirror is used to transmit signal light and reflect polarized pump light, guiding the two to be combined into a nonlinear crystal. The signal light and polarized pump light are simultaneously focused into the nonlinear crystal to generate a sum frequency, and then transferred to S2.

[0012] S2. Control the nonlinear crystal to meet the quasi-phase matching condition, so that the passive signal light and the polarization pump light can interact via a sum-frequency reaction, converting the mid-infrared image information carried by the signal light into an image signal. The image signal includes a visible light signal or an up-converted image signal in the near-infrared band. The image signal and the polarization pump light signal are simultaneously sent to the second dichroic mirror and then transferred to S3.

[0013] S3. The remaining pump light is filtered out by the second dichroic mirror. The separated polarized pump light is introduced into the beam attenuator for safe absorption. The image signal is collected by the second lens, filtered by the filter assembly to suppress the remaining pump leakage light and the second harmonic component. After the light signal is enhanced by the image intensifier, it enters the detector and proceeds to S4.

[0014] S4. The detector acquires time-series images and performs regional statistics and stability calibration on the time-series images to suppress the influence of pump power fluctuations, temperature drift and system noise on the imaging results, thereby obtaining a calibrated high-speed mid-infrared image.

[0015] The beneficial effects of this invention are:

[0016] (1) By upconverting the broadband mid-infrared radiation (3-5μm) to the visible / near-infrared band, combined with the high frame rate CMOS to achieve a physical frame rate of 100kHz in the fast dynamic mode, it can clearly capture the complete evolution process of transient thermal events such as arc discharge and combustion process, filling the gap between frame rate and sensitivity in traditional cryogenic cooling cameras.

[0017] (2) Introducing a chirped periodically polarized crystal to broaden the phase matching bandwidth. The chirped periodic structure effectively increases the quasi-phase-matched receiving bandwidth, enabling broadband incoherent mid-infrared signals to be converted efficiently while maintaining high conversion efficiency and image fidelity.

[0018] (3) A cavity blackbody radiation source is used as a passive incoherent illumination source, covering the 3-5μm band. No active illumination or synchronous modulation is required, avoiding the complex optical path and timing control of active solutions. The system has a simple structure, strong concealment, and is easy to deploy in engineering. It is particularly suitable for incoherent high-speed imaging monitoring of natural thermal radiation scenes in remote and open environments. Attached Figure Description

[0019] Figure 1 This is a flowchart of an incoherent high-speed mid-infrared imaging method based on frequency upconversion according to the present invention.

[0020] Figure 2 The curves show the relationship between the polarization period and the wavelength of the matching signal for a periodically polarized lithium niobate crystal at different operating temperatures.

[0021] Figure 3 This is an embodiment of an incoherent high-speed mid-infrared imaging technology based on frequency upconversion according to the present invention.

[0022] Figure 4 The relationship between the sum-frequency conversion efficiency and the waist radius of the signal beam is shown for different crystal lengths.

[0023] Figure 5 This is the spectral intensity distribution curve of passive incoherent mid-infrared radiation.

[0024] Figure 6 These are images taken at 10kHz by a high-frame-rate CMOS camera. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. Rather, embodiments of this application include all variations, modifications, and equivalents falling within the spirit and scope of the appended claims.

[0027] The technical solutions of the various embodiments of the present invention can be combined with each other, but only if they can be implemented by those skilled in the art. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0028] The following section will further introduce the specific implementation method, as well as the technical difficulties and inventive points of this invention, using this design example as an example:

[0029] Combination Figure 1 and Figure 3 A noncoherent high-speed mid-infrared imaging method based on frequency upconversion, comprising the following steps:

[0030] S1. Construct a passive incoherent mid-infrared upconversion high-speed imaging system;

[0031] The passive incoherent mid-infrared upconversion high-speed imaging system includes a cavity blackbody radiation source 1, a first filter 2, a first lens 3, a first dichroic mirror 4, a semiconductor laser 5, a half-wave plate 6, a reflector 7, a nonlinear crystal 8, a second dichroic mirror 9, a second lens 10, a filter assembly 11, an image intensifier 12, a detector 13, and a beam attenuator 14.

