Optical difference frequency terahertz wave generation device and method based on organic nonlinear crystal

Abstract

The invention discloses an optical difference frequency terahertz wave generation device and method based on an organic nonlinear crystal, and belongs to the technical field of terahertz waves. The invention provides an optical difference frequency terahertz wave generation method based on organic nonlinear crystals, which comprises the following steps of: combining two paths of continuous laser beams with different wavelengths, dividing the combined laser beams into two paths, respectively emitting the two paths into two nonlinear crystals to generate terahertz waves, and then shaping and combining the terahertz waves. According to the method, the pumping laser can be fully utilized to generate terahertz waves, and meanwhile, the risk of damage caused by heat accumulation of the organic crystal is reduced; and the air drying chamber is utilized to prevent organic crystals from being combined with water molecules to form hydrates, so that the absorption of water vapor to terahertz waves is reduced, the complexity of the system is reduced, and the stability of the system is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of terahertz waves, and in particular relates to an optical difference frequency terahertz wave generating device and method based on organic nonlinear crystals. Background Art

[0002] With the rapid development of laser technology, the electromagnetic radiation properties of the terahertz band have been widely studied and have begun to be applied in the fields of communications, radar, biomedicine, chemical analysis, non-destructive testing, safety inspection, etc., and are considered to have great development potential and application prospects in the future. The power of the current continuous terahertz source is roughly in the nanowatt level, while the terahertz band background noise in the environment is usually higher than the terahertz wave power, which is not conducive to detection and application, affecting the development of terahertz technology.

[0003] At present, the method of using organic crystals to generate terahertz waves through optical difference frequency is not able to increase the power of the laser due to the sensitive thermal effect of organic crystals and the low damage threshold. Under the continuous pumping irradiation of strong lasers, it is easy to produce heat accumulation damage, which affects the high power output of terahertz waves at room temperature. In addition, the current optical difference frequency system combines two laser beams into one beam through a beam combiner. Since the beam combiner itself has a splitting effect, it also loses part of the laser energy, resulting in a decrease in laser utilization and a decrease in the power of the generated terahertz waves. Furthermore, some organic crystals, such as DAST crystals, are easy to combine with water molecules in the air to form hydrates. The hydrates of DAST crystals will not only increase their absorption coefficients, but also make their spatial structure centrally symmetrical, which will significantly affect their second-order nonlinear performance and reduce the efficiency of terahertz wave generation. Due to the characteristic that DAST crystals are easy to combine with water molecules, each time the optical difference frequency system test is completed, the DAST crystal must be placed in a drying oven, and the crystal must be installed back into the system when the experiment is carried out. The system needs to be recalibrated, which affects the stability of the system.

[0004] The main methods of generating terahertz radiation using optical methods include terahertz gas lasers, optical rectification related to ultrashort laser pulses that can generate broadband sub-picosecond terahertz radiation, photoconductivity, plasma four-wave mixing, nonlinear optical difference frequency methods, and terahertz parametric oscillation related to lattice vibration. Among the many methods of achieving terahertz radiation, nonlinear optical collinear difference frequency can achieve high-power, wide-band, and continuously tunable terahertz radiation, but it also has the disadvantage of low conversion efficiency. The key to the difference frequency method of generating terahertz waves is to obtain pump light and signal light with high power and close wavelengths, as well as nonlinear difference frequency crystals with large second-order nonlinear coefficients and small absorption coefficients in the terahertz wave range.

[0005] There are two main types of nonlinear crystals used in difference frequency THz experiments: inorganic crystal materials and organic crystal materials. Inorganic crystals often have problems such as photorefractive effect and low damage threshold. Their advantage is that they have a high damage threshold, but their THz wave photon absorption in the high frequency band is very serious. The main advantage of organic crystals is that they have a large second-order nonlinear coefficient and broadband transmission characteristics for THz waves. They are the main materials for realizing broadband tunable THz waves. Conventional organic crystals used are: DAST, DSTMS, OH1 and HMQ.

