A tunable dual-frequency terahertz wave radiation source

Abstract

The application aims to provide a tunable dual-frequency terahertz wave radiation source, comprising a pump source, an AFB-KTP crystal, a first APPLN crystal, a second APPLN crystal, a polarizer, a first parabolic mirror, a second parabolic mirror, a first mirror constituting a resonant cavity, a second mirror, and a beamsplitter; the terahertz wave intensity can be enhanced, and the terahertz wave energy conversion efficiency can be improved. The characteristics of the AFB-KTP crystal for generating a pair of signal lights and a pair of idler lights can be used to simultaneously generate two terahertz waves with different frequencies.

Description

Technical Field

[0001] This invention belongs to the field of terahertz wave application technology, specifically relating to a tunable dual-frequency terahertz wave radiation source. 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 THz range, lie between millimeter waves and infrared radiation in the electromagnetic spectrum, representing a transitional region between photonics and electronics, and between macroscopic and microscopic theories. Their unique position makes them of significant scientific research value and have 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) Communication field

[0006] THz communication technology features seamless data transmission, unlimited bandwidth, microsecond latency, and ultra-fast download speeds, which will revolutionize the field of communication and change how people exchange and access information. In space communication, unlike the limited atmospheric penetration of THz waves on the ground, propagation in atmospheric-free environments is not affected by atmospheric attenuation.

[0007] (3) National defense and military

[0008] Because terahertz radiation is more directional than microwaves, it can be used to create radar with high spatial resolution and can provide accurate positioning information in sandstorm or smoky environments.

[0009] (4) Non-destructive testing field

[0010] The penetrating power of THz waves makes them well-suited for non-destructive testing and THz imaging. THz time-domain spectroscopy allows for the penetration of non-polar dielectric materials such as clothing, cardboard boxes, and plastics under non-contact and non-destructive conditions. Therefore, it can not only detect the chemical properties of the medium but also determine the outline and shape of objects.

[0011] (5) Security inspection

[0012] The fingerprint characteristics of terahertz spectroscopy can be used to detect drugs, explosives, and other dangerous goods hidden on terrorists, and can be carried out over long distances, without contact, and covertly. Summary of the Invention

[0013] The purpose of this invention is to provide a tunable dual-frequency terahertz wave radiation source that can enhance the intensity of terahertz waves and improve the energy conversion efficiency of terahertz waves.

[0014] The object of the present invention is achieved in the following manner: a tunable dual-frequency terahertz wave radiation source, comprising a pump source, an AFB-KTP crystal, a first APPLN crystal, a second APPLN crystal, a polarizer, a first parabolic mirror, a second parabolic mirror, a first reflecting mirror, a second reflecting mirror, and a beam splitter constituting a resonant cavity;

[0015] Pump light emitted from the pump source is incident on the AFB-KTP crystal through the first reflector to generate first mixed light, which includes two idler beams and two signal beams. The signal beams oscillate and are amplified in the resonant cavity formed by the first and second reflectors and are output from the second reflector. The pump light and the two idler beams are transmitted and output from the second reflector. The pump light, signal beams, and idler beams output from the second reflector form the second mixed light. The second mixed light is split into pump light and third mixed light by a beam splitter. The pump light is reflected and output by the beam splitter, and the third mixed light is transmitted and output from the beam splitter. The third mixed light is split into two paths by a polarizer, namely two signal beams λ. s1 , λ s2 and two beams of idle frequency light λ i1 , λ i2 ;Signal light λ s1 , λ s2 An incident light from the first APPLN crystal generates a first terahertz wave and a first cascaded optical wave through cascaded difference frequency modulation. The first terahertz wave is output through the first parabolic mirror, and the first cascaded optical wave is transmitted out from the first parabolic mirror; the idler light λ... i1 , λ i2 After total internal reflection by a plane mirror, the light is incident on the second APPLN crystal, and a second terahertz wave and a second cascaded light wave are generated through cascaded difference frequency. The second terahertz wave is output through the second parabolic mirror; the second cascaded light wave is transmitted out from the second parabolic mirror.

[0016] 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 emitted from the pump source is the positive X-axis; the propagation directions of the first, second, and third mixer beams are also the positive X-axis; the idler beam λ... i1 , λ i2The initial propagation direction and the direction of incident on the second APPLN crystal are both positive along the X-axis, and the signal light λ s1 , λ s2 The propagation direction of the first terahertz wave is the positive direction of the X-axis, the propagation direction of the second terahertz wave is the positive direction of the Y-axis, and the propagation direction of the first cascaded light wave is the negative direction of the Y-axis; the propagation direction of the first cascaded light wave and the second cascaded light wave is the positive direction of the X-axis.

