High-power terahertz radiation source and product quality detection system

Abstract

The invention discloses a high-power terahertz radiation source and a product quality detection system, is applied to the technical field of terahertz, and is specifically characterized in that the high-power terahertz radiation source comprises a high-power near-infrared laser pumping source, an OPO module and a DFG module which are sequentially arranged on the same light path; the OPO module comprises a first periodically poled nonlinear optical crystal, and the DFG module comprises a second periodically poled nonlinear optical crystal; the high-power near-infrared laser pumping source provides high-power near-infrared pumping laser which is incident to the first periodically poled nonlinear optical crystal, and the first periodically poled nonlinear optical crystal converts the high-power near-infrared pumping laser into dual-wavelength pumping laser which is incident to the second periodically poled nonlinear optical crystal. And the second periodically poled nonlinear optical crystal converts the dual-wavelength pumping laser into terahertz waves and outputs the terahertz waves. Therefore, through the OPO module and the DFG module which are optimally designed, stable output of high-power terahertz waves is realized.

Description

Technical Field

[0001] This application relates to the field of terahertz technology, and in particular to a high-power terahertz radiation source and a product quality testing system. Background Technology

[0002] Terahertz waves typically refer to electromagnetic waves with frequencies between 0.1 THz and 10 THz. The rotational, vibrational, or translational energy levels of various molecules, ions, free radicals, and biomolecules all fall within this frequency range, exhibiting distinct fingerprint characteristics. Therefore, the spectral information of substances in this frequency band contains rich and specific fingerprint information, which has high application potential in many fields such as material detection, life science exploration, molecular spectroscopy analysis, and bioimaging.

[0003] Terahertz radiation sources, as core components in the practical applications of terahertz technology, play a crucial role in fields such as spectral analysis, multispectral / hyperspectral imaging, product identification, and quality inspection. However, current terahertz radiation sources face bottlenecks such as low energy conversion efficiency, low terahertz wave output power, and poor operational stability, which significantly limit the application of terahertz technology in spectral analysis, material detection, and biomedicine. Therefore, researching and exploring high-power, high-performance, and highly stable terahertz radiation sources has become one of the current research hotspots in the field of terahertz technology. Summary of the Invention

[0004] This application provides a high-power terahertz radiation source and a product quality inspection system to solve the problems of low terahertz wave output power, high operation and maintenance costs, and poor operational stability in existing terahertz radiation sources. The technical solution provided by this application is as follows: On the one hand, this application provides a high-power terahertz radiation source, including a high-power near-infrared laser pump source, an OPO (Optical Parametric Oscillation) module, and a DFG (Difference Frequency Generation) module arranged sequentially on the same optical path; A high-power near-infrared laser pump source is used to provide high-power near-infrared pump laser and incident it onto the OPO module; The OPO module includes a resonant cavity and a first-period polarized nonlinear optical crystal located within the resonant cavity. The first-period polarized nonlinear optical crystal is used to convert high-power near-infrared pump laser into dual-wavelength pump laser through optical parametric oscillation technology. The resonant cavity is used to oscillate the dual-wavelength pump laser back and forth through the first-period polarized nonlinear optical crystal until a stable oscillation state is reached before it is incident on the DFG module. The polarization period of the first-period polarized nonlinear optical crystal is set based on the wave vector mismatch between the high-power near-infrared pump laser and the dual-wavelength pump laser. The DFG module includes a second-period polarized nonlinear optical crystal, which is used to convert the dual-wavelength pump laser into a terahertz wave and output it through nonlinear difference frequency technology; wherein, the polarization period of the second-period polarized nonlinear optical crystal is set based on the wave vector mismatch between the dual-wavelength pump laser and the terahertz wave.

[0005] Optionally, the high-power near-infrared laser pump source includes a high-power near-infrared laser; High-power near-infrared lasers are used to provide pump lasers with nanosecond-level pulse widths, megahertz-level repetition rates, millijoule-level single-pulse energy, high beam quality, and near-infrared wavelengths as high-power near-infrared pump lasers incident on the OPO module.

[0006] Optionally, the OPO module also includes a first focusing lens disposed in front of the resonant cavity; The first focusing lens is used to focus the high-power near-infrared pump laser onto the active region of the first periodically polarized nonlinear optical crystal, while simultaneously matching the spatial morphology of the high-power near-infrared pump laser with the eigenmode of the resonant cavity.

[0007] Optionally, the resonant cavity includes a front cavity mirror and a rear cavity mirror; the front cavity mirror is a concave mirror and the rear cavity mirror is a plane mirror.

[0008] Optionally, the DFG module also includes a second focusing lens disposed in front of the second periodically polarized nonlinear optical crystal; The second focusing lens is used to focus the dual-wavelength pump laser onto the operating region of the second periodically polarized nonlinear optical crystal.

[0009] Optionally, the high-power terahertz radiation source provided in this application also includes a first laser collection module disposed between the OPO module and the DFG module; The first laser collection module is used to filter out and collect the remaining high-power near-infrared pump laser output from the OPO module that has not been converted into dual-wavelength pump laser.

[0010] Optionally, the high-power terahertz radiation source provided in this application also includes a second laser collection module disposed after the DFG module; The second laser collection module is used to absorb all wavelengths of laser light output from the DFG module except for terahertz waves.

[0011] Optionally, the high-power terahertz radiation source provided in this application also includes a temperature synchronization control module; The temperature synchronization control module is used to synchronously control the operating temperature of the first period polarized nonlinear optical crystal and the second period polarized nonlinear optical crystal, so that the center frequency of the terahertz wave output by the DFG module is kept synchronized with the frequency difference of the dual-wavelength pump laser output by the OPO module in real time.

[0012] On the other hand, this application provides a product quality inspection system, including the above-mentioned high-power terahertz radiation source, two-dimensional moving platform, terahertz wave detector and data processing equipment; the high-power terahertz radiation source, two-dimensional moving platform and terahertz wave detector are sequentially arranged on the same optical path, and the terahertz wave detector is communicatively connected to the data processing equipment. High-power terahertz radiation source, used to provide high-power terahertz waves; A two-dimensional moving platform is used to control the movement of the product to be tested within the testing area so that high-power terahertz waves are transmitted or reflected from the product to be tested; Terahertz wave detectors are used to collect terahertz wave signals after high-power terahertz waves are transmitted or reflected from the product under test. Data processing equipment is used to perform quality inspection on the product under test based on the terahertz wave signal collected by the terahertz wave detector to obtain the quality inspection result.

[0013] Optionally, the data processing equipment is used to identify defects in the product to be inspected based on terahertz wave signals using a deep learning model to obtain defect identification results; and to determine the quality inspection results of the product to be inspected based on the defect identification results.

[0014] The beneficial effects of this application are as follows: In the high-power terahertz radiation source and product quality inspection system provided in this application, the high-power near-infrared laser pump source, OPO module, and DFG module are sequentially arranged on the same optical path. This ensures that the propagation directions of the high-power near-infrared pump laser, the dual-wavelength pump laser, and the terahertz wave are the same, effectively avoiding the problem of beam separation due to crystal birefringence or dispersion characteristics affecting energy conversion efficiency when the propagation directions are different. Moreover, the OPO module uses a periodically polarized nonlinear optical crystal located in the resonant cavity for optical parametric oscillation, and the DFG module uses another periodically polarized nonlinear optical crystal for nonlinear difference frequency. By setting the polarization period of these two periodically polarized nonlinear optical crystals, the high-energy dual-wavelength pump laser and the dual-wavelength pump laser can be aligned in the same direction. Both the pump laser and the dual-wavelength pump laser satisfy the corresponding quasi-phase matching conditions, thus achieving stable output of high-energy dual-wavelength pump laser and stable output of high-power terahertz wave. In addition, both the OPO module and DFG module use periodically polarized nonlinear optical crystals. These crystals have high transmittance and stable nonlinear coefficients at room temperature, and can maintain efficient energy conversion at room temperature without low-temperature cooling, fundamentally eliminating the need for a cooling system and reducing the size of the terahertz radiation source. This achieves a stable high-power terahertz wave output while also considering room temperature operation and miniaturization, meeting the application requirements of high-power, high-performance, and high-stability terahertz wave radiation sources for product quality testing.

