A dual-axis optical fiber transmission engineering type terahertz time domain spectroscopy system

Abstract

The application discloses a kind of dual-axis optical fiber transmission engineering type terahertz time-domain spectroscopy systems, including terahertz host computer, transmission cable, terahertz detection module, detection sample and robot;Terahertz detection module is fixed in the end of robot manipulator, and terahertz host computer is connected with terahertz detection module by transmission cable 2;By the output of terahertz host computer polarization direction perpendicular to each other pump light and probe light is incident into terahertz detection module and excitation generates terahertz time-domain pulse, and terahertz time-domain pulse passes through detection sample, and after carrying the phase information of detection sample, it is reflected to terahertz detection module and generates induced current, and is returned to terahertz host computer by transmission cable, and terahertz host computer carries out detection path simulation to detection sample, adjusts robot detection posture and carries out scanning according to planning path, and completes in situ terahertz detection of detection sample.The application can be flexibly applied to a variety of engineering field detection environment.

Description

Technical Field

[0001] This invention relates to a terahertz time-domain spectroscopy system, specifically an engineering-type terahertz time-domain spectroscopy system with biaxial fiber transmission for field use in terahertz nondestructive testing. Background Technology

[0002] Terahertz time-domain spectroscopy has significant application prospects in numerous fields, including biomedicine, materials science, quality inspection, security inspection, and non-destructive testing. In the field of non-destructive testing, terahertz time-domain spectroscopy is widely used in industries such as aerospace, automotive and shipbuilding, biopharmaceuticals, and cultural relic preservation. It demonstrates particular advantages in the non-destructive testing of coatings, composite materials, and artworks, successfully characterizing defects such as delamination, cracks, inclusions, debonding, and porosity in the tested samples.

[0003] In practical engineering applications, typical terahertz time-domain nondestructive testing systems often face challenges such as a wide variety of test samples, significant differences in sample thickness, diverse testing scenarios, and varying testing distance requirements. Especially in in-situ sample testing at engineering sites, automated robots are typically used in conjunction with terahertz time-domain spectroscopy systems. The pose changes of different joints of the robot can generate external stress on the optical fiber in the terahertz transmission cable. The varying external stress experienced by the uniaxial polarization-maintaining fiber during testing directly affects the fiber's polarization and birefringence characteristics, leading to a decrease in the signal-to-noise ratio of the terahertz signal and impacting the stability and reliability of the terahertz detection signal. Summary of the Invention

[0004] To reduce the impact of external stress on the beam quality of polarization-maintaining fiber transmission, this invention provides an engineering-grade terahertz time-domain spectroscopy system with biaxial fiber transmission, which can be flexibly applied to various engineering field testing environments.

[0005] The objective of this invention is achieved through the following technical solution, in conjunction with the accompanying drawings:

[0006] A dual-axis fiber optic transmission-based engineering terahertz time-domain spectroscopy system includes a terahertz host 1, a transmission cable 2, a terahertz detection module 3, a test sample 4, and a robot 5. The terahertz detection module 3 is fixed to the end effector of the robot 5. The terahertz host 1 and the terahertz detection module 3 are connected via the transmission cable 2. Pump light and probe light with mutually perpendicular polarization directions output from the terahertz host 1 are incident on the terahertz detection module 3 via the transmission cable 2 and excited to generate terahertz time-domain pulses. The terahertz time-domain pulses pass through the test sample 4, carrying the phase information of the test sample, and are reflected back to the terahertz detection module 3 to generate an induced current. The induced current is then transmitted back to the terahertz host 1 via the transmission cable 2. The terahertz host 1 performs a detection path simulation on the test sample 4, adjusts the detection posture of the robot 5, and scans according to the planned path to complete the in-situ terahertz detection of the test sample 4.