[0032] Along the first optical axis, a cavity blackbody radiation source 1, a first filter 2, a first lens 3, a first dichroic mirror 4, a nonlinear crystal 8, a second dichroic mirror 9, a second lens 10, a filter assembly 11, an image intensifier 12, and a detector 13 are arranged sequentially; along the second optical axis, a semiconductor laser 5, a half-wave plate 6, and a reflector 7 are arranged in sequence; a beam attenuator 14 is fixed next to the second dichroic mirror 9.

[0033] The temperature of the cavity blackbody radiation source 1 is adjusted to generate passive broadband incoherent mid-infrared radiation light. After the stray light is filtered by the first filter 2, it becomes signal light. The first lens 3 is adjusted so that the signal light is focused by the first lens 3 onto the first dichroic mirror 4.

[0034] The power of the semiconductor laser 5 is adjusted to emit pump light. The polarization state of the pump light is adjusted by the half-wave plate 6 to obtain polarized pump light. The pump light is sent into the reflector 7, which is a silver-plated reflector, and the polarized pump light is reflected to the first dichroic mirror 4.

[0035] The first dichroic mirror 4 is used to transmit signal light and reflect polarized pump light, guiding the two to be combined into a nonlinear crystal 8. The signal light and polarized pump light are simultaneously focused into the nonlinear crystal 8 to generate a sum frequency, and then proceed to step S2.

[0036] Furthermore, the passive broadband incoherent mid-infrared radiation is the incoherent mid-infrared radiation generated by the target's own thermal radiation.

[0037] Furthermore, the nonlinear crystal 8 is a chirped periodically polarized lithium niobate crystal with a crystal size of 4mm×2mm×30mm and a polarization period range of 21.6-23.4μm. Through the chirped polarization period design, the nonlinear crystal 8 forms a continuously changing quasi-phase-matched structure inside the crystal. Each periodic structure serves as a sub-channel with a thickness of 1mm, covering a response band. Under multi-channel integration, the full-band tuning range covers 3-5μm, achieving mid-infrared broadband detection. The crystal surface is polished and coated with an anti-reflection film, exhibiting high transmittance in the 780-880nm, 1064nm, and 2800-5500nm bands to reduce the reflection loss of signal light, pump light, and upconversion light at the crystal end face, thereby improving frequency upconversion efficiency and imaging signal intensity.

[0038] Furthermore, detector 13 is a high frame rate CMOS camera, and image intensifier (12) enhances the light signal, making it easier for detector 13 to acquire.

[0039] S2. Control the nonlinear crystal 8 to satisfy the quasi-phase matching condition, so that the passive signal light and the polarization pump light can interact and convert the mid-infrared image information carried by the signal light into an image signal. The image signal includes a visible light signal or an up-converted image signal in the near-infrared band. The image signal and the polarization pump light signal are simultaneously sent into the second dichroic mirror.

[0040] The nonlinear frequency upconversion physical process described in this invention is essentially a frequency of Low-energy mid-infrared signal photons with a frequency of The pump photon annihilation produces a frequency of Upconverted photons. Among them... Equal to the incident signal photon frequency With pump photon frequency The sum of This process is called the sum-frequency generation process, which upconverts mid-infrared signals to the visible light band.

[0041] Its physical mechanism follows the strict law of conservation of energy:

[0042] (1),

[0043] in, It is Planck's constant. , , These correspond to the angular frequencies of the mid-infrared input signal, pump light, and upconversion light, respectively. To achieve efficient frequency conversion, the momentum conservation condition must also be satisfied. This is reflected in the phase mismatch during the sum-frequency process. Then it can be expressed by the following formula:

[0044] (2),

[0045] , , It is the corresponding wave vector. When momentum conservation is not satisfied... Under certain conditions, the efficiency of the total frequency generation process will drop sharply.

[0046] Existing technologies often employ traditional angle or temperature phase matching, which relies on adjusting the material's refractive index. However, it is easily limited by narrow bandwidth and material dispersion. To overcome this difficulty, a suitable polarization period is selected for the periodically polarized crystal. To compensate for phase mismatch This significantly broadens the phase-matching bandwidth and reduces the sensitivity to the inherent dispersion of the material.