[0015] Other features and advantages of this application will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the application. The objectives and other advantages of this application may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings. Attached Figure Description

[0016] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, are illustrative and descriptive in nature and are used to interpret this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a schematic diagram of the composition and structure of the high-power terahertz radiation source in the embodiments of this application; Figure 2 This is a schematic diagram of the specific structure of the high-power terahertz radiation source in the embodiments of this application; Figure 3 These are the temperature tuning curves of the signal light and idler light under different polarization periods in the embodiments of this application; Figure 4 This is a schematic diagram of the OPO module in an embodiment of this application; Figure 5 This is a schematic diagram showing the relationship between the effective length and curvature of different resonant cavities and the resonant cavity mode waist in the embodiments of this application; Figure 6 This is a schematic diagram of the geometric model for generating terahertz waves using collinear difference frequency in MgO:PPLN crystals in an embodiment of this application. Figure 7 This is a schematic diagram showing the relationship between the polarization period of the second periodically polarized nonlinear optical crystal and the frequency of the output terahertz wave in an embodiment of this application. Figure 8 This is a schematic diagram showing the relationship between the terahertz wave output power and the length of the second periodically polarized nonlinear optical crystal in an embodiment of this application. Figure 9 This is a schematic diagram of the tuning curve of the high-power terahertz radiation source outputting the terahertz wave in an embodiment of this application; Figure 10 This is a schematic diagram of the product quality inspection system in the embodiments of this application; Figure 11 This is a flowchart illustrating the product quality testing method in the embodiments of this application; Figure 12 This is a schematic diagram of the hardware structure of the data processing device in the embodiments of this application. Detailed Implementation

[0017] To make the objectives, technical solutions, and beneficial effects of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0018] Terahertz radiation sources, as core components in the practical applications of terahertz technology, play a crucial role in fields such as spectral analysis, multispectral / hyperspectral imaging, product identification, and quality inspection. These fields have a significant demand for high-power, miniaturized terahertz radiation sources that operate stably at room temperature. However, current terahertz radiation sources face bottlenecks such as low terahertz wave output power, high operating and maintenance costs, stringent environmental requirements, and poor operational stability, which greatly limit the application of terahertz technology in spectral analysis, material detection, and biomedicine. Therefore, researching and exploring high-performance, highly stable, and low-cost terahertz radiation sources has become one of the current hot topics in the field of terahertz technology.

[0019] Nonlinear optical frequency conversion is an effective terahertz wave generation technique, offering advantages such as high output power, high stability, compact structure, and room temperature operation. Currently, this field primarily utilizes near-infrared pump lasers and nonlinear crystals to generate terahertz waves. However, common nonlinear crystals are limited by their dispersion characteristics, requiring stringent angle and phase matching conditions, complex tuning methods, and poor system stability. Furthermore, the high absorption of terahertz waves in nonlinear crystals restricts the interaction length between the nonlinear crystal and the pump laser, severely limiting the energy conversion efficiency in the nonlinear process. These two shortcomings significantly impact the application requirements of terahertz radiation sources.

[0020] Based on this, the high-power terahertz radiation source and product quality inspection system provided in this application include a high-power near-infrared laser pump source, an OPO module, and a DFG module sequentially arranged on the same optical path. The OPO module includes a resonant cavity and a first periodically polarized nonlinear optical crystal located within the resonant cavity, and the polarization period of the first periodically polarized nonlinear optical crystal satisfies the first quasi-phase matching condition based on the high-power near-infrared pump laser and the dual-wavelength pump laser. The DFG module includes a second periodically polarized nonlinear optical crystal, and the polarization period of the second periodically polarized nonlinear optical crystal... The system aims to satisfy the second quasi-phase matching condition based on dual-wavelength pump laser and terahertz wave; a high-power near-infrared laser pump source provides high-power near-infrared pump laser and incident on the OPO module; a first-period polarized nonlinear optical crystal converts the high-power near-infrared pump laser into a dual-wavelength pump laser through optical parametric oscillation technology; a resonant cavity oscillates the dual-wavelength pump laser back and forth through the first-period polarized nonlinear optical crystal until it reaches a stable oscillation state and is then incident on the DFG module; a second-period polarized nonlinear optical crystal converts the dual-wavelength pump laser into a terahertz wave through nonlinear difference frequency technology and outputs it.

[0021] In this way, the high-power near-infrared laser pump source, OPO module, and DFG module are sequentially arranged on the same optical path, ensuring that the propagation directions of the high-power near-infrared pump laser, dual-wavelength pump laser, and terahertz wave are the same. This effectively avoids the problem of beam separation due to crystal birefringence or dispersion characteristics affecting energy conversion efficiency when propagation directions are different. Moreover, the OPO module uses a periodically polarized nonlinear optical crystal located in the resonant cavity for optical parametric oscillation, and the DFG module uses another periodically polarized nonlinear optical crystal for nonlinear difference frequency. By setting the polarization period of these two periodically polarized nonlinear optical crystals, phase symmetry can be satisfied between the high-energy dual-wavelength pump laser and between the dual-wavelength pump laser and the terahertz wave. The corresponding quasi-phase matching conditions are met to achieve stable output of high-energy dual-wavelength pump laser and stable output of high-power terahertz waves. In addition, both the OPO module and DFG module adopt periodically polarized nonlinear optical crystals. These crystals have high transmittance (≥90% transmittance in the near-infrared and terahertz bands) and stable nonlinear coefficients at room temperature (e.g., 5-40℃). They can maintain efficient energy conversion at room temperature without the need for low-temperature cooling, fundamentally eliminating the need for a cooling system and reducing the size of the terahertz radiation source. This achieves a stable output of high-power terahertz waves while also ensuring room temperature operation and miniaturization, meeting the application requirements of high-power, high-performance, and high-stability terahertz wave radiation sources for product quality testing.

[0022] After introducing the application scenarios and design concepts of this application, the technical solutions provided by this application will be described in detail below.

[0023] This application provides a high-power terahertz radiation source, see reference. Figure 1 As shown, the high-power terahertz radiation source 100 provided in this application embodiment includes a high-power near-infrared laser pump source 110, an OPO module 120 and a DFG module 130 arranged sequentially on the same optical path; A high-power near-infrared laser pump source 110 is used to provide a high-power near-infrared pump laser and incident it onto the OPO module 120; The OPO module 120 includes a resonant cavity 121 and a first periodically polarized nonlinear optical crystal 122 located within the resonant cavity 121. The first periodically polarized nonlinear optical crystal 122 is used to convert high-power near-infrared pump laser into dual-wavelength pump laser through optical parametric oscillation technology. The resonant cavity 121 is used to allow the dual-wavelength pump laser to pass back and forth through the first periodically polarized nonlinear optical crystal 122 through oscillation until it reaches a stable oscillation state and is then incident on the DFG module 130. The polarization period of the first periodically polarized nonlinear optical crystal 122 satisfies the first quasi-phase matching condition based on the high-power near-infrared pump laser and the dual-wavelength pump laser. DFG module 130 includes a second periodically polarized nonlinear optical crystal 131, which is used to convert dual-wavelength pump laser into terahertz wave and output it through nonlinear difference frequency technology; wherein, the polarization period of the second periodically polarized nonlinear optical crystal 131 satisfies the second quasi-phase matching condition based on dual-wavelength pump laser and terahertz wave.