[0017] The pump source is a pulsed laser, and the polarization direction of the emitted pump light is parallel to the Y-axis; the signal light λ s1 , λ s2 The polarization direction is parallel to the Z-axis, and the idler frequency λ i1 , λ i2 Its polarization direction is parallel to the Y-axis.

[0018] Both the first and second reflecting mirrors are concave lenses; the first reflecting mirror focuses on the idler frequency light λ. i1 , λ i2 and signal light λ s1 , λ s2 High reflectivity, high transmission of pump light; the second mirror reflects the signal light λ. s1 , λ s2 Partial transmission, for pump light and idler light λ i1 , λ i2 High transmission; the beam splitter is a plane mirror, which highly reflects the pump light and highly reflects the idler light. i1 , λ i2 and signal light λ s1 , λ s2 High transmittance.

[0019] The first reflecting mirror targets the idler light λ. i1 , λ i2 and signal light λ s1 , λ s2 The reflectivity of the first mirror is 0.99, and the transmittance for the pump light is 0.99; the second mirror transmits the signal light λ. s1 , λ s2 Its transmittance is 0.5, which is suitable for both pump light and idler light λ. i1 , λ i2 The transmittance is 0.99; the reflectance of the beam splitter for the pump light is 0.99, and for the idler light λ... i1 , λ i2 and signal light λ s1 , λ s2 Its transmittance is 0.99.

[0020] The AFB-KTP crystal, the first APPLN crystal, and the second APPLN crystal are all cuboids, which are rectangular in the XY plane, and the length direction of the crystal is consistent with the positive X-axis. The AFB-KTP crystal is a KTP crystal without adhesive bonding. The optical axis of the first APPLN crystal is parallel to the Z-axis, and the optical axis of the second APPLN crystal is parallel to the Y-axis.

[0021] The frequency difference between adjacent order optical waves of the first cascaded optical wave, the frequency of the first terahertz wave, and the signal light λ s1 , λ s2 The frequency differences of the three are equal; the frequency difference between adjacent order light waves in the second cascade, the frequency of the second terahertz wave, and the idler frequency λ i1 , λ i2 The frequency difference among the three is equal.

[0022] The polarization period distribution of the first APPLN crystal satisfies the following conditions: from the first-order Stokes cascaded difference frequency to the M-order, where M is greater than the first order and less than the order {(frequency of pump light 2 - 60 THz) / frequency of the first terahertz wave}, and the phase mismatch of the Stokes cascaded difference frequency equals 0 step by step along the crystal length. The polarization period distribution of the second APPLN crystal satisfies the following conditions: from the first-order Stokes cascaded difference frequency to the N-order, where N is greater than the first order and less than the order {(frequency of pump light - 60 THz) / frequency of the second terahertz wave}, and the phase mismatch of the Stokes cascaded difference frequency equals 0 step by step along the crystal length.

[0023] Compared with existing technologies, the tunable dual-frequency terahertz wave radiation source provided by this invention has the following advantages over existing terahertz radiation sources based on optical difference frequency effects:

[0024] (1) By utilizing the characteristics of AFB-KTP crystal to generate a pair of signal lights and a pair of idler lights, two terahertz waves of different frequencies can be generated simultaneously. By changing the polarization period of AFB-KTP crystal, the wavelengths of the idler light and the signal light can be changed, thereby changing the frequencies of the first terahertz wave and the second terahertz wave.

[0025] (2) By setting the reflectivity of the cavity mirror, the signal light is amplified by oscillation within the cavity.

[0026] (3) By setting the first and second APPLN polarization cycles, energy is transferred to the higher-order Stokes region, thereby improving the terahertz wave conversion efficiency. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the present invention.

[0028] Figure 2This refers to the wavelength output characteristics of the signal light and idler light as a function of the KTP polarization period when the pump light wavelength is 532 nm.

[0029] Figure 3 The graph shows the variation of the polarization period of the first and second APPLN crystals with their respective crystal lengths.

[0030] Figure 4 The graph shows the intensity of the first and second terahertz waves as a function of the lengths of the first and second APPLN crystals, respectively. Detailed Implementation

[0031] The present invention will now be described in detail with reference to specific embodiments. It should be noted that these embodiments are only used to further illustrate 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 above description of the present invention.

[0032] As attached Figure 1 As shown, a tunable dual-frequency terahertz wave radiation source is characterized by comprising: a pump source 1, an AFB-KTP crystal 5, a first APPLN crystal 13, a second APPLN crystal 14, a polarizer 10, a first parabolic mirror 19, a second parabolic mirror 20, a first reflecting mirror 3 constituting a resonant cavity, a second reflecting mirror 4, and a beam splitter 7 for reflecting the pump wave 2.

