Intermediate infrared single-photon imaging system

Abstract

The utility model belongs to the technical field of infrared detection and imaging, and particularly relates to an intermediate infrared single-photon imaging system. In order to solve the problems of low infrared detection efficiency, low sensitivity, easy background interference, incapability of long-distance imaging and the like in the prior art, 4mu m infrared light collected by a telescope system is transformed and shaped by a shaping lens group to obtain light spots with uniform area, and the light spots enter an up-conversion module. The 1064nm laser in the up-conversion module and the collected infrared light coincide in light path and then enter the PPLN crystal 6 together to achieve the up-conversion process, and then 840nm sum frequency light is obtained. And imaging the obtained sum frequency light through a CCD (Charge Coupled Device) or a single photon array detector.

Description

Technical Field

[0001] The utility model belongs to the technical field of infrared detection and imaging, and in particular relates to a mid-infrared single-photon imaging system. Background Art

[0002] Infrared detection is a detection and imaging technology based on infrared radiation, with important applications in military, security, medical, and industrial fields. Both active and passive imaging rely on infrared detection and imaging systems. Existing infrared detectors can be divided into two categories: thermal detectors and photon detectors. Thermal detectors use the material's response to temperature changes to detect infrared radiation. Common types include thermopiles and pyroelectric detectors. These detectors capture infrared signals by measuring changes in the surface temperature of an object. Photon detectors, on the other hand, are based on the quantum effects of semiconductor materials and can generate a measurable electrical signal when receiving infrared photons. Typical examples include HgCdTe (mercury cadmium telluride) detectors.

[0003] Currently available detectors have functions such as thermal imaging, target detection, and temperature detection. The most advanced infrared direct detection technologies are mainly based on thermal detectors (low cost, but slow speed and low sensitivity), semiconductor detectors (high sensitivity, but require special cooling and complex processing), or superconducting nanowire single-photon detectors (high sensitivity, fast, but extremely low operating temperature). Compared with visible light single-photon detectors, the performance of infrared detectors needs to be improved. The telescope system is currently relatively mature. As long as the distance between the primary and secondary mirrors and the aperture size are reasonably controlled and the principle of light reflection is used, long-distance observation and collection of infrared light can be achieved. In general, existing infrared detectors have technical problems such as low sensitivity, susceptibility to background interference, low conversion efficiency, and inability to image at long distances, which limit the research and application of the mid-infrared band.

[0004] Therefore, it is necessary to design a mid-infrared single-photon imaging system to solve the above technical problems. Utility Model Content

[0005] To address these issues, this utility model provides a mid-infrared single-photon imaging system. By combining nonlinear crystal upconversion technology with a telescope system, this system addresses current infrared detection issues such as low efficiency, low sensitivity, susceptibility to background interference, and inability to image at long distances. The system primarily relates to the fields of infrared light detection, upconversion technology, and imaging.

[0006] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0007] A mid-infrared single-photon imaging system includes an infrared light module, an upconversion module, and a sum-frequency light receiving and imaging module. The infrared light module is used to collect and transform infrared light from a distance. The infrared light output by the infrared light module enters the upconversion module through a third convex lens and a dichroic mirror. The upconversion module is used to upconvert the infrared light into sum-frequency light. The sum-frequency light output by the upconversion module enters the sum-frequency light receiving and imaging module through a fourth convex lens. The sum-frequency light receiving and imaging module is used to collect, process, and form an image of the sum-frequency light.

[0008] The infrared light module includes a telescope system and a shaping lens group arranged in sequence;

[0009] The up-conversion module includes a PPLN crystal, a neodymium-doped yttrium vanadate crystal, a laser, a first lens, a second lens, a third lens, and a fourth lens. The first lens, the second lens, the third lens, and the fourth lens form a circular resonant cavity to achieve the purpose of increasing power. The laser outputs visible light, which is reflected by the first lens, the neodymium-doped yttrium vanadate crystal, the second lens, the third lens, the PPLN crystal, and the fourth lens to the first lens for further circulation. The infrared light entering the up-conversion module through the dichroic mirror passes through the fourth lens, the PPLN crystal, and the third lens in sequence to output sum frequency light.

[0010] The sum frequency light receiving imaging module includes a detector and a computer. The sum frequency light output by the third lens is input into the detector via the fourth convex lens. The detector is connected to the computer and an image is displayed on the computer.

[0011] Furthermore, the telescope system is a reflective system, including a primary mirror and a secondary mirror. Infrared light from a distance is collected over a large area by the primary mirror and then reflected onto the secondary mirror. The light on the secondary mirror is reflected to the light outlet of the telescope system.

