A device for simultaneously generating dual-frequency terahertz waves

Abstract

The application aims to provide a device for simultaneously generating double-frequency terahertz waves, comprising a pump source, an AFB-KTP crystal, a beam splitter, a first APPLN crystal with different polarization period distributions, a second APPLN crystal, a first mirror, a second mirror, a third mirror, a fourth mirror, a fifth mirror, a sixth mirror, a seventh mirror, an eighth mirror, a first parabolic mirror and a second parabolic mirror. The device can simultaneously generate terahertz waves of two frequencies and improve the conversion efficiency of the terahertz waves. The non-periodic polarization distribution of the APPLN crystal can enhance Stokes cascade difference frequency and suppress anti-Stokes cascade difference frequency, thereby improving the optical conversion efficiency of the terahertz waves.

Description

Technical Field

[0001] This invention belongs to the field of terahertz wave application technology, specifically relating to a device for simultaneously generating dual-frequency terahertz waves. Background Technology

[0002] Terahertz waves (THz) refer to waves with frequencies between 0.1 and 10 THz (1 THz = 10 THz). 12 Terahertz waves, falling within the electromagnetic spectrum from millimeter waves to infrared radiation (Hz), represent a transitional region between photonics and electronics, and between macroscopic and microscopic theories. Their unique position within the spectrum gives them significant scientific research value and broad application prospects in fundamental research fields such as physics, chemistry, astronomy, molecular spectroscopy, life sciences, and medical sciences, as well as applied research fields such as medical imaging, environmental monitoring, materials testing, food testing, radio astronomy, mobile communications, satellite communications, and military radar. Terahertz waves are primarily used in the following areas:

[0003] (1) Imaging field

[0004] Unlike conventional optical or X-ray imaging, each pixel in a pulsed THz wave image contains the entire THz waveform, not just the intensity of the beam. The Fourier transform of the THz waveform can also extract the spectral information of that pixel. Therefore, THz wave imaging not only identifies targets by their contours but also obtains composite information about the target.

[0005] (2) Biomedical technology field

[0006] The "fingerprint" characteristic of the THz band allows it to contain rich physical and chemical information when interacting with a medium, while its low energy ensures its application in fields such as biomedical imaging. Since THz light sources are composed of light waves with different composite polarizations, information can be collected from the medium using different polarized light to obtain more accurate diagnostic information about pathological tissues. Therefore, THz waves play a significant role in the clinical diagnosis and treatment of cancer.

[0007] (3) Non-destructive testing field

[0008] The penetrating power of THz waves makes them well-suited for non-destructive testing and THz imaging. Utilizing THz time-domain spectroscopy, non-contact and non-destructive methods can penetrate non-polar dielectric materials such as clothing, cardboard boxes, and plastics, thus enabling the detection of the chemical properties of the medium. This provides new biological characteristics and identification criteria for stored grain pests in the terahertz band, establishing a new method for identification and research that complements other detection technologies. This allows for rapid and convenient detection of stored grain pests and their species, and has significant practical implications for pest surveys and monitoring, accelerating rapid pest detection and quarantine at ports of entry, and accurately detecting stored grain pests in grain depots.

[0009] (4) Communication field

[0010] THz waves have a wide bandwidth, good directionality, and high transmission rate, making them highly promising for high-speed space communication and radar applications, with a promising future for both military and civilian applications and balanced, coordinated development. Because THz waves are sensitive to water molecules, secure communication can be achieved through atmospheric transmission. Compared to visible light and infrared light, THz waves, due to their longer wavelength and better directionality, enable space communication with extremely high bandwidth even in clouds and fog.

[0011] (5) Homeland security

[0012] THz waves have good directionality and narrow beams, giving them strong penetration capabilities through clouds and smoke. In military applications, THz waves are used for terminal precision guidance of missiles to improve guidance accuracy, making them extremely valuable for military applications.

[0013] The main problem currently faced is the lack of terahertz sources that can generate high-power, high-quality, and high-efficiency terahertz waves at low cost and can operate at room temperature. Summary of the Invention

[0014] The purpose of this invention is to provide a device for simultaneously generating dual-frequency terahertz waves, which can generate terahertz waves of two frequencies at the same time, thereby improving the terahertz wave conversion efficiency.