[0006] At present, the difference frequency module based on organic crystal is mainly composed of beam combiner, focusing lens, nonlinear crystal, TPX lens, etc. Figure 1 As shown. Two near-infrared beams with similar wavelengths are combined into one beam through a beam combiner, and then the beam diameter reaches hundreds of microns or even smaller after being focused and shrunk by a focusing lens. The two near-infrared beams focus on the crystal, and generate terahertz waves in the crystal based on the nonlinear difference frequency effect. The terahertz waves are beam-shaped under the action of the TPX lens and enter the detector. The terahertz wave resolution output by the system is related to the tuning step of the pump laser, and the terahertz power is related to the pump laser power, the second-order nonlinear coefficient of the crystal, etc.

[0007] The existing technical solutions are difficult to enhance the power output of terahertz waves by increasing the power of the laser due to the low damage threshold of organic crystals, which are prone to thermal accumulation damage under continuous strong laser pumping. Second, when the beam combiner in the current optical difference frequency system combines two laser beams, it also produces splitting, which loses part of the laser energy and reduces the laser utilization rate. Third, DAST crystals are easily combined with water molecules in the air, causing the crystals to form hydrates, which not only increases its absorption coefficient, but also significantly affects its second-order nonlinear performance, reducing the efficiency of terahertz wave generation. Finally, each time an experiment is conducted, the DAST crystal must be installed back into the system, and the system needs to be recalibrated, which affects the stability of the system. Summary of the invention

[0008] In view of the above technical problems existing in the prior art, the present invention proposes an optical difference frequency terahertz wave generating device and method based on organic nonlinear crystal, which has a reasonable design, overcomes the shortcomings of the prior art and has good effects.

[0009] In order to achieve the above object, the present invention adopts the following technical solution:

[0010] An optical difference frequency terahertz wave generating device based on organic nonlinear crystal, comprising a fixed wavelength laser, a tunable laser, an optical fiber amplifier, a chopper, a beam reduction system, a reflector, a beam combining mirror, a focusing lens, an organic nonlinear crystal, a TPX lens, an off-axis super lens and a detector;

[0011] An optical fiber amplifier, comprising a first optical fiber amplifier and a second optical fiber amplifier;

[0012] A shrinking system, comprising a first shrinking system and a second shrinking system;

[0013] A reflector, comprising a first reflector and a second reflector;

[0014] A focusing lens, comprising a first focusing lens and a second focusing lens;

[0015] An organic nonlinear crystal, comprising a first organic nonlinear crystal and a second organic nonlinear crystal;

[0016] A TPX lens, comprising a first TPX lens and a second TPX lens;

[0017] a fixed wavelength laser configured to be used as a near infrared light source for an organic nonlinear crystal in optical difference frequency;

[0018] A tunable laser, as another wavelength tunable light source of the organic nonlinear crystal in the system, is configured to generate tunable terahertz waves;

[0019] The first optical fiber amplifier and the second optical fiber amplifier are configured to respectively amplify the power of the two near-infrared laser beams to the W level, so as to generate a higher-power terahertz wave by difference frequency through the nonlinear effect of the organic crystal;

[0020] The chopper is configured to chop two continuous near-infrared lasers into intermittent light, thereby reducing the heat accumulation of the organic crystal and avoiding crystal damage. At the same time, the chopping also enables the detector to work normally to detect signals;

[0021] The first and second beam reduction systems are configured to reduce the collimated light output from the optical fiber amplifier to the same diameter;

[0022] A first reflector is configured to reflect the laser light of a fixed wavelength so as to vertically incident on the beam combining mirror;

[0023] The beam combiner is configured to combine two near-infrared laser beams of different wavelengths into one beam, so as to produce a difference frequency effect in the organic nonlinear crystal. Since the beam combiner will simultaneously reflect and transmit any laser beam, the two wavelength beams and the beams will still be divided into two paths, each containing two wavelengths of laser beams.