[0012] Furthermore, the diameter of the primary mirror is 230 mm, the thickness is 40 mm, and the reflectivity is greater than 96%. The diameter of the secondary mirror is 72.5 mm, the thickness is 12.5 mm, and the reflectivity is greater than 96%.

[0013] Furthermore, the telescope system is coated with a silver film.

[0014] Furthermore, the shaping lens group includes a first convex lens and a second convex lens arranged in sequence.

[0015] Furthermore, the central wavelength of the laser is 808 nm, the output power is 4.5 W, and the power is adjustable.

[0016] Furthermore, the first lens and the second lens have high transmittance at 808nm and high reflectance at 1064nm, the third lens has high transmittance at 840nm and high reflectance at 1064nm, and the fourth lens has high transmittance at infrared light and high reflectance at 1064nm.

[0017] Furthermore, the PPLN crystal has five polarization periods, a refractive index of 2.33, a surface coated with a high-transmittance film of 3800-4500 nm, and a size of 25×1×1 mm.

[0018] Furthermore, a polarizing plate is provided on the optical path between the fourth lens and the first lens.

[0019] Furthermore, the detector is a CCD camera or a single photon detector.

[0020] Compared with the prior art, the utility model has the following advantages:

[0021] (1) The utility model consists of three parts: an infrared light module, an up-conversion module, and a sum-frequency light collection and imaging module. Each part is correctly connected and debugged. Infrared light from a distance is collected into the infrared light module, and it is ensured that the optical path is free of vibration during field experiments. Only fine-tuning of the optical path in the up-conversion module and simple operation of the software used in the sum-frequency light collection and imaging module are required to obtain a clearer sum-frequency light signal (image). The method of converting mid-infrared light into visible light by up-conversion is combined with a telescope system to improve the efficiency and sensitivity of mid-infrared light detection, avoid the disadvantage of being easily affected by background, and realize mid-infrared long-distance imaging.

[0022] (2) The coating of the telescope system of the utility model can improve the reflectivity of infrared light and better collect infrared light.

[0023] (3) The cavity mirror of the utility model can oscillate the obtained 1064nm light back and forth to increase the intensity of the light. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic structural diagram of a mid-infrared single-photon imaging system of the present invention;

[0025] Figure 2 is a schematic diagram of the telescope system of the present utility model;

[0026] Figure 3 Schematic diagram of the up-conversion process of the present invention. DETAILED DESCRIPTION

[0027] In order to further illustrate the technical solution of the present invention, the present invention will be further described below through embodiments.

[0028] like Figure 1As shown, a mid-infrared single-photon imaging system of this embodiment includes an infrared light module, an up-conversion module, and a sum-frequency light receiving and imaging module. The infrared light module is used to collect and transform infrared light from a distance. The infrared light output by the infrared light module enters the up-conversion module through a third convex lens 4 and a dichroic mirror 5. The up-conversion module is used to up-convert the infrared light into sum-frequency light. The sum-frequency light output by the up-conversion module enters the sum-frequency light receiving and imaging module through a fourth convex lens 7. The sum-frequency light receiving and imaging module is used to collect, process, and form an image of the sum-frequency light.

[0029] The infrared light module includes a telescope system 1 and a shaping lens group arranged in sequence;

[0030] like Figure 2 As shown, the telescope system 1 is a reflective system, including a primary mirror 13 and a secondary mirror 14. The infrared light from a distance is collected by the primary mirror 13 over a large area and then reflected onto the secondary mirror 14. The light on the secondary mirror 14 is reflected to the light outlet of the telescope system 1. The diameter of the primary mirror (13) is 230 mm, the thickness is 40 mm, and the reflectivity is greater than 96%. The diameter of the secondary mirror (14) is 72.5 mm, the thickness is 12.5 mm, and the reflectivity is greater than 96%. The telescope system (1) is coated with a layer of silver film. By adjusting the distance between the primary and secondary mirrors, the infrared light from a distance is collected by the reflection of light, and then the beam size of the infrared light is adjusted by the shaping lens group to adapt to the subsequent up-conversion module.

[0031] The shaping lens assembly of this embodiment includes a first convex lens 2 and a second convex lens 3, which are arranged in sequence. The first convex lens 2 is a calcium fluoride plano-convex lens with a focal length of 200 mm, and the second convex lens 3 is a calcium fluoride plano-concave lens with a focal length of 15 mm. The third convex lens 4 is a calcium fluoride plano-convex lens with a focal length of 20 cm, and the fourth convex lens 7 is a plano-convex lens with a focal length of 10 cm.

