Terahertz laser based on free space Brillouin laser driving

Abstract

The invention discloses a terahertz laser based on free space Brillouin laser driving, and relates to the technical field of terahertz band lasers. The laser comprises a first pumping source, a first electro-optical modulation module, a first main oscillator power amplifier, a first 45-degree beam combiner, a first optical isolator, a first telescope assembly, a first half-wave plate, a free space Brillouin annular cavity, a second photoelectric detector, a first feedback control system and a first photoelectric detector. A second main oscillator power amplifier, a second electro-optical modulation module, a second pumping source, a second feedback control system, a first 45-degree reflector, a polarization control system and a difference frequency crystal; the characteristic that low-noise single-frequency laser can be achieved through Brillouin scattering is utilized, a space Brillouin laser structure is adopted, high-power and low-noise-level pump light in the difference frequency conversion process is obtained, and high-power and low-noise difference frequency conversion terahertz output is achieved. According to the invention, the output power and the signal purity of the terahertz laser are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of terahertz laser technology, and more specifically to a terahertz laser driven by a free-space Brillouin laser. Background Technology

[0002] Terahertz (THz) light sources have broad application prospects in fields such as medical imaging, biosensing, agricultural detection, materials characterization, security inspection, broadband communication, and astronomical observation. They exhibit irreplaceable strategic value, particularly in cutting-edge areas such as high-speed wireless communication, precision spectroscopy, coherent imaging, deep space exploration, and strong-field nonlinear physics. Traditional difference-frequency technology refers to using a higher-frequency pump light ω... p and lower frequency signal light ω s Simultaneously incident on a nonlinear crystal, the frequency ω is generated using the second-order nonlinear effect of the nonlinear crystal. i =ω p -ω s The difference frequency light needs to meet certain phase matching conditions during the process.

[0003] However, existing terahertz wave generation technologies, such as optoelectronic mixing, quantum cascade lasers, optical rectification, and traditional difference frequency methods, generally face inherent performance bottlenecks such as limited output power, high phase noise, and insufficient frequency stability, making it difficult to simultaneously meet the comprehensive requirements of high power, low noise, and wideband tunability. In contrast, Brillouin lasers based on stimulated Brillouin scattering (SBS) exhibit unique advantages in achieving ultra-narrow linewidth and ultra-low phase noise. Terahertz lasers driven by on-chip waveguide Brillouin lasers possess ultra-low phase noise and tunable output wavelength, which significantly improves the overall quality of terahertz light sources in terms of spectral purity, frequency stability, and coherence performance, providing an ideal light source foundation for applications such as high-resolution imaging and precision metrology.

[0004] Currently, although waveguide-type Brillouin lasers can easily achieve Brillouin laser output with low threshold and narrow linewidth, they still have significant limitations in terms of structural scale and power expansion: their cavity modes are extremely small and have extremely high precision, resulting in output power that is usually limited to the microwatt to milliwatt range, and the cascaded SBS process is difficult to control effectively; in addition, the waveguide material system has inherent limitations on the operating wavelength, and the fiber structure may introduce spontaneous emission noise, further reducing the signal-to-noise ratio; at the same time, the complex nanofabrication process also restricts its expansion and integration under higher power and wider frequency band conditions. Summary of the Invention

[0005] To address or mitigate one or more of the aforementioned problems, this invention proposes a terahertz laser driven by a free-space Brillouin laser.

[0006] A terahertz laser driven by a free-space Brillouin laser includes: a first pump source, a first electro-optic modulation module, a first master oscillator power amplifier, a first 45° beam combiner, a first optical isolator, a first telescope assembly, a first half-wave plate, a free-space Brillouin ring cavity, a second photodetector, a first feedback control system, a second master oscillator power amplifier, a second electro-optic modulation module, a second pump source, a second feedback control system, a first 45° reflector, a polarization control system, and a difference frequency crystal;

[0007] The working process of the terahertz laser is as follows:

[0008] The first pump source emits the first frequency. The pump light enters the first electro-optic modulation module for electro-optic phase modulation to obtain a first pump light signal with a sideband period equal to the modulation frequency; then, the first pump light signal enters the first master oscillator power amplifier for power amplification; then, the power-amplified light signal enters the first 45° beam combiner.