[0024] A second reflecting mirror is configured to reflect the second combined laser beam so as to be incident on the focusing lens;

[0025] The first focusing lens and the second focusing lens are configured to focus the combined laser beam containing two wavelengths. When the focused spot is reduced to the order of tens of microns, it is more conducive to the difference frequency effect of the organic nonlinear crystal.

[0026] The first organic nonlinear crystal and the second organic nonlinear crystal are configured to be used as a medium for optical difference frequency generation of terahertz waves, and two near-infrared laser beams with different wavelengths generate nonlinear effects in the crystals;

[0027] The first TPX lens and the second TPX lens are configured to collimate the generated divergent terahertz wave and output it;

[0028] An off-axis metalens configured to focus the terahertz wave to a point for easy detection;

[0029] The detector is configured to detect the generated terahertz wave.

[0030] Preferably, the device further comprises an air drying chamber configured to reduce the water vapor content in the air, firstly to prevent the organic crystals from combining with water molecules to form hydrates, and secondly to reduce the absorption of terahertz waves by water vapor.

[0031] In addition, the present invention also mentions a method for generating optical difference frequency terahertz waves based on organic nonlinear crystals. The method adopts the optical difference frequency terahertz wave generating device based on organic nonlinear crystals as described above, and specifically comprises the following steps:

[0032] Step 1: A fixed wavelength laser and a wavelength tunable laser output two near-infrared laser beams, which are respectively sent to a first optical fiber amplifier and a second optical fiber amplifier;

[0033] Step 2: The first optical fiber amplifier and the second optical fiber amplifier respectively amplify the power of the two near-infrared laser beams to the W level;

[0034] Step 3: Using a chopper, two continuous near-infrared lasers with different wavelengths are chopped to form discontinuous light;

[0035] Step 4: adjusting the diameters and divergence angles of the two laser beams chopped by the chopper to be the same through the first beam reduction system and the second beam reduction system;

[0036] Step 5: Reflect the first laser beam through the first reflector so that it is vertically incident on the beam combiner;

[0037] Step 6: Use a beam combiner to combine two near-infrared lasers with different wavelengths into one beam. Since the beam combiner will simultaneously reflect and transmit any laser beam, the two wavelength beams will still be divided into two paths after the beam is combined. At this time, the two paths contain laser beams of two wavelengths at the same time.

[0038] Step 7: Reflect the second combined laser beam through the second reflector so that it is incident on the second focusing lens;

[0039] Step 8: focusing the combined laser beam containing two wavelengths through a first focusing lens and a second focusing lens;

[0040] Step 9: The focused combined laser beam is incident on the first organic nonlinear crystal and the second organic nonlinear crystal respectively, generating nonlinear effects in the first organic nonlinear crystal and the second organic nonlinear crystal respectively, and generating divergent terahertz waves by difference frequency action;

[0041] Step 10: shaping the generated divergent terahertz wave into a nearly parallel beam through the first TPX lens and the second TPX lens;

[0042] Step 11: Through the off-axis superlens, the two terahertz waves are redirected and incident on the detector for detection.

[0043] Beneficial technical effects brought by the present invention:

[0044] The present invention proposes an optical difference frequency terahertz wave generation method based on organic nonlinear crystals, which combines two continuous laser beams with different wavelengths and then divides them into two beams to be incident on two nonlinear crystals to generate terahertz waves, and then shapes and combines the terahertz waves. This method can make full use of the pump laser to generate terahertz waves, while reducing the risk of thermal accumulation damage to organic crystals. An air drying chamber is used to prevent organic crystals from combining with water molecules to form hydrates, reduce the absorption of terahertz waves by water vapor, reduce the complexity of the system, and improve the stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a structural diagram of a difference frequency module based on organic crystals;

[0046] Among them, 1-reflector; 2-beam combiner; 3-light trap; 4-focusing lens; 5-organic nonlinear crystal; 6-TPX lens; 7-detector;

[0047] Figure 2 Schematic diagram of an optical difference frequency terahertz wave generating device based on organic nonlinear crystal;

