High-power terahertz difference-frequency resonant radiation source system

Abstract

The present invention discloses a high-power terahertz difference-frequency resonant radiation source system, which relates to the field of terahertz application technology. The key technical solutions include: a 1064nm nanosecond laser, a first near-infrared beam delay line module, a near-infrared optical parametric oscillator, a second near-infrared beam delay line module, a near-infrared polarization-coupled prism, a terahertz diffraction resonant cavity module, a terahertz focusing lens, a terahertz detector, an oscilloscope, a precision motor control system, and a computer. The first near-infrared beam delay line module is located near the emitting end of the 1064nm nanosecond laser, and the second near-infrared beam delay line module is located near the emitting end of the near-infrared optical parametric oscillator. This radiation source system utilizes the significant wavelength difference between near-infrared and terahertz beams. By constructing a pair of diffractive optical elements outside a nonlinear crystal, the transmission behavior characteristics of the terahertz diffracted beam within the cavity are controlled, ultimately achieving terahertz echo resonant amplification.

Description

Technical Field

[0001] The present invention relates to the field of terahertz application technology, and more particularly, to a high-power terahertz difference-frequency resonant radiation source system. Background Art

[0002] Terahertz waves, a bridge between microwaves and infrared, have attracted significant attention due to their unique spectral properties. Terahertz technology, hailed as "one of the ten key technologies that will transform the future world," plays a unique and crucial role in scientific research, the civil economy, and national security.

[0003] After decades of research, especially the rapid development in the past two decades, terahertz science and technology has gradually formed its own unique terahertz ecosystem. Research areas include terahertz radiation sources, new high-sensitivity terahertz detection devices, and terahertz wave transmission functional components. In the future, it will shine in multiple application fields centered on spectral analysis, imaging applications, high-definition communications, and other fields.

[0004] Research on high-power terahertz radiation sources has always been the core and foundation of terahertz application technology. Together with highly sensitive terahertz detectors, these sources constrain the scope and application limits of terahertz application technology. However, terahertz radiation sources derived from microwave electronics frequency doubling chain technology still have weak radiation power in the high terahertz frequency band, failing to meet the requirements of practical application systems. On the other hand, terahertz radiation sources generated by nonlinear optical frequency conversion generally exhibit broadband radiation characteristics and high power levels in the high terahertz frequency band, potentially meeting the needs of practical applications. A typical example of this success is the terahertz time-domain spectrometer system that meets the needs of spectral application analysis.

[0005] However, because terahertz radiation generated by femtosecond ultrashort pulse excitation is broadband, it is fundamentally difficult to overcome the strong absorption of terahertz radiation by water vapor in free space. Therefore, long-distance transmission and application of terahertz waves in free space cannot be achieved. To meet these special application requirements, especially for terahertz remote sensing, terahertz radar, and terahertz communication, it is urgent to develop new terahertz radiation source technologies with high peak power, high frequency, and narrow linewidth.

[0006] Near-infrared difference frequency technology, based on the characteristics of nanosecond narrow-linewidth pulses, will provide a potential path for the aforementioned long-distance terahertz applications. However, the nonlinear crystals of the current major terahertz difference frequency radiation sources are still primarily based on materials such as gallium selenide, lithium niobate, gallium phosphide, gallium arsenide, zinc germanium phosphide, and organic crystals such as DAST and OH1. These essentially "single-shot" terahertz waves emitted by near-infrared pump beams remain at the terahertz "traveling wave generation" stage and have not yet entered the terahertz "multiple echo radiation" resonant amplification stage. Therefore, high conversion efficiency and higher-power terahertz wave radiation cannot yet be achieved. The root of this problem lies in the inadequate understanding of the optoelectronic properties of materials in the terahertz band. A database of key optoelectronic property parameters, theoretical frameworks, and process conditions for thin-film functional material systems meeting the requirements for terahertz band performance have not yet been established. This makes it extremely difficult to achieve dielectric functional structure film systems that meet both high reflectivity in the terahertz band and high transmittance in the near-infrared band. Summary of the Invention

[0007] The purpose of the present invention is to provide a high-power terahertz difference-frequency resonant radiation source system. By utilizing the significant difference in wavelength between near-infrared and terahertz beams, a pair of diffraction optical elements are constructed outside the nonlinear crystal to regulate the transmission behavior characteristics of the terahertz diffraction beam in the cavity, ultimately achieving terahertz echo resonant amplification.

