Efficient terahertz wave difference frequency generation method and system based on dual-wavelength energy balance

Abstract

The invention discloses an efficient terahertz wave difference frequency generation method and system based on dual-wavelength energy balance. The system comprises a pump laser, a laser energy regulator, a dual-wavelength generator, a terahertz wave generator and a terahertz wave detector. Wherein the pump laser is used as a pump source, and the pump dual-wavelength generator generates dual wavelengths; the laser energy regulator is used for regulating the energy of the pumping laser entering the dual-wavelength generator; the terahertz wave generator generates terahertz waves based on the dual-wavelength difference frequency effect in the nonlinear crystal; and the terahertz wave detector is used for collecting and detecting terahertz waves. According to the invention, the output energy of dual wavelengths is balanced, so that high-efficiency terahertz wave difference frequency generation is realized.

Description

Technical Field

[0001] The present invention relates to the field of terahertz technology, and in particular to a method and system for generating high-efficiency terahertz wave difference frequency based on dual-wavelength energy balance. Background Art

[0002] Terahertz waves generally refer to electromagnetic waves with a frequency in the 0.1-10THz band. Due to its unique characteristics, it has attracted widespread attention in recent years. In nature, the vibrations of many biological macromolecules are in this frequency band, which provides an effective means for the detection of biological characteristics; terahertz photons have low energy and will not cause damage to the detected object, enabling non-destructive testing; terahertz has the ability to penetrate many dielectric materials and non-polar substances, and can be used as a means of detecting hidden objects.

[0003] High-power terahertz sources are the core components for realizing the above applications. Difference frequency generation based on the principle of nonlinear optics is one of the photonic methods to obtain a miniaturized, room-temperature operating narrow-band, high-peak-power, and widely-tuned terahertz radiation source. The input of the difference frequency generation process is generally two beams of infrared light with similar frequencies (commonly referred to as "dual wavelengths"), and the frequency of the output terahertz wave is the difference between the dual-wavelength frequencies. In addition to being related to the physical properties and phase matching conditions of the difference frequency crystal itself, the efficiency of difference frequency generation is also related to the ratio of the two components in the dual-wavelength energy. When the dual-wavelength energy ratio is 1:1, the efficiency of difference frequency generation is the highest under the same conditions.

[0004] At present, the most commonly used dual-wavelength generator is a laser-pumped dual-parameter crystal optical parametric oscillator, such as a reflective dual KTP-OPO, which has the advantages of compact structure, high conversion efficiency, narrow linewidth and low threshold. However, the two parametric crystals compete with each other for the energy of the pump laser, and the output dual-wavelength energy ratio is usually unbalanced, deviating from the optimal ratio (i.e. 1:1) required for difference frequency generation. Theoretically, for a dual-wavelength with an energy ratio of 1:7, the conversion efficiency of the difference frequency process is only 44% of that of 1:1 under the same conditions. Therefore, balancing the dual-wavelength energy is a very effective means to improve the performance of the difference frequency terahertz source. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a method and system for efficiently generating terahertz wave difference frequency based on dual-wavelength energy balance, which realizes the balance of dual-wavelength energy in a commonly used dual-wavelength generator, thereby realizing efficient terahertz wave difference frequency generation.

[0006] The technical solution adopted by the present invention to achieve the above-mentioned purpose is:

[0007] A high-efficiency terahertz wave difference frequency generation system based on dual-wavelength energy balance, characterized in that it includes a pump laser, a laser energy regulator, a dual-wavelength generator, a terahertz wave generator and a terahertz wave detector; the pump laser is used as a pump source to emit pump laser; the laser energy regulator is used to adjust the energy of the pump laser and output it to the dual-wavelength generator; the dual-wavelength generator is used to convert the pump laser into a dual-wavelength in the near-infrared light band that meets the energy ratio requirement and output it; the terahertz wave generator is used to convert the dual wavelengths into difference-frequency terahertz waves; and the terahertz wave detector is used to collect and detect the difference-frequency terahertz waves.

[0008] The pump laser is a frequency-doubled Nd:YAG laser, and the central wavelength of its output laser is 532nm.

