Hundred-milliwatt high-power high-repetition-rate terahertz source generation device at room temperature

Abstract

This invention relates to a high-power, high-repetition-rate terahertz source generating device at room temperature with a capacity of hundreds of milliwatts, belonging to the field of nonlinear optical frequency conversion technology. It solves the problems of low terahertz conversion efficiency and the need for additional cooling equipment in existing technologies. The device comprises, arranged sequentially along the optical path: a pump laser for providing femtosecond pump laser light; a beam-expanding lens group for expanding the femtosecond pump laser beam to twice its original diameter; a plane mirror group for guiding the expanded pump laser; a first half-wave plate, a reflective diffraction grating, a gold mirror, and a third ultrafast mirror for adjusting polarization and diffraction reflection; a 4-f telescope imaging lens group for reducing the diameter of the received pump laser beam and imaging it onto a lithium niobate crystal; a lithium niobate crystal for generating terahertz pulse radiation perpendicular to the wavefront; a terahertz collection module for receiving and focusing the terahertz pulse radiation; and a measurement device for receiving and measuring the focused terahertz pulse radiation.

Description

Technical Field

[0001] This invention relates to the field of nonlinear optical frequency conversion technology, specifically to a device for generating a 100-milliwatt high-power, high-repetition-rate terahertz strong source at room temperature. Background Technology

[0002] Terahertz waves typically refer to electromagnetic waves with frequencies in the range of 0.1-10 THz, possessing significant characteristics such as fingerprint properties, penetrability, security, and transient response. Terahertz high-power sources, on the other hand, refer to electromagnetic pulses, which, due to their high peak electric field (>100 kV / cm) and strong peak magnetic field characteristics, have become an important source of optoelectronic signals for applications such as phonon vibration, induced molecular resonance, exploration of strong field effects, and development of high-frequency devices.

[0003] Currently, terahertz high-intensity sources mainly utilize femtosecond lasers (repetition frequency of kHz or lower) to pump lithium niobate nonlinear optical crystals, generating strong-field terahertz radiation pulses based on the optical rectification effect. This is a highly efficient method for terahertz generation. This technology offers the following advantages: 1) Lithium niobate crystals possess high nonlinear coefficients, high damage thresholds (>100 mJ / cm²), and excellent stability, facilitating integration into time-domain spectroscopy systems; 2) By optimizing the wavefront tilt design during the optical rectification process, the phase matching with the crystal can be significantly improved, thereby enhancing the conversion efficiency, output energy, and average power of terahertz radiation. However, these systems suffer from low repetition frequencies, poor signal-to-noise ratios, high costs, and large size, severely limiting their practical applications.

[0004] Chinese invention patent application CN118589287A, entitled "Strong Field Terahertz Generating Device," discloses a terahertz generating device including a lithium niobate crystal, multiple mirrors, a grating, multiple lenses, and a square vacuum cavity and a cylindrical vacuum cavity housing it. However, this device also requires a cooling frame for cooling the lithium niobate crystal with externally introduced liquid nitrogen. This makes the device more complex, significantly increases the cost, and makes operation more difficult.

[0005] Therefore, there is a need in this technical field for novel terahertz high-power sources with high average power, high repetition frequency, and no need for cooling systems at room temperature, in order to provide improved solutions for realizing low-cost, highly integrated terahertz systems, which have important application value in fields such as non-destructive testing, state manipulation, and spectral measurement. Summary of the Invention

[0006] In view of the above problems, according to the embodiments of the present invention, a high-power, high-repetition-rate terahertz strong source generating device with a capacity of 100 milliwatts at room temperature is provided, which can generate a strong field terahertz signal with high average power and high repetition rate. It can also be integrated into a time-domain spectroscopy system and has the following characteristics: the terahertz power, single pulse energy, repetition frequency and focusing electric field intensity can all be adjusted according to the requirements.

[0007] The high-power, high-repetition-rate, terahertz source generating device for room temperature at 100 milliwatts, according to an embodiment of the present invention, comprises the following components arranged sequentially along the optical path:

[0008] Pumped lasers provide femtosecond pumped lasers;

[0009] The beam-expanding lens group expands the femtosecond pump laser beam to twice the initial beam diameter;

[0010] Planar mirror assembly, used to guide the expanded pump laser;

[0011] The first half-wave plate, the reflective diffraction grating, the gold mirror, and the third ultrafast mirror are used to adjust polarization and diffraction reflection.

[0012] The 4-f telescope imaging lens group is used to reduce the spot diameter of the received pump laser and image it onto a lithium niobate crystal;

[0013] Lithium niobate crystals produce terahertz pulsed radiation in a direction perpendicular to the wavefront.

[0014] Terahertz collection module, which receives and focuses terahertz pulse radiation;

[0015] The measuring device receives focused terahertz pulse radiation for measurement.

[0016] Optionally, the beam-expanding lens group includes, in sequence: a concave lens, which is a biconcave lens with a nominal focal length of -50 mm; and a first convex lens, which is a biconvex lens with a nominal focal length of 100 mm; wherein the distance between the concave lens and the first convex lens is 50 mm.

[0017] Optionally, the pump laser is a ytterbium-doped fiber-amplified femtosecond laser, configured with a single-pulse energy range of 1 mJ - 2 mJ, a repetition frequency range of 1 kHz - 100 kHz, a center wavelength of 1030 nm, and a pulse width range of 950 fs - 1050 fs.