[0015] The object of the present invention is achieved in the following manner: a device for simultaneously generating dual-frequency terahertz waves, comprising a pump source, an AFB-KTP crystal, a beam splitter, a first APPLN crystal and a second APPLN crystal with different polarization period distributions, a first mirror, a second mirror, a third mirror, a fourth mirror, a fifth mirror, a sixth mirror, a seventh mirror, an eighth mirror, a first parabolic mirror, and a second parabolic mirror;

[0016] Pump light emitted from the pump source is incident on the AFB-KTP crystal through the first reflector, generating two signal beams and two idler beams. The two signal beams pass through a beam splitter and are reflected by the second and third reflectors, then incident on the first APPLN crystal in a direction parallel to the pump light. Through the cascaded optical difference frequency effect, a first set of cascaded light and a first terahertz wave are generated. The first terahertz wave is output by the first parabolic mirror. The first set of cascaded light passes through the first parabolic mirror and is reflected by the fourth and first reflectors before being incident on the AFB-KTP crystal. The first set of cascaded light oscillates back and forth in the resonant cavity composed of the first, second, third, and fourth reflectors.

[0017] Two idler beams are split by a beam splitter, then reflected by the fifth and sixth mirrors and incident on the second APPLN crystal in a direction parallel to the pump beam. A second set of cascaded beams and a second terahertz wave are generated through the cascaded optical difference frequency effect. The second terahertz wave is output from the second parabolic mirror. The second set of cascaded beams passes through the second parabolic mirror, is reflected by the seventh and eighth mirrors, then through the fourth mirror, and finally by the first mirror before being incident on the AFB-KTP crystal. The second set of cascaded beams oscillates back and forth in a resonant cavity composed of the fifth, sixth, seventh, eighth, and first mirrors. The pump beam emitted from the AFB-KTP crystal passes through the beam splitter and then exits through or via the second mirror.

[0018] The frequency of the first terahertz wave is equal to the frequency difference between the two signal beams; the frequency of the second terahertz wave is equal to the frequency difference between the two idler beams.

[0019] The plane in which the light beam propagates is defined by the X-axis and Y-axis, with the Z-axis perpendicular to the plane of light beam propagation. The initial propagation direction of the pump light emitted from the pump source is the positive X-axis, the propagation direction of the first terahertz wave generated by the first APPLN crystal is the positive Y-axis, and the propagation direction of the second terahertz wave generated by the second APPLN crystal is the negative Y-axis. The polarization directions of the pump light, the two idler beams, the second cascaded beams, and the second terahertz wave are all along the Y-axis, while the polarization directions of the two signal beams, the first cascaded beams, and the first terahertz wave are all along the Z-axis.

[0020] The first, second, third, and fourth reflecting mirrors are all concave mirrors; the fifth, sixth, seventh, and eighth reflecting mirrors are all plane mirrors. The first reflecting mirror has high transmittance of the pump light (99.9%) and high reflectance of the two signal beams, two idler beams, the first cascaded beam, and the second cascaded beam (99.9%). The second reflecting mirror has high transmittance of the pump light (99.9%) and high reflectance of the two signal beams and the first cascaded beam (99.9%). The third reflecting mirror has high reflectance of the two signal beams and the first cascaded beam (99.9%). The fourth mirror has a high reflectivity of 99.9% for the two signal beams and the first cascaded beam, and a high transmittance of 99.9% for the two idler beams and the second cascaded beam. The fifth, sixth, seventh, and eighth mirrors all have high reflectivity of 99.9% for the two idler beams and the second cascaded beam. The two signal beams and the first cascaded beam, with propagation directions along the positive X-axis and polarization directions along the Z-axis, do not change their propagation direction after passing through the beam splitter. The two idler beams and the second cascaded beam, with propagation directions along the positive X-axis and polarization directions along the Y-axis, propagate in the negative Y-axis direction after passing through the beam splitter.