[0009] The laser energy regulator includes a half-wave plate, a polarization beam splitter cube and an absorber; the pump laser is irradiated on the polarization beam splitter cube through the half-wave plate to generate polarization beam splitting; wherein the vertical polarization component enters the dual-wavelength generator through reflection, and the horizontal polarization component enters the absorber and is collected by it.

[0010] The dual-wavelength generator comprises a laser input mirror, a coupling cavity mirror, a parametric crystal A, a parametric crystal B, a total reflection cavity mirror and an infrared attenuation film; the laser input mirror is a 45° reflecting mirror, and the surface coating is highly reflective to 532nm and highly transparent to 1300-1600nm; the surface coating of the coupling cavity mirror is highly transparent to 532nm and 1300-1600nm and highly reflective to 800-900nm; the coating of the total reflection cavity mirror is highly reflective to 532nm, 1300-1600nm and 800-900nm; the parametric crystal A and the parametric crystal B are The parametric crystal B is made of potassium titanyl phosphate, and the wavelength of the near-infrared light it outputs is about 1300-1600nm, and both sides are coated with high-transmittance films of 532nm, 1300-1600nm and 800-900nm; the vertical polarization component of the pump laser is reflected by the laser input mirror to the coupling cavity mirror, and then irradiates the parametric crystal A and the parametric crystal B in turn to generate two near-infrared lights with different wavelengths and adjustable energy ratios in the range of 1300-1600nm, which are reflected by the total reflection cavity mirror and returned to the laser input mirror and the infrared attenuation film along the original path for output.

[0011] The terahertz wave generator includes a focusing lens and a difference frequency crystal; the difference frequency crystal is placed at the focal position of the focusing lens; the near-infrared light of two wavelengths generates a difference frequency terahertz wave after passing through the difference frequency crystal, and the frequency of the wave is the difference between the frequencies of the two wavelengths.

[0012] The focusing lens is a convex lens or a beam reduction telescope; the difference frequency crystal is a nonlinear crystal; the difference frequency crystal realizes the difference frequency generation of terahertz waves to meet the corresponding angle phase matching, temperature phase matching or quasi-phase matching conditions.

[0013] The terahertz wave detector includes a filter, a detection element, and a gold-plated off-axis parabolic mirror A and a gold-plated off-axis parabolic mirror B; the filter is a low-pass filter for cutting off the remaining dual wavelengths; the detection element is a Golay cell or a pyroelectric detector for detecting difference-frequency terahertz waves.

[0014] A method for efficiently generating terahertz wave difference frequency based on dual-wavelength energy balance, the steps for achieving dual-wavelength energy balance are as follows:

[0015] S1. Measure the light output thresholds of the two parametric crystals in the dual-wavelength generator, set the parametric crystal with a lower threshold as parametric crystal B, and place it close to the total reflective cavity mirror;

[0016] S2. Change the pump energy input to the dual-wavelength generator through a laser energy regulator; measure the relationship between the input pump energy and the output dual-wavelength energy ratio, and obtain the pump energy size E when the dual-wavelength energy ratio is 1:1. p ;

[0017] S3, control the pump energy output by the laser energy regulator to E p ;

[0018] S4, changing the attenuation magnification of the infrared attenuation plate (36) in the dual-wavelength generator so that the total energy of the dual wavelengths is less than the damage threshold of the difference frequency crystal.

[0019] The method of changing the pump energy input to the dual-wavelength generator by the laser energy regulator includes: changing the incident direction of the pump laser irradiated on the polarization beam splitter cube by rotating the half-wave plate with the laser direction as the axis, and adjusting the proportion of the horizontal polarization component and the vertical polarization component.

[0020] Compared with the prior art, the present invention has the following beneficial effects and advantages:

[0021] 1. The present invention can stably balance the dual-wavelength energy output by the commonly used dual-wavelength generator to 1:1, thereby improving the conversion efficiency of the difference frequency process;

[0022] 2. The terahertz wave difference frequency generation system in the present invention has a relatively compact structure and is suitable for occasions requiring a low-cost, miniaturized, portable terahertz source. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of a top view of the structure of the present invention.