[0018] Optionally, the angles of the first half-wave plate, the reflective diffraction grating, and the gold mirror are set such that the pump laser, after being polarized by the first half-wave plate, is incident at an angle of 41.37° onto the reflective diffraction grating.

[0019] Optionally, the 4-f telescope imaging lens reduces the diameter of the received pump laser spot by a factor of 1.85 and includes, in sequence: a second convex lens with a focal length of 370 mm; a second half-wave plate for generating polarization matching the tilted wavefront; and a third convex lens with a focal length of 200 mm; wherein the distance between the second and third convex lenses is 570 mm.

[0020] Optionally, the distance between the reflective diffraction grating and the second convex lens is 370 mm; the distance between the third convex lens and the lithium niobate crystal is 200 mm.

[0021] Optionally, the terahertz collection module includes, in sequence:

[0022] The first off-axis parabolic mirror, with a 2-inch aperture diameter and a 2-inch focal length, collimates the terahertz pulse radiation emitted from the lithium niobate crystal into a parallel beam.

[0023] ITO flat glass is used for filtering to remove 1030nm doped pump laser and reflect terahertz pulse radiation.

[0024] The second off-axis parabolic mirror, with a 2-inch aperture diameter and a 4-inch focal length, focuses the received terahertz pulse radiation.

[0025] Optionally, the distance between the first off-axis parabolic reflector and the ITO flat glass is 5cm, and the distance between the ITO flat glass and the second off-axis parabolic reflector is 5cm.

[0026] Optionally, the distance between the lithium niobate crystal and the first off-axis parabolic mirror is 5 cm, and the distance between the second off-axis parabolic mirror and the measuring device is 10 cm.

[0027] Optionally, the spot diameter of the femtosecond pump laser provided by the pump laser ranges from 3.75 mm to 3.85 mm; the spot diameter of the femtosecond pump laser after the beam expander lens group expands the spot size of the femtosecond pump laser ranges from 7.5 mm to 7.9 mm; and the spot diameter of the received pump laser after the 4-f telescope imaging lens group reduces the spot size of the pump laser ranges from 3.5 mm to 3.8 mm.

[0028] Compared with the prior art, the high-power, high-repetition-rate, terahertz strong source generating device at room temperature provided according to the embodiments of the present invention has at least the following beneficial effects.

[0029] 1. The terahertz radiation source designed in this invention has advantages such as high average output power, high repetition frequency, large single pulse energy, high energy conversion efficiency, and controllable polarization, and can work stably and reliably at room temperature.

[0030] 2. The strong-field terahertz radiation source of this invention has the advantage of tunable parameters, including average power, repetition frequency, single-pulse energy, and polarization. This light source not only retains the functionality of traditional terahertz weak-field time-domain spectroscopy systems but also enhances testing capabilities and expands the sample testing range.

[0031] 3. This invention optimizes the tilted wavefront, including precise angle control of the grating and optimized settings of the 4-f telescope imaging lens group, as well as settings for the pump light spot and pulse width, resulting in a high-field terahertz radiation source conversion efficiency of up to 0.1%, reducing heat loss within the system, and thus enabling operation at room temperature without the need for a cooling device, effectively reducing application costs.

[0032] 4. By optimizing the pump spot size and pulse width, this invention maintains high pump intensity while ensuring the effective interaction distance with the lithium niobate crystal, and can provide terahertz radiation output at the level of hundreds of milliwatts. It can meet the needs of scientific research and can also be applied to non-destructive testing, industrial thickness measurement and other scenarios, and is especially suitable for transmission time-domain spectroscopy testing of thicker samples.

[0033] 5. In practical applications, this invention optimizes the tilted wavefront, including precise angle control of the grating, precise polarization control, and optimization of the beam shape, to achieve high-average-power terahertz pulses without damaging the lithium niobate crystal under high laser power pumping. This significantly improves the signal-to-noise ratio, detection speed, and efficiency of the terahertz time-domain spectroscopy system, meeting diverse sample thickness testing needs and shortening measurement time. Furthermore, this system can also be used to observe a large number of terahertz absorbing materials, biological cell apoptosis, and state manipulation.

[0034] 6. By optimizing the pump pulse width parameters, the optimal working length matching with the lithium niobate crystal was achieved, thereby obtaining a terahertz conversion efficiency of 0.1%. By increasing the repetition frequency and output power of the pump laser, a maximum average terahertz power output of 103.8 mW and a repetition frequency of 100 kHz were achieved without damaging the lithium niobate crystal. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the embodiments will be briefly introduced below. The features and advantages of the present invention can be more clearly understood by referring to the accompanying drawings. The accompanying drawings are schematic and should not be construed as limiting the present invention in any way. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of a high-power, high-repetition-rate terahertz source generating device at room temperature with a capacity of 100 milliwatts, provided according to an embodiment of the present invention.

[0037] Figure 2a A schematic diagram of the spot of the pump laser before it enters the lithium niobate crystal after passing through the 4-f telescope imaging lens group, in one embodiment of the high-power, high-repetition-rate terahertz source generating device for room temperature of 100 milliwatts provided according to an embodiment of the present invention.

[0038] Figure 2b In this embodiment, a schematic diagram shows the spot of the pump laser before and after beam expansion by the beam expanding lens group, as well as the spot after passing through the 4-f telescope imaging lens group.