[0024] In this embodiment, a high-power near-infrared pump laser provided by a high-power near-infrared laser pump source 110 is incident on an OPO module 120. In the OPO module 120, a first periodically polarized nonlinear optical crystal 122, under the condition of satisfying a first quasi-phase matching condition based on the high-power near-infrared pump laser and a dual-wavelength pump laser, undergoes optical parametric oscillation with the high-power near-infrared pump laser to efficiently generate signal light and idler light as dual-wavelength pump laser, which is then incident on a DFG module 130. In the DFG module 130, a second periodically polarized nonlinear optical crystal 131, under the condition of satisfying a second quasi-phase matching condition based on the dual-wavelength pump laser and a terahertz wave, undergoes nonlinear difference frequency interaction with the dual-wavelength pump laser to efficiently generate and output a terahertz wave. In this way, the OPO module 120 uses a first periodically polarized nonlinear optical crystal 122 that enables the high-power near-infrared pump laser and the dual-wavelength pump laser to meet the first quasi-phase matching condition, and the DFG module 130 uses a second periodically polarized nonlinear optical crystal 131 that enables the dual-wavelength pump laser and the terahertz wave to meet the second quasi-phase matching condition. Moreover, the high-power near-infrared pump laser, the dual-wavelength pump laser and the terahertz wave are collinear, which not only ensures high stability and small size, but also avoids the problem of low energy conversion efficiency caused by walk-off effect. Thus, through the optimized design of the OPO module and DFG module, a terahertz radiation source that can stably output high-power terahertz waves while taking into account room temperature operation and miniaturization is realized, which meets the application requirements of high power, high performance and high stability of terahertz wave radiation source for product quality testing.

[0025] In a specific implementation, in one embodiment, the first periodically polarized nonlinear optical crystal 122 and the second periodically polarized nonlinear optical crystal 131 can be the same periodically polarized nonlinear optical crystal material. For example, both the first periodically polarized nonlinear optical crystal 122 and the second periodically polarized nonlinear optical crystal 131 are MgO:PPLN (magnesium oxide-doped periodically polarized lithium niobate crystal). In another embodiment, the first periodically polarized nonlinear optical crystal 122 and the second periodically polarized nonlinear optical crystal 131 can also be different periodically polarized nonlinear optical crystal materials. For example, the first periodically polarized nonlinear optical crystal 122 is PPKTP (periodically polarized potassium titanium phosphate), and the second periodically polarized nonlinear optical crystal 131 is MgO:PPLN.

[0026] In this embodiment, it is preferred that the first periodic polarization nonlinear optical crystal 122 and the second periodic polarization nonlinear optical crystal 131 are made of the same periodic polarization nonlinear optical crystal material. As mentioned above, both the first periodic polarization nonlinear optical crystal 122 and the second periodic polarization nonlinear optical crystal 131 can be MgO:PPLN; specifically, both the first periodic polarization nonlinear optical crystal 122 and the second periodic polarization nonlinear optical crystal 131 can be MgO:PPLN with a molar concentration of 4%-7%, preferably, both can be MgO:PPLN with a molar concentration of 5%; wherein, the polarization period of the first periodic polarization nonlinear optical crystal 122 and the second periodic polarization nonlinear optical crystal 131 = 2pi / wave vector mismatch, where pi is pi; The calculation process for the polarization period of the first-period polarized nonlinear optical crystal 122 and the second-period polarized nonlinear optical crystal 131 is the same. However, the polarization periods will be different due to the different phase mismatch caused by the refractive index of the two nonlinear processes. For example, the polarization period of the first-period polarized nonlinear optical crystal 122 is 31-32.5 μm, preferably 31.98 μm, and the size is 30 mm × 5 mm × 2 mm. The incident end face is coated with antireflection coatings (AR) in the 1064 nm and 2050-2150 nm bands. The polarization period of the second-period polarized nonlinear optical crystal 131 is 180-186 μm, preferably 182.34 μm, and the size is 30 mm × 5 mm × 2 mm. The incident end face is coated with an antireflection coating in the 2050-2150 nm band.

[0027] In specific implementations, the high-power near-infrared laser pump source 110 in the high-power terahertz radiation source provided in this application embodiment can have various specific structures to realize its function. For example Figure 2 As shown, the high-power near-infrared laser pump source 110 may include a high-power near-infrared laser 111; A high-power near-infrared laser 111 is used to provide a pump laser with nanosecond-level pulse width, megahertz-level repetition rate, millijoule-level single-pulse energy, high beam quality, and near-infrared wavelength as a high-power near-infrared pump laser incident on the OPO module 120.

[0028] In one embodiment of this application, the high-power near-infrared laser 111 can be a microchip laser. Using a microchip laser as the high-power near-infrared laser pump source 110 ensures high output power while significantly reducing the radiation source size, effectively lowering manufacturing costs. In another embodiment, the high-power near-infrared laser 111 can also be a Q-switched diode-pumped solid-state laser. When a Q-switched diode-pumped solid-state laser replaces the microchip laser as the high-power near-infrared laser pump source 110, its key parameters can be set as follows: output wavelength 1064nm ± 0.1nm, repetition frequency 10-30kHz, pulse width 5-15ns, and average power... 20W, thus enabling high output power without increasing size and complexity.

[0029] For specific implementation, please refer to Figure 2 As shown, the OPO module 120 may also include a first focusing lens 123 disposed in front of the resonant cavity 121; The first focusing lens 123 is used to focus the high-power near-infrared pump laser onto the active region of the first periodically polarized nonlinear optical crystal 122, while simultaneously matching the spatial morphology of the high-power near-infrared pump laser with the eigenmode of the resonant cavity 121.

[0030] In this embodiment, the first focusing lens 123 can be a plano-convex lens with a focal length f. OPO =50-400mm, preferably 300mm, coated with an anti-reflection film in the 1064nm band; the first focusing lens 123 is used to focus the high-power near-infrared pump laser to improve the pump power density, and is also used in conjunction with the resonant cavity 121 to match the spatial shape of the high-power near-infrared pump laser with the eigenmode of the resonant cavity 121, so as to improve the interaction length between the high-power near-infrared pump laser and the first periodically polarized nonlinear optical crystal 122 during the OPO process, so that the entire length of the first periodically polarized nonlinear optical crystal 122 becomes the effective interaction region, thereby improving the energy conversion efficiency.

[0031] In specific implementations, the resonant cavity 121 in the high-power terahertz radiation source provided in this application embodiment can have various specific structures to realize its function. For example... Figure 2 As shown, the resonant cavity 121 includes a front cavity mirror 1211 and a rear cavity mirror 1212; the front cavity mirror 1211 is a concave mirror and the rear cavity mirror 1212 is a plane mirror.

[0032] In this embodiment, the front cavity mirror 1211 is a plano-concave mirror with a radius of curvature R = 100-500 mm, preferably 300 mm, and is coated with an antireflection coating for the 1064 nm band and a high reflectance coating (HR) for the 2050-2150 nm band; the rear cavity mirror 1212 is a plane mirror, coated with a high transmittance coating (HT) for the 1064 nm band and a high transmittance coating (HT) for the 2050-2150 nm band. The transmittance of the high transmittance coating (HT) is 10%-60%, preferably 25%. Thus, the front cavity mirror 1211 and the rear cavity mirror 1212 form a plano-concave cavity as a resonant cavity. Compared with plano-plano cavities, double concave cavities, and other cavity shapes, the plano-concave cavity has advantages such as short cavity length and strong stability, which can further meet the requirements of high power, high stability, and miniaturization for terahertz radiation sources.

[0033] For specific implementation, please refer to Figure 2As shown, the DFG module 130 may also include a second focusing lens 132 disposed before the second periodically polarized nonlinear optical crystal 131; The second focusing lens 132 is used to focus the dual-wavelength pump laser onto the active region of the second periodically polarized nonlinear optical crystal 131.

[0034] In this embodiment, the second focusing lens 132 is a plano-convex lens with a focal length f. DFG =10mm-50mm, preferably 25mm, coated with an anti-reflection film in the 2050nm-2150nm band, the second focusing lens 132 is used to focus the dual-wavelength pump laser and improve the pump power density in the difference frequency process.

[0035] For specific implementation, please refer to Figure 1 As shown, the high-power terahertz radiation source 100 provided in this application embodiment may further include a first laser collection module 140 disposed between the OPO module 120 and the DFG module 130; The first laser collection module 140 is used to filter out and collect the remaining high-power near-infrared pump laser output from the OPO module 120 that has not been converted into dual-wavelength pump laser.