[0009] The frequency-adjustable second pump source emits a third frequency. The pump light enters the second electro-optic modulation module for electro-optic phase modulation to obtain a second pump light signal with a sideband period equal to the modulation frequency; then, the second pump light signal enters the second master oscillator power amplifier for power amplification; then, the power-amplified light signal enters the first 45° beam combiner.

[0010] The first 45° beam combiner combines the two amplified light signals. The combined beam enters the first optical isolator, then the first telescope assembly for beam aperture adjustment and collimation, then the first half-wave plate for polarization adjustment; finally, it enters the free-space Brillouin ring cavity to generate the second frequency. First-order Stokes light and fourth frequency The first-order Stokes beam returns and sequentially enters the first half-wave plate, the first telescope assembly, and the first optical isolator, then is output in reverse to the first 45° reflector. The first 45° reflector reflects the beam into the polarization control system to adjust the polarization mode of the two first-order Stokes beams. The terahertz laser is then output through the difference frequency crystal.

[0011] Corresponding to the first frequency The pump light signal is transmitted through the free space Brillouin ring cavity into the first photodetector, and then enters the first feedback control system to be mixed with the first pump light signal output by the first electro-optic modulation module to generate a first error signal that is fed back to the first pump source to adjust the wavelength of the pump light output by the first pump source.

[0012] Corresponding to the third frequency The pump light signal is transmitted through the free-space Brillouin ring cavity into the second photodetector, and then enters the second feedback control system to be mixed with the second pump light signal output by the second electro-optic modulation module to generate a second error signal that is fed back to the second pump source to adjust the wavelength of the pump light output by the second pump source.

[0013] Furthermore, the free-space Brillouin annular cavity includes a first planar mirror, a second planar mirror, a first plano-concave mirror, a Brillouin crystal, and a second plano-concave mirror; the pump light signal corresponding to the first frequency λ1 is transmitted through the second planar mirror of the free-space Brillouin annular cavity into the second photodetector, and the pump light signal corresponding to the third frequency λ3 is transmitted through the first plano-concave mirror of the free-space Brillouin annular cavity into the first photodetector.

[0014] Furthermore, the first frequency Second frequency The following Brillouin frequency shift relationship is satisfied:

[0015] ;

[0016] Third frequency and the fourth frequency The following Brillouin frequency shift relationship is satisfied:

[0017] ;

[0018] Where n is the refractive index of the Brillouin crystal, Let c be the speed of sound propagating within a Brillouin crystal, and c be the speed of light. =180°.

[0019] Furthermore, the formula for calculating the resonant cavity length L of the terahertz laser is as follows:

[0020] and ;

[0021] in, This indicates the distance light travels within a Brillouin crystal; This represents the distance between the first and second plane mirrors; This represents the distance between the second plane mirror and the first plano-concave mirror; This represents the distance between the first plano-concave mirror and the Brillouin crystal; This represents the distance between the Brillouin crystal and the second plano-concave mirror. This represents the distance between the second plano-concave mirror and the first planar mirror; i and j are both integers.

[0022] Further, the polarization control system includes a first 45° beam splitter, a second half-wave plate, a second 45° beam combiner, a second 45° reflecting mirror, a third half-wave plate, and a third 45° reflecting mirror; wherein, the first 45° beam splitter separates the first-order Stokes light of the second frequency λ2 from the first-order Stokes light of the fourth frequency λ4, and the first-order Stokes light of the second frequency λ2, after passing through, undergoes polarization state adjustment by the second half-wave plate, adjusting it to the polarization state of the e-light or o-light corresponding to the difference-frequency crystal; the second... The first-order Stokes beam with frequency λ2 and the first-order Stokes beam with frequency λ4 are combined by the second 45° beam combiner and output to the second 45° reflector. The first-order Stokes beam with frequency λ4 is then reflected by the second 45° reflector and polarized by the third half-wave plate to be adjusted to the polarization state of the o-light or e-light of the corresponding difference frequency crystal. After being reflected by the third 45° reflector, the first-order Stokes beam with frequency λ2 and the first-order Stokes beam with frequency λ4 are obtained after polarization adjustment.

[0023] Furthermore, one side of the first 45° beam combiner is coated with a coating for the first frequency. The anti-reflection coating for the pump light, with a coating for the third frequency deposited on the other side. A total reflection coating for the pump light; the first 45° reflector is coated with a coating for the second frequency. First-order Stokes light and fourth frequency Total reflection film for first-order Stokes light.