[0021] The AFB-KTP crystal, the first APPLN crystal, and the second APPLN crystal are all cuboids, rectangular in the XY plane, with their length direction aligned with the positive X-axis. The optical axis of the first APPLN crystal is along the Z-axis, and the optical axis of the second APPLN crystal is along the Y-axis. The AFB-KTP crystal is a binder-free KTP crystal. The first and second APPLN crystals are both aperiodic polarized crystals. The aperiodic polarization distribution of the first APPLN crystal, along its length, shows a phase mismatch that gradually decreases to zero from the first-order Stokes difference frequency to the nth-order Stokes difference frequency, where nth order is greater than one order. The first APPLN crystal has a phase mismatch of less than the first pump light frequency - 60 THz / the first terahertz wave frequency. The second APPLN crystal's aperiodic polarization distribution has a phase mismatch of 0 along the crystal length from the first Stokes difference frequency to the m-th order Stokes difference frequency. The m-th order is any order greater than one order but less than the first pump light frequency - 60 THz / the second terahertz wave frequency. The first order Stokes difference frequency of the first APPLN crystal contains two difference frequency beams, which are two signal beams. The first order Stokes difference frequency of the second APPLN crystal contains two difference frequency beams, which are two idler beams.

[0022] The first parabolic mirror has a small aperture at its center that allows only two signal beams and the first set of cascaded beams to pass through. The second parabolic mirror has a small aperture at its center that allows only two idler beams and the second set of cascaded beams to pass through. The second mirror transmits pump light.

[0023] The first group of cascaded light and the second group of cascaded light are mixed light composed of each group of cascaded light; the frequency difference between adjacent cascaded light in the first group of cascaded light is the frequency difference between the two signal light beams; the frequency difference between adjacent cascaded light in the second group of cascaded light is the frequency difference between the two idler light beams.

[0024] Compared with existing technologies, the device for simultaneously generating dual-frequency terahertz waves provided by this invention has the following advantages over existing terahertz radiation sources based on optical difference frequency effects:

[0025] (1) By setting the inversion period of the AFB-KTP crystal, the wavelengths of the two output o-lights and two output e-lights can be changed, thereby changing the frequency of the two output terahertz waves.

[0026] (2) By setting the distribution of aperiodic polarization of the APPLN crystal, the Stokes cascade difference frequency can be enhanced while the anti-Stokes cascade difference frequency is suppressed, thereby improving the optical conversion efficiency of terahertz waves. Attached Figure Description

[0027] Figure 1This is a structural schematic diagram of an embodiment of the present invention.

[0028] Figure 2 This relates the different inversion periods of the AFB-KTP crystal to the wavelengths of the two signal beams and two idler beams generated.

[0029] Figure 3(a) shows the intensity of the first terahertz wave generated as a function of the length of the first APPLN crystal.

[0030] Figure 3(b) shows the polarization period distribution of the first APPLN crystal with respect to crystal length.

[0031] Figure 4(a) shows the intensity of the generated second terahertz wave as a function of the length of the second APPLN crystal.

[0032] Figure 4(b) shows the polarization period distribution of the second APPLN crystal with respect to crystal length. Detailed Implementation

[0033] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. It should be understood that the preferred embodiments described herein are only for illustration and explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments based on the following content of the present invention. In this invention, unless otherwise expressly specified and limited, the technical terms used in this application should have the ordinary meaning understood by those skilled in the art.

[0034] As attached Figure 1 As shown, a device for simultaneously generating dual-frequency terahertz waves includes a pump source 1, an AFB-KTP crystal 11, a beam splitter 16, a first APPLN crystal 12 and a second APPLN crystal 13 with different polarization period distributions, a first reflector 3, a second reflector 4, a third reflector 5, a fourth reflector 6, a fifth reflector 7, a sixth reflector 8, a seventh reflector 9, an eighth reflector 10, a first parabolic mirror 14, and a second parabolic mirror 15.

[0035] Pump light 2 emitted from pump source 1 is incident on AFB-KTP crystal 11 through first reflector 3, generating two signal beams 17 and two idler beams 18. The two signal beams 17 pass through beam splitter 16 and are reflected by second reflector 4 and third reflector 5, then incident on the first APPLN crystal 12 in a direction parallel to pump light 2. Through cascaded optical difference frequency effect, a first set of cascaded light 19 and a first terahertz wave 21 are generated. The first terahertz wave 21 is output by first parabolic mirror 14. The first set of cascaded light 19 passes through first parabolic mirror 14 and is reflected by fourth reflector 6 and first reflector 3 before incident on AFB-KTP crystal 11. The first set of cascaded light 19 oscillates back and forth in the resonant cavity composed of first reflector 3, second reflector 4, third reflector 5, and fourth reflector 6.