[0039] Figure 3 This is a graph showing the relationship between terahertz radiation energy under different pump laser pulse widths in an embodiment of the high-power, high-repetition-rate terahertz source generating device at room temperature provided according to an embodiment of the present invention.

[0040] Figure 4a This is an embodiment of the high-power, high-repetition-rate terahertz source generating device at room temperature of 100 milliwatts provided according to an embodiment of the present invention. Under the condition of fixed pump laser pulse width, the relationship between pump laser energy and generated terahertz energy is measured by changing the pump laser repetition rate.

[0041] Figure 4b This is a graph showing the relationship between pump power and generated terahertz power at a pump laser repetition rate of 100 kHz in an embodiment of the high-power, high-repetition-rate terahertz source generating device at room temperature provided according to an embodiment of the present invention.

[0042] Explanation of reference numerals in the attached figures:

[0043] 1-Pump laser;

[0044] 2-Concave lens;

[0045] 3-First convex lens;

[0046] 4- First ultrafast reflecting mirror;

[0047] 5-Second ultrafast reflecting mirror;

[0048] 6-First half-wave plate;

[0049] 7-Reflection diffraction grating;

[0050] 8-Gold reflector;

[0051] 9-Third ultrafast reflecting mirror;

[0052] 10 - Second convex lens;

[0053] 11-Second half-wave plate;

[0054] 12-Third convex lens;

[0055] 13 - The light spot incident on the lithium niobate crystal;

[0056] 14-Lithium niobate crystals;

[0057] 15 - First off-axis parabolic reflector;

[0058] 16-ITO flat glass;

[0059] 17-Second off-axis parabolic mirror;

[0060] 18 - Measuring device. Detailed Implementation

[0061] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0062] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0063] The following describes in detail, with reference to the accompanying drawings, a high-power, high-repetition-rate terahertz source generating apparatus for room temperature at 100 milliwatts provided according to an embodiment of the present invention.

[0064] like Figure 1 As shown, the high-power, high-repetition-rate terahertz source generating device at room temperature of 100 milliwatts provided according to an embodiment of the present invention includes, sequentially arranged along the optical path: a pump laser 1, a beam expander lens group, a plane mirror group, a first half-wave plate 6, a reflective diffraction grating 7, a gold mirror 8, a third ultrafast mirror 9, a 4-f telescope imaging lens group, a lithium niobate crystal 14, a terahertz collection module, and a measuring device 18. The measuring device 18 can be a pyroelectric detector or a terahertz power meter. Figure 2a As shown, a schematic diagram is illustrated in one embodiment where the optical signal incident on the lithium niobate crystal 14 is formed as a light spot 13 incident on the lithium niobate crystal.

[0065] The working process of the high-power, high-repetition-rate terahertz source generating device at room temperature of 100 milliwatts provided in this embodiment is as follows: the femtosecond pump laser output from the pump laser 1 is expanded by the beam-expanding lens group, then guided by the plane mirror group and polarized by the first half-wave plate 6, and then incident on the reflective diffraction grating 7. After being diffracted and reflected by the reflective diffraction grating 7, it is incident on the gold reflector 8. After being reflected by the gold reflector 8, it is reflected by the third ultrafast reflector 9 and passed through the 4-f telescope imaging lens group to obtain the pump laser with a reduced spot diameter. It is then incident on the lithium niobate crystal 14, and the lithium niobate crystal 14 generates terahertz pulse radiation in the direction perpendicular to the wavefront. The terahertz pulse radiation is focused by the terahertz collection module to the measuring device 18, i.e., a pyroelectric detector or a terahertz power meter, for energy and power measurement. The high-power, high-repetition-rate terahertz source generator at room temperature of 100 milliwatts provided in this embodiment achieves a high terahertz conversion efficiency of 0.1% by jointly modulating the pump spot and pulse width of the tilted wavefront, while ensuring that the damage threshold of the lithium niobate crystal is not damaged. This efficiency is comparable to terahertz generators using liquid nitrogen cooling systems. Therefore, the high-power, high-repetition-rate terahertz source generator at room temperature of 100 milliwatts provided in this embodiment achieves a high terahertz conversion rate without requiring expensive cooling equipment.

[0066] The single-pulse energy, repetition frequency, and average power of the terahertz pulse radiation generated by the room-temperature 100-milliwatt high-power, high-repetition-frequency terahertz strong source generation device provided in the embodiments of the present invention can be adjusted by adjusting parameters such as the single-pulse energy and repetition frequency of the pump laser (pump source) 1.

[0067] Pump laser 1 can be a femtosecond laser used to generate the pump laser. Optionally, pump laser 1 can be a ytterbium-doped fiber amplified femtosecond laser. In this embodiment, the pump laser output by pump laser 1 has a maximum single-pulse energy of 2 mJ, a repetition frequency adjustable from 1 Hz to 100 kHz, a center wavelength of 1030 nm, and a pulse width adjustable from 650 to 2000 fs. This type of industrial-grade laser has advantages such as high stability and good environmental adaptability. In this embodiment, the single-pulse energy range of the pump laser generated by pump laser 1 is set to 1 mJ to 2 mJ, the repetition frequency range is 1 kHz to 100 kHz, the center wavelength is 1030 nm, and the pulse width range is 950 fs to 1050 fs. The spot diameter range of the pump laser generated by pump laser 1 can be approximately 3.5 mm to 3.85 mm. Optionally, the spot diameter of the pump laser can be set to a range of approximately 3.75 mm to 3.85 mm (1 / e²).