[0036] In this embodiment, by filtering out and collecting the remaining high-power near-infrared pump laser output from the OPO module 120 that has not been converted into dual-wavelength pump laser by the first laser collection module 140, the thermal load of the second periodically polarized nonlinear optical crystal 131 can be reduced, thereby reducing the phase mismatch caused by temperature drift and thus reducing the power drift of the terahertz wave.

[0037] In specific implementations, the first laser collection module 140 in the high-power terahertz radiation source provided in this application embodiment can have various specific structures to realize its function. For example... Figure 2 As shown, the first laser collection module 140 may include a filter 141 and a laser collector 142; Filter 141 is used to filter out the remaining high-power near-infrared pump laser that has not been converted into dual-wavelength pump laser from dual-wavelength pump laser; Laser collector 142 is used to convert the remaining high-power near-infrared pump laser filtered out by filter 141 into thermal energy for heat dissipation.

[0038] In this embodiment, the filter 141 is coated with a high-reflection film in the 1064nm band and an anti-reflection film in the 2050nm-2150nm band, thereby effectively filtering out the remaining high-power near-infrared pump laser in the dual-wavelength pump laser; the laser collector 142 is a miniaturized collector that uses high thermal conductivity materials and heat dissipation structures to convert light energy into heat energy and then dissipate heat efficiently, thereby effectively absorbing the remaining high-power near-infrared pump laser filtered out by the filter 141.

[0039] For specific implementation, please refer to Figure 1 As shown, the high-power terahertz radiation source 100 provided in this application embodiment may further include a second laser collection module 150 disposed after the DFG module 130; The second laser collection module 150 is used to absorb all wavelengths of laser light except terahertz waves output by the DFG module 130.

[0040] In this embodiment, the second laser collection module 150 absorbs all wavelengths of laser light except terahertz waves output by the DFG module 130, which can avoid residual laser interference with terahertz wave detection and improve the accuracy of terahertz wave detection.

[0041] In specific implementations, the second laser collection module 150 in the high-power terahertz radiation source provided in this application embodiment can have various specific structures to realize its function. For example... Figure 2 As shown, the second laser collection module 150 includes a terahertz window 151; The terahertz window 151 is used to convert laser energy of all wavelengths other than terahertz waves into heat energy and then dissipate it.

[0042] In this embodiment, the terahertz window 151 is a broadband filter that can absorb near-infrared light below 3μm and maintain high transmittance for terahertz waves. This allows it to filter out all other wavelengths of laser light except for terahertz waves, and enables the use of high thermal conductivity materials and heat dissipation structures to efficiently dissipate light energy after converting it into heat energy.

[0043] For specific implementation, please refer to Figure 1 As shown, the high-power terahertz radiation source 100 provided in this application embodiment may further include a source-end terahertz wave detector 160 disposed after the second laser collection module 150. The source-end terahertz wave detector 160 is used to monitor the real-time terahertz wave power output by the second laser collection module 150, and to detect whether the high-power terahertz radiation source 100 stably outputs terahertz waves of a set power (e.g., whether it reaches the design value of 100mW) based on the real-time terahertz wave power.

[0044] In this embodiment, the source-end terahertz wave detector 160 is essentially a terahertz wave power monitor, used to monitor the real-time terahertz wave power output by the second laser collection module 150. If the power fluctuation exceeds the set fluctuation range (e.g., ±5%) based on the real-time terahertz wave power, a terahertz wave radiation source fault alarm is triggered (e.g., indicating aging of the periodic polarization nonlinear optical crystal, insufficient pump light power, etc.) so as to locate and repair the terahertz wave radiation source and ensure that the terahertz wave radiation source stably outputs high-power terahertz waves.

[0045] For specific implementation, please refer to Figure 1 As shown, the high-power terahertz radiation source 100 provided in this application embodiment may further include a temperature synchronization control module 170; The temperature synchronization control module 170 is used to synchronously control the operating temperature of the first periodic polarization nonlinear optical crystal 122 and the second periodic polarization nonlinear optical crystal 131, so that the center frequency of the terahertz wave output by the DFG module 130 is kept synchronized with the frequency difference of the dual-wavelength pump laser output by the OPO module 120 in real time.

[0046] In this embodiment, a first temperature regulating device (such as a temperature control station, thermoelectric cooler, etc.) is provided on the periphery of the first periodically polarized nonlinear optical crystal 122 (such as the periphery of the non-optical light-transmitting surface), and a second temperature regulating device (such as a temperature control station, thermoelectric cooler, etc.) is provided on the periphery of the second periodically polarized nonlinear optical crystal 131 (such as the periphery of the non-optical light-transmitting surface); wherein, the optical light-transmitting surface (such as the transmission surface of a high-power near-infrared pump laser, a dual-wavelength pump laser, or a terahertz wave) faces the optical path direction and does not contact the temperature regulating device, maintaining the exposure of the optical light-transmitting surface and alignment with the optical path. When the temperature synchronization control module 170 synchronously controls the operating temperature of the first periodically polarized nonlinear optical crystal 122 and the second periodically polarized nonlinear optical crystal 131, it can adopt, but is not limited to, the following methods: (1) Establish the temperature-frequency tuning curve of the first periodic polarization nonlinear optical crystal 122. The temperature-frequency tuning curve characterizes the nonlinear mapping relationship between the operating temperature of the first periodic polarization nonlinear optical crystal 122 and the frequency difference of the dual-wavelength pump laser (i.e., signal light and idler light). As the operating temperature increases, the frequency difference of the dual-wavelength pump laser decreases. (2) Construct the temperature-frequency response curve of the second periodic polarization nonlinear optical crystal 131. The temperature-frequency response curve characterizes the relationship between the operating temperature of the second periodic polarization nonlinear optical crystal 131 and the center frequency of the terahertz wave. (3) Based on the temperature-frequency tuning curve of the first periodic polarization nonlinear optical crystal 122 and the temperature-frequency response curve of the second periodic polarization nonlinear optical crystal 131, a unique nonlinear correlation relationship is established between the operating temperature of the first periodic polarization nonlinear optical crystal 122 and the operating temperature of the second periodic polarization nonlinear optical crystal 131. (4) Based on the temperature-frequency response curve of the second periodically polarized nonlinear optical crystal 131, determine the second target operating temperature of the second periodically polarized nonlinear optical crystal 131 corresponding to the target terahertz wave frequency; based on the unique nonlinear correlation between the operating temperature of the first periodically polarized nonlinear optical crystal 122 and the operating temperature of the second periodically polarized nonlinear optical crystal 131, determine the first target operating temperature of the first periodically polarized nonlinear optical crystal 122 corresponding to the second target operating temperature of the second periodically polarized nonlinear optical crystal 131.

[0047] (5) Based on the first target working temperature, a first temperature control signal is generated and sent to the first temperature adjustment device of the first periodic polarization nonlinear optical crystal 122 to adjust the working temperature. Based on the second target working temperature, a second temperature control signal is generated and sent to the second temperature adjustment device of the second periodic polarization nonlinear optical crystal 131 to adjust the working temperature, so that the real-time working temperature of the second periodic polarization nonlinear optical crystal 131 and the real-time working temperature of the first periodic polarization nonlinear optical crystal 122 satisfy a unique nonlinear correlation relationship, so that the center frequency of the terahertz wave output by the DFG module 130 and the frequency difference of the dual-wavelength pump laser output by the OPO module 120 are kept synchronized in real time.

[0048] For example, if it is necessary to adjust the terahertz wave output frequency to a target frequency within the range of 0.4-0.8THz, the operating temperature of the second periodically polarized nonlinear optical crystal 131 is controlled to the second target operating temperature. At the same time, according to the unique nonlinear correlation, the operating temperature of the first periodically polarized nonlinear optical crystal 122 is synchronously adjusted to the first target operating temperature. The actual operating temperatures of the first periodically polarized nonlinear optical crystal 122 and the second periodically polarized nonlinear optical crystal 131 are fed back in real time through a closed loop, and the first temperature control signal and the second temperature control signal are dynamically corrected to ensure that the operating temperatures of the two crystals always satisfy the unique nonlinear correlation.