[0048] Among them, 8-fixed wavelength laser; 9-tunable laser; 10-first optical fiber amplifier; 11-second optical fiber amplifier; 12-chopper; 13-first beam reduction system; 14-second beam reduction system; 15-first reflector; 16-second reflector; 17-first focusing lens; 18-second focusing lens; 19-first organic nonlinear crystal; 20-second organic nonlinear crystal; 21-first TPX lens; 22-second TPX lens; 23-off-axis super lens; 24-air drying chamber;

[0049] Figure 3 Schematic diagram of the optical path propagation of the beam combiner;

[0050] Among them, 25 is the first incident light; 26 is the second incident light; 27 is the first reflected light; 28 is the first transmitted light; 29 is the second transmitted light; 30 is the second reflected light. DETAILED DESCRIPTION

[0051] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0052] Embodiment 1:

[0053] In order to solve the technical problems existing in the current optical difference frequency generation terahertz system based on DAST crystal, the present invention adopts Figure 2 The technical solution shown in the figure combines two continuous laser beams and then divides them into two paths to be incident on the nonlinear crystal to generate terahertz waves, and finally shapes and combines the terahertz waves; specifically, it includes a fixed wavelength laser 8, a tunable laser 9, an optical fiber amplifier, a chopper 12, a beam reduction system, a reflector, a beam combining mirror 2, a focusing lens, an organic nonlinear crystal, a TPX lens, an off-axis super lens 23, an air drying chamber 24 and a detector 7;

[0054] The optical fiber amplifier comprises a first optical fiber amplifier 10 and a second optical fiber amplifier 11;

[0055] A shrinking system, comprising a first shrinking system 13 and a second shrinking system 14;

[0056] A reflector, comprising a first reflector 15 and a second reflector 16;

[0057] A focusing lens, comprising a first focusing lens 17 and a second focusing lens 18;

[0058] An organic nonlinear crystal, comprising a first organic nonlinear crystal 19 and a second organic nonlinear crystal 20;

[0059] The TPX lens comprises a first TPX lens 21 and a second TPX lens 22;

[0060] a fixed wavelength laser 8 configured to be used as a near infrared light source for the organic nonlinear crystal in optical difference frequency;

[0061] The tunable laser 9, as another wavelength tunable light source of the organic nonlinear crystal in the system, is configured to generate a tunable terahertz wave;

[0062] The first optical fiber amplifier 10 and the second optical fiber amplifier 11 are configured to respectively amplify the power of two near-infrared laser beams to the W level, so as to generate a higher-power terahertz wave by difference frequency through the nonlinear effect of the organic crystal;

[0063] The chopper 12 is configured to chop two continuous near-infrared lasers into intermittent light, thereby reducing the heat accumulation of the organic crystal and avoiding crystal damage. The chopping also enables the detector to work normally to detect the signal;

[0064] The first beam reduction system 13 and the second beam reduction system 14 are configured to reduce the collimated light output from the optical fiber amplifier to the same diameter;

[0065] The first reflector 15 is configured to reflect the laser light of a fixed wavelength so that it is vertically incident on the beam combining mirror;

[0066] The beam combiner 2 is configured to combine two near-infrared laser beams with different wavelengths into one beam, so as to produce a difference frequency effect in the organic nonlinear crystal; since the beam combiner will simultaneously reflect and transmit any laser beam, the two wavelengths of the light beam and the beam will still be divided into two paths, each of which contains two wavelengths of laser beam;

[0067] The second reflecting mirror 16 is configured to reflect the second combined laser beam so as to be incident on the focusing lens;

[0068] The first focusing lens 17 and the second focusing lens 18 are configured to focus the combined laser beam containing two wavelengths. When the focused spot is reduced to the order of tens of microns, it is more conducive to the difference frequency effect of the organic nonlinear crystal.