[0007] Furthermore, the terahertz host 1 includes a linearly polarized femtosecond laser 11, an adaptive dispersion compensation module 12, a first polarization-maintaining fiber beam splitter 13, a polarization-maintaining fiber circulator 14, a scanning delay line module 15, a polarization-maintaining fiber combiner 16, a digital acquisition module 17, and a host computer processor 18. The femtosecond laser pulses emitted from the linearly polarized femtosecond laser 11 are pre-compensated for pulse width by the adaptive dispersion compensation module 12, and then split into pump light and probe light with mutually perpendicular polarization directions by the first polarization-maintaining fiber beam splitter 13. The probe light is directly transmitted to the polarization-maintaining fiber combiner 16. 6; The pump light is incident on the scanning delay line module 15 through the polarization-maintaining fiber circulator 14. The scanning delay line module 15 changes the optical path difference between the probe light and the pump light and transmits it back to the polarization-maintaining fiber circulator 14. The polarization-maintaining fiber circulator 14 then transmits it to the polarization-maintaining fiber combiner 16. The polarization-maintaining fiber combiner 16 mixes the pump light and the probe light together and outputs them to the transmission cable 2. The terahertz instantaneous signal transmitted back by the terahertz detection module 3 through the transmission cable 2 is acquired by the digital acquisition module 17. The acquired signal is processed and displayed by the host computer processor 18.

[0008] Furthermore, the scanning delay line module 15 includes a displacement stage and a reflector; the movement of the displacement stage causes a change in the optical path difference, and the movement position of the displacement stage is acquired by the digital acquisition module 17; the pump light is incident into the scanning delay line module 15 through the polarization-maintaining fiber circulator 14, and is reflected back into the polarization-maintaining fiber circulator 14 by the reflector.

[0009] Furthermore, the adaptive dispersion compensation module 12 is used to pre-compensate for pulse width broadening caused by the transmission of pump light and probe light in the terahertz host 1, transmission cable 2 and terahertz detection module 3; the adaptive dispersion compensation module 12 compensates for fiber lengths of 5m to 40m.

[0010] Furthermore, the transmission cable 2 is composed of a cable and a biaxial polarization-maintaining fiber; the cable provides voltage to the terahertz detection module 3 and transmits the terahertz instantaneous signal; the fast and slow axes of the biaxial polarization-maintaining fiber work simultaneously to transmit pump light and probe light with mutually perpendicular polarization directions at the same time.

[0011] Furthermore, the biaxial polarization-maintaining fiber is a panda-type polarization-maintaining fiber, with the fast axis 22 transmission direction perpendicular to the panda eye 21 direction and the slow axis 23 transmission direction parallel to the panda eye 21 direction.

[0012] Furthermore, the terahertz detection module 3 includes a second polarization-maintaining fiber beam splitter 31, a photoconductive transmitting antenna 32, a bias voltage module 33, a photoconductive detection antenna 34, a microcurrent amplification module 35, a terahertz beam splitter 36, and a terahertz lens 37. The second polarization-maintaining fiber beam splitter 31 directs the pump light and probe light, whose polarization directions are perpendicular to each other, from the transmission cable 2 into the photoconductive transmitting antenna 32 and the photoconductive detection antenna 34, respectively. Under the action of the bias voltage module 33, the photoconductive transmitting antenna 32 generates terahertz waves. The terahertz time-domain pulse is split by the terahertz beam splitter 36. The transmitted terahertz time-domain pulse is focused by the terahertz lens 37 and then incident on the detection sample 4. After passing through the detection sample 4 and carrying the sample information, the terahertz time-domain pulse is reflected again by the terahertz beam splitter 36 through the terahertz lens 37 and onto the photoconductive detection antenna 34. Under the simultaneous action of the terahertz time-domain pulse and the detection light, the photoconductive detection antenna 34 generates an induced current, which is amplified by the micro-current amplification module 35 and then transmitted back to the terahertz host 1 via the transmission cable 2.

[0013] Furthermore, the detection sample 4 is a terahertz signal-transmissible sample.

[0014] The present invention has the following beneficial effects:

[0015] Compared with existing conventional systems, this invention provides an engineering-grade terahertz time-domain spectroscopy system with dual-axis fiber transmission. Primarily designed for in-situ sample detection in engineering settings, it replaces the separate pump and probe fibers in conventional systems with dual-axis polarization-maintaining fibers that operate simultaneously on both the fast and slow axes. This simplifies the terahertz transmission cable and reduces the impact of uneven fiber stress caused by changes in the robot's automated pose during detection on the quality of the terahertz detection signal. By modularly separating the terahertz host, transmission cable, and terahertz detection system, it facilitates the integration and replacement of the transmission cable and terahertz detection module, enabling the detection of samples of varying thicknesses and other diverse detection scenarios. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of an engineering-type terahertz time-domain spectroscopy system for dual-axis fiber optic transmission according to an embodiment of the present invention;

[0017] Figure 2 This is a schematic diagram illustrating the composition principle of the terahertz host described in this embodiment of the invention;

[0018] Figure 3 This is a schematic diagram of the fast and slow axes of the biaxial polarization-maintaining fiber described in an embodiment of the present invention;

[0019] Figure 4 This is a schematic diagram of the terahertz detection module described in this embodiment of the invention, illustrating its composition and working principle.