[0049] By using the above-mentioned synchronous control method of the working temperature of the first periodic polarization nonlinear optical crystal 122 and the second periodic polarization nonlinear optical crystal 131, the center frequency of the terahertz wave output by the DFG module 130 can be kept synchronized with the frequency difference of the dual-wavelength pump laser output by the OPO module 120 in real time, thereby enabling continuous or stepped terahertz frequency tuning output in the range of 0.4-0.8THz.

[0050] The following describes in detail the high-power terahertz radiation source provided in the embodiments of this application, taking the first periodic polarized nonlinear optical crystal 122 and the second periodic polarized nonlinear optical crystal 131 both having a 5% molar concentration of MgO:PPLN.

[0051] In practical applications, the e-ray refractive index equation for a 5% mol MgO:PPLN crystal is: (1) In the formula, f is a function of Celsius temperature t, expressed as: f = (t - 24.5)(t + 570.82), where t is the temperature. This equation is applicable in the range of 400-4000 nm. Using a 1064 nm high-power near-infrared pump laser, a 5% mol MgO:PPLN crystal generates a dual-wavelength pump laser output near 2128 nm. Based on the quasi-phase matching condition and the crystal refractive index model, the temperature tuning curves under different polarization periods can be calculated as follows: Figure 3 As shown. Calculation results show that the wavelength of the idler light shifts towards shorter wavelengths with increasing temperature, while the signal light shifts in the opposite direction. Using a 5% mol MgO:PPLN crystal with a polarization period of 31-32.5 μm as the first-period polarized nonlinear optical crystal, at an operating temperature of 20℃, the wavelength range of the signal light and idler light output by the OPO module is 2121 nm-2135 nm. Based on this, it is calculated that the DFG module using these two beams as dual-wavelength pump lasers can generate terahertz waves with a frequency of 0-1 THz.

[0052] Considering the requirements for high power, high stability, and miniaturization of terahertz radiation sources, a plano-concave cavity is adopted as the cavity shape for the OPO resonator. Compared with plano-plano and biconcave cavities, the plano-concave cavity has advantages such as shorter cavity length and stronger stability. Based on the ABCD matrix theory, the OPO resonator is designed, including some parameters and cavity lengths of the first focusing lens, front cavity mirror, first periodically polarized nonlinear optical crystal, and rear cavity mirror. The lengths of each part of the resonator composed of the front and rear cavity mirrors are as follows: Figure 4 As shown, the total resonant cavity length can be expressed as L= + + ,in, This is the distance from the front cavity mirror to the first-period polarized nonlinear optical crystal. This is the distance from the rear cavity mirror to the first-period polarized nonlinear optical crystal. The length of the first-period polarization nonlinear optical crystal is given. To achieve efficient optical parametric oscillation, the spot mode of the pump laser within the first-period polarization nonlinear optical crystal needs precise control. When stable oscillation can be formed within the resonant cavity, the Gaussian beam parameters should satisfy the self-consistency condition. At this point, the Gaussian beam at any position can reproduce itself after one revolution, and the beam waist radius and position of the Gaussian beam at any position within the resonant cavity can be calculated. Let the q-parameter value of the Gaussian beam originating from a certain reference plane be q0. The matrix M starting from this reference plane can be expressed as: (2) The q parameter for a round trip can then be expressed as: (3) Solving for the given information yields: (4) Therefore, the stability criterion |A+D|<2 is derived. According to the definition of the q parameter, the relationship between the wavefront curvature radius ρ and the spot radius ω of the Gaussian beam on the reference plane and the q parameter satisfies: (5) Regarding the aforementioned settings in the embodiments of this application, matrix M can be specifically calculated as follows: (6) Substituting the calculated values ​​of A, B, C, and D into the stability condition and the relevant equations for the q parameter, the cavity stability can be determined, and the fundamental frequency light ω and ρ in the first-period polarized nonlinear optical crystal can be calculated. Based on the above calculation process, under the condition of satisfying the cavity stability criterion, the relationship between the effective length Leff of different resonators and the radius of curvature R of the concave mirror and the beam waist radius is as follows: Figure 5As shown in the figure, the calculation results show that the upper limit of the waist radius increases significantly with the increase of the radius of curvature R. For example, when the radius of curvature R increases from 50 mm to 550 mm, the maximum waist radius of the corresponding curve increases by more than several times. The radius of curvature R can effectively control the waist radius length. Under the condition of fixed radius of curvature R, the waist radius shows a trend of first increasing and then decreasing with the change of the effective length Leff of the resonant cavity. The waist radius reaches its maximum value when Leff = R / 2, at which point the resonant cavity is a semi-confocal cavity. In addition, the distribution of multiple curve clusters in the figure further reveals that under larger radii of curvature, the difference in waist radius corresponding to different effective lengths Leff of the resonant cavity is small, and the waist radius length is less sensitive to the change of the effective length Leff of the resonant cavity; while when the radius of curvature is small, the gradient of the waist radius with the change of the effective length Leff of the resonant cavity increases significantly. Based on the pump parameters of the high-power near-infrared laser and the damage threshold of the first-period polarized nonlinear optical crystal, for example, the beam waist radius can be designed to be 200 μm, the curvature radius of the concave mirror as the front cavity mirror can be designed to be 300 mm, and the effective length of the resonant cavity can be designed to be about 70 mm, so that ideal results can be obtained.

[0053] After the resonant cavity design optimization is completed, the threshold condition of the OPO module needs to be determined. The gain of the optical parametric oscillation process is proportional to the pump power density. When the pump power density is low, the gain of the optical parametric oscillation process is less than the cavity loss, and a stable oscillation cannot be formed, resulting in no stable output from the OPO module. When the gain of the OPO process is slightly greater than the loss, i.e., when the pump threshold is reached, the signal light and idler light begin to oscillate within the cavity. At this time, the oscillating signal light and idler light are relatively weak. In the embodiments of this application, the threshold condition of the OPO module can be described by the following formula (small signal approximation): (7) Where τ is the pulse width, κ is the OPO process gain coefficient, and g s L is the output optical coupling coefficient. eff Where L is the effective gain length, P is the resonant cavity length, and P is the effective gain length. n / P0 represents the ratio of threshold power to noise power, and α is the crystal absorption coefficient. Let R5 be the crystal length, and R5 be the reflectivity of the rear cavity mirror for λs and λi. Considering both high conversion efficiency and miniaturization requirements, and while ensuring pump power density, the focal length of the first focusing lens in the OPO module can be designed as f. OPO =50-400mm, the cavity length of the resonant cavity can be designed to be L=40-70mm, and the length of the first periodically polarized nonlinear optical crystal can be designed to be... =30-50mm, placed at the center of the resonant cavity.

[0054] In this embodiment, the DFG module is designed using QPM technology. The polarization period Λ of the 5% molar concentration MgO:PPLN crystal is designed accordingly. DFG This allows the terahertz wave generated by the difference frequency to propagate collinearly with the two pump beams. This method effectively overcomes the wave vector mismatch problem caused by refractive index dispersion in lithium niobate crystals in the infrared and terahertz bands, significantly increases the three-wave interaction length, and effectively avoids walk-off effects, thereby significantly improving the conversion efficiency. Figure 6 A geometric model for generating terahertz waves using collinear difference frequency in a 5% molar concentration MgO:PPLN crystal is used. Signal beams with frequencies ω1 and ω2 are incident on the crystal, and the reciprocal lattice vector k... Λ =2π / Λ, when the QPM condition is satisfied, that is, the reciprocal lattice vector and the propagation constant of each wavelength satisfy k1-k2-k3+k Λ When the value is 0, the DFG module can efficiently generate terahertz waves.