[0024] Furthermore, the difference frequency crystal comprises LiNbO3 or GaP, GaSe; the Brillouin crystal comprises diamond.

[0025] Furthermore, the free spectral range (FSR) of the resonant cavity of the terahertz laser satisfies the following condition:

[0026] ;

[0027] ;

[0028] In the formula, the ordinal number of the cavity mode closest to the gain center frequency. The ordinal number of the cavity mode closest to the gain center frequency They are respectively: , First Brillouin frequency shift Second Brillouin frequency shift ; This represents the Brillouin gain bandwidth.

[0029] Furthermore, the first frequency Pump light and third frequency The frequency difference of the pump light is an integer multiple of the free spectral range FSR.

[0030] The beneficial technical effects of this invention are:

[0031] In this invention, the two pump beams required for the difference frequency technology are obtained through a dual-pumped common-cavity Brillouin laser. Through stimulated Brillouin scattering and optical injection locking, two highly correlated, ultra-narrow linewidth, ultra-low phase noise, and frequency difference-tunable laser outputs can be generated in the same cavity. The frequency difference directly determines the terahertz output band, achieving wide-range continuous tunability. Its common-cavity structure and optical injection locking mechanism ensure long-term mode-hopping-free operation, avoiding the bandwidth limitations and servo peak introduction problems of traditional electronic phase-locked loops, and significantly improving frequency stability and signal purity.

[0032] This invention is the first to adopt a free-space stimulated Brillouin scattering laser-driven terahertz output scheme. Compared with traditional waveguide structure Brillouin lasers, it offers greater design flexibility, more efficient thermal management, and the ability to select different materials such as diamond and fused silica as Brillouin media, resulting in a wider applicable wavelength range and stronger high-power carrying capacity. Attached Figure Description

[0033] The above and other objects, features, and advantages of exemplary embodiments of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings. Several embodiments of the invention are illustrated in the drawings by way of example and not limitation, wherein:

[0034] Figure 1 This is a schematic diagram of the structure of a terahertz laser driven by a free-space Brillouin laser, as described in this invention.

[0035] Figure 2 This is a schematic diagram of the free-space Brillouin annular cavity in this invention;

[0036] Figure 3 This is a schematic diagram illustrating the gain and cavity length matching of the pump light and Stokes light dual resonators under single-wavelength pumping in this invention.

[0037] Figure 4 This is a schematic diagram of the polarization control system in this invention;

[0038] Figure 5 This is a schematic diagram showing the matching of the four-wavelength resonant gain and cavity length of the pump light and Stokes light under dual-wavelength pumping in this invention;

[0039] Figure 6 This is a simulation diagram of the angle matching relationship calculation in the difference frequency process of this invention. Detailed Implementation

[0040] The principles and spirit of the invention will now be described with reference to several exemplary embodiments. It should be understood that these embodiments are given merely to enable those skilled in the art to better understand and implement the invention, and are not intended to limit the scope of the invention in any way. Rather, these embodiments are provided to make this disclosure more thorough and complete, and to fully convey the scope of this disclosure to those skilled in the art.

[0041] To address the problems of low output power and high noise levels in existing terahertz light sources, this invention provides a terahertz laser driven by a free-space Brillouin laser. Specifically, it utilizes a free-space dual-pumped common-cavity Brillouin laser to achieve high-correlation, low-noise, and high-power single-frequency Brillouin laser output, and then achieves high-power, low-noise terahertz output through difference-frequency conversion. This invention combines difference-frequency conversion technology with free-space Brillouin laser technology, employing a dual-pumped free-space Brillouin structure to achieve high-power, frequency-differential-tunable single-frequency narrow-linewidth dual Brillouin laser output. Further external difference-frequency conversion yields high-power, frequency-tunable single-frequency narrow-linewidth terahertz laser output. This invention leverages the structural advantages of free-space laser modes—large volume and superior thermal management—combined with the inherent low-noise and narrow-linewidth characteristics of Brillouin lasers, and introduces frequency-locking technology. Finally, through difference-frequency conversion, high-power, tunable, and low-noise terahertz laser output is achieved. This invention utilizes the characteristics of Brillouin scattering to achieve low-noise, single-frequency lasers, and employs a free-space Brillouin laser structure to achieve high-power output of Brillouin lasers. This enables the pump light in the difference-frequency conversion process to achieve high-power, low-noise levels, thus realizing high-power, low-noise difference-frequency conversion terahertz output.