[0020] In the picture:

[0021] 1-Terahertz main unit; 2-Transmission cable; 3-Terahertz detection module; 4-Test sample; 5-Robot;

[0022] 11-Linearly polarized femtosecond laser; 12-Adaptive dispersion compensation module; 13-First polarization-maintaining fiber beam splitter; 14-Polarization-maintaining fiber circulator; 15-Scanning delay line module; 16-Polarization-maintaining fiber combiner; 17-Digital acquisition module; 18-Host computer processor;

[0023] 21 - Panda Eye; 22 - Fast Axis; 23 - Slow Axis;

[0024] 31-Second polarization-maintaining fiber beam splitter; 32-Photoconductive transmitting antenna; 33-Bias voltage module; 34-Photoconductive detection antenna; 35-Micro current amplification module; 36-Terahertz beam splitter; 37-Terahertz lens. Detailed Implementation

[0025] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] like Figure 1 As shown, this embodiment is an engineering-grade terahertz time-domain spectroscopy system with dual-axis fiber optic transmission, comprising five parts: a terahertz host 1, a transmission cable 2, a terahertz detection module 3, a detection sample 4, and a robot 5; the terahertz detection module 3 is fixed to the end of the robot 5's manipulator using tooling, and the terahertz host 1 and the terahertz detection module 3 are connected by the transmission cable 2, which is fixed along the arm of the robot 5. The terahertz host 1 outputs linearly polarized pump light and probe light with mutually perpendicular polarization directions. These light are transmitted through the transmission cable 2 and incident into the terahertz detection module 3, where they excite and generate terahertz time-domain pulses. The terahertz time-domain pulses pass through the detection sample 4, carrying the phase information of the detection sample, and are reflected back into the terahertz detection module 3 to generate an induced current (the magnitude of the induced current is proportional to the amplitude of the terahertz time-domain pulse signal and is in phase with the terahertz time-domain pulse signal). The induced current is transmitted to the terahertz host 1 through the transmission cable 2 and displayed by the host computer processor in the terahertz host module 1. The terahertz host 1 performs detection path simulation on the detection sample 4, adjusts the robot 5 to a suitable detection posture, and scans according to the planned path to complete the in-situ terahertz detection of the detection sample 4.

[0027] Furthermore, such as Figure 2As shown, the terahertz host 1 consists of a linearly polarized femtosecond laser 11, an adaptive dispersion compensation module 12, a first polarization-maintaining fiber beam splitter 13, a polarization-maintaining fiber circulator 14, a scanning delay line module 15, a polarization-maintaining fiber combiner 16, a digital acquisition module 17, and a host computer processor 18. The femtosecond laser pulse emitted from the linearly polarized femtosecond laser 11 is pre-compensated for pulse width by the adaptive dispersion compensation module 12, and then split into pump light and probe light with mutually perpendicular polarization directions by the first polarization-maintaining fiber beam splitter 13. The probe light is directly transmitted to the polarization-maintaining fiber combiner 16. The pump light is incident on the scanning delay line module 15 through the polarization-maintaining fiber circulator 14. The scanning delay line module 15 changes the optical path difference between the probe light and the pump light and transmits it back to the polarization-maintaining fiber circulator 14, and then transmits it to the polarization-maintaining fiber combiner 16. Finally, the polarization-maintaining fiber combiner 16 mixes the pump light and the probe light together and outputs them to the transmission cable 2. The terahertz instantaneous signal transmitted back by the terahertz detection module 3 through the transmission cable 2 is acquired by the digital acquisition module 17. Finally, the host computer processor 18 performs feature recognition, extraction and other processing on the acquired signal and displays it.

[0028] Furthermore, the scanning delay line module 15 includes a displacement stage and a reflector; the movement of the displacement stage causes a change in the optical path difference, and the movement position of the displacement stage is acquired by the digital acquisition module 17; the pump light is incident into the scanning delay line module 15 through the polarization-maintaining fiber circulator 14, and is reflected back into the polarization-maintaining fiber circulator 14 by the reflector.