[0036] Two idler beams 18 are split by beam splitter 16, then reflected by fifth mirror 7 and sixth mirror 8, and incident on the second APPLN crystal 13 in a direction parallel to the pump beam 2. Through cascaded optical difference frequency effect, a second set of cascaded beams 20 and a second terahertz wave 22 are generated. The second terahertz wave 22 is output from the second parabolic mirror 15. The second set of cascaded beams 20 passes through the second parabolic mirror 15, is reflected by seventh mirror 9 and eighth mirror 10, then passes through fourth mirror 6, and is reflected by first mirror 3 before being incident on the AFB-KTP crystal 11. The second set of cascaded beams 20 oscillates back and forth in the resonant cavity composed of fifth mirror 7, sixth mirror 8, seventh mirror 9, eighth mirror 10, and first mirror 3. The pump beam 2 emitted from the AFB-KTP crystal 11 passes through beam splitter 16 and second mirror 4 before exiting.

[0037] In this embodiment, pump source 1 is a green pulsed laser, pump light 2 has a wavelength of 532 nm, and pump power density is 1000 MW / cm². 2 The pump light has a pulse width of 8 ns, a repetition frequency of 10 Hz, and a beam diameter of 1 mm. The pump light 2 reacts with the AFB-KTP crystal 11 to generate two signal beams 17—signal beam I and signal beam II—and two idler beams 18—idle beam I and idler beam II. The wavelengths of the two signal beams 17 and the two idler beams 18 depend on the magnitude of the inversion period of the AFB-KTP crystal 11. The relationship between different inversion periods of the AFB-KTP crystal and the wavelengths of the generated two signal beams 17 and two idler beams 18 is shown in the figure below. Figure 2As shown, the inversion period of the AFB-KTP crystal 11 is 13710 μm. The wavelengths of the two signal beams 17 generated are 1.0406 μm and 1.0390 μm, respectively, and the wavelengths of the two idler beams 18 generated are 1.0902 μm and 1.0885 μm, respectively. The frequency of the first terahertz wave 21 is equal to the frequency difference between the two signal beams 17, i.e., 0.4439 THz; the frequency of the second terahertz wave 22 is equal to the frequency difference between the two idler beams 18, i.e., 0.4297 THz.

[0038] The plane in which the light beam propagates is defined by the X and Y axes, with the Z axis perpendicular to the plane. The initial propagation direction of the pump light 2 emitted from pump source 1 is the positive X-axis. The propagation direction of the first terahertz wave 21 generated by the first APPLN crystal 12 is the positive Y-axis, and the propagation direction of the second terahertz wave 22 generated by the second APPLN crystal 13 is the negative Y-axis. The polarization directions of the pump light 2, the two idler beams 18, the second cascaded beams 20, and the second terahertz wave 22 are all along the Y-axis, while the polarization directions of the two signal beams 17, the first cascaded beams 19, and the first terahertz wave 21 are all along the Z-axis.