[0042] This invention proposes a terahertz laser source driven by a free-space Brillouin laser, such as... Figure 1 As shown, the laser includes: a first pump source 1, a first electro-optic modulation module 2, a first master oscillator power amplifier 3, a first 45° beam combiner 4, a first optical isolator 5, a first telescope assembly 6, a first half-wave plate 7, a free-space Brillouin ring cavity 8, a second photodetector 9, a first feedback control system 10, a first photodetector 11, a second master oscillator power amplifier 12, a second electro-optic modulation module 13, a second pump source 14, a second feedback control system 15, a first 45° reflector 16, a polarization control system 17, and a difference frequency crystal 18; the working process of the terahertz laser is as follows:

[0043] The first pump source 1 emits the first frequency. The pump light enters the first electro-optic modulation module 2 for electro-optic phase modulation to obtain a first pump light signal with a sideband period equal to the modulation frequency; then, the first pump light signal enters the first master oscillator power amplifier 3 for power amplification; then, the power-amplified light signal enters the first 45° beam combiner 4.

[0044] The frequency-adjustable second pump source 14 emits a third frequency. The pump light enters the second electro-optic modulation module 13 for electro-optic phase modulation to obtain a second pump light signal with a sideband period equal to the modulation frequency; then, the second pump light signal enters the second master oscillator power amplifier 12 for power amplification; then, the power-amplified light signal enters the first 45° beam combiner 4.

[0045] The first 45° beam combiner 4 combines the two amplified light signals. The combined light enters the first optical isolator 5, then the first telescope assembly 6 for beam aperture adjustment and collimation, then the first half-wave plate 7 to adjust the polarization state; finally, it enters the free-space Brillouin ring cavity 8 to generate the second frequency. First-order Stokes light and fourth frequency The first-order Stokes beam returns and sequentially enters the first half-wave plate 7, the first telescope assembly 6, and the first optical isolator 5, and is output in reverse to the first 45° reflector 16. It is then reflected by the first 45° reflector 16 and enters the polarization control system 17 to adjust the polarization mode of the two first-order Stokes beams. Subsequently, the output of the terahertz laser is realized through the difference frequency crystal 18.

[0046] Corresponding to the first frequency The pump light signal is transmitted through the free space Brillouin ring cavity 8 into the first photodetector 11, and then enters the first feedback control system 10 to be mixed with the first pump light signal output by the first electro-optic modulation module 2 to generate a first error signal that is fed back to the first pump source 1 to adjust the wavelength of the pump light output by the first pump source 1.

[0047] Corresponding to the third frequency The pump light signal is transmitted through the free-space Brillouin ring cavity 8 into the second photodetector 9, and then enters the second feedback control system 15 to be mixed with the second pump light signal output by the second electro-optic modulation module 13 to generate a second error signal that is fed back to the second pump source 14 to adjust the wavelength of the pump light output by the second pump source 14.

[0048] According to an embodiment of the present invention, the first pump source 1 emits a first frequency. The pump light sequentially passes through the first electro-optic modulation module 2, the first master oscillator power amplifier 3, the first 45° beam combiner 4, the first optical isolator 5, the first telescope assembly 6, and the first half-wave plate 7, before entering the free-space Brillouin ring cavity 8 (e.g., composed of the first plane mirror 8-1, the second plane mirror 8-2, the first plano-concave mirror 8-3, the Brillouin crystal 8-4, and the second plano-concave mirror 8-5). Figure 2 (As shown), generating a second frequency. A first-order Stokes beam, which is reverse-output by the first optical isolator 5 to the first 45° reflector 16; wherein the first frequency Second frequency The following Brillouin frequency shift relationship is satisfied:

[0049] ;

[0050] Where n is the refractive index of Brillouin crystal 8-4. Let c be the speed of sound propagating within a Brillouin crystal (8-4), and c be the speed of light. =180°, and the Brillouin frequency shift is typically on the order of GHz.