[0033] Pump light 2 emitted from pump source 1 is incident on AFB-KTP crystal 5 through first reflector 3 to generate first mixing light 6, which contains two idler beams and two signal beams.

[0034] The signal light oscillates and amplifies in the resonant cavity formed by the first reflecting mirror 3 and the second reflecting mirror 4, and is output from the second reflecting mirror 4. The pump light 2 and two idler beams are transmitted and output from the second reflecting mirror 4. The pump light 2, signal light, and idler beams output from the second reflecting mirror 4 form the second mixed light 8. The second mixed light 8 is split into pump light 2 and third mixed light 9 by the beam splitter 7. Pump light 2 is reflected and output by the beam splitter 7, and third mixed light 9 is transmitted and output by the beam splitter 7. The third mixed light 9 is split into two paths by the polarizer 10, which are two signal beams. 12 and two idle frequency beams 11. Signal light λ s1 , λ s2 12 is incident on the first APPLN crystal 13, generating a first terahertz wave 15 and a first cascaded optical wave 17 through cascaded difference frequency generation. The first cascaded optical wave 17 is transmitted through the first parabolic mirror 19, and the first terahertz wave 15 is output through the first parabolic mirror 19. Idle light After total internal reflection by plane mirror 21, light 11 is incident on the second APPLN crystal 14, and after cascaded difference frequency generation, a second terahertz wave 16 and a second cascaded light wave 18 are generated. The second terahertz wave 16 is output through the second parabolic mirror 20, and the second cascaded light wave 18 is transmitted out from the second parabolic mirror 20.

[0035] 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 pump light 2 emitted from pump source 1 is the positive X-axis direction. The propagation directions of the first mixer light 6, the second mixer light 8, and the third mixer light 9 are all in the positive X-axis direction. Idle light... The initial propagation direction of 11 and the direction of incident on the second APPLN crystal 14 are both positive along the X-axis, and the signal light... The propagation direction of wave 12 is in the positive X-axis direction, the propagation direction of the first terahertz wave 15 is in the positive Y-axis direction, and the propagation direction of the second terahertz wave 16 is in the negative Y-axis direction. The propagation direction of the first cascaded light wave 17 and the second cascaded light wave 18 is in the positive X-axis direction.

[0036] In this embodiment, the first pump source 1 is a pulsed laser with a wavelength of 532 nm and a power density of 1500 MW / cm². 2 The repetition frequency is 10 Hz, the beam diameter is 2 mm, and the pulse width is 15 ns. The polarization direction of the emitted pump light 2 is parallel to the Y-axis. Signal light... The polarization direction of 12 is parallel to the Z-axis, and the idler light... The polarization direction of 11 is parallel to the Y-axis. At this time, the signal light (Signal2) and the idler light... (Idler2) Wavelength output characteristics as a function of KTP polarization period are as follows: Figure 2 As shown.

[0037] In this embodiment, both the first reflecting mirror 3 and the second reflecting mirror 4 are concave lenses. The first reflecting mirror 3 focuses on intermittent light. 11 and signal light Mirror 12 has high reflectivity (0.99) and high transmittance (0.99) for pump light 2. Mirror 4 is for signal light. The transmittance of 12 is 0.5, which is relevant to both pump light 2 and idler light. 11 has high transmission, with a transmittance of 0.99. Beam splitter 7 is a plane mirror, highly reflective of pump light 2, with a reflectance of 0.99, and for idler light... 11 and signal light 12 High transmittance, with a transmittance of 0.99.

[0038] In this embodiment, the AFB-KTP crystal 5, the first APPLN crystal 13, and the second APPLN crystal 14 are all cuboids, rectangular in the XY plane, with their length direction aligned with the positive X-axis. The AFB-KTP crystal 5 is a KTP crystal bonded without adhesive. The dimensions of the AFB-KTP crystal 7 (X×Y×Z) are 45mm×6mm×5mm, the dimensions of the first APPLN crystal 13 (X×Y×Z) are 5mm×2mm×2mm, and the dimensions of the second APPLN crystal 14 (X×Y×Z) are 5mm×2mm×2mm. The optical axis of the first APPLN crystal 13 is parallel to the Z-axis, and the optical axis of the second APPLN crystal 14 is parallel to the Y-axis. The polarization periods of the first and second APPLN crystals change with their respective crystal lengths as follows: Figure 3 As shown.