[0024] Among them, 1 is a pump laser, 2 is a laser energy regulator, 3 is a dual-wavelength generator, 4 is a terahertz wave generator, and 5 is a terahertz wave detector. 21 is a half-wave plate, 22 is a polarization beam splitter cube, 23 is an absorber, 31 is a laser input mirror, 32 is a coupling cavity mirror, 33 is a parametric crystal A, 34 is a parametric crystal B, 35 is a total reflection cavity mirror, 36 is an infrared attenuation plate, 41 is a focusing lens, 42 is a difference frequency crystal, 51 is a gold-plated off-axis parabolic mirror A, 52 is a filter, 53 is a gold-plated off-axis parabolic mirror B, and 54 is a detection element. DETAILED DESCRIPTION

[0025] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation method of the present invention is further described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the invention, so the present invention is not limited by the specific implementation disclosed below.

[0026] like Figure 1 As shown, the present invention provides a high-efficiency terahertz wave difference frequency generation method and system based on dual-wavelength energy balance, including a pump laser 1, a laser energy regulator 2, a dual-wavelength generator 3, a terahertz wave generator 4 and a terahertz wave detector 5. Among them, the laser energy regulator 2 is composed of a half-wave plate 21, a polarization beam splitter cube 22 and an absorber 23; the dual-wavelength generator 3 is composed of a laser input mirror 31, a coupling cavity mirror 32, a parametric crystal A33, a parametric crystal B34, a total reflection cavity mirror 35 and an infrared attenuation plate 36; the terahertz wave generator 4 is composed of a focusing lens 41 and a difference frequency crystal 42; the terahertz wave detector 5 is composed of a filter 52, a detection element 54, and a gold-plated off-axis parabolic mirror A51 and a gold-plated off-axis parabolic mirror B53.

[0027] Figure 1 It is also a top view schematic diagram of a specific embodiment of the present invention. In the figure, the pump laser 1 is a laser that outputs a fixed wavelength. A frequency-doubled neodymium-doped yttrium aluminum garnet laser (frequency-doubled Nd:YAG laser) is used, and the central wavelength of its output laser is 532nm.

[0028] The laser energy regulator 2 includes a half-wave plate 21, a polarization beam splitter cube 22 and an absorber 23; the polarization direction of the pump laser is changed by rotating the half-wave plate 21 with the laser direction as the axis, and the proportion of its horizontal polarization component (the polarization direction is parallel to the laser propagation direction) and the vertical polarization component (the polarization direction is perpendicular to the laser propagation direction) is adjusted; the polarization beam splitter cube 22 is used to separate the horizontal polarization component and the vertical polarization component, wherein the vertical polarization component enters the dual-wavelength generator 3 through reflection, and the horizontal polarization component enters the absorber 23; the absorber 23 is used to collect excess horizontal polarization components.

[0029] The dual-wavelength generator 3 includes a laser input mirror 31, a coupling cavity mirror 32, a parametric crystal A33, a parametric crystal B34, a total reflection cavity mirror 35 and an infrared attenuation plate 36; the laser input mirror 31 is a 45° reflector, and the surface coating is highly reflective to 532nm and highly transparent to 1300-1600nm; the surface coating of the coupling cavity mirror 32 is highly transparent to 532nm and 1300-1600nm, and highly reflective to 800-900nm; the total reflection cavity The mirror 35 coating is highly reflective at 532nm, 1300-1600nm and 800-900nm; the parameter crystal A33 and the parameter crystal B34 are made of potassium titanium phosphate, and the near-infrared light wavelength they output is about 1300-1600nm, and both sides should be coated with high-transmittance films of 532nm, 1300-1500nm and 800-900nm; the infrared attenuation plate 36 is used to regulate the dual-wavelength energy output by the dual-wavelength generator 3.

[0030] The terahertz wave generator 4 includes a focusing lens 41 and a difference frequency crystal 42; the frequency of the generated terahertz wave is the difference between the frequencies of the two wavelengths; the focusing lens 41 is a convex lens or a beam reduction telescope; in the embodiment of the present invention, the difference frequency crystal 42 is an organic crystal DAST; the difference frequency crystal 42 is placed at the focal position of the focusing lens 41. By rotating the DAST in a plane perpendicular to the laser propagation direction, the requirement of the terahertz wave difference frequency generation type 0 phase matching angle is met.