[0068] A beam-expanding lens assembly, used to expand the laser spot, may include a concave lens 2 and a first convex lens 3. The assembly consists of a biconcave lens with a nominal focal length of -50 mm and a biconvex lens with a nominal focal length of 100 mm, installed sequentially at specific intervals. The distance between the concave lens 2 and the first convex lens 3 can be set to 50 mm. This beam-expanding lens assembly can expand the pump laser spot size to approximately twice its original size, reducing the power density of the pump laser to below the damage threshold of the lithium niobate crystal 14, enabling the lithium niobate crystal 14 to withstand femtosecond pump lasers with a maximum average power of 10⁴ W. This design prevents the pump laser from forming a focal point in the air, thus avoiding air ionization. The lenses included in the beam-expanding lens assembly, namely the concave lens 2 and the first convex lens 3, are both coated with a 10³⁰ nm anti-reflection coating to allow higher power pump lasers to pass through, used to generate strong-field terahertz radiation. After the pump laser beam is expanded by the beam expanding lens group, it is incident on the plane mirror group.

[0069] Optionally, the room-temperature 100-milliwatt high-power, high-repetition-rate terahertz source generator provided in this embodiment may further include a precision displacement stage for mounting a beam-expanding lens group. This allows for precise adjustment of the positions of the concave lens 2 and the first convex lens 3 within the beam-expanding lens group, enabling the pump laser to form a spot with a diameter of 7.5 mm to 7.9 mm (1 / e²) after passing through the beam-expanding lens group. The concave lens 2 and the first convex lens 3 are respectively mounted on the precision displacement stage in a horizontal plane, used to adjust the positions and angles of the concave lens 2 and the first convex lens 3 according to actual conditions, thereby fine-tuning the size and laser directivity of the laser spot emitted from the beam-expanding lens group. This precision displacement stage can be a two-dimensional, manually operated precision displacement stage.

[0070] The planar mirror assembly is used to guide the direction of the pump laser and may include a first ultrafast mirror 4 and a second ultrafast mirror 5.

[0071] The pump laser, after being expanded by the beam-expanding lens group, is incident on the first ultrafast mirror 4, then reflected by the first ultrafast mirror 4 and incident on the second ultrafast mirror 5. After being guided, it is incident on the first half-wave plate 6. After being polarized by the first half-wave plate 6, it is incident on the reflective diffraction grating 7.

[0072] Continue to refer to Figure 1A reflective diffraction grating 7 diffracts the incident pump laser to form a tilted wavefront pulsed laser. The reflective diffraction grating 7 can be a blazed grating with a grating line count G = 1400 lines / mm and a blaze wavelength of 1030 nm. According to the blazed grating diffraction equation, when the incident angle is 41.37° and the incident laser is to the left of the normal of the reflective diffraction grating 7, the diffraction angle corresponding to the negative first diffraction order is 51.37°, and the diffracted laser is to the left of the normal of the reflective diffraction grating 7. According to the blazed grating tilt angle formula, after diffraction by the reflective diffraction grating 7, the wavefront tilt angle is 46.4°, tilting upwards. This wavefront tilt angle is tuned by rotating and adjusting the angle of the reflective diffraction grating 7 and adjusting the incident angle of the pulsed laser. The pump laser incident on the reflective diffraction grating 7 is diffracted and reflected by the grating 7 before being incident on the gold reflector 8. After being reflected by the gold reflector 8, it is reflected by the third ultrafast reflector 9 and provided to the imaging lens group of the 4-f telescope, ultimately satisfying a 63° tilted wavefront angle with the tilt direction downwards. The third ultrafast reflector 9 can be coated with a 1030 nm antireflection coating.

[0073] A precision displacement rotary stage can also be set up. In order to make the pump laser after diffraction propagate along the optical axis of the system, the rotation center of the reflective diffraction grating 7 can be fixed on the precision displacement rotary stage. The reflective diffraction grating 7 can be adjusted within a range of 30° with an accuracy of 0.02° so that the incident laser is located to the left of the normal of the reflective diffraction grating 7 and the incident angle is 41.37°, thereby achieving a wavefront tilt angle of 46.4°.

[0074] The 4-f telescope imaging lens group may include a second convex lens 10, a second half-wave plate 11, and a third convex lens 12. The 4-f telescope imaging lens group consists of two convex lenses with focal lengths of 370 mm and 200 mm, respectively, mounted sequentially at a specific interval. The second convex lens 10 has a focal length of 370 mm; the third convex lens 12 has a focal length of 200 mm. Both convex lenses are coated with a 1030 nm anti-reflection coating. The distance between the second convex lens 10 and the third convex lens 12 can be set to 570 mm. This 4-f telescope imaging lens group has a magnification of 1.85, enabling the pump laser spot diameter after passing through the reflective diffraction grating 7 to be reduced by approximately 1.85 times and imaged onto the lithium niobate crystal 14. This reduced spot size maintains high pump intensity while ensuring an effective working distance with the lithium niobate crystal 14. According to the imaging formula, the wavefront tilt angle after passing through this 4-f telescope imaging lens group is 62.9°, tilted downwards. The 4-f telescope imaging lens group can generate a polarization matching the tilted wavefront by rotating the second half-wave plate 11; and the spot 13 incident on the lithium niobate crystal can be measured by a CCD camera to make corresponding adjustments.