[0055] Unlike the near-infrared refractive index characteristics, for the terahertz band, the e-ray refractive index formula for a 5% molar concentration MgO:PPLN crystal is: (8) Based on the refractive index characteristics of 5% molar concentration MgO:PPLN crystals in the near-infrared and terahertz bands, the required polarization period Λ to satisfy the phase matching condition can be calculated. DFG In the embodiments of this application, when the dual-wavelength pump laser is around 2128nm, the polarization period calculation results of the second-period polarized nonlinear optical crystal are as follows: Figure 7 As shown.

[0056] Calculation results show that the polarization period of the second-period polarized nonlinear optical crystal is 182 μm when the output frequency is 0.6 THz. Considering the absorption of the second-period polarized nonlinear optical crystal in the terahertz band, the output intensity of the difference-frequency generated terahertz wave can be expressed as: (9) Where, ω THz For THz wave angular frequency, d eff For effective nonlinear coefficients, n1, n2, n T ε0 represents the refractive index of the crystal under dual-wavelength pump laser and terahertz wave, respectively; ε0 is the vacuum permittivity; c is the speed of light; I1 and I2 are the intensity of the dual-wavelength pump light; α0 is the refractive index of the crystal under dual-wavelength pump laser and terahertz wave, respectively; ε THz Let be the absorption coefficient of the crystal for terahertz waves, and Δk be the phase mismatch. The length of the second-period polarized nonlinear optical crystal is given. Considering factors such as the absorption coefficient, damage threshold, pump power density, and pump dual-wavelength beam mode of the second-period polarized nonlinear optical crystal, and to ensure long-term stable operation of the system while maintaining high energy conversion efficiency, the focal length of the second focusing lens in the DFG module can be selected as 25mm. Under this condition, the terahertz wave output power varies with the length of the second-period polarized nonlinear optical crystal as follows: Figure 8 As shown in the figure, the terahertz wave output power increases with the increase of the length of the second-period polarized nonlinear optical crystal. Beyond 30mm, the trend flattens out. Considering the limitations of short focal length lenses leading to shorter Rayleigh lengths and crystal processing costs, the length of the second-period polarized nonlinear optical crystal can be designed to be l. DFG =30-50mm. Furthermore, the gain G of the difference frequency generation terahertz wave process can be approximated as: (10) By adjusting the operating temperature of the first-cycle polarized nonlinear optical crystal, the wavelengths of the signal light and idler light participating in the difference frequency can be fine-tuned, thereby achieving tuning of the output terahertz frequency. The terahertz output tuning characteristics of this embodiment are as follows: Figure 9 As shown, it can maintain a high output power in the range of 0.5THz to 0.7THz.

[0057] Based on the same inventive concept, embodiments of this application provide a product quality inspection system, see below. Figure 10 As shown, the product quality inspection system provided in this application embodiment includes the above-mentioned high-power terahertz radiation source 100, two-dimensional moving platform 200, terahertz wave detector 300 and data processing device 400; the high-power terahertz radiation source 100, two-dimensional moving platform 200 and terahertz wave detector 300 are sequentially arranged on the same optical path, and the terahertz wave detector 300 is communicatively connected to the data processing device 400; High-power terahertz radiation source 100, used to provide high-power terahertz waves; A two-dimensional moving platform 200 is used to control the movement of the product to be tested within the testing area so that high-power terahertz waves are transmitted or reflected through the product to be tested. Terahertz wave detector 300 is used to collect terahertz wave signals after high-power terahertz waves are transmitted or reflected from the product under test. Data processing equipment 400 is used to perform quality inspection on the product under test based on the terahertz wave signal collected by terahertz wave detector 300.

[0058] In this embodiment, the combination of a high-power terahertz radiation source, an automated mobile platform, and terahertz wave detection and data processing analysis solves the pain points of traditional detection methods, such as inability to penetrate, damage to products, and low accuracy. It also meets the needs of industrial scenarios for batch production, high efficiency, and low cost, and can be widely applied in the fields of product quality inspection such as semiconductors, composite materials, pharmaceutical packaging, and automotive parts, providing a high-precision, non-destructive, and automated solution for product quality control.

[0059] In one possible implementation, the product quality inspection system provided in this application embodiment may further include a third focusing lens 500 disposed between the high-power terahertz radiation source 100 and the two-dimensional moving platform 200; The third focusing lens 500 is used to focus the high-power terahertz wave provided by the high-power terahertz radiation source onto the detection area (i.e., the product placement position) of the two-dimensional moving platform 200 through focusing.

[0060] In this embodiment, the high-power terahertz wave provided by the high-power terahertz radiation source is focused onto the detection area (i.e., the product placement position) of the two-dimensional moving platform 200 by the third focusing lens 500, which can further ensure that the high-power terahertz wave can be completely transmitted or reflected to the product to be tested, thereby achieving all-round accurate detection of the product to be tested.

[0061] Based on the above embodiments, this application provides a product quality inspection method, applied to the data processing device 400 in the above product quality inspection system, see reference. Figure 11 As shown, the general flow of the product quality testing method provided in this application embodiment is as follows: Step 101: Obtain the terahertz wave signal after high-power terahertz waves are transmitted or reflected through the product under test; wherein, the terahertz wave signal includes time domain signal, frequency domain signal and spatial distribution signal.

[0062] Step 102: Based on the terahertz wave signal, a deep learning model is used to identify defects in the product to be inspected and obtain the defect identification results.

[0063] In this embodiment of the application, when obtaining defect identification results by using a deep learning model to identify defects in the product to be inspected based on terahertz wave signals, the following methods may be used, but are not limited to: First, the terahertz wave signal undergoes multi-dimensional fusion filtering preprocessing across the time, frequency, and spatial domains. This multi-dimensional fusion filtering preprocessing includes: applying adaptive wavelet threshold filtering to the terahertz wave time-domain signal, dynamically adjusting the wavelet basis function and decomposition level based on the statistical characteristics of noise in the time-domain signal to filter out environmental electromagnetic interference; applying spectral feature constraint filtering to the terahertz wave frequency-domain signal, extracting the characteristic frequency band signal of the terahertz wave corresponding to the material of the product under test, and suppressing optical path scattering noise in non-characteristic frequency bands; and applying neighborhood signal consistency verification to the terahertz wave spatial distribution signal, eliminating abnormal signal points caused by surface reflections through correlation analysis of signals from adjacent acquisition points.

[0064] Then, based on the terahertz wave signal preprocessed by multi-dimensional fusion filtering, a deep learning model is used to identify defects in the product under inspection, yielding defect identification results. The deep learning model is a CNN-LSTM-Attention hybrid network, which includes a convolutional neural network (CNN), a long short-term memory network (LSTM), an attention mechanism module, and a defect identification module. The CNN is used to extract local spatial features of the terahertz wave signal, the LSTM is used to extract temporal correlation features, and the attention module is used to dynamically weight and fuse the local spatial features and temporal correlation features to obtain multimodal features. The defect identification module is used to identify defects based on the multimodal features, yielding defect identification results. The defect identification results include the defect type and its confidence level.

[0065] In this embodiment of the application, when using a deep learning model to identify defects in the product to be inspected based on the terahertz wave signal after multi-dimensional fusion filtering preprocessing, the following methods can be used, but are not limited to: Step 1020: Reconstruct the dimensions of the terahertz wave signal (including time-domain signal, frequency-domain signal, and spatial distribution signal) after multi-dimensional fusion filtering preprocessing in the time-frequency-spatial domain to obtain tensor data adapted to the input format of the CNN-LSTM-Attention hybrid network, specifically including: The spatially distributed signal is sampled in a grid pattern to generate a spatial dimension of The spatial feature tensor; where H and W are the spatial height and width dimensions of the detection area of ​​the product to be detected, respectively, and C is the number of channels of the terahertz wave signal (including basic feature channels such as power attenuation rate, phase offset, spectral distortion degree and signal rise time delay). The time-domain signal is sorted according to the sampling time sequence, generating a time dimension of The time-series characteristic sequence; where T is the sampling time step, and F is the frequency domain signal characteristic (including amplitude, phase and other parameters of the characteristic frequency segment) at each time step. Spatial feature tensors and temporal feature sequences are dimensionally aligned to form a unified multi-dimensional input data volume, which serves as the input source for the CNN-LSTM-Attention hybrid network.