[0008] The above technical objectives of the present invention are achieved through the following technical solutions: a high-power terahertz difference frequency resonant radiation source system, including a 1064nm nanosecond laser, a first near-infrared beam delay line module, a near-infrared optical parametric oscillator, a second near-infrared beam delay line module, a near-infrared polarization coupling prism, a terahertz diffraction resonant cavity module, a terahertz focusing mirror, a terahertz detector, an oscilloscope, a precision motor control system and a computer; the first near-infrared beam delay line module is close to the emitting end of the 1064nm nanosecond laser, and the second near-infrared beam delay line module is close to the near-infrared The terahertz optical system is configured to be close to the transmitting end of the optical parametric oscillator, the first near-infrared beam delay line module and the second near-infrared beam delay line module are respectively close to two adjacent sides of the near-infrared polarization coupling prism; the terahertz diffraction resonant cavity module is close to the side of the near-infrared polarization coupling prism away from the first near-infrared beam delay line module, and the terahertz focusing mirror is close to the transmitting end of the terahertz diffraction resonant cavity module; the terahertz detector is close to the transmitting end of the terahertz focusing mirror, the terahertz detector and the computer are both electrically connected to the oscilloscope, and the computer and the terahertz diffraction resonant cavity module are both electrically connected to the precision motor control system.

[0009] By adopting the above technical solution, a 1064nm nanosecond laser is used to provide a high-power near-infrared pump source required by a terahertz difference frequency source; a first near-infrared beam delay line module is set to provide a suitable pulse delay for the 1064nm nanosecond pulse laser; a near-infrared optical parametric oscillator is set to provide another wavelength pump beam required by the terahertz difference frequency source; a second near-infrared beam delay line module is set to provide a suitable pulse delay for the near-infrared optical parametric oscillator; a near-infrared polarization coupling prism is set to transmit the 1064nm nanosecond laser to the terahertz difference frequency source. The light beams output by the oscillator and the near-infrared optical parametric oscillator are coupled into a beam of light; a terahertz diffraction resonant cavity module is set up to amplify the terahertz light signal; a terahertz focusing mirror is set up to block and absorb the infrared pump beam on the one hand, and focus the terahertz light into the terahertz detector on the other hand; a terahertz detector is set up for terahertz photoelectric conversion; an oscilloscope is set up for sampling and displaying the terahertz electrical signal; a precision motor control system is set up for fine adjustment of the terahertz resonant cavity length; and a computer is set up to integrate the control software of the terahertz radiation source system.

[0010] The present invention is further configured as follows: the terahertz diffraction resonant cavity module includes a first terahertz resonant cavity mirror, a nonlinear terahertz crystal and a second terahertz resonant cavity mirror; the first terahertz resonant cavity mirror is close to the near-infrared polarization coupling prism, the second terahertz resonant cavity mirror is close to the terahertz focusing mirror, the nonlinear terahertz crystal is located between the first terahertz resonant cavity mirror and the second terahertz resonant cavity mirror, and the second terahertz resonant cavity mirror is electrically connected to the precision motor control system.

[0011] By adopting the above technical solution, the first terahertz resonant cavity mirror and the second terahertz resonant cavity mirror are set to realize the transmission of the near-infrared pump light beam, and at the same time can realize the complete reflection of the terahertz light in the cavity; a nonlinear terahertz crystal is set to realize terahertz difference frequency radiation.

[0012] The present invention is further configured such that: the center of the first terahertz resonant cavity mirror is a blank area, and the periphery of the blank area of ​​the first terahertz resonant cavity mirror is a metal film-plated area.

[0013] By adopting the above technical solution, the center of the first terahertz resonant cavity mirror is set as a blank area to achieve the transmission of the near-infrared pump beam; the metal film-coated area of ​​the first terahertz resonant cavity mirror achieves complete reflection of the terahertz light in the cavity.

[0014] The present invention is further configured as follows: the center of the second terahertz resonant cavity mirror is a blank area; the periphery of the blank area of ​​the second terahertz resonant cavity mirror is a metal film-plated area with multiple blank rings.