[0051] The frequency-adjustable second pump source 14 emits a third frequency. The pump light sequentially passes through the second electro-optic modulation module 13, the second master oscillator power amplifier 12, the first 45° beam combiner 4, the first optical isolator 5, the first telescope assembly 6, and the first half-wave plate 7, before entering the free-space Brillouin ring cavity 8 composed of the first plane mirror 8-1, the second plane mirror 8-2, the first plano-concave mirror 8-3, the Brillouin crystal 8-4, and the second plano-concave mirror 8-5, generating the fourth frequency. The first-order Stokes beam, which is reverse-output by the first optical isolator 5 to the first 45° reflector 16; wherein the third frequency and the fourth frequency The following Brillouin frequency shift relationship is satisfied:

[0052] ;

[0053] Among them, the first frequency Pump light and third frequency The pump light frequency difference is adjustable, specifically controlled by a second pump source 14 whose frequency can be tuned over a wide range.

[0054] Second frequency First-order Stokes light and fourth frequency The first-order Stokes light is reflected by the first 45° reflector 16 and enters the polarization control system 17 to adjust the polarization mode of the two first-order Stokes lights. Then, the output of the terahertz laser is realized through the difference frequency crystal 18.

[0055] First frequency The pump light transmitted through the first plano-concave reflector 8-3 enters the first photodetector 11, and then is mixed with the local oscillator signal of the first electro-optic modulation module 2 in the first feedback control system 10 to generate an error signal, which is then fed back to the first pump source 1 to achieve the first frequency. The pump light wavelength is tuned to achieve resonance enhancement matching between the resonant wavelength and the Brillouin cavity length. Similarly, the third frequency... The pump light transmitted through the second plane mirror 8-2 enters the second photodetector 9, and then is mixed with the local oscillator signal of the second electro-optic modulation module 13 in the second feedback control system 15 to generate an error signal, which is then fed back to the second pump source 14 to achieve the third frequency. The pump light wavelength is tuned to achieve resonance enhancement matching between the resonant wavelength and the Brillouin cavity length. At this point, the laser's resonant cavity satisfies... , , , Four waves resonate together.

[0056] The resonance condition of a resonant cavity requires that its length be an integer multiple of the output half-wavelength. Furthermore, to achieve dual resonance, the cavity length... Let i and j be integers, and satisfy the following conditions: , It is the distance that light travels within the Brillouin crystal 8-4 medium. These are the distances between the first plane mirror 8-1 and the second plane mirror 8-2, the distance between the second plane mirror 8-2 and the first plano-concave mirror 8-3, the distance between the first plano-concave mirror 8-3 and the Brillouin crystal 8-4, the distance between the Brillouin crystal 8-4 and the second plano-concave mirror 8-5, and the distance between the second plano-concave mirror 8-5 and the first plane mirror 8-1.

[0057] Brillouin frequency shift during single-wavelength pumping If the Stokes beam cavity mode is required to be in the Brillouin gain region, then the laser's cavity free spectral range (FSR) must satisfy the following condition: ;in It represents the Brillouin gain bandwidth; N represents the ordinal number of the cavity mode closest to the gain center frequency. The square brackets denote the floor function. The resonant point and cavity length matching relationship of the pump light and Stokes double resonance corresponding to single-wavelength pumping are as follows: Figure 3 As shown.

[0058] In the case of dual-wavelength pumping as described in this invention, the first Brillouin frequency shift Second Brillouin frequency shift At this point, the free spectral range (FSR) of the laser's resonant cavity must satisfy the following condition:

[0059] ;

[0060] ;

[0061] In the formula, the ordinal number of the cavity mode closest to the gain center frequency. The ordinal number of the cavity mode closest to the gain center frequency They are respectively: , .

[0062] Furthermore, the first frequency Pump light and third frequency The frequency difference of the pump light is an integer multiple of the free spectral range FSR, that is, the two frequency differences an integer multiple of FSR : .

[0063] The first pump source 1 is used to generate a first frequency with a narrow linewidth. The pump light; the second pump source 14 is used to generate a third frequency with a narrow linewidth. Pump light. The first optical isolator 5 is used for the first frequency. Pump light and third frequency Unidirectional transmission of pump light and second frequency First-order Stokes light and fourth frequency The output of a first-order Stokes beam. One side of the first 45° beam combiner 4 is coated with a material for the first frequency... The anti-reflection coating for the pump light, with a coating for the third frequency deposited on the other side. A total reflection film for the pump light. The first telescope assembly 6, used for beam aperture adjustment and collimation, is well-known to those skilled in the art and will not be described in detail here. The first half-wave plate 7 is used for adjusting the first frequency. Pump light and third frequency The pump light is polarization-mode tuned to match the maximum gain axis of the Brillouin crystal. A free-space Brillouin ring cavity 8 is used to carry the dual-pumped Brillouin laser generation. A first 45° reflector 16 is coated with a polarization mode for the second frequency. First-order Stokes light and fourth frequency A first-order Stokes light total reflection film.