[0069] The first organic nonlinear crystal 19 and the second organic nonlinear crystal 20 are configured to be used as a medium for optical difference frequency generation of terahertz waves, and two near-infrared laser beams with different wavelengths generate nonlinear effects in the crystals;

[0070] The first TPX lens 21 and the second TPX lens 22 are configured to collimate and output the generated divergent terahertz waves;

[0071] An off-axis superlens 23 is configured to focus the terahertz wave to a point for easy detection;

[0072] The air drying chamber 24 is configured to reduce the water vapor content in the air, firstly to prevent the organic crystals from combining with water molecules to form hydrates, and secondly to reduce the absorption of terahertz waves by water vapor;

[0073] The detector 7 is configured to detect the generated terahertz wave.

[0074] The principle is as follows:

[0075] The two near-infrared laser beams output by the fixed wavelength laser 8 and the wavelength tunable laser 9 have a power of about mW level, and the power reaches W level after passing through the optical fiber amplifier. Then the two lasers with different wavelengths pass through the chopper to form non-continuous light. On the one hand, the non-continuous light can effectively slow down the heat accumulation of organic crystals and reduce the damage to the crystals caused by high-power lasers. On the other hand, it is to meet the needs of normal operation of the detector. Then, the laser beam reduction system is used to adjust the diameters and divergence angles of the two laser beams to the same, which is conducive to the combination of the two beams and the nonlinear effects of the two beams in the crystal. The two shaped laser beams are then combined into one through the beam combiner 2. Since the beam combiner 2 will simultaneously reflect and transmit any laser beam, the two wavelengths of the light beam will still be divided into two beams, but the two beams of light at this time contain two wavelengths of light at the same time, such as Figure 2 As shown, both lights can be used to be incident on the nonlinear crystal to generate terahertz waves, and then the two combined laser spots are reduced to about tens of microns by a focusing lens. After the two beams of light are incident on the organic crystal, a difference frequency effect occurs to generate terahertz waves. The generated terahertz waves are divergent. The TPX lens is used to shape the divergent terahertz waves into approximately parallel beams, and then the off-axis super lens is used to change the direction of the two terahertz waves and incident on the detector for detection.

[0076] In the solution of the present invention, since the beam combiner has both reflection (deflection 90 degrees) and transmission of the incident light, the two beams of light (the first incident light 25 and the second incident light 26) with perpendicular incident directions are respectively divided into two paths, the first incident light 25 is divided into the first reflected light 27 and the first transmitted light 28, and the second incident light 26 is divided into the second transmitted light 29 and the second reflected light 30. Figure 3 As shown, the first reflected light 27 and the second transmitted light 29 are combined into one light, and the second reflected light 30 and the first transmitted light 28 are combined into another light. Therefore, both light paths contain incident light of two wavelengths at the same time, which can be incident on the nonlinear crystal at the same time to generate terahertz waves. Compared with the system that only uses one combined light path to generate terahertz waves, this greatly improves the utilization rate of near-infrared lasers, avoids the waste of pumping near-infrared lasers, is conducive to the improvement of the power of the generated terahertz waves, and greatly improves the performance of the optical difference frequency system.

[0077] The two combined laser beams are respectively incident on two nonlinear crystals, and then the terahertz waves generated by the two beams are aggregated through an off-axis superlens. This can not only improve the utilization rate of near-infrared lasers and enhance the power of terahertz waves, but also indirectly reduce the risk of organic crystals being damaged by thermal effects of high-power lasers. The laser power that originally needed to be borne by one crystal is now shared by two crystals, which will effectively protect the crystals, extend the service life of the organic crystals, and improve the stability of the system.

[0078] Water vapor not only has a strong absorption effect on the generated terahertz waves, but also causes the organic crystal to form hydrates, increasing its absorption coefficient, significantly affecting its second-order nonlinear performance, and reducing the efficiency of terahertz wave generation. In the scheme of the present invention, an air drying chamber is used to reduce the water vapor content in the air, so that the organic crystal can be placed in the system for a longer time, reducing the number of crystal calibrations, improving the stability of the system, and greatly reducing the absorption of terahertz waves by water vapor, thereby enhancing the power of terahertz waves.