[0015] By adopting the above technical solution, the center of the second terahertz resonant cavity mirror is set as a blank area for realizing the transmission of the near-infrared pump beam; the peripheral series of metal film distribution areas of the second terahertz resonant cavity mirror are used to adjust the reflection of the terahertz light field in the cavity.

[0016] The present invention is further configured such that: the terahertz focusing mirror is made of high-density polyethylene material.

[0017] By adopting the above technical solution, on the one hand, it is used to block and absorb the near-infrared pump beam, and on the other hand, the terahertz light is focused into the terahertz detector.

[0018] In summary, the present invention has the following beneficial effects: It utilizes a high-power 1064nm laser and a wavelength-tunable near-infrared optical parametric oscillator as a terahertz difference-frequency pump source. After passing through a series of optical components (reflectors, half-wave plates, polarizers, and polarization coupling prisms), the two near-infrared pump beams achieve complete spatial and temporal collinearity, ultimately entering a terahertz resonant cavity module to achieve enhanced amplification of terahertz light of a specific wavelength. This terahertz resonant cavity module, on the one hand, generates single-pass terahertz light radiation through difference-frequency interaction between the two near-infrared pump beams in a nonlinear terahertz crystal, and on the other hand, superimposes the resulting single-sequence terahertz light signal onto the next-sequence terahertz light signal of the same pulse, further enhancing the conversion efficiency of the terahertz difference-frequency three-wave interaction and thus achieving terahertz light power amplification. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the generation of a high-power terahertz difference-frequency resonant radiation source system in an embodiment of the present invention;

[0020] Figure 2 Schematic diagram of the geometric structure of the first terahertz resonant cavity mirror in an embodiment of the present invention;

[0021] Figure 3 Schematic diagram of the geometric structure of the second terahertz resonant cavity mirror in an embodiment of the present invention.

[0022] In the figure: 1. 1064nm nanosecond laser; 2. First near-infrared beam delay line module; 3. Near-infrared optical parametric oscillator; 4. Second near-infrared beam delay line module; 5. Near-infrared polarization coupling prism; 6. First terahertz resonant cavity mirror; 7. Nonlinear terahertz crystal; 8. Second terahertz resonant cavity mirror; 9. Terahertz focusing mirror; 10. Terahertz detector; 11. Oscilloscope; 12. Precision motor control system; 13. Computer. DETAILED DESCRIPTION

[0023] The following is combined with Figure 1-3 The present invention is described in further detail.

[0024] Example: High-power terahertz difference frequency resonance radiation source system, such as Figures 1 to 3 As shown, it includes a 1064nm nanosecond laser 1, a first near-infrared beam delay line module 2, a near-infrared optical parametric oscillator 3, a second near-infrared beam delay line module 4, a near-infrared polarization coupling prism 5, a terahertz diffraction resonant cavity module, a terahertz focusing mirror 9, a terahertz detector 10, an oscilloscope 11, a precision motor control system 12 and a computer 13; the first near-infrared beam delay line module 2 is close to the emission end of the 1064nm nanosecond laser 1, the second near-infrared beam delay line module 4 is close to the emission end of the near-infrared optical parametric oscillator 3, the first near-infrared The beam delay line module 2 and the second near-infrared beam delay line module 4 are respectively close to the two adjacent sides of the near-infrared polarization coupling prism 5; the terahertz diffraction resonant cavity module is close to the side of the near-infrared polarization coupling prism 5 away from the first near-infrared beam delay line module 2, and the terahertz focusing mirror 9 is close to the emitting end of the terahertz diffraction resonant cavity module; the terahertz detector 10 is close to the emitting end of the terahertz focusing mirror 9, the terahertz detector 10 and the computer 13 are both electrically connected to the oscilloscope 11, and the computer 13 and the terahertz diffraction resonant cavity module are both electrically connected to the precision motor control system 12.