[0039] In this embodiment, the first reflector 3, the second reflector 4, the third reflector 5, and the fourth reflector 6 are all concave mirrors; the fifth reflector 7, the sixth reflector 8, the seventh reflector 9, and the eighth reflector 10 are all plane mirrors. The first reflector 3 has high transmission of pump light 2 with a transmittance of 99.9%; it also has high reflectance of the two signal beams 17, the two idler beams 18, the first cascaded beam 19, and the second cascaded beam 20, with a reflectance of 99.9%. The second reflector 4 has high transmission of pump light 2 with a transmittance of 99.9%; it also has high reflectance of the two signal beams 17 and the first cascaded beam 19, with a reflectance of 99.9%. The third reflector 5 has high reflectance of the two signal beams 17 and the first cascaded beam 19, with a reflectance of 99.9%. The fourth reflector 6 has high reflectance of the two signal beams 17 and the first cascaded beam 19, with a reflectance of 99.9%; it also has high transmission of the two idler beams 18 and the second cascaded beam 20, with a transmittance of 99.9%. The fifth, sixth, seventh, and eighth reflectors 7, 8, 9, and 10 all have high reflectance of the two idler beams 18 and the second cascaded beam 20, with a reflectance of 99.9%. Two beams of signal light 17, with propagation direction along the positive X-axis and polarization direction along the Z-axis, and the first set of cascaded light 19, do not change their propagation direction after passing through beam splitter 16. Two beams of idler light 18, with propagation direction along the positive X-axis and polarization direction along the Y-axis, and the second set of cascaded light 20, with propagation direction along the positive X-axis and polarization direction along the Y-axis, propagate in the negative Y-axis direction after passing through beam splitter 16.

[0040] The aperiodic polarization distribution of the first APPLN crystal 12 exhibits a phase mismatch that gradually decreases to zero along its length from the first-order Stokes difference frequency to the nth-order Stokes difference frequency. The nth-order Stokes difference frequency is any order within the range greater than one order but less than {(frequency of the first pump light 2 - 60 THz) / frequency of the first terahertz wave 21}. Similarly, the aperiodic polarization distribution of the second APPLN crystal 13 exhibits a phase mismatch that gradually decreases to zero along its length from the first-order Stokes difference frequency to the m-order Stokes difference frequency. The m-order Stokes difference frequency is any order within the range greater than one order but less than {(frequency of the first pump light 2 - 60 THz) / frequency of the second terahertz wave 22}. The first-order Stokes difference frequency of the first APPLN crystal contains two beams of difference frequency light, which are both signal beams. The first-order Stokes difference frequency of the second APPLN crystal contains two beams of difference frequency light, which are both idler beams.

[0041] Specifically, in this embodiment, the AFB-KTP crystal 11, the first APPLN crystal 12, and the second APPLN crystal 13 are all cuboids, rectangular in the XY plane, with their length direction aligned with the positive X-axis. The optical axes of the AFB-KTP crystal 11 and the first APPLN crystal 12 are along the Z-axis, while the optical axis of the second APPLN crystal 13 is along the Y-axis. The AFB-KTP crystal 11 is a KTP crystal without adhesive bonding. The dimensions of the AFB-KTP crystal 11 are 54.8 mm × 4 mm × 2 mm (X×Y×Z). The first APPLN crystal 12 and the second APPLN crystal 13 are both aperiodic polarized crystals. The dimensions of the first APPLN crystal 12 are 10 mm × 5 mm × 2 mm (X×Y×Z), and the dimensions of the second APPLN crystal 13 are 14 mm × 5 mm × 2 mm (X×Y×Z).

[0042] Among them, the first APPLN crystal 12 contains two signal beams 17 in the first Stokes difference frequency, and its polarization period distribution is shown in Figure 3(b). It decreases from 246.47 μm to 244.89 μm. The phase mismatch of the non-periodic polarization distribution along the crystal length from the first Stokes difference frequency to the 101st Stokes difference frequency is gradually equal to 0. The intensity of the first terahertz wave 21 generated varies with the length of the first APPLN crystal as shown in Figure 3(a). The first-order Stokes difference frequency corresponding to the second APPLN crystal 13 contains two beams of difference frequency light, which are two beams of idler frequency light 18. The polarization period distribution is shown in Figure 4(b), which decreases from 253.46 μm to 251.86 μm. The phase mismatch of the non-periodic polarization distribution along the crystal length from the first-order Stokes difference frequency to the 141st-order Stokes difference frequency is gradually equal to 0. The intensity of the generated second terahertz wave 22 varies with the length of the second APPLN crystal as shown in Figure 4(a).

[0043] In this embodiment, the first parabolic mirror 14 has a small aperture at its center that allows only two beams of signal light 17 and the first set of cascaded light 19 to pass through, and the second parabolic mirror 15 has a small aperture at its center that allows only two beams of idler light 18 and the second set of cascaded light 20 to pass through. The diameter of both apertures is 1 mm. The second reflector 4 transmits the pump light 2.