[0032] Up-conversion module (such as Figure 3 As shown), it includes a PPLN crystal 6, a neodymium-doped yttrium vanadate crystal 9, a laser 10, a first lens 15, a second lens 16, a third lens 18 and a fourth lens 17, wherein the first lens 15, the second lens 16, the third lens 18 and the fourth lens 17 form a circular resonant cavity, and the laser 10 outputs visible light, which is reflected by the first lens 15, the neodymium-doped yttrium vanadate crystal 9, the second lens 16, the third lens 18, the PPLN crystal 6, and the fourth lens 17 to the first lens 15 for further circulation, and the infrared light entering the up-conversion module through the dichroic mirror 5 passes through the fourth lens 17, the PPLN crystal 6, and the third lens 18 in sequence to output sum frequency light;

[0033] The laser 10 in this embodiment has a central wavelength of 808 nm and an output power of 4.5 W, with adjustable power. The first and second lenses 15 and 16 have high transmittance at 808 nm and high reflectance at 1064 nm. The third lens 18 has high transmittance at 840 nm and high reflectance at 1064 nm. The fourth lens 17 has high transmittance for infrared light and high reflectance at 1064 nm. The 808 nm light and the collected infrared light must be centered in the lens, ensuring the spot brightness is at its highest.

[0034] The PPLN crystal 6 has five polarization periods, a refractive index of 2.33, and is coated with a high-transmittance film of 3800-4500nm on the surface. The size is 25×1×1mm. The neodymium-doped yttrium vanadate crystal 9 converts 808nm laser into 1064nm light. Its parameters are 0.5% Nd:YVO4, the size is 3x3x15mm, the smoothness is 20 / 10, the wavefront is 1 / 10L, and the surface is coated with an 808-1064nm anti-reflection film.

[0035] A polarizing plate 21 is provided on the optical path between the fourth lens 17 and the first lens 15 to change the polarization direction of light so that the light becomes linearly polarized light.

[0036] The sum frequency light receiving imaging module includes a detector 8 and a computer. The sum frequency light output by the third lens 18 is input into the detector 8 via the fourth convex lens 7. The detector 8 is connected to the computer. The computer is installed with image display software that matches the detector 8 to display the image.

[0037] The detector 8 in this embodiment is a CCD camera or a single photon detector, both of which are relatively sensitive to the received signal of sum frequency light. The wavelength of the received sum frequency light is 840 nm.

[0038] This embodiment provides a mid-infrared single-photon imaging system. 4μm infrared light collected by a telescope system 1 is transformed and shaped by a shaping lens assembly to produce a uniform spot that enters an upconversion module. The 1064nm laser in the upconversion module overlaps with the collected infrared light, and both enter a polycrystalline polysilicon dioxide (PPLN) crystal 6 for upconversion. This produces 840nm sum-frequency light. This sum-frequency light is imaged using a CCD or single-photon array detector.

[0039] Telescope system 1 consists of a primary mirror 13 and a secondary mirror 14. When debugging telescope system 1, an eyepiece 12 is installed for focusing, allowing distant targets to be viewed through eyepiece 12. Once debugging is complete, eyepiece 12 can be removed, and telescope system 1 can be placed into an infrared light module. Telescope system 1 collects infrared light based on the principle that infrared light from a distance first enters primary mirror 13 in telescope system 1. After being collected over a large area by primary mirror 13, it is reflected onto secondary mirror 14. The light from secondary mirror 14 then reflects back to the light exit of telescope system 1. This back-and-forth reflection between the primary and secondary mirrors increases the intensity of the infrared light.

[0040] The specific process of debugging the optical path of the upconversion module is divided into the following six points:

[0041] 1. Use a 532nm laser to make the emitted visible light in the center of each lens. It is necessary to place two reflectors outside the optical path to reflect the visible light into the cavity. By adjusting the height and left and right of the two reflectors and the four lenses, the light passes through the center of the lens and has the maximum intensity.

[0042] 2. Two apertures are placed between the first lens 15 and the second lens 16 to calibrate the optical path for repeated oscillations in the cavity, thereby increasing the intensity of the obtained 1064 nm light;

[0043] 3. Place a polarizer 20 between the first lens 15 and the fourth lens 17 to change the polarization direction of the light so that the light becomes linearly polarized;

[0044] 4. After adjusting with visible light, turn on the 808nm laser and observe whether the light spot passes through the centers of the two apertures in step 2. If it does, it indicates that the optical path can well transmit the 808nm light through the Nd:YVO crystal to obtain the 1064nm light. If it does not, continue to adjust the lens so that the 808nm light spot passes through the center of the aperture.

[0045] 5. Use two apertures to calibrate the optical path between the fourth lens 17 and the third lens 18 so that the 4μm infrared light collected by the telescope system 1 can smoothly pass through the third convex lens 4 and enter the upconversion module after lens transformation and shaping, thereby completing the upconversion process;

[0046] 6. Place the PPLN crystal 6 between the optical paths of the fourth lens 17 and the third lens 18 to perform an up-conversion process to obtain sum-frequency light. Repeat the above optical path debugging steps to maximize the intensity of the final sum-frequency light.