[0079] Embodiment 2:

[0080] On the basis of the above-mentioned embodiment 1, the present invention further provides a method for generating optical difference frequency terahertz waves based on organic nonlinear crystals, which specifically comprises the following steps:

[0081] Step 1: A fixed wavelength laser and a wavelength tunable laser output two near-infrared laser beams, which are respectively sent to a first optical fiber amplifier and a second optical fiber amplifier;

[0082] Step 2: The first optical fiber amplifier and the second optical fiber amplifier respectively amplify the power of the two near-infrared laser beams to the W level;

[0083] Step 3: Using a chopper, two continuous near-infrared lasers with different wavelengths are chopped to form discontinuous light;

[0084] Step 4: adjusting the diameters and divergence angles of the two laser beams chopped by the chopper to be the same through the first beam reduction system and the second beam reduction system;

[0085] Step 5: Reflect the first laser beam through the first reflector so that it is vertically incident on the beam combiner;

[0086] Step 6: Use a beam combiner to combine two near-infrared lasers with different wavelengths into one beam. Since the beam combiner will simultaneously reflect and transmit any laser beam, the two wavelength beams will still be divided into two paths after the beam is combined. At this time, the two paths contain laser beams of two wavelengths at the same time.

[0087] Step 7: Reflect the second combined laser beam through the second reflector so that it is incident on the second focusing lens;

[0088] Step 8: focusing the combined laser beam containing two wavelengths through a first focusing lens and a second focusing lens;

[0089] Step 9: The focused combined laser beam is incident on the first organic nonlinear crystal and the second organic nonlinear crystal respectively, generating nonlinear effects in the first organic nonlinear crystal and the second organic nonlinear crystal respectively, and generating divergent terahertz waves by difference frequency action;

[0090] Step 10: shaping the generated divergent terahertz wave into a nearly parallel beam through the first TPX lens and the second TPX lens;

[0091] Step 11: Through the off-axis superlens, the two terahertz waves are redirected and incident on the detector for detection.

[0092] The present invention proposes a solution of combining two continuous laser beams and then dividing them into two paths to respectively inject into a nonlinear crystal to generate terahertz waves and then shaping and combining the terahertz waves, which solves the problem of low laser energy utilization and also reduces the risk of damage to organic crystals due to heat accumulation from high-power continuous lasers.

[0093] Placing the difference frequency module in an air-dried chamber greatly reduces the absorption of terahertz waves by water vapor and enhances the power of terahertz waves. At the same time, it prevents organic crystals from combining with water molecules in the air to form hydrates, avoids repeated calibration and installation of crystals, and improves system stability.

[0094] The present invention proposes a solution for combining two continuous laser beams and then dividing them into two beams to respectively inject into a nonlinear crystal to generate terahertz waves and then shaping and combining the terahertz waves.

[0095] The present invention proposes a method for enhancing the power of terahertz waves by utilizing an air drying chamber to prevent organic crystals from forming hydrates and simultaneously reduce the absorption of terahertz waves by water vapor.