[0064] like Figure 4As shown, the polarization control system 17 is used to adjust the second frequency. The first-order Stokes light and the fourth frequency are The polarization state of the first-order Stokes light is composed of a first 45° beam splitter 17-1, a second half-wave plate 17-2, a second 45° beam combiner 17-3, a second 45° reflecting mirror 17-4, a third half-wave plate 17-5, and a third 45° reflecting mirror 17-6, which can be used to adjust the second frequency. The first-order Stokes light and the fourth frequency are The polarization mode of the first-order Stokes light is used to achieve phase matching of the corresponding difference frequency. Specifically, the first 45° beam splitter 17-1 separates the first-order Stokes light of the second frequency λ2 from the first-order Stokes light of the fourth frequency λ4. After the first-order Stokes light of the second frequency λ2 passes through, it undergoes polarization state adjustment by the second half-wave plate 17-2, adjusting it to the polarization state of the e-light or o-light corresponding to the difference frequency crystal 18. The first-order Stokes light of the second frequency λ2 and the first-order Stokes light of the fourth frequency λ4, after polarization state adjustment, are combined by the second 45° beam combiner 17-3 and output to the second 45° reflector 17-4. The first-order Stokes light of the fourth frequency λ4 is then reflected by the second 45° reflector 17-4 and polarized by the third half-wave plate 17-5, adjusting it to the polarization state of the o-light or e-light corresponding to the difference frequency crystal 18. Subsequently, it is reflected by the third 45° reflector 17-6 and output, resulting in the first-order Stokes light of the second frequency λ2 and the first-order Stokes light of the fourth frequency λ4 after polarization state adjustment.

[0065] The first 45° beam splitter 17-1 is coated with a second frequency... Antireflection coating for first-order Stokes light, and for fourth frequency Total reflection coating for first-order Stokes light; second 45° beam combiner 17-3 coated with a second frequency... Antireflection coating for first-order Stokes light, and for fourth frequency Total reflection film for first-order Stokes light.

[0066] In this embodiment, the difference frequency crystal 18 can be one of LiNbO3, GaP, GaSe, etc. After determining it, the phase matching angle of the laser and the polarization mode of the pump light need to be calculated to achieve difference frequency conversion at high power output. The Brillouin crystal 8-4 can be made of materials such as fused silica or diamond with a wide transmission spectrum.

[0067] The following uses diamond crystals and GaSe as examples to demonstrate the specific operation.

[0068] Brillouin crystal 8-4 is made of diamond, and its refractive index is... =2.39, length =5mm, first pump source 1 pump light wavelength =1064.2 nm, its excited Brillouin first-order Stokes frequency =1064.5 nm, second pump source 14 pump light wavelength The excitation frequency of the Brillouin first-order Stokes light is tunable in the range of 1065–1075 nm. =1065.3 ~1075.3nm. Under the above conditions, Figure 5 The paper demonstrates the four-wavelength resonant point and cavity length matching relationship under dual-wavelength pumping at 1064nm and 1075nm, with output in the 2.83 terahertz band. Under the above conditions... The diameters of the mirrors are 239 mm, 177 mm, 53 mm, 53 mm, and 177 mm, respectively. The left side of the first plane mirror 8-1 is coated with a high-transmittance film for wavelengths of 1064-1075 nm, and the right side is coated with a dielectric film with 96% reflectivity for wavelengths of 1064-1075 nm. The second plane mirror 8-2, the first plano-concave mirror 8-3, and the second plano-concave mirror 8-5 are coated with a total reflection film for wavelengths of 1064-1075 nm. The radius of curvature of the plano-concave mirror is R=100 mm.

[0069] The corresponding phase-matching interior angle can be calculated using the Sellmier equation for the infrared band of GaSe crystals:

[0070]

[0071]

[0072] in, Represents the ordinary refractive index. Indicates unusual refractive index, Indicates the wavelength of the incident light.