[0039] In this embodiment, the first parabolic mirror 19 and the second parabolic mirror 20 have small holes at their centers that allow only the first cascaded light wave 21 and the second cascaded light wave 22 to pass through. The diameter of the small holes is 2mm.

[0040] In this embodiment, the polarization period of the AFB-KTP crystal 5 is 6087 μm, and the wavelengths of the signal light 12 are 1.0874 μm and 1.0913 μm, respectively, and the idler light... The wavelengths of 11 are 1.0416 μm and 1.0381 μm, respectively. Idle frequency light. 11 and signal light The power densities of 12 are 95 MW / cm². 2 86 MW / cm 2 151 MW / cm 2 132MW / cm 2 The frequency difference between adjacent order light waves of the first cascaded light wave 17, the frequency of the first terahertz wave 15, and the signal light. The frequency differences of the three waves are equal, all being 1.0 THz. The frequency differences of the adjacent waves of the second cascaded light wave 18, the frequency of the second terahertz wave 16, and the frequency difference of the idler light 11 are all equal, all being 0.97 THz.

[0041] The polarization period distribution of the first APPLN crystal 13 satisfies the following conditions: from the first-order Stokes cascaded difference frequency to the M-order, where the range of M is greater than the first order and less than the order {(frequency of pump light 2 - 60 THz) / frequency of the first terahertz wave}, and the phase mismatch of the Stokes cascaded difference frequency equals 0 step by step along the crystal length. The polarization period distribution of the second APPLN crystal 14 satisfies the following conditions: from the first-order Stokes cascaded difference frequency to the N-order, where the N-order is greater than the first order and less than the order {(frequency of pump light 2 - 60 THz) / frequency of the second terahertz wave}, and the phase mismatch of the Stokes cascaded difference frequency equals 0 step by step along the crystal length.

[0042] At this point, the intensities of the first terahertz wave and the second terahertz wave change with the lengths of the first APPLN crystal and the second APPLN crystal, respectively, as follows: Figure 4 As shown.

[0043] Specifically, in this embodiment, the polarization period distribution of the first APPLN crystal 13 satisfies the phase mismatch from the 1st-order Stokes cascaded difference frequency to the 200th-order Stokes cascaded difference frequency gradually equaling 0 along the crystal length, and the polarization period distribution of the second APPLN crystal 14 satisfies the phase mismatch from the 1st-order Stokes cascaded difference frequency to the 150th-order Stokes cascaded difference frequency gradually equaling 0 along the crystal length. Since the lengths of the first and second APPLN crystals are both 5 mm, the intensity of the first terahertz wave is 2.83 MW / cm². 2 The intensity of the second terahertz wave was 0.91 MW / cm. 2 (The intensity of the first and second terahertz waves generated here refers to...) Figure 4 The intensity corresponding to the highest point in the curve.

[0044] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. It should be noted that for those skilled in the art and any person skilled in the art, any equivalent substitutions or changes made to the technical solution and inventive concept of the present invention without departing from the overall concept of the present invention, as well as any changes and improvements made, should also be considered within the scope of protection of the present invention.

Claims

1. A tunable dual-frequency terahertz wave radiation source, characterized in that: Includes a pump source (1), an AFB-KTP crystal (5), a first APPLN crystal (13), a second APPLN crystal (14), a polarizer (10), a first parabolic mirror (19), a second parabolic mirror (20), a first reflecting mirror (3), a second reflecting mirror (4), and a beam splitter (7) that form the resonant cavity. Pump light (2) emitted from pump source (1) is incident on AFB-KTP crystal (5) through first reflector (3) to generate first mixed light (6). The first mixed light (6) contains two idler beams and two signal beams. The signal beams oscillate and amplify in the resonant cavity formed by the first reflector (3) and the second reflector (4) and are output from the second reflector (4). Pump light (2) and two idler beams are transmitted and output from the second reflector (4). Pump light (2), signal beams and idler beams output from the second reflector (4) form second mixed light (8). Second mixed light (8) is split into pump light (2) and third mixed light (9) by beam splitter (7). Pump light (2) is reflected and output by beam splitter (7). Third mixed light (9) is transmitted and output by beam splitter (7). Third mixed light (9) is split into two paths by polarizer (10), namely two signal beams λ. s1 , λ s2 (12) and two idler beams λ i1 , λ i2 (11); Signal light λ s1 , λ s2 (12) An incident first APPLN crystal (13) generates a first terahertz wave (15) and a first cascaded light wave (17) through cascaded difference frequency generation. The first terahertz wave (15) is output through the first parabolic mirror (19), and the first cascaded light wave (17) is transmitted out from the first parabolic mirror (19); the idler light λ i1 , λ i2 (11) After total internal reflection by the plane mirror (21), the light is incident on the second APPLN crystal (14), and a second terahertz wave (16) and a second cascaded light wave (18) are generated by cascaded difference frequency. The second terahertz wave (16) is output through the second parabolic mirror (20); the second cascaded light wave (18) is transmitted out from the second parabolic mirror (20). The plane in which the beam propagates is defined by the X and Y axes, 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 direction; the propagation directions of the first mixing light (6), the second mixing light (8), and the third mixing light (9) are the positive X-axis direction; the idler light λ i1 , λ i2 The initial propagation direction of (11) and the direction of incident on the second APPLN crystal (14) are the positive X-axis, and the signal light λ s1 , λ s2 (12) propagates in the positive direction of the X-axis, the first terahertz wave (15) propagates in the positive direction of the Y-axis, the second terahertz wave (16) propagates in the negative direction of the Y-axis; the first cascaded light wave (17) and the second cascaded light wave (18) propagate in the positive direction of the X-axis.