[0047] Quasi-phase matching techniques are generally divided into collinear and non-collinear schemes. This invention employs a collinear transmission design, which simplifies the optical path architecture while achieving a larger nonlinear coefficient and a longer interaction length, resulting in higher frequency conversion efficiency and enabling a wide tunable response for mid-infrared spectral signals at different wavelengths. In collinear quasi-phase matching, the three wave vectors propagating collinearly along the periodically polarized crystal... , , Reciprocal lattice vectors of nonlinear crystals The expression for the phase mismatch between the mid-infrared signal light, pump light, and upconversion light, which are located on the same optical axis and propagate collinearly along a periodically polarized crystal, is as follows:

[0048] (3),

[0049] in , The polarization period of the periodically polarized lithium niobate crystal is given by equation (3). According to equation (3), under perfect phase matching, the signal wavelength, pump wavelength and crystal polarization period are in one-to-one correspondence.

[0050] Furthermore, as can be seen from the dispersion equation, the upconversion process is also closely related to the crystal's operating temperature.

[0051] (4),

[0052] The function f related to the crystal's operating temperature T is as follows:

[0053] ,

[0054] See the table for specific parameters:

[0055]

[0056] in, The square of the optical refractive index, which is related to wavelength and temperature, is categorized according to polarization state into those representing unusual optical refractive indices. , representing the ordinary refractive index , This indicates the wavelength of light propagating in a crystal. The unit is ℃. ~ Represents the coefficient. ~ Represents the coefficient.

[0057] Figure 2 This paper illustrates the relationship between the polarization period of a periodically polarized lithium niobate crystal and the wavelength of the matched mid-infrared signal at different crystal operating temperatures. As shown in the figure, under all temperature conditions, the polarization period exhibits a non-monotonic trend of first gradually increasing, reaching a certain critical value, and then decreasing, indicating a peak characteristic in the curve. The peak positions of the curves at different temperatures do not show significant shifts, but the required polarization period value for the same wavelength changes with increasing temperature. This figure reveals the quantitative influence of temperature on phase-matching conditions, providing a design basis for using chirped periodically polarized crystals in this invention to broaden the phase-matching bandwidth and adapt to broadband incoherent mid-infrared imaging.

[0058] Figure 4The figure illustrates the relationship between the sum-frequency conversion efficiency and the nonlinear crystal length under optimized beam waist radius conditions. As shown in the figure, the conversion efficiency gradually increases with increasing crystal length; however, once the crystal length reaches a certain threshold, the conversion efficiency reaches its maximum value. Further increases in crystal length thereafter result in a relatively constant conversion efficiency, indicating the system has entered the saturation region. This demonstrates that simply increasing the crystal length does not continuously improve conversion efficiency; instead, it may introduce greater phase mismatch or increase system size. This figure provides a quantitative basis for the optimized selection of the nonlinear crystal length in this invention, ensuring sufficient up-conversion light intensity is obtained with a compact structure under 100 kHz high-speed imaging conditions, meeting the detection requirements of high-frame-rate CMOS cameras.

[0059] Figure 5 The spectral intensity distribution curves of the infrared radiation in the passive incoherent medium are shown, with the horizontal axis representing wavelength. (i.e., mid-infrared signal wavelength), with the vertical axis representing signal intensity. This curve is calculated using a spectrometer to measure the spectrum of the upconverted light (corresponding to the sum-frequency wavelength). ), and combined with the known pump light wavelength By reverse deduction, that is As shown in the figure, the radiation intensity exhibits a specific broadband incoherent distribution characteristic within the 3-5 μm wavelength range. This spectral curve directly characterizes the wavelength coverage and energy distribution of the mid-infrared signal processed in this invention, providing key input parameters for phase matching design in the nonlinear frequency up-conversion process. Specifically, based on this spectral distribution, the polarization period tuning range of the chirped periodically polarized lithium niobate crystal can be determined, aligning the quasi-phase-matching bandwidth of the crystal with the main peak region of the signal spectrum. This maintains high sum-frequency conversion efficiency across a wide spectral range and avoids signal loss due to spectral component mismatch.

[0060] Switch to S3.

[0061] S3. The remaining pump light is filtered out by the second dichroic mirror 9. The separated polarized pump light is introduced into the beam attenuator 14 for safe absorption. The image signal is collected by the second lens 10, filtered by the filter assembly 11 to suppress the remaining pump leakage light and the second harmonic component, and then enters the detector 13 after the light signal is enhanced by the image intensifier 12, and then proceeds to S4.

[0062] S4. Detector 13 acquires time-series images and performs regional statistics and stability calibration on the time-series images to suppress the influence of pump power fluctuations, temperature drift and system noise on the imaging results, thereby obtaining calibrated high-speed mid-infrared images.