[0073] For anisotropic crystal GaSe, unusual optical refractive index With the angle of incidence The changes are as follows:

[0074] ;

[0075] in, This is the difference frequency output wavelength.

[0076] For oe→e difference frequency phase matching, the effective nonlinear coefficient of the GaSe crystal is:

[0077] ;

[0078] in, Represents the main nonlinear tensor components of GaSe crystals. It is the phase-matching interior angle (i.e., the angle of incidence). It is the azimuth angle.

[0079] when At this time, the effective nonlinear gain of the crystal is maximized. Under the collinear phase-matching condition oe→e, the result of difference frequency calculation using two wavelengths at the near-degenerate point (1064 nm) is as follows: Figure 6 As shown. When the two wavelengths are 1064.5 nm and 1075.3 nm, the wavelength of the difference frequency is 105.99 µm, which satisfies the inner angle of the difference frequency phase matching of the GaSe crystal. The angle is approximately 6.63°, and the corresponding exterior angle is approximately 18.8°. At this point, the differential frequency light can be tuned within the range of 0.21~2.83THz.

[0080] While the spirit and principles of the invention have been described with reference to several specific embodiments, it should be understood that the invention is not limited to the disclosed specific embodiments, and the division of aspects does not imply that features in these aspects cannot be combined for benefit; such division is merely for ease of description. The invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A terahertz laser driven by a free-space Brillouin laser, characterized in that, include: First pump source (1), first electro-optic modulation module (2), first master oscillator power amplifier (3), first 45° beam combiner (4), first optical isolator (5), first telescope assembly (6), first half-wave plate (7), free-space Brillouin ring cavity (8), second photodetector (9), first feedback control system (10), first photodetector (11), second master oscillator power amplifier (12), second electro-optic modulation module (13), second pump source (14), second feedback control system (15), first 45° reflector (16), polarization control system (17), difference frequency crystal (18); The working process of the terahertz laser is as follows: The first pump source (1) emits the first frequency The pump light enters the first electro-optic modulation module (2) for electro-optic phase modulation to obtain a first pump light signal with a sideband period equal to the modulation frequency; then, the first pump light signal enters the first master oscillator power amplifier (3) for power amplification; then, the power-amplified light signal enters the first 45° beam combiner (4). The frequency-adjustable second pump source (14) emits a third frequency. The pump light enters the second electro-optic modulation module (13) for electro-optic phase modulation to obtain a second pump light signal with a sideband period equal to the modulation frequency; Subsequently, the second pump optical signal enters the second master oscillator power amplifier (12) for power amplification; then, the power-amplified optical signal enters the first 45° beam combiner (4). The first 45° beam combiner (4) combines the two amplified light signals. The combined light enters the first optical isolator (5), then the first telescope assembly (6) for beam aperture adjustment and collimation, then the first half-wave plate (7) for polarization adjustment; then it enters the free-space Brillouin ring cavity (8) to generate the second frequency. First-order Stokes light and fourth frequency The first-order Stokes beam returns sequentially to the first half-wave plate (7), the first telescope assembly (6), and the first optical isolator (5), and is output in reverse to the first 45° reflector (16). It is then reflected by the first 45° reflector (16) and enters the polarization control system (17) to adjust the polarization mode of the two first-order Stokes beams. Subsequently, the output of the terahertz laser is realized through the difference frequency crystal (18). Corresponding to the first frequency The pump light signal is transmitted through the free space Brillouin ring cavity (8) into the first photodetector (11), and then enters the first feedback control system (10) to be mixed with the first pump light signal output by the first electro-optic modulation module (2) to generate a first error signal that is fed back to the first pump source (1) to adjust the pump light wavelength output by the first pump source (1). Corresponding to the third frequency The pump light signal is transmitted through the free space Brillouin ring cavity (8) into the second photodetector (9), and then enters the second feedback control system (15) to be mixed with the second pump light signal output by the second electro-optic modulation module (13) to generate a second error signal that is fed back to the second pump source (14) to adjust the wavelength of the pump light output by the second pump source (14).