[0029] Furthermore, the adaptive dispersion compensation module 12 is used to pre-compensate for pulse width broadening caused by the transmission of pump light and probe light through the terahertz host 1, transmission cable 2, and terahertz detection module 3. Pulse width broadening occurs during transmission through the fiber optic terahertz host 1, transmission cable 2, and terahertz detection module 3. The adaptive dispersion compensation module pre-compensates for this pulse width broadening, ensuring that the pump light and probe light meet the pulse width requirements when they reach the photoconductive antenna.

[0030] Preferably, the adaptive dispersion compensation module 12 compensates for an optical fiber length of 5m to 40m.

[0031] Furthermore, the transmission cable 2 consists of two parts: a power cable and a biaxial polarization-maintaining fiber. The power cable is responsible for providing voltage to the terahertz detection module 3 and transmitting the terahertz instantaneous signal. The fast and slow axes of the biaxial polarization-maintaining fiber work simultaneously to transmit pump light and probe light with mutually perpendicular polarization directions at the same time.

[0032] like Figure 3As shown, preferably, the biaxial polarization-maintaining fiber is a panda-type polarization-maintaining fiber, and the fast and slow axes of the biaxial polarization-maintaining fiber work simultaneously. The direction perpendicular to the panda eye 21 is the fast axis 22 transmission direction, and the direction parallel to the panda eye 21 is the slow axis 23 transmission direction. The fast and slow axes are used to simultaneously transmit pump light and probe light with mutually perpendicular polarization directions.

[0033] Preferably, the transmission cable 2 is connected to the terahertz host 1 and the terahertz detection module 3 only by a cable port and an optical fiber port, and different lengths can be changed according to different detection scenarios.

[0034] Furthermore, such as Figure 4 As shown, the terahertz detection module 3 consists of a second polarization-maintaining fiber beam splitter 31, a photoconductive transmitting antenna 32, a bias voltage module 33, a photoconductive detection antenna 34, a microcurrent amplification module 35, a terahertz beam splitter 36, and a terahertz lens 37. The second polarization-maintaining fiber beam splitter 31 directs the pump light and probe light, whose polarization directions are perpendicular to each other, from the transmission cable 2 into the photoconductive transmitting antenna 32 and the photoconductive detecting antenna 34, respectively. Under the action of the bias voltage module 33, the photoconductive transmitting antenna 32 generates a terahertz time-domain pulse. The terahertz time-domain pulse is split by the terahertz beam splitter 36, and the transmitted terahertz time-domain pulse is focused by the terahertz lens 37 and then incident on the detection sample 4. After passing through the detection sample 4 and carrying the sample information, the terahertz time-domain pulse is reflected again by the terahertz beam splitter 36 through the terahertz lens 37 and onto the photoconductive detecting antenna 34. Under the simultaneous action of the terahertz time-domain pulse and the probe light, the photoconductive detecting antenna 34 generates an induced current, which is amplified by the micro-current amplification module 35 and then transmitted back to the terahertz host 1 through the transmission cable 2.

[0035] The test sample 4 is a terahertz signal-transmissible sample, which can be a single-dielectric material or a multi-layer composite material.