[0063] Example 1

[0064] See Figure 3The passive incoherent mid-infrared upconversion high-speed imaging system includes: a cavity blackbody radiation source 1, a first filter 2, a first lens 3, a first dichroic mirror 4, a semiconductor laser 5, a half-wave plate 6, a reflector 7, a nonlinear crystal 8, a second dichroic mirror 9, a second lens 10, a filter assembly 11, an image intensifier 12, a detector 13, and a beam attenuator 14.

[0065] The temperature of the cavity blackbody radiation source 1 is adjusted, set within the range of 400℃-1000℃, to emit signal light covering the mid-infrared band of 3-5μm. For example, setting the temperature to 800℃ will yield thermal radiation of corresponding intensity. Various stray lights in the non-probe light signal band are filtered out by the first filter 2, and the waist of the signal beam is compressed to below 1 mm by the first lens 3. The compressed signal light is then focused by the first lens 3 onto the first dichroic mirror 4.

[0066] Based on the temperature of the cavity blackbody radiation source 1, the output power of the semiconductor laser 5 is adjusted accordingly (adjustment range: 0-20W) to match the signal light intensity and ensure that the sum-frequency conversion is in the linear operating region. For example, when the blackbody temperature is 800℃, the pump power is set to 5W. The semiconductor laser 5 emits pump light with a center wavelength of 1064nm. After passing through a half-wave plate 6, the polarization state of the pump light is adjusted to be perpendicular to the cross-section of the nonlinear crystal 8 to enhance the subsequent sum-frequency conversion efficiency. The pump light with the adjusted polarization state is sent to a reflector 7, which is a 1064nm high-reflectivity silver-plated plane mirror, to reflect the pump light to the first dichroic mirror 4. The first dichroic mirror 4 is used to transmit the signal light and reflect the pump light, guiding them to be combined into the nonlinear crystal 8. The 3-5 μm signal light and the 1064 nm pump light are simultaneously focused into the nonlinear crystal 8 for sum-frequency generation.

[0067] The second lens 10 is adjusted to collimate the output of the sum-frequency light generated in the nonlinear crystal 8. The unconsumed 1064nm pump light is separated by the second dichroic mirror 9, and the remaining 1064nm pump light is guided into the beam attenuator 14 for safe absorption. The second lens 10 is adjusted to collect the upconverted light. The residual leaked pump light and second harmonic components are filtered out by the filter assembly 11, which consists of two long-pass filters with a center wavelength of 850 nm and an FWHM of 50 nm and a short-pass filter of 900 nm. After the light signal is enhanced by the image intensifier 12, it is detected and received by the detector 13. The detector is a high-sensitivity CMOS camera that can capture high frame rate images.

[0068] The detector 13 is connected to an external processor to adjust the camera frame rate (range 100Hz-100kHz) to obtain the corresponding images. See details... Figure 6 .

[0069] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A noncoherent high-speed mid-infrared imaging method based on frequency upconversion, characterized in that, The steps are as follows: S1. Construct a passive incoherent mid-infrared upconversion high-speed imaging system; The passive incoherent mid-infrared upconversion high-speed imaging system includes a cavity blackbody radiation source (1), a first filter (2), a first lens (3), a first dichroic mirror (4), a semiconductor laser (5), a half-wave plate (6), a reflector (7), a nonlinear crystal (8), a second dichroic mirror (9), a second lens (10), a filter assembly (11), an image intensifier (12), a detector (13), and a beam attenuator (14); Along the first optical axis, a cavity blackbody radiation source (1), a first filter (2), a first lens (3), a first dichroic mirror (4), a nonlinear crystal (8), a second dichroic mirror (9), a second lens (10), a filter assembly (11), an image intensifier (12), and a detector (13) are arranged in sequence; along the second optical axis, a semiconductor laser (5), a half-wave plate (6), and a reflector (7) are arranged in sequence; a beam attenuator (14) is fixed next to the second dichroic mirror (9); Adjust the temperature of the cavity blackbody radiation source (1) to generate passive broadband incoherent mid-infrared radiation light. After the stray light is filtered by the first filter (2), it becomes signal light. Adjust the first lens (3) and the signal light is focused by the first lens (3) onto the first dichroic mirror (4). The power of the semiconductor laser (5) is adjusted to emit pump light. The polarization state of the pump light is adjusted by the half-wave plate (6) to obtain polarized pump light. The polarized pump light is sent into the reflector (7), which is a silver-plated reflector, and the polarized pump light is reflected to the first dichroic mirror (4). The first dichroic mirror (4) is used to transmit signal light and reflect polarized pump light, guiding the two to be combined into a nonlinear crystal (8). The signal light and polarized pump light are simultaneously focused into the nonlinear crystal (8) to generate a sum frequency, and then enter S2. S2. Control the nonlinear crystal (8) to meet the quasi-phase matching condition, so that the passive signal light and the polarization pump light can interact and convert the mid-infrared image information carried by the signal light into an image signal. The image signal includes visible light signal or upconverted image signal in the near-infrared band. The above image signal and the polarization pump light are sent into the second dichroic mirror (9) at the same time and then into S3. S3. The remaining pump light is filtered out by the second dichroic mirror (9). The separated polarized pump light is introduced into the beam attenuator (14) to achieve safe absorption. The image signal is collected by the second lens (10), filtered by the filter assembly (11) to suppress the remaining pump leakage light and the second harmonic component. After the light signal is enhanced by the image intensifier (12), it enters the detector (13) and enters S4. S4. The detector (13) acquires time-series images and performs regional statistics and stability calibration on the time-series images to suppress the influence of pump power fluctuations, temperature drift and system noise on the imaging results, and obtains calibrated high-speed mid-infrared images.