[0066] Step 1021: Input the reconstructed spatial feature tensor into the CNN, and extract the local spatial features of the terahertz wave signal through hierarchical operations of convolutional layers and pooling layers. The specific process is as follows: Employing multi-layer convolutional kernels (such as...) , The spatial feature tensor is convolved with the size of the sample, and the ReLU activation function is used to achieve nonlinear feature mapping. This extracts the local texture features, regional signal abrupt change features, and spatial distribution patterns of each spatial acquisition point of the product under test, resulting in an N1-dimensional local spatial feature vector. N1 is the feature dimension of the CNN output, and the feature vector elements correspond to the spatial modal features of the terahertz wave signal, such as the spatial power attenuation distribution and the spatial phase shift distribution. The feature map after convolution is reduced in dimensionality by using a global average pooling layer to eliminate redundant spatial information and retain key local spatial features related to defects.

[0067] Step 1022: Input the reconstructed time-series feature sequence into the LSTM, and capture the long- and short-term time-series correlation features of the terahertz wave signal through a gating mechanism (input gate, forget gate, output gate). The specific process is as follows: The forget gate filters and retains historical effective temporal information of terahertz wave signals (such as the temporal changes in signal rise time delay and the temporal evolution of spectral distortion) based on the current temporal feature sequence and the cell state at the previous time step. The input gate assigns weights to the frequency domain features at the current time step, incorporates effective features into the cell state, and updates the internal representation of the temporal features; The output gate outputs an N2-dimensional temporal correlation feature vector based on the updated cell state. N2 is the feature dimension of the LSTM output, and the feature vector elements correspond to the time-series mode features of the terahertz wave signal, such as the change in time-series power attenuation rate and the trend of time-series phase shift.

[0068] Step 1023: Convert the local spatial feature vector F extracted by CNN CNN Temporal correlation feature vector F extracted by LSTM LSTM Concatenate into a multimodal feature matrix The input is dynamically weighted and fused into the Attention module. The specific process is as follows: For the multimodal feature matrix F fusionA linear transformation is performed to generate a query vector Q, a key vector K, and a value vector V; where the query vector Q represents the feature requirement of the defect to be identified, the key vector K represents the attribute information of the multimodal feature, and the value vector V represents the actual value of the multimodal feature. The attention weight matrix A is calculated using the scaled dot product attention function, as follows:

[0069] Where, d K Given the dimension of the key vector K, the Softmax function normalizes the attention weights to the [0,1] interval, thereby quantifying the importance of different modal features (e.g., assigning higher weights to spectral distortion features that are sensitive to defects, and assigning lower weights to irrelevant background noise features). The attention weight matrix A and the value vector V are weighted together to obtain the weighted fused feature vector. This vector integrates the local spatial features and temporal correlation features of the terahertz wave signal, highlighting key multimodal features (power attenuation rate, phase shift, spectral distortion, and signal rise time delay) related to defect identification.

[0070] Step 1024: Calculate the weighted fusion feature vector F att The dual-branch detection layer of the input defect identification module outputs the defect identification result. The specific process is as follows: (1) Based on the fusion feature vector F through classification branch att Output the defect types and their confidence levels, including: The fused feature vector F is processed through a fully connected layer. att Dimensional transformation and feature integration are performed to generate an N3-dimensional final feature vector adapted to the classification task; where N3 is the sum of the total number of defect types of the product to be detected and the confidence calculation dimension. The final feature vector is probabilistically processed using a Softmax classifier to obtain the predicted probability value for each defect; the predicted probability value is the confidence level of the defect type. Select the defect type corresponding to the maximum confidence level as the final defect type (such as crack, bubble, uneven thickness, etc.), and output the defect type (such as crack, bubble, uneven thickness, etc.) and its confidence level.

[0071] (2) Based on the fusion feature vector F through the regression branch att Output the quantified value of defect severity, including: By using a multi-scale fully connected network and leveraging the nonlinear mapping rule from the feature space to the physical quantity space, the fused feature vector F att Mapped to quantitative values ​​of defect severity (such as defect size, depth, area, strength, etc.).

[0072] (3) The defect types (such as cracks, bubbles, uneven thickness, etc.) output by the classification branch and their confidence levels and the defect severity quantification values ​​output by the regression branch are integrated into the defect identification results.

[0073] Step 103: Determine the quality inspection results of the product to be inspected based on the defect identification results.

[0074] In this embodiment of the application, when determining the quality inspection result of the product to be inspected based on the defect identification result, the following methods may be used, but are not limited to: Dynamic grading thresholds are generated based on the production parameters of the product to be inspected. The generation process of dynamic grading thresholds includes: using a production parameter-dynamic grading threshold mapping model, based on the production parameters such as the material, thickness and inspection standards of the product to be inspected, a support vector machine algorithm is used to generate dynamic grading thresholds for each defect type. The dynamic grading thresholds include at least one grading threshold. When the confidence level of the defect type in the defect identification result is not lower than a set threshold (e.g., 0.9), the quality grade of the product to be tested is determined as the quality inspection result based on the comparison between the quantified value of the defect severity of the defect type in the defect identification result and the dynamic grading threshold of the defect type. For example, assuming the dynamic grading threshold includes a first grading threshold, when the quantified value of the defect severity is greater than or equal to the first grading threshold, the quality grade of the product to be tested is determined to be unqualified; when the quantified value of the defect severity is less than the first grading threshold, the quality grade of the product to be tested is determined to be qualified. Alternatively, assuming the dynamic grading threshold includes a first grading threshold and a second grading threshold, and the first grading threshold is greater than the second grading threshold, when the quantified value of the defect severity is greater than or equal to the first grading threshold, the quality grade of the product to be tested is determined to be unqualified; when the quantified value of the defect severity is greater than or equal to the second grading threshold and less than the first grading threshold, the quality grade of the product to be tested is determined to be suspected qualified, requiring further quality inspection in conjunction with other quality inspection rules; when the quantified value of the defect severity is less than the second grading threshold, the quality grade of the product to be tested is determined to be qualified. When the confidence level of the defect type in the defect identification result is lower than the set threshold (e.g., 0.9), the secondary detection process is triggered. The two-dimensional moving platform is controlled to return to the defect area. After adjusting the output power of the high-power terahertz radiation source and the sampling rate of the terahertz wave detector, the terahertz wave signal is reacquired and the quality detection is performed again.

[0075] After introducing the high-power terahertz radiation source, product quality inspection system and method provided in the embodiments of this application, the data processing equipment provided in the embodiments of this application will be briefly introduced next.

[0076] The data processing device provided in this application embodiment may be, but is not limited to, a computer, a laptop computer, etc., see reference. Figure 12 As shown, the data processing device 400 provided in this application embodiment includes at least a processor 401, a memory 402, and a computer program stored in the memory 402 and executable on the processor 401. When the processor 401 executes the computer program, it implements the product quality testing method provided in this application embodiment.

[0077] The data processing device 400 provided in this application embodiment may further include a bus 403 connecting different components (including processor 401 and memory 402). The bus 403 represents one or more types of bus structures, including memory bus, peripheral bus, local area bus, etc.

[0078] Memory 402 may include a readable storage medium in the form of volatile memory, such as random access memory (RAM) 4021 and / or cache memory 4022, and may further include read-only memory (ROM) 4023. Memory 402 may also include a program tool 4025 having a set (at least one) of program modules 4024, including but not limited to an operating subsystem, one or more application programs, other program modules, and program data, each or some combination of these examples may include an implementation of a network environment.

[0079] Processor 401 can be a single processing element or a collective term for multiple processing elements. For example, processor 401 can be a central processing unit (CPU) or one or more integrated circuits configured to implement the product quality inspection method provided in the embodiments of this application. Specifically, processor 401 can be a general-purpose processor, including but not limited to CPUs, application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc.