[0096] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. An optical difference frequency terahertz wave generating device based on organic nonlinear crystal, characterized in that: Including fixed wavelength lasers, tunable lasers, fiber amplifiers, choppers, beam reduction systems, mirrors, beam combiners, focusing lenses, organic nonlinear crystals, TPX lenses, off-axis super lenses and detectors; An optical fiber amplifier, comprising a first optical fiber amplifier and a second optical fiber amplifier; A shrinking system, comprising a first shrinking system and a second shrinking system; A reflector, comprising a first reflector and a second reflector; A focusing lens, comprising a first focusing lens and a second focusing lens; An organic nonlinear crystal, comprising a first organic nonlinear crystal and a second organic nonlinear crystal; A TPX lens, comprising a first TPX lens and a second TPX lens; a fixed wavelength laser configured to be used as a near infrared light source for an organic nonlinear crystal in optical difference frequency; A tunable laser, as another wavelength tunable light source of the organic nonlinear crystal in the system, is configured to generate tunable terahertz waves; The first optical fiber amplifier and the second optical fiber amplifier are configured to respectively amplify the power of the two near-infrared laser beams to the W level, so as to generate a higher-power terahertz wave by difference frequency through the nonlinear effect of the organic crystal; The chopper is configured to chop two continuous near-infrared lasers into intermittent light, thereby reducing the heat accumulation of the organic crystal and avoiding crystal damage. At the same time, the chopping also enables the detector to work normally to detect signals; The first and second beam reduction systems are configured to reduce the collimated light output from the optical fiber amplifier to the same diameter; A first reflector is configured to reflect the laser light of a fixed wavelength so as to vertically incident on the beam combining mirror; The beam combiner is configured to combine two near-infrared laser beams of different wavelengths into one beam, so as to produce a difference frequency effect in the organic nonlinear crystal. Since the beam combiner will simultaneously reflect and transmit any laser beam, the two wavelength beams and the beams will still be divided into two paths, each containing two wavelengths of laser beams. A second reflecting mirror is configured to reflect the second combined laser beam so as to be incident on the focusing lens; The first focusing lens and the second focusing lens are configured to focus the combined laser beam containing two wavelengths. When the focused spot is reduced to the order of tens of microns, it is more conducive to the difference frequency effect of the organic nonlinear crystal. The first organic nonlinear crystal and the second organic nonlinear crystal are configured to be used as a medium for optical difference frequency generation of terahertz waves, and two near-infrared laser beams with different wavelengths generate nonlinear effects in the crystals; The first TPX lens and the second TPX lens are configured to collimate the generated divergent terahertz wave and output it; An off-axis metalens configured to focus the terahertz wave to a point for easy detection; The detector is configured to detect the generated terahertz wave.

2. The optical difference frequency terahertz wave generating device based on organic nonlinear crystal according to claim 1, characterized in that: The apparatus also includes an air drying chamber configured to reduce water vapor content in the air.

3. A method for generating optical difference frequency terahertz waves based on organic nonlinear crystals, characterized in that: The optical difference frequency terahertz wave generating device based on organic nonlinear crystal as claimed in claim 1 specifically comprises the following steps: Step 1: A fixed wavelength laser and a wavelength tunable laser output two near-infrared laser beams, which are respectively sent to a first optical fiber amplifier and a second optical fiber amplifier; Step 2: The first optical fiber amplifier and the second optical fiber amplifier respectively amplify the power of the two near-infrared laser beams to the W level; Step 3: Using a chopper, two continuous near-infrared lasers with different wavelengths are chopped to form discontinuous light; Step 4: adjusting the diameters and divergence angles of the two laser beams chopped by the chopper to be the same through the first beam reduction system and the second beam reduction system; Step 5: Reflect the first laser beam through the first reflector so that it is vertically incident on the beam combiner; Step 6: Use a beam combiner to combine two near-infrared lasers with different wavelengths into one beam. Since the beam combiner will simultaneously reflect and transmit any laser beam, the two wavelength beams will still be divided into two paths after the beam is combined. At this time, the two paths contain laser beams of two wavelengths at the same time. Step 7: Reflect the second combined laser beam through the second reflector so that it is incident on the second focusing lens; Step 8: focusing the combined laser beam containing two wavelengths through a first focusing lens and a second focusing lens; Step 9: The focused combined laser beam is incident on the first organic nonlinear crystal and the second organic nonlinear crystal respectively, generating nonlinear effects in the first organic nonlinear crystal and the second organic nonlinear crystal respectively, and generating divergent terahertz waves by difference frequency action; Step 10: shaping the generated divergent terahertz wave into a nearly parallel beam through the first TPX lens and the second TPX lens; Step 11: Through the off-axis superlens, the two terahertz waves are redirected and incident on the detector for detection.

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