[0047] The sum frequency light collection imaging module uses the software corresponding to the CCD or single photon array detector. When the sum frequency light is generated, it is collected by the above detector and the image is then displayed on the software.

[0048] The measurable 840nm sum frequency light intensity is an important indicator for evaluating mid-infrared single-photon imaging systems. The sum frequency light intensity measured by the present invention is limited by the beam waist convergence of the PPLN crystal and the vibration caused by the experiment, thereby limiting the sum frequency light intensity of the entire system.

[0049] In summary, the present invention adopts the above-mentioned mid-infrared single-photon imaging system, combines the technology of up-conversion using nonlinear crystals with a telescope system, and solves the current problems of low infrared detection efficiency, low sensitivity, susceptibility to background interference, and inability to long-distance imaging.

[0050] The above shows and describes the main features and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive. The scope of the present invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be encompassed within the present invention.

[0051] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A mid-infrared single-photon imaging system, characterized in that: The invention comprises an infrared light module, an up-conversion module and a sum-frequency light receiving and imaging module. The infrared light module is used to collect and transform infrared light from a distance. The infrared light output by the infrared light module enters the up-conversion module through a third convex lens (4) and a dichroic mirror (5). The up-conversion module is used to up-convert the infrared light into sum-frequency light. The sum-frequency light output by the up-conversion module enters the sum-frequency light receiving and imaging module through a fourth convex lens (7). The sum-frequency light receiving and imaging module is used to collect, process and image the sum-frequency light. The infrared light module comprises a telescope system (1) and a shaping lens group which are arranged in sequence; The up-conversion module comprises a PPLN crystal (6), a neodymium-doped yttrium vanadate crystal (9), a laser (10), a first lens (15), a second lens (16), a third lens (18) and a fourth lens (17); the first lens (15), the second lens (16), the third lens (18) and the fourth lens (17) form a circulating resonant cavity; the laser (10) outputs visible light; the visible light passes through the first lens (15), the neodymium-doped yttrium vanadate crystal (9), the second lens (16), the third lens (18), the PPLN crystal (6) and the fourth lens (17) in sequence and is reflected to the first lens (15) to circulate again; the infrared light entering the up-conversion module through the dichroic mirror (5) passes through the fourth lens (17), the PPLN crystal (6) and the third lens (18) in sequence and outputs sum frequency light; The sum frequency light receiving imaging module comprises a detector (8) and a computer. The sum frequency light output by the third lens (18) is input into the detector (8) via the fourth convex lens (7). The detector (8) is connected to the computer and an image is displayed on the computer.

2. A mid-infrared single-photon imaging system according to claim 1, characterized in that: The telescope system (1) is a reflective system, comprising a primary mirror (13) and a secondary mirror (14). Infrared light from a distance is collected by the primary mirror (13) over a large area and then reflected onto the secondary mirror (14). The light on the secondary mirror (14) is reflected to the light outlet of the telescope system (1).

3. A mid-infrared single-photon imaging system according to claim 2, characterized in that: The diameter of the primary mirror (13) is 230 mm, the thickness is 40 mm, and the reflectivity is greater than 96%. The diameter of the secondary mirror (14) is 72.5 mm, the thickness is 12.5 mm, and the reflectivity is greater than 96%.

4. A mid-infrared single-photon imaging system according to claim 2, characterized in that: The telescope system (1) is coated with a silver film.

5. The mid-infrared single-photon imaging system according to claim 1, characterized in that: The shaping lens group comprises a first convex lens (2) and a second convex lens (3) which are arranged in sequence.

6. A mid-infrared single-photon imaging system according to claim 1, characterized in that: The central wavelength of the laser (10) is 808 nm, the output power is 4.5 W, and the power is adjustable.

7. A mid-infrared single-photon imaging system according to claim 6, characterized in that: The first lens (15) and the second lens (16) have high transmittance at 808 nm and high reflectance at 1064 nm, the third lens (18) has high transmittance at 840 nm and high reflectance at 1064 nm, and the fourth lens (17) has high transmittance for infrared light and high reflectance at 1064 nm.

8. The mid-infrared single-photon imaging system according to claim 1, characterized in that: The PPLN crystal (6) has five polarization periods, a refractive index of 2.33, a surface coated with a high-transmittance film of 3800-4500 nm, and a size of 25×1×1 mm.

9. The mid-infrared single-photon imaging system according to claim 1, characterized in that: A polarizing plate (21) is provided on the optical path between the fourth lens (17) and the first lens (15).

10. The mid-infrared single-photon imaging system according to claim 1, characterized in that: The detector (8) is a CCD camera or a single photon detector.

Images