[0080] The data processing device 400 can communicate with one or more external devices 404 (e.g., keyboard, mouse, remote control, etc.), and also with one or more devices that enable users to interact with the data processing device 400 (e.g., mobile phone, computer, etc.), and / or with devices that enable the data processing device 400 to communicate with one or more other data processing devices 400 (e.g., router, modem, etc.). This communication can be performed through the input / output (I / O) interface 405. Furthermore, the data processing device 400 can also communicate with one or more networks (e.g., local area network (LAN), wide area network (WAN), and / or public networks, such as the Internet) through a network adapter 406. Figure 12 As shown, network adapter 406 communicates with other modules of data processing device 400 via bus 403. It should be understood that, although... Figure 12 As not shown, other hardware and / or software modules may be used in conjunction with the data processing device 400, including but not limited to microcode, device drivers, redundant processors, external disk drive arrays, Redundant Arrays of Independent Disks (RAID) subsystems, tape drives, and data backup storage subsystems.

[0081] It should be noted that, Figure 12 The data processing device 400 shown is merely an example and should not impose any limitations on the functionality and scope of use of the embodiments of this application.

[0082] The computer-readable storage medium provided in the embodiments of this application is described below. The computer-readable storage medium provided in the embodiments of this application stores computer instructions, which, when executed by a processor, implement the product quality inspection method provided in the embodiments of this application. Specifically, the computer instructions can be built into or installed in the processor, so that the processor can implement the product quality inspection method provided in the embodiments of this application by executing the built-in or installed computer instructions.

[0083] In addition, the product quality testing method provided in this application embodiment can also be implemented as a computer program product, which includes program code. The program code implements the product quality testing method provided in this application embodiment when it runs on a processor.

[0084] The computer program product provided in this application embodiment may employ one or more computer-readable storage media, which may be, but is not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination thereof. Specifically, more specific examples (a non-exhaustive list) of computer-readable storage media include electrical connections with one or more wires, portable disks, hard disks, RAM, ROM, erasable programmable read-only memory (EPROM), optical fibers, portable compact disc read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination thereof.

[0085] The computer program product provided in this application embodiment can be a CD-ROM and include program code, and can also run on electronic devices such as computers and laptops. However, the computer program product provided in this application embodiment is not limited to this. In this application embodiment, the computer-readable storage medium can be any tangible medium that contains or stores program code, which can be used by or in conjunction with an instruction execution system, device, or apparatus.

[0086] It should be noted that although several units or sub-units of the device have been mentioned in the detailed description above, this division is merely exemplary and not mandatory. In fact, according to embodiments of this application, the features and functions of two or more units described above can be embodied in one unit. Conversely, the features and functions of one unit described above can be further divided and embodied by multiple units.

[0087] Furthermore, although the operations of the method of this application are described in a specific order in the accompanying drawings, this does not require or imply that these operations must be performed in that specific order, or that all the operations shown must be performed to achieve the desired result. Additionally or alternatively, certain steps may be omitted, multiple steps may be combined into one step, and / or one step may be broken down into multiple steps.

[0088] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0089] Obviously, those skilled in the art can make various modifications and variations to the embodiments of this application without departing from the spirit and scope of the embodiments of this application. Therefore, if these modifications and variations to the embodiments of this application fall within the scope of the claims of this application and their equivalents, this application also intends to include these modifications and variations.

Claims

1. A high-power terahertz radiation source, characterized in that, It includes a high-power near-infrared laser pump source, an OPO module, and a DFG module, which are sequentially arranged on the same optical path; The high-power near-infrared laser pump source is used to provide high-power near-infrared pump laser and incident it onto the OPO module; The OPO module includes a resonant cavity and a first periodically polarized nonlinear optical crystal located within the resonant cavity. The first periodically polarized nonlinear optical crystal is used to convert the high-power near-infrared pump laser into a dual-wavelength pump laser using optical parametric oscillation technology. The resonant cavity is used to oscillate the dual-wavelength pump laser back and forth through the first periodically polarized nonlinear optical crystal until a stable oscillation state is reached before it is incident on the DFG module. The polarization period of the first periodically polarized nonlinear optical crystal is set based on the wave vector mismatch between the high-power near-infrared pump laser and the dual-wavelength pump laser. The DFG module includes a second periodically polarized nonlinear optical crystal, which is used to convert the dual-wavelength pump laser into a terahertz wave and output it through nonlinear difference frequency technology; wherein, the polarization period of the second periodically polarized nonlinear optical crystal is set based on the wave vector mismatch between the dual-wavelength pump laser and the terahertz wave.

2. The high-power terahertz radiation source as described in claim 1, characterized in that, The high-power near-infrared laser pump source includes a high-power near-infrared laser; The high-power near-infrared laser is used to provide a pump laser with nanosecond-level pulse width, megahertz-level repetition rate, millijoule-level single-pulse energy, high beam quality, and near-infrared wavelength as a high-power near-infrared pump laser incident on the OPO module.

3. The high-power terahertz radiation source as described in claim 1, characterized in that, The OPO module also includes a first focusing lens disposed in front of the resonant cavity; The first focusing lens is used to focus the high-power near-infrared pump laser onto the active region of the first periodically polarized nonlinear optical crystal, while simultaneously matching the spatial morphology of the high-power near-infrared pump laser with the eigenmode of the resonant cavity.

4. The high-power terahertz radiation source as described in claim 1, characterized in that, The resonant cavity includes a front cavity mirror and a rear cavity mirror; the front cavity mirror is a concave mirror and the rear cavity mirror is a plane mirror.

5. The high-power terahertz radiation source as described in claim 1, characterized in that, The DFG module also includes a second focusing lens disposed in front of the second periodically polarized nonlinear optical crystal; The second focusing lens is used to focus the dual-wavelength pump laser onto the active region of the second periodically polarized nonlinear optical crystal.

6. The high-power terahertz radiation source as described in claim 1, characterized in that, It also includes a first laser collection module disposed between the OPO module and the DFG module; The first laser collection module is used to filter out and collect the remaining high-power near-infrared pump laser output by the OPO module that has not been converted into the dual-wavelength pump laser.

7. The high-power terahertz radiation source as described in claim 1, characterized in that, It also includes a second laser collection module disposed after the DFG module; The second laser collection module is used to absorb all wavelengths of laser light output from the DFG module except for the terahertz wave.

8. The high-power terahertz radiation source according to any one of claims 1-7, characterized in that, It also includes a temperature synchronization control module; The temperature synchronization control module is used to synchronously control the operating temperatures of the first periodically polarized nonlinear optical crystal and the second periodically polarized nonlinear optical crystal, so that the center frequency of the terahertz wave output by the DFG module is kept synchronized with the frequency difference of the dual-wavelength pump laser output by the OPO module in real time.

9. A product quality inspection system, characterized in that, It includes a high-power terahertz radiation source, a two-dimensional moving platform, a terahertz wave detector, and a data processing device as described in any one of claims 1-8; the high-power terahertz radiation source, the two-dimensional moving platform, and the terahertz wave detector are sequentially arranged on the same optical path, and the terahertz wave detector is communicatively connected to the data processing device; The high-power terahertz radiation source is used to provide high-power terahertz waves; The two-dimensional moving platform is used to control the movement of the product to be tested within the testing area so that the high-power terahertz wave is transmitted or reflected through the product to be tested; The terahertz wave detector is used to collect the terahertz wave signal after the high-power terahertz wave is transmitted or reflected through the product under test; The data processing device is used to perform quality inspection on the product to be inspected based on the terahertz wave signal collected by the terahertz wave detector to obtain the quality inspection result.

10. The product quality inspection system as described in claim 9, characterized in that, The data processing device is used to identify defects in the product under test based on the terahertz wave signal using a deep learning model to obtain defect identification results; and to determine the quality inspection results of the product under test based on the defect identification results.

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