[0044] In this embodiment, the first group of cascaded light 19 and the second group of cascaded light 20 are mixed light composed of each cascaded light. The frequency difference between adjacent cascaded light in the first group of cascaded light 19 is the frequency difference between the two signal light beams 17, which is 0.4439 THz; the frequency difference between adjacent cascaded light in the second group of cascaded light 20 is the frequency difference between the two idler light beams 18, which is 0.4297 THz.

[0045] The embodiments described above are merely examples and illustrations of the technical solutions of the present invention, intended to facilitate understanding of the technical solutions of this application by those skilled in the art, and are not all implementation methods. The scope of protection of the present invention is not limited thereto. The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention. The basic idea of ​​the present invention lies in the above basic solution. For those skilled in the art and any person skilled in the art, designing various modified models, formulas, and parameters based on the teachings of the present invention does not require creative effort without departing from the overall concept of the invention and the spirit of the principles of the present invention. Changes, modifications, substitutions, equivalent substitutions, and variations made to the implementation methods without departing from the principles and spirit of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A device for simultaneously generating dual-frequency terahertz waves, characterized in that: Includes a pump source (1), an AFB-KTP crystal (11), a beam splitter (16), a first APPLN crystal (12) and a second APPLN crystal (13) with different polarization period distributions, a first mirror (3), a second mirror (4), a third mirror (5), a fourth mirror (6), a fifth mirror (7), a sixth mirror (8), a seventh mirror (9), an eighth mirror (10), a first parabolic mirror (14), and a second parabolic mirror (15); Pump light (2) emitted from pump source (1) is incident on AFB-KTP crystal (11) through first reflector (3) to generate two signal beams (17) and two idler beams (18); the two signal beams (17) pass through beam splitter (16) and are reflected by second reflector (4) and third reflector (5) and then incident on the first APPLN crystal (12) in a direction parallel to pump light (2), generating the first set of cascaded light (19) through cascaded optical difference frequency effect. The first terahertz wave (21) is output by the first parabolic mirror (14), and the first set of cascaded light (19) passes through the first parabolic mirror (14) and is reflected by the fourth mirror (6) and the first mirror (3) before being incident on the AFB-KTP crystal (11). The first set of cascaded light (19) oscillates back and forth in the resonant cavity composed of the first mirror (3), the second mirror (4), the third mirror (5), and the fourth mirror (6). Two beams of idler light (18) are split by a beam splitter (16), and then reflected by a fifth mirror (7) and a sixth mirror (8). They are then incident on a second APPLN crystal (13) in a direction parallel to the pump light (2). A second set of cascaded light (20) and a second terahertz wave (22) are generated through the cascaded optical difference frequency effect. The second terahertz wave (22) is output by a second parabolic mirror (15). The second set of cascaded light (20) passes through the second parabolic mirror (15) and then through a seventh mirror (9) and an eighth mirror (8). After being reflected by the mirror (10), the light passes through the fourth mirror (6) and is then reflected by the first mirror (3) before entering the AFB-KTP crystal (11). The second set of cascaded light (20) oscillates back and forth in the resonant cavity composed of the fifth mirror (7), the sixth mirror (8), the seventh mirror (9), the eighth mirror (10), and the first mirror (3). The pump light (2) emitted from the AFB-KTP crystal (11) passes through the beam splitter (16) and then passes through or is transmitted out through the second mirror (4). The frequency of the first terahertz wave (21) is equal to the frequency difference between the two signal beams; the frequency of the second terahertz wave (22) is equal to the frequency difference between the two idler beams; The plane in which the beam propagates is the plane defined by the X-axis and Y-axis, and the Z-axis is perpendicular to the plane in which the beam propagates. The initial propagation direction of the pump light (2) emitted from the pump source (1) is the positive X-axis. The propagation direction of the first terahertz wave (21) generated by the first APPLN crystal (12) is the positive Y-axis. The propagation direction of the second terahertz wave (22) generated by the second APPLN crystal (13) is the negative Y-axis. The polarization directions of the pump light (2), the two idler beams (18), the second cascaded beams (20), and the second terahertz wave (22) are all Y-axis. The polarization directions of the two signal beams (17), the first cascaded beams (19), and the first terahertz wave (21) are all Z-axis.