2. The tunable dual-frequency terahertz wave radiation source according to claim 1, characterized in that: The pump source (1) is a pulsed laser, and the polarization direction of the emitted pump light (2) is parallel to the Y-axis; the signal light λ s1 , λ s2 (12) The polarization direction is parallel to the Z-axis, and the idler light λ i1 , λ i2 (11) has a polarization direction parallel to the Y-axis.

3. The tunable dual-frequency terahertz wave radiation source according to claim 1, characterized in that: Both the first reflecting mirror (3) and the second reflecting mirror (4) are concave lenses; the first reflecting mirror (3) focuses on the idler frequency light λ. i1 , λ i2 (11) and signal light λ s1 , λ s2 (12) High reflectivity, high transmission of pump light (2); second mirror (4) for signal light λ s1 , λ s2 (12) Partial transmission, for pump light (2) and idler light λ i1 , λ i2 (11) High transmission; the beam splitter (7) is a plane mirror, which has high reflection of the pump light (2) and low reflection of the idler light λ. i1 , λ i2 (11) and signal light λ s1 , λ s2 (12) High transmission.

4. The tunable dual-frequency terahertz wave radiation source according to claim 3, characterized in that: The first reflecting mirror (3) targets the idler light λ. i1 , λ i2 (11) and signal light λ s1 , λ s2 (12) has a reflectivity of 0.99 and a transmittance of 0.99 for pump light (2); the second mirror (4) transmits 0.99 for signal light λ. s1 , λ s2 (12) has a transmittance of 0.5, which is significant for both pump light (2) and idler light λ. i1 , λ i2 The transmittance of (11) is 0.99; the reflectance of the beam splitter (7) for the pump light (2) is 0.99, and for the idler light λ i1 , λ i2 (11) and signal light λ s1 , λ s2 (12) has a transmittance of 0.

99.

5. The tunable dual-frequency terahertz wave radiation source according to claim 1, characterized in that: The AFB-KTP crystal (5), the first APPLN crystal (13), and the second APPLN crystal (14) are all cuboids, which are rectangular in the XY plane. The length direction of the crystal is consistent with the positive X-axis. The AFB-KTP crystal (5) is a KTP crystal without adhesive. The optical axis of the first APPLN crystal (13) is parallel to the Z-axis, and the optical axis of the second APPLN crystal (14) is parallel to the Y-axis.

6. The tunable dual-frequency terahertz wave radiation source according to claim 1, characterized in that: The frequency difference between adjacent order light waves of the first cascaded light wave (17), the frequency of the first terahertz wave (15), and the signal light λ s1 , λ s2 (12) The frequency difference of the three is equal; the frequency difference of the adjacent order light waves of the second cascaded light wave (18), the frequency of the second terahertz wave (16), and the idler light λ i1 , λ i2 (11) The frequency difference of the three is equal.

7. The tunable dual-frequency terahertz wave radiation source according to claim 1, characterized in that: The polarization period distribution of the first APPLN crystal (13) satisfies the following: from the first-order Stokes cascaded difference frequency to the M-order, where the range of M is greater than the first order and less than the order {(frequency of pump light - 60THz) / frequency of the first terahertz wave}, and the phase mismatch of the Stokes cascaded difference frequency is equal to 0 step by step along the crystal length. The polarization period distribution of the second APPLN crystal (14) satisfies the following: from the first-order Stokes cascaded difference frequency to the N-order, where the N-order is greater than the first order and less than the order {(frequency of pump light - 60THz) / frequency of the second terahertz wave}, and the phase mismatch of the Stokes cascaded difference frequency is equal to 0 step by step along the crystal length.

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