Claims

1. An engineering-grade terahertz time-domain spectroscopy system with dual-axis fiber optic transmission, characterized in that, The system includes a terahertz host (1), a transmission cable (2), a terahertz detection module (3), a test sample (4), and a robot (5). The terahertz detection module (3) is fixed to the end of the robot (5) manipulator. The terahertz host (1) and the terahertz detection module (3) are connected through the transmission cable (2). Pump light and probe light with mutually perpendicular polarization directions are output from the terahertz host (1) and incident into the terahertz detection module (3) through the transmission cable (2) to generate terahertz time-domain pulses. The terahertz time-domain pulses pass through the test sample (4), carry the phase information of the test sample, and are reflected back into the terahertz detection module (3) to generate induced current. The current is then transmitted back to the terahertz host (1) through the transmission cable (2). The terahertz host (1) performs a test path simulation on the test sample (4), adjusts the test posture of the robot (5), and scans according to the planned path to complete the in-situ terahertz detection of the test sample (4). The terahertz host (1) includes a linearly polarized femtosecond laser (11), an adaptive dispersion compensation module (12), a first polarization-maintaining fiber beam splitter (13), a polarization-maintaining fiber circulator (14), a scanning delay line module (15), a polarization-maintaining fiber combiner (16), a digital acquisition module (17), and a host computer processor (18). The femtosecond laser pulse emitted from the linearly polarized femtosecond laser (11) is pre-compensated for pulse width by the adaptive dispersion compensation module (12), and then split into pump light and probe light with mutually perpendicular polarization directions by the first polarization-maintaining fiber beam splitter (13). The probe light is directly transmitted to the polarization-maintaining fiber combiner (16). The pump light is incident on the scanning delay line module (15) through the polarization-maintaining fiber circulator (14). The scanning delay line module (15) changes the optical path difference between the probe light and the pump light and transmits it back to the polarization-maintaining fiber circulator (14). The polarization-maintaining fiber circulator (14) then transmits it to the polarization-maintaining fiber combiner (16). The polarization-maintaining fiber combiner (16) mixes the pump light and the probe light together and outputs them to the transmission cable (2). The terahertz instantaneous signal transmitted back by the terahertz detection module (3) through the transmission cable (2) is acquired by the digital acquisition module (17). The acquired signal is processed and displayed by the host computer processor (18). The transmission cable (2) consists of a cable and a biaxial polarization-maintaining fiber; the cable provides voltage and transmits terahertz instantaneous signals to the terahertz detection module (3); the fast and slow axes of the biaxial polarization-maintaining fiber work simultaneously to transmit pump light and probe light with mutually perpendicular polarization directions at the same time. The terahertz detection module (3) includes a second polarization-maintaining fiber beam splitter (31), a photoconductive transmitting antenna (32), a bias voltage module (33), a photoconductive detection antenna (34), a microcurrent amplification module (35), a terahertz beam splitter (36), and a terahertz lens (37). The second polarization-maintaining fiber beam splitter (31) directs the pump light and the probe light, whose polarization directions are perpendicular to each other, from the transmission cable (2) into the photoconductive transmitting antenna (32) and the photoconductive detection antenna (34), respectively. The photoconductive transmitting antenna (32) generates terahertz waves under the action of the bias voltage module (33). The time-domain pulse and the terahertz time-domain pulse are split by the terahertz beam splitter (36). The transmitted terahertz time-domain pulse is focused by the terahertz lens (37) and then incident on the detection sample (4). After the terahertz time-domain pulse passes through the detection sample (4) and carries the sample information, it is reflected again by the terahertz lens (37) and the terahertz beam splitter (36) onto the photoconductive detection antenna (34). Under the simultaneous action of the terahertz time-domain pulse and the detection light, the photoconductive detection antenna (34) generates an induced current, which is amplified by the microcurrent amplification module (35) and then transmitted back to the terahertz host (1) via the transmission cable (2).

2. The engineering-grade terahertz time-domain spectroscopy system with dual-axis fiber optic transmission as described in claim 1, characterized in that, The scanning delay line module (15) includes a displacement stage and a reflector; the movement of the displacement stage causes a change in the optical path difference, and the movement position of the displacement stage is acquired by the digital acquisition module (17); the pump light is incident into the scanning delay line module (15) through the polarization-maintaining fiber circulator (14), and is reflected back into the polarization-maintaining fiber circulator (14) by the reflector.

3. The engineering-grade terahertz time-domain spectroscopy system with dual-axis fiber optic transmission as described in claim 1, characterized in that, The adaptive dispersion compensation module (12) is used to pre-compensate for the pulse width broadening caused by the transmission of pump light and probe light in the terahertz host (1), transmission cable (2) and terahertz detection module (3); the adaptive dispersion compensation module (12) compensates for fiber lengths of 5m to 40m.

4. The engineering-grade terahertz time-domain spectroscopy system with biaxial fiber transmission as described in claim 1, characterized in that, The biaxial polarization-maintaining fiber is a panda-type polarization-maintaining fiber. The direction perpendicular to the panda eye (21) is the fast axis (22) transmission direction, and the direction parallel to the panda eye (21) is the slow axis (23) transmission direction.

5. The engineering-grade terahertz time-domain spectroscopy system with biaxial fiber transmission as described in claim 1, characterized in that, The test sample (4) is a terahertz signal-transmittable sample.

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