[0075] The front surfaces of the gold reflector 8 and the lithium niobate crystal 14 are respectively positioned at the object plane and image plane of the 4-f telescope imaging lens group. The distance between the reflective diffraction grating 7 and the second convex lens 10 can be set to 370 mm, the distance between the second convex lens 10 and the third convex lens 12 to 570 mm, and the distance between the third convex lens 12 and the lithium niobate crystal 14 to 200 mm. Through these settings, the spot size of the pump laser can be adjusted by the 4-f telescope imaging lens group. The pump laser is reflected from the gold reflector 8 to the second convex lens 10 of the 4-f telescope imaging lens group, and after passing through the second convex lens 10, the second half-wave plate 11, and the third convex lens 12, a pump laser with a spot size reduced by approximately 1.85 times is obtained and incident on the lithium niobate crystal 14. Figure 2a As shown, the pump laser output from the imaging lens group of the 4-f telescope has a spot diameter ranging from approximately 3.5 mm to 3.8 mm (1 / e²), forming a spot 13 that is incident on the lithium niobate crystal.

[0076] like Figure 2b The diagram illustrates a light spot formed in one embodiment, including... Figure 2a The light spot 13 shown is incident on the lithium niobate crystal. Figure 2b The image on the left shows the spot of the pump laser emitted by pump laser 1, i.e., the spot of the pump laser before it is expanded by the beam expanding lens group. At this point, the major and minor axes of the spot are approximately 3.8 mm and 3.85 mm (1 / e²). The image in the middle shows the spot of the pump laser after it has been expanded by the beam expanding lens group. At this point, the major and minor axes of the spot are approximately 7.5 mm and 7.9 mm (1 / e²). The image on the right shows the spot of the pump laser after it has passed through the imaging lens group of the 4-f telescope. Figure 2a The light spot shown was reduced by approximately 1.85 times by the pump laser after processing by the imaging lens group of the 4-f telescope, with major and minor axes of approximately 3.8 mm and 3.5 mm (1 / e²). Due to angular astigmatism caused by the reflective diffraction grating 7, the diameter of the resulting light spot deviates slightly.

[0077] The pump laser incident on the lithium niobate crystal 14 interacts with the lithium niobate crystal 14, radiating terahertz waves through optical rectification. The lithium niobate crystal 14 can be a triangular prism-shaped lithium niobate crystal with dimensions of 20 mm × 20 mm × 30 mm. The terahertz radiation efficiency inside the lithium niobate crystal 14 is flexibly controlled by the wavefront tilt angle. The lithium niobate crystal 14 has a triangular prism shape with a base angle of 63° to adapt to the tilted wavefront angle and improve the terahertz generation efficiency. The 63° prism-shaped lithium niobate crystal can efficiently couple the terahertz pulse radiation generated by the output optical rectification and also filter the pump laser. The output surface of the lithium niobate crystal 14 uses a 0.02 mm polyimide black film to achieve filtering and terahertz coupling output. The incident surface of the lithium niobate crystal 14 is coated with a 1030 nm antireflection film to improve the pump laser utilization and increase the terahertz output. The pump laser passes through the lithium niobate crystal 14 and emits terahertz waves, which are then supplied to the terahertz collection module.

[0078] Optionally, the room-temperature 100-milliwatt high-power, high-repetition-rate terahertz source generator provided in this embodiment may further include a precision displacement rotary stage for mounting the lithium niobate crystal 14 to precisely adjust the position and angle of the lithium niobate crystal 14, thereby precisely adjusting the internal pulse wavefront tilt angle of the lithium niobate crystal 14 to 55°-70° with an adjustment accuracy of 0.02°. The precision displacement rotary stage may be a two-dimensional rotary stage. A 4-f telescope imaging lens group is configured such that the pump laser emitted from it is perpendicular to the incident surface of the lithium niobate crystal 14, satisfying a 63-degree crystal incident angle (because the lithium niobate crystal 14 has a 63° cutting angle). The angle of the lithium niobate crystal 14 can also be adjusted by precisely controlling the precision displacement rotary stage, with angle compensation within a 1-degree range.

[0079] The terahertz collection module may include a first off-axis parabolic mirror 15 (OAP), an ITO (transparent conductive film) flat glass plate 16, and a second off-axis parabolic mirror 17.

[0080] The first off-axis parabolic mirror 15 is gold-plated and collimates the terahertz pulse radiation, while the second off-axis parabolic mirror 17 focuses it. Compared to using a terahertz lens, this design minimizes terahertz loss and dispersion. The first off-axis parabolic mirror 15 may have a 2-inch aperture diameter and a 2-inch focal length for collection. The second off-axis parabolic mirror 17 may have a 2-inch aperture diameter and a 4-inch focal length for focusing, thereby improving the collection efficiency of the terahertz radiation signal by approximately 25%. The measuring device 18 is positioned at the focal point of the second off-axis parabolic mirror 17. The ITO plate glass 16 in the terahertz collection module is positioned between the first off-axis parabolic mirror 15 and the second off-axis parabolic mirror 17. The ITO plate glass 16 is used for filtering and reflection, has a resistivity of 1Ω-2Ω, an aperture size of 10 cm × 10 cm, and a terahertz reflectivity of over 99.9%. ITO flat glass 16 can be used to filter out 1030nm doped pump lasers and reflect terahertz pulse radiation.