2. A terahertz laser driven by a free-space Brillouin laser according to claim 1, characterized in that, The free-space Brillouin ring cavity (8) includes a first plane mirror (8-1), a second plane mirror (8-2), a first plano-concave mirror (8-3), a Brillouin crystal (8-4), and a second plano-concave mirror (8-5). The pump light signal corresponding to the first frequency λ1 is transmitted through the second plane mirror (8-2) of the free-space Brillouin ring cavity (8) into the second photodetector (9), and the pump light signal corresponding to the third frequency λ3 is transmitted through the first plano-concave mirror (8-3) of the free-space Brillouin ring cavity (8) into the first photodetector (11).

3. A terahertz laser driven by a free-space Brillouin laser according to claim 2, characterized in that, First frequency Second frequency The following Brillouin frequency shift relationship is satisfied: ； Third frequency and the fourth frequency The following Brillouin frequency shift relationship is satisfied: ； Where n is the refractive index of the Brillouin crystal (8-4), Let c be the speed of sound propagating within the Brillouin crystal (8-4), and c be the speed of light. =180°.

4. A terahertz laser driven by a free-space Brillouin laser according to claim 3, characterized in that, The formula for calculating the resonant cavity length L of the terahertz laser is as follows: and ; in, This represents the distance light travels within the Brillouin crystal (8-4); This represents the distance between the first plane mirror (8-1) and the second plane mirror (8-2); This indicates the distance between the second plane mirror (8-2) and the first plano-concave mirror (8-3); This indicates the distance between the first plano-concave mirror (8-3) and the Brillouin crystal (8-4); This represents the distance between the Brillouin crystal (8-4) and the second plano-concave mirror (8-5); This represents the distance between the second plano-concave mirror (8-5) and the first planar mirror (8-1); i and j are both integers.

5. A terahertz laser driven by a free-space Brillouin laser according to claim 3, characterized in that, The polarization control system (17) includes a first 45° beam splitter (17-1), a second half-wave plate (17-2), a second 45° beam combiner (17-3), a second 45° reflector (17-4), a third half-wave plate (17-5), and a third 45° reflector (17-6); wherein, the first 45° beam splitter (17-1) separates the first-order Stokes light of the second frequency λ2 from the first-order Stokes light of the fourth frequency λ4, and the first-order Stokes light of the second frequency λ2 passes through the second half-wave plate (17-2) for polarization state adjustment, adjusting it to the polarization state of the e-light or o-light corresponding to the difference frequency crystal (18); after polarization... The first-order Stokes beam of the second frequency λ2 after state adjustment and the first-order Stokes beam of the fourth frequency λ4 are combined by the second 45° beam combiner (17-3) and output to the second 45° reflector (17-4). The first-order Stokes beam of the fourth frequency λ4 is then reflected by the second 45° reflector (17-4) and polarized by the third half-wave plate (17-5) to be adjusted to the polarization state of the o-light or e-light of the corresponding difference frequency crystal (18). Then, it is reflected by the third 45° reflector (17-6) and output to obtain the first-order Stokes beam of the second frequency λ2 after polarization state adjustment and the first-order Stokes beam of the fourth frequency λ4 after polarization state adjustment.

6. A terahertz laser driven by a free-space Brillouin laser according to claim 5, characterized in that, The first 45° beam combiner (4) is coated with a coating on one side for the first frequency. The anti-reflection coating for the pump light, with a coating for the third frequency deposited on the other side. Total reflection coating for pump light; the first 45° reflector (16) is coated with a coating for the second frequency. First-order Stokes light and fourth frequency Total reflection film for first-order Stokes light.

7. A terahertz laser driven by a free-space Brillouin laser according to claim 3, characterized in that, The difference frequency crystal (18) includes LiNbO3 or GaP, GaSe; the Brillouin crystal (8-4) includes diamond.

8. A terahertz laser driven by a free-space Brillouin laser according to claim 3, characterized in that, The free spectral range (FSR) of the resonant cavity of the terahertz laser satisfies the following condition: ； ； In the formula, the ordinal number of the cavity mode closest to the gain center frequency. The ordinal number of the cavity mode closest to the gain center frequency They are respectively: , First Brillouin frequency shift Second Brillouin frequency shift ; This represents the Brillouin gain bandwidth.

9. A terahertz laser driven by a free-space Brillouin laser according to claim 8, characterized in that, First frequency Pump light and third frequency The frequency difference of the pump light is an integer multiple of the free spectral range FSR.

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