2. The device for simultaneously generating dual-frequency terahertz waves according to claim 1, characterized in that: The first reflector (3), the second reflector (4), the third reflector (5), and the fourth reflector (6) are all concave mirrors; the fifth reflector (7), the sixth reflector (8), the seventh reflector (9), and the eighth reflector (10) are all plane mirrors; the first reflector (3) has high transmission for the pump light (2) with a transmittance of 99.9%, and high reflection for the two signal lights (17), the two idler lights (18), the first cascaded light (19), and the second cascaded light (20) with a reflectance of 99.9%; the second reflector (4) has high transmission for the pump light (2) with a transmittance of 99.9%, and high reflection for the two signal lights (17) and the first cascaded light (19) with a reflectance of 99.9%; the third reflector (5) has high reflection for the two signal lights (17) and the first cascaded light (19) with a reflectance of 99.9%. 99.9%; The fourth reflector (6) has high reflectivity for the two signal beams (17) and the first cascade beam (19), with a reflectivity of 99.9%, and high transmittance for the two idler beams (18) and the second cascade beam (20), with a transmittance of 99.9%; The fifth reflector (7), the sixth reflector (8), the seventh reflector (9), and the eighth reflector (10) all have high reflectivity for the two idler beams (18) and the second cascade beam (20), with a reflectivity of 99.9%; The two signal beams (17) and the first cascade beam (19) with the propagation direction along the positive X-axis and the polarization direction along the Z-axis do not change their propagation direction after passing through the beam splitter (16), and the two idler beams (18) and the second cascade beam (20) with the propagation direction along the positive X-axis and the polarization direction along the Y-axis have their propagation direction along the negative Y-axis after passing through the beam splitter (16).

3. The device for simultaneously generating dual-frequency terahertz waves according to claim 1, characterized in that: The AFB-KTP crystal (11), the first APPLN crystal (12), and the second APPLN crystal (13) are all cuboids, rectangular in the XY plane, with the length direction of the crystal aligned with the positive X-axis. The optical axis of the first APPLN crystal (12) is along the Z-axis, and the optical axis of the second APPLN crystal (13) is along the Y-axis. The AFB-KTP crystal (11) is a KTP crystal without adhesive bonding. The first APPLN crystal (12) and the second APPLN crystal (13) are both aperiodic polarized crystals. The aperiodic polarization distribution of the first APPLN crystal (12) gradually equals zero along the crystal length from the first-order Stokes difference frequency to the nth-order Stokes difference frequency. The nth-order Stokes difference frequency is... Any order within the range of greater than the first order and less than {(frequency of the first pump light - 60THz) / frequency of the first terahertz wave (21)}; the phase mismatch of the non-periodic polarization distribution of the second APPLN crystal (13) along the crystal length from the first order Stokes difference frequency to the m order Stokes difference frequency is equal to 0 step by step, and the m order is any order within the range of greater than the first order and less than {(frequency of the first pump light - 60THz) / frequency of the second terahertz wave (22)}; wherein, the two difference frequency beams contained in the first order Stokes difference frequency corresponding to the first APPLN crystal (12) are two signal beams (17), and the two difference frequency beams contained in the first order Stokes difference frequency corresponding to the second APPLN crystal (13) are two idler beams (18).

4. The device for simultaneously generating dual-frequency terahertz waves according to claim 1, characterized in that: The first parabolic mirror (14) has a small hole in the center that allows only two signal beams (17) and the first set of cascaded beams (19) to pass through. The second parabolic mirror (15) has a small hole in the center that allows only two idler beams (18) and the second set of cascaded beams (20) to pass through. The second mirror (4) transmits the pump light (2).

5. The device for simultaneously generating dual-frequency terahertz waves according to claim 1, characterized in that: The first group of cascaded light (19) and the second group of cascaded light (20) are mixed light composed of each group of cascaded light; the frequency difference between adjacent cascaded light in the first group of cascaded light (19) is the frequency difference between the two signal light beams (17); the frequency difference between adjacent cascaded light in the second group of cascaded light (20) is the frequency difference between the two idler light beams (18).

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