[0081] The terahertz wave (i.e., terahertz pulse radiation or terahertz radiation) emitted by the lithium niobate crystal 14 is provided to the first off-axis parabolic mirror 15, which collects and shapes it into a parallel beam for emission. The beam is filtered and reflected by the ITO flat glass 16 to the second off-axis parabolic mirror 17, which focuses it onto the location of the measuring device 18.

[0082] The distance between the lithium niobate crystal 14 and the first off-axis parabolic mirror 15 can be set to 5 cm, the distance between the first off-axis parabolic mirror 15 and the ITO flat glass 16 can be set to 5 cm, the distance between the ITO flat glass 16 and the second off-axis parabolic mirror 17 can be set to 5 cm, and the distance between the second off-axis parabolic mirror 17 and the measuring device 18 can be set to 10 cm. This combination can effectively collect terahertz radiation and reduces system complexity by using components with the same parameters.

[0083] In measuring device 18, the pyroelectric detector can be a Gentec-EO SDX-1152-MT with a sensitivity of 3.83 × 10⁻⁶. 5 V / J; The terahertz power meter can use the Ophi 3A-P-THz.

[0084] The terahertz collection module may also include a precision displacement rotary stage for mounting the ITO flat glass 16 to precisely adjust its angle. The positions of the components of the terahertz collection module are configured such that the terahertz waves generated by the lithium niobate crystal 14 are incident at a 45° angle onto the first off-axis parabolic reflector 15, exit at a 45° angle from the first off-axis parabolic reflector 15, and are incident on the ITO flat glass 16. By adjusting the angle of the ITO flat glass 16, the terahertz waves reflected from the ITO flat glass 16 can be incident at a 45° angle onto the second off-axis parabolic reflector 17, and are reflected at a 45° angle from the second off-axis parabolic reflector 17, focusing the terahertz waves onto the location where the measuring device 18 is placed.

[0085] The high-power, high-repetition-rate terahertz source generating device at room temperature with a pump laser 1 is configured to emit a pump laser with a center wavelength of 1030 nm, a single pulse energy range of 1 mJ - 2 mJ, a pump power range of 100 W - 150 W, a pulse width range of 950 fs - 1050 fs, and a laser spot diameter range of 3.5 mm - 3.85 mm, capable of outputting terahertz radiation pulses of over 100 milliwatts. When generating terahertz radiation pulses of over 100 milliwatts, the device of this embodiment operates at room temperature without cooling and does not damage the lithium niobate crystal 14.

[0086] The high-power, high-repetition-rate terahertz source generation device with a hundred milliwatts at room temperature provided by this embodiment is configured such that the pump laser emitted by the pump laser 1 has a center wavelength of 1030 nm, a pulse width range of 950 fs-1050 fs, and a repetition frequency range of 1 kHz-100 kHz, and can achieve a terahertz conversion efficiency of 0.1% or higher.

[0087] The operating process of the high-power, high-repetition-rate terahertz source generation device at room temperature of 100 milliwatts provided according to an embodiment of the present invention is as follows: The pump laser emitted by the pump laser 1 passes through a beam-expanding lens group composed of a concave lens 2 and a first convex lens 3, which expands the beam of the pump laser, increasing the beam size (beam diameter) to approximately twice its initial size; subsequently, the pump laser is guided by the first ultrafast reflecting mirror 4 and the second ultrafast reflecting mirror 5, and after its polarization is adjusted by the first half-wave plate 6, it is incident on the reflective diffraction grating 7 at an angle of 41.37°, achieving a diffraction efficiency of 95% on the negative first-order diffraction order of the reflective diffraction grating 7 with a diffraction angle of 51.37°; after passing through the reflective diffraction grating 7... The pump laser, after reflection and diffraction, is incident on the gold mirror 8. After being reflected by the gold mirror 8, the pump laser is reflected again by the third ultrafast mirror 9 and passes through the 4-f telescope imaging lens group composed of the second convex lens 10, the second half-wave plate 11, and the third convex lens 12, resulting in a pump laser with a spot size reduced by approximately 1.85 times, which is then incident on the lithium niobate crystal 14. The pump laser interacts with the lithium niobate crystal 14, radiating terahertz waves through optical rectification. The radiated terahertz waves are collected and shaped into a parallel beam by the first off-axis parabolic mirror 15, and after being reflected by the ITO flat glass 16, are focused by the second off-axis parabolic mirror 17 onto the location of the pyroelectric detector or terahertz power meter. The single-pulse energy, repetition frequency, and average power of the generated terahertz radiation can be adjusted by adjusting the single-pulse energy, repetition frequency, and other parameters of the femtosecond laser (pump source) used as the pump laser 1.

[0088] In another embodiment, a two-dimensional translation stage may be provided for the concave lens 2, the first convex lens 3, the second convex lens 10, the third convex lens 12, the first off-axis parabolic mirror 15, the second off-axis parabolic mirror 17, and the measuring device 18, respectively, for precisely adjusting the position and angle of the components. This two-dimensional translation stage can be a two-dimensional manual translation stage, with a minimum movement scale of 10 μm.

[0089] Figure 3 This is a graph showing the relationship between terahertz radiation energy under different pump laser pulse widths in one embodiment of the high-power, high-repetition-rate terahertz source generation device at room temperature provided according to an embodiment of the present invention.