2. The incoherent high-speed mid-infrared imaging method based on frequency upconversion according to claim 1, characterized in that: In S1, the passive broadband incoherent mid-infrared radiation is the incoherent mid-infrared radiation generated by the target's own thermal radiation.

3. The incoherent high-speed mid-infrared imaging method based on frequency upconversion according to claim 1, characterized in that: In S1, the pump light emitted by the semiconductor laser (5) is a continuous pump light of 1064nm.

4. The incoherent high-speed mid-infrared imaging method based on frequency upconversion according to claim 1, characterized in that: The nonlinear crystal (8) is a chirped periodically polarized lithium niobate crystal with a crystal size of 4mm×2mm×30mm and a polarization period range of 21.6-23.4μm. Through the chirped polarization period design, the nonlinear crystal (8) forms a continuously changing quasi-phase matching structure inside the crystal. Each periodic structure serves as a sub-channel with a thickness of 1mm, covering a response band. Under multi-channel integration, the full-band tuning range covers 3-5μm, realizing mid-infrared broadband detection. The crystal surface is polished and coated with an anti-reflection film, which has high transmittance in the 780-880nm, 1064nm and 2800-5500nm bands to reduce the reflection loss of signal light, pump light and upconversion light at the crystal end face, and improve the frequency upconversion efficiency and imaging signal intensity.

5. The incoherent high-speed mid-infrared imaging method based on frequency upconversion according to claim 1, characterized in that: In S1, the detector (13) is a high frame rate CMOS camera, and the image intensifier (12) enhances the light signal, making it easier for the detector (13) to acquire it.

6. The incoherent high-speed mid-infrared imaging method based on frequency upconversion according to claim 1, characterized in that, In S2, the phase matching condition is satisfied, as follows: During collinear quasi-phase matching, the three-wave vectors propagating collinearly along the nonlinear crystal (8) , , Reciprocal lattice vectors of nonlinear crystal (8) Located on the same optical axis, phase mismatch The expression is as follows: ， in, , The polarization period of the nonlinear crystal (8) is denoted as . Under perfect phase matching, the signal wavelength, pump wavelength, and crystal polarization period of the nonlinear crystal (8) have a one-to-one correspondence; at the same time, it can be seen from the dispersion equation that the upconversion process is also closely related to the crystal operating temperature: ， The function f, which is related to the crystal's operating temperature T, is as follows: ， in, This represents the square of the optical refractive index as a function of wavelength and temperature, and is categorized into unusual optical refractive indices based on polarization state. And the ordinary refractive index ; This represents the wavelength of light propagating in the nonlinear crystal (8). The unit is ℃. ~ Represents the coefficient. ~ Represents the coefficient.

7. The incoherent high-speed mid-infrared imaging method based on frequency upconversion according to claim 6, characterized in that, Unusual optical refractive index Ordinary refractive index ,coefficient ~ as well as ~ The specific values ​​are shown in the table below: 。

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