[0031] The terahertz wave detector 5 includes a filter 52, a detection element 54, and a gold-plated off-axis parabolic mirror A51 and a gold-plated off-axis parabolic mirror B53; the filter 52 is a low-pass filter for cutting off the remaining dual wavelengths; the detection element 54 is a Golay cell or a pyroelectric detector.

[0032] The steps to achieve dual-wavelength energy balance (i.e., the ratio of dual-wavelength energy is close to 1:1) are as follows:

[0033] A. After measuring the light output thresholds of the two parametric crystals in the dual-wavelength generator 3, the parametric crystal with a lower threshold is set as parametric crystal B and placed close to the total reflective cavity mirror 35;

[0034] B. Change the pump energy input to the dual-wavelength generator 3 through the laser energy regulator 2, measure the relationship between the input pump energy and the output dual-wavelength energy ratio, and determine the pump energy size when the dual-wavelength energy ratio is 1:1, set as E p ; Among them, the pump energy input to the dual-wavelength generator 3 is changed by the laser energy regulator 2 by: changing the incident direction of the pump laser irradiated on the polarization beam splitter cube 22 by rotating the half-wave plate 21 with the laser direction as the axis, and adjusting the proportion of the horizontal polarization component and the vertical polarization component therein.

[0035] C. Adjust the pump energy input to the dual wavelength generator 3 to E through the laser energy regulator 2 p ;

[0036] D. Change the attenuation ratio of the infrared attenuation plate 36 in the dual-wavelength generator 3 so that the total energy of the dual wavelengths meets the requirements of terahertz wave difference frequency generation (avoiding crystal damage). The attenuation ratio of the infrared attenuation plate 36 in the dual-wavelength generator 3 is changed by replacing attenuation plates with different attenuation ratios.

[0037] In summary, the present invention provides a method and system for efficiently generating terahertz wave difference frequency based on dual-wavelength energy balance, which can stably balance the dual-wavelength energy output by a commonly used dual-wavelength generator to 1:1, thereby achieving efficient terahertz wave difference frequency generation.

[0038] It should be noted that the present invention is not limited to the embodiments described above. The above specific embodiments are merely illustrative and not restrictive. Without departing from the scope of the present invention and the scope of protection of the claims, a person of ordinary skill in the art may make many forms of specific changes under the guidance of the present invention, which all fall within the scope of protection of the present invention.

Claims

1. An efficient terahertz wave difference frequency generation system based on dual-wavelength energy balance, characterized in that: The invention comprises a pump laser (1), a laser energy regulator (2), a dual-wavelength generator (3), a terahertz wave generator (4) and a terahertz wave detector (5); the pump laser (1) is used as a pump source to emit pump laser light; the laser energy regulator (2) is used to regulate the energy of the pump laser light and output it to the dual-wavelength generator (3); the dual-wavelength generator (3) is used to convert the pump laser light into dual-wavelengths in the near-infrared light band that meet energy ratio requirements and output them; the terahertz wave generator (4) is used to convert the dual-wavelengths into difference-frequency terahertz waves; and the terahertz wave detector (5) is used to collect and detect the difference-frequency terahertz waves.

2. According to claim 1, a high-efficiency terahertz wave difference frequency generation system based on dual-wavelength energy balance is characterized in that: The pump laser (1) is a frequency-doubled Nd:YAG laser, and the central wavelength of its output laser is 532 nm.

3. The high-efficiency terahertz wave difference frequency generation system based on dual-wavelength energy balance according to claim 1, characterized in that: The laser energy regulator (2) comprises a half-wave plate (21), a polarization beam splitter cube (22) and an absorber (23); the pump laser is transmitted through the half-wave plate (21) and irradiated onto the polarization beam splitter cube (22) to generate polarization beam splitting; wherein the vertical polarization component enters the dual-wavelength generator (3) through reflection, and the horizontal polarization component enters the absorber (23) and is collected by the absorber (23).