[0090] like Figure 3As shown in the figure, in this embodiment, the pump laser 1 provides a pump laser repetition frequency of 100 Hz and a pulse width range of 650 fs - 1400 fs. As can be seen from the figure, as the pulse width increases from 650 fs to 1000 fs and then to 1400 fs, the corresponding terahertz energy increases from 1.9 µJ to 2.15 µJ and then to 1.86 µJ, and the terahertz energy conversion efficiency increases and then decreases accordingly. Specifically, the terahertz energy conversion efficiency at a pulse width of 1000 fs is approximately 14.96% higher than that at a pulse width of 650 fs. In this embodiment, the pump laser has a repetition frequency of 100 Hz, and the maximum output power at this frequency is 0.2 W, which is not very high and will not cause heating of the lithium niobate crystal 14 during the experiment. In this embodiment, the energy probe of the measuring device 18 does not have a black film, as the black film can transmit 80% of the terahertz waves. The energy probe uses a pyroelectric detector (sensitivity coefficient 3.83 × 10⁻⁶). 5 (V / J) can be used by connecting to an oscilloscope. After reading the voltage on the oscilloscope, the energy can be calculated using the sensitivity coefficient.

[0091] Figure 4a This is another embodiment of the high-power, high-repetition-rate terahertz source generating device at room temperature of 100 milliwatts provided according to an embodiment of the present invention. Under the condition of fixed pump laser pulse width, the relationship between pump laser energy and generated terahertz energy is measured by changing the pump laser repetition rate. Figure 4b This is a graph showing the relationship between pump power and generated terahertz power at a pump laser repetition rate of 100 kHz in an embodiment of the high-power, high-repetition-rate terahertz source generating device at room temperature provided according to an embodiment of the present invention.

[0092] See Figure 4a and 4b With a pump laser of 100 kHz repetition frequency and 109.1 W pump power, the pump laser 1 produced terahertz radiation with a maximum average power of 103.8 mW, corresponding to a pump pulse energy of 1.125 mJ.

[0093] like Figure 4aAs shown, at a repetition frequency of 100 kHz, further extending the pump power to 123.3 W, corresponding to a pump pulse energy of 1.2 mW, results in an inflection point where the average terahertz power of the generated terahertz radiation decreases to 60 mW. This reduction is due to damage to the gold mirror 8 caused by the high pump power. Therefore, even at a pump power of 123.3 W and a pump pulse energy of 1.2 mW, the room-temperature 100-mW high-power, high-repetition-rate terahertz source generator of this embodiment can ensure that the lithium niobate crystal 14 remains undamaged, requiring only the replacement of the gold mirror 8. At this inflection point, the terahertz conversion efficiency is approximately 0.1%, indicating that thermal effects under high-power pump lasers reduce the terahertz conversion efficiency.

[0094] Continue to refer to Figure 4a The pump laser provided by pump laser 1 has a pulse width of 1000 fs, a repetition frequency of 5 kHz, and a maximum pump energy density of 14.76 mJ / cm². 2 Under the given conditions, the optimal terahertz conversion efficiency was 0.123%; at a repetition rate of 10 kHz, the terahertz conversion efficiency was 0.121%; at a repetition rate of 20 kHz, the terahertz conversion efficiency was 0.118%; at a repetition rate of 33.3 kHz, the terahertz conversion efficiency was 0.117%; and when the repetition rate increased to 50 kHz, the terahertz conversion efficiency slightly decreased to 0.114%. The provided pump laser had a repetition rate of 100 kHz and a repetition rate of 10.33 mJ / cm². 2 At the given pump energy density, a terahertz conversion efficiency of 0.099% can be obtained. This can be explained by the thermal effect that occurs at higher repetition frequencies. The pump energy density is the value obtained by dividing the pump energy by the area of ​​the light spot 13 incident on the lithium niobate crystal.

[0095] according to Figure 3 and Figure 4a For the room-temperature high-power, high-repetition-rate terahertz source generating device of this embodiment, by adjusting the pump laser provided by pump laser 1 at a center wavelength of 1030 nm, a pulse width of 950 fs-1050 fs, and a repetition frequency range of 1 kHz-100 kHz, a terahertz conversion efficiency of greater than or equal to 0.1% can be achieved.

[0096] According to another embodiment of the present invention, a novel terahertz power source system with high average power and high repetition frequency based on room temperature uncooled operation is provided, comprising the following components arranged sequentially along the optical path: a femtosecond laser, a plane mirror, a laser beam expander lens group, a half-wave plate, a reflective grating, a 4-f telescope imaging lens group, a triangular prism lithium niobate crystal, and a terahertz collection device (off-axis parabolic mirror-ITO-off-axis parabolic mirror). The working process is as follows: the femtosecond pump laser output from the femtosecond laser is formed into a 7.9 mm (1 / e²) diameter spot by a beam-expanding lens group adjusted by a precision displacement stage. After reflection by a plane mirror and polarization state modulation by a half-wave plate, it is diffracted by a reflection grating to form a tilted wavefront pulse laser. The spot is then reduced to 3.8 mm (1 / e²) by a 4-f telescope imaging lens group and imaged onto the surface of a lithium niobate crystal. Terahertz pulse radiation is generated perpendicular to the wavefront direction through optical rectification. The precision displacement stage can accurately adjust the tilt angle of the pulse wavefront inside the crystal (adjustment range 55° to 70°, adjustment accuracy 0.02°). The terahertz pulse radiation is collected by a first off-axis parabolic mirror, filtered and reflected by ITO flat glass, and then focused by a second off-axis parabolic mirror. Finally, a pyroelectric detector (Gentec-EO SDX-1152-MT, sensitivity 3.83 × 10⁻⁶) is used. 5 Energy and power measurements were performed using a V / J voltmeter and a terahertz power meter (Ophi 3A-P-THz).