[0025] In this embodiment, the 1064nm nanosecond laser 1 adopts a high-power narrow-linewidth 1064nm nanosecond pulse Q-switched Nd:YAG laser with a laser frequency of 10Hz, a pulse width of 8ns, and a line width of 0.003cm. -1 Another pump beam is excited by the triple frequency (355nm) of the 1064nm beam to generate a narrow linewidth angle tunable near-infrared optical parametric oscillator 3. The wavelength tuning range of the near-infrared optical parametric oscillator 3 is 1050-1080nm, with continuously adjustable radiation wavelength, frequency 10Hz, pulse width 4ns, and narrow linewidth 0.075cm -1, and high radiation power (up to 150mW near 1070nm); the terahertz focusing mirror 9 is made of black high-density polyethylene material; the 1064nm pump light beam passes through the first near-infrared beam delay line module 2 and is horizontally polarized and incident on the near-infrared polarization coupling prism 5; the near-infrared optical parametric oscillator 3 outputs near-infrared light in the band near 1064nm (such as 1070nm wavelength), which passes through the second near-infrared beam delay line module 4 and is vertically incident on the near-infrared polarization coupling prism 5; the two near-infrared pump laser beams (such as 1064nm laser and 1070nm laser) pass through the near-infrared polarization coupling prism 5 and finally completely overlap in beam propagation space and time; then the two near-infrared pump laser beams are vertically incident on the terahertz diffraction resonant cavity module to achieve terahertz light signal amplification, and then the terahertz The terahertz optical signal is focused by the terahertz focusing mirror 9 into the terahertz detector 10, while the remaining emitted near-infrared pump light signal is blocked and absorbed by the terahertz focusing mirror 9; the terahertz optical signal is detected by the terahertz detector 10 and converted into an electrical pulse signal, which is finally collected and displayed by the oscilloscope 11; in the terahertz difference frequency resonance process, the stable resonance enhancement conditions of the terahertz wave in the resonant cavity need to be met, and the cavity length is adjusted by a precision stepping motor control system, and finally the software system integration of the terahertz difference frequency resonance radiation source is realized through the terminal computer 13; since the wavelength of terahertz light differs from that of near-infrared light by 2-3 orders of magnitude, the terahertz light and near-infrared light have significant diffraction characteristic differences; according to the Rayleigh criterion, the divergence angle of the terahertz beam is 2-3 orders of magnitude of the divergence angle of the near-infrared beam, which is much larger than the emission angle of the near-infrared beam.

[0026] The terahertz diffraction resonant cavity module includes a first terahertz resonant cavity mirror 6, a nonlinear terahertz crystal 7 and a second terahertz resonant cavity mirror 8; the first terahertz resonant cavity mirror 6 is close to the near-infrared polarization coupling prism 5, the second terahertz resonant cavity mirror 8 is close to the terahertz focusing mirror 9, the nonlinear terahertz crystal 7 is located between the first terahertz resonant cavity mirror 6 and the second terahertz resonant cavity mirror 8, and the second terahertz resonant cavity mirror 8 is electrically connected to the precision motor control system 12.

[0027] In this embodiment, two beams of pump near-infrared laser light pass through the near-infrared polarization coupling prism 5 and then sequentially pass through the first terahertz resonant cavity mirror 6, the nonlinear terahertz crystal 7 and the second terahertz resonant cavity mirror 8, thereby realizing terahertz light signal amplification; both surfaces of the nonlinear terahertz crystal 7 are polished with high precision, thereby realizing terahertz difference frequency radiation.

[0028] The center of the first terahertz resonant cavity mirror 6 is a blank area, and the periphery of the blank area of ​​the first terahertz resonant cavity mirror 6 is a metal film-plated area.

[0029] In this embodiment, if Figure 2As shown, the cavity mirror is formed based on the metal film coated on the surface of the terahertz transparent material. The central blank area is without any material and is hollow as a whole. It is also the effective pumping space area of ​​the near-infrared pump beam spot. The outer black area is the metal film coated area, which is the effective reflection area of ​​the resonant cavity echo terahertz. The first terahertz resonant cavity mirror 6 reflects all the terahertz beams into the cavity space.

[0030] The center of the second terahertz resonant cavity mirror 8 is a blank area; the periphery of the blank area of ​​the second terahertz resonant cavity mirror 8 is a metal film-plated area with multiple blank rings.

[0031] In this embodiment, if Figure 3 As shown, the second terahertz resonant cavity mirror 8 is slightly more complex in geometric structure than the first terahertz resonant cavity mirror 6. It is also made of a metal film coated on the surface of a terahertz transparent material. The central blank area is consistent with the first terahertz resonant cavity mirror 6 and is also hollow as a whole, which is the effective pumping space area of ​​the near-infrared pump beam spot; the outer black area is the metal film coated area, the blank area is the uncoated area, and the bottom is supported by a terahertz transparent substrate; this series of outer blank circular areas will modulate the transmittance of the terahertz resonant cavity mirror, thereby achieving the purpose of external effective output of the terahertz resonance-enhanced light field energy in the cavity.