4. The high-efficiency terahertz wave difference frequency generation system based on dual-wavelength energy balance according to claim 1, characterized in that: The dual-wavelength generator (3) comprises a laser input mirror (31), a coupling cavity mirror (32), a parametric crystal A (33), a parametric crystal B (34), a total reflection cavity mirror (35) and an infrared attenuation plate (36); the laser input mirror (31) is a 45° reflection mirror, and the surface coating has high reflection to 532nm and high transmittance to 1300-1600nm; the surface coating of the coupling cavity mirror (32) has high transmittance to 532nm and 1300-1600nm and high reflection to 800-900nm; the coating of the total reflection cavity mirror (35) has high reflection to 532nm, 1300-1600nm and 800-900nm; the parametric crystal A (33) and parameter crystal B (34) are made of potassium titanyl phosphate, and the wavelength of the near-infrared light they output is about 1300-1600nm, and high-transmittance films of 532nm, 1300-1600nm and 800-900nm are coated on both sides; the vertical polarization component of the pump laser is reflected by the laser input mirror (31) to the coupling cavity mirror (32), and then irradiates the parameter crystal A (33) and the parameter crystal B (34) in turn to generate two paths of near-infrared light with different wavelengths and adjustable energy ratio within the range of 1300-1600nm, which are reflected by the total reflection cavity mirror (35) and returned to the laser input mirror (31) and the infrared attenuation plate (36) along the original path before being output.

5. The high-efficiency terahertz wave difference frequency generation system based on dual-wavelength energy balance according to claim 1, characterized in that: The terahertz wave generator (4) comprises a focusing lens (41) and a difference frequency crystal (42); the difference frequency crystal (42) is placed at the focal position of the focusing lens (41); and the near-infrared light of the dual wavelengths passes through the difference frequency crystal (42) to generate a difference frequency terahertz wave, the frequency of which is the difference between the frequencies of the dual wavelengths.

6. The high-efficiency terahertz wave difference frequency generation system based on dual-wavelength energy balance according to claim 5, characterized in that: The focusing lens (41) is a convex lens or a beam reduction telescope; the difference frequency crystal (42) is a nonlinear crystal; the difference frequency crystal (42) realizes the difference frequency generation of terahertz waves to meet corresponding angle phase matching, temperature phase matching or quasi-phase matching conditions.

7. The high-efficiency terahertz wave difference frequency generation system based on dual-wavelength energy balance according to claim 1, characterized in that: The terahertz wave detector (5) comprises a filter (52), a detection element (54), a gold-plated off-axis parabolic mirror A (51) and a gold-plated off-axis parabolic mirror B (53); the filter (52) is a low-pass filter for cutting off the remaining dual wavelengths; the detection element (54) is a Golay cell or a pyroelectric detector for detecting difference-frequency terahertz waves.

8. The method for generating high-efficiency terahertz wave difference frequency based on dual-wavelength energy balance according to claim 1, characterized in that: The steps to achieve dual-wavelength energy balance are as follows: S1, measuring the light output thresholds of two parametric crystals in the dual-wavelength generator (3), setting the parametric crystal with a lower threshold as parametric crystal B, and placing it close to the total reflective cavity mirror (35); S2. The pump energy input to the dual-wavelength generator (3) is changed by the laser energy regulator (2); the relationship between the input pump energy and the output dual-wavelength energy ratio is measured to obtain the pump energy value E when the dual-wavelength energy ratio is 1:

1. p ; S3, control the pump energy output by the laser energy regulator (2) to E p ; S4, changing the attenuation magnification of the infrared attenuation plate (36) in the dual-wavelength generator (3) so that the total energy of the dual wavelengths is less than the damage threshold of the difference frequency crystal (42).

9. The method for generating high-efficiency terahertz wave difference frequency based on dual-wavelength energy balance according to claim 8, characterized in that: The method of changing the pump energy input to the dual-wavelength generator (3) by means of a laser energy regulator (2) comprises: changing the incident direction of the pump laser irradiating the polarization beam splitting cube (22) by rotating a half-wave plate (21) with the laser direction as an axis, thereby regulating the proportion of the horizontal polarization component and the vertical polarization component therein.

Images