[0097] All of the above-mentioned optional technical solutions can be combined in any way to form optional embodiments of the present invention, and will not be described in detail here.

[0098] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0099] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-power, high-repetition-rate terahertz source generating device with a capacity of 100 milliwatts at room temperature, characterized in that, Including those arranged sequentially along the optical path: Pump laser (1) provides femtosecond pump laser; The beam-expanding lens group expands the femtosecond pump laser beam to twice the initial beam diameter; Planar mirror assembly, used to guide the expanded pump laser; The first half-wave plate (6), the reflective diffraction grating (7), the gold reflector (8), and the third ultrafast reflector (9) are used to adjust polarization and diffraction reflection; The 4-f telescope imaging lens group is used to reduce the spot diameter of the received pump laser and image it onto the lithium niobate crystal (14). Lithium niobate crystal (14) generates terahertz pulse radiation in a direction perpendicular to the wavefront; Terahertz collection module, which receives and focuses terahertz pulse radiation; The measuring device (18) receives focused terahertz pulse radiation for measurement.

2. The high-power, high-repetition-rate terahertz source generating device at room temperature of 100 milliwatts according to claim 1, characterized in that, The beam expander lens group includes, in sequence: Concave lens (2) is a biconcave lens with a nominal focal length of -50 mm; and The first convex lens (3) is a biconvex lens with a nominal focal length of 100 mm. The distance between the concave lens (2) and the first convex lens (3) is 50 mm.

3. The high-power, high-repetition-rate terahertz source generating device at room temperature of 100 milliwatts according to claim 1, characterized in that, The pump laser (1) is a ytterbium-doped fiber amplified femtosecond laser, with the output pump laser having a single pulse energy range of 1 mJ - 2 mJ, a repetition frequency range of 1 kHz - 100 kHz, a center wavelength of 1030 nm, and a pulse width range of 950 fs - 1050 fs.

4. The high-power, high-repetition-rate terahertz source generating device at room temperature of 100 milliwatts according to claim 1, characterized in that: The angles of the first half-wave plate (6), the reflective diffraction grating (7), and the gold reflector (8) are set such that the pump laser, after being polarized by the first half-wave plate (6), is incident at an angle of 41.37° onto the reflective diffraction grating (7).

5. The high-power, high-repetition-rate terahertz source generating device at room temperature of 100 milliwatts according to claim 1, characterized in that, The 4-f telescope imaging lens reduces the diameter of the received pump laser spot by a factor of 1.85, and includes, in sequence: The second convex lens (10) is a convex lens with a focal length of 370 mm; The second half-wave plate (11) is used to generate polarization matching the tilted wavefront; The third convex lens (12) is a convex lens with a focal length of 200 mm; The distance between the second convex lens (10) and the third convex lens (12) is 570 mm.

6. The high-power, high-repetition-rate terahertz source generating device at room temperature of 100 milliwatts according to claim 5, characterized in that: The distance between the reflective diffraction grating (7) and the second convex lens (10) is 370 mm; The distance between the third convex lens (12) and the lithium niobate crystal (14) is 200 mm.

7. The room-temperature 100-milliwatt high-power, high-repetition-rate terahertz strong source generating device according to claim 1, characterized in that, The terahertz collection module includes, in sequence: The first off-axis parabolic mirror (15) has a 2-inch aperture diameter and a 2-inch focal length to collimate the terahertz pulse radiation emitted from the lithium niobate crystal (14) into a parallel beam. ITO flat glass (16) is used for filtering to remove 1030nm doped pump laser and reflect terahertz pulse radiation; The second off-axis parabolic mirror (17), with a 2-inch aperture diameter and a 4-inch focal length, focuses the received terahertz pulse radiation.

8. The high-power, high-repetition-rate terahertz source generating device at room temperature of 100 milliwatts according to claim 7, characterized in that: The distance between the first off-axis parabolic reflector (15) and the ITO flat glass (16) is 5cm, and the distance between the ITO flat glass (16) and the second off-axis parabolic reflector (17) is 5cm.

9. The high-power, high-repetition-rate terahertz source generating device at room temperature of 100 milliwatts according to claim 7, characterized in that: The distance between the lithium niobate crystal (14) and the first off-axis parabolic mirror (15) is 5 cm, and the distance between the second off-axis parabolic mirror (17) and the measuring device (18) is 10 cm.

10. The high-power, high-repetition-rate terahertz source generating device at room temperature of 100 milliwatts according to claim 1, characterized in that: The spot diameter of the femtosecond pumped laser provided by the pump laser (1) ranges from 3.75 mm to 3.85 mm; The beam-expanding lens group expands the spot diameter of the femtosecond pump laser to a range of 7.5 mm to 7.9 mm. The 4-f telescope imaging lens group reduces the spot size of the received pump laser to a range of 3.5 mm to 3.8 mm in diameter.

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