[0032] The terahertz focusing mirror 9 is made of black high-density polyethylene material.

[0033] In this embodiment, the terahertz focusing mirror 9 is made of black high-density polyethylene material, which is used to block and absorb the near-infrared pump light beam on the one hand, and to focus the terahertz light into the terahertz detector 10 on the other hand.

[0034] Working Principle: This invention utilizes a high-power 1064nm laser and a wavelength-tunable near-infrared optical parametric oscillator as a terahertz difference-frequency pump source. These two near-infrared pump beams, after passing through a series of optical components (reflectors, half-wave plates, polarizers, and polarization coupling prisms), achieve complete spatial and temporal collinearity. They are then incident on a terahertz resonant cavity module, achieving enhanced amplification of terahertz light of a specific wavelength. This terahertz resonant cavity module, on the one hand, generates single-pass terahertz light emission through difference-frequency interaction between the two near-infrared pump beams in a nonlinear terahertz crystal 7. On the other hand, the resulting single-sequence terahertz light signal is superimposed on the next-sequence terahertz light signal of the same pulse, further enhancing the conversion efficiency of the terahertz difference-frequency three-wave interaction, thereby achieving terahertz light power amplification.

[0035] This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. After reading this specification, those skilled in the art may make non-creative modifications to this embodiment as needed. However, as long as such modifications are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A high-power terahertz difference-frequency resonant radiation source system, characterized by: Including 10 64nm nanosecond laser (1), a first near-infrared beam delay line module (2), a near-infrared optical parametric oscillator (3), a second near-infrared beam delay line module (4), a near-infrared polarization coupling prism (5), a terahertz diffraction resonant cavity module, a first terahertz resonant cavity mirror (6), a second terahertz resonant cavity mirror (8), a terahertz focusing mirror (9), a terahertz detector (10), an oscilloscope (11), a precision motor control system (12) and a computer (13); the first near-infrared beam delay line module (2) is close to the emission end of the 1064nm nanosecond laser (1), the second near-infrared beam delay line module (4) is close to the emission end of the near-infrared optical parametric oscillator (3), the first near-infrared beam delay line module (2) and the second near-infrared beam delay line module (4) are respectively close to two adjacent sides of the near-infrared polarization coupling prism (5); the terahertz diffraction resonant cavity module is close to the near-infrared polarization The polarization coupling prism (5) is away from the side of the first near-infrared beam delay line module (2); the terahertz focusing mirror (9) is close to the emission end of the terahertz diffraction resonant cavity module; the terahertz detector (10) is close to the emission end of the terahertz focusing mirror (9); the terahertz detector (10) and the computer (13) are both electrically connected to the oscilloscope (11); the computer (13) and the terahertz diffraction resonant cavity module are both electrically connected to the precision motor control system (12); the 1064nm nanosecond laser (1) and the near-infrared optical parametric oscillator (3) achieve spatial and temporal beam overlap through the polarization coupling prism (5); the periphery of the central blank area of ​​the first terahertz resonant cavity mirror (6) is a metal film-plated area; the center of the second terahertz resonant cavity mirror (8) is a blank area; the periphery of the blank area of ​​the second terahertz resonant cavity mirror (8) is a metal film-plated area with multiple blank rings.

2. The high-power terahertz difference-frequency resonant radiation source system according to claim 1, characterized in that: The terahertz diffraction resonant cavity module comprises a first terahertz resonant cavity mirror (6), a nonlinear terahertz crystal (7) and a second terahertz resonant cavity mirror (8); the first terahertz resonant cavity mirror (6) is close to a near-infrared polarization coupling prism (5), the second terahertz resonant cavity mirror (8) is close to a terahertz focusing mirror (9), the nonlinear terahertz (7) crystal is located between the first terahertz resonant cavity mirror (6) and the second terahertz resonant cavity mirror (8), and the second terahertz resonant cavity mirror (8) is electrically connected to a precision motor control system (12).

3. The high-power terahertz difference-frequency resonance radiation source system according to claim 1, characterized in that: The terahertz focusing mirror (9) is made of high-density polyethylene material.

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