Method for testing radiation damage of photoconductive switch

Abstract

The invention relates to a method for testing radiation damage of a photoconductive switch. A test device involved in the method is composed of a picosecond pulse laser, a beam expander, a deflecting mirror, a focusing mirror, a light energy meter, a photoconductive switch test board, a high-voltage direct-current power supply, an attenuator, an oscilloscope, a first coaxial cable, a clamp table, a high-voltage cable, a third coaxial cable, an optical slit and a second coaxial cable. Meanwhile, the circuit structure is simplified, the electromagnetic interference of an electrical loop is small, and the signal transmission damage is low. The light energy intensity and the light spot size of the pulse laser can be changed by adjusting the focus lens or the optical slit, and the light energy intensity of the pulse laser is monitored by the light energy meter, so that the light path is accurately controlled. The oscilloscope collects pulse signals on the attenuator, and key performance parameters of the photoconductive switch, such as on resistance, rise time, fall time, half-peak width and load peak power, can be obtained through calculation. And the requirements of the photoconductive switch irradiation damage effect test are met. The existing test problems of poor repeatability, low precision and the like of the photoconductive switch test are solved.

Description

Technical Field

[0001] The present invention relates to the field of performance testing of photoconductive switches, and particularly to a method for testing radiation damage of photoconductive switches. Background Art

[0002] A photoconductive semiconductor switch (PCSS) is a switch device based on the principle of semiconductor photoconductivity. Compared with traditional switches, the photoconductive switch (PCSS) has excellent characteristics such as fast response time (ps level), high transmission power, low trigger jitter (ps level), high repetition frequency, small size, light weight, simple device structure, immunity to electromagnetic interference, and high synchronization accuracy. It is widely used in the field of pulsed power, such as pulsed power generators, accelerators, and electromagnetic accelerators. In addition, many medical devices such as nuclear magnetic resonance imaging machines and particle accelerators also use photoconductive switches.

[0003] In the application of photoconductive switches, they will face the influence of radiation environment, resulting in the attenuation of the performance of photoconductive switches or even the loss of switch function. The incidence of high-energy particles causes the generation of defect energy levels in the device material, forming new carrier capture-emission centers in the forbidden band. X-rays, γ-rays, protons, electrons, neutrons, and heavy ions introduce different defect energy level positions and defect numbers in the substrate material of the photoconductive switch, and the situation of the pulses generated by the photoconductive switch under laser excitation is also different. Defects with a small number and far from the donor and acceptor impurity energy levels often do not significantly change the performance of the photoconductive switch. However, they will also change the off-resistance in the dark state, increasing the leakage current and reducing the off-resistance. For defects with a large number and defect energy levels close to the light absorption energy level, they will greatly change the pulse peak value of the photoconductive switch, resulting in a serious decline in performance, and even causing the device to burn out or break down. Therefore, it is necessary to carry out radiation effect research on photoconductive switches. In order to analyze the performance degradation of photoconductive switch devices caused by radiation damage, the test device and method for photoconductive switches are required to have high precision, strong repeatability, and a simple link. However, most of the current test devices focus on testing their optimal performance, with poor repeatability and accuracy. They can almost only meet the requirement of testing the conduction performance of photoconductive switches, and cannot meet the test requirements for analyzing the influence of their defects and more refined research. In addition, most of the test processes will be affected by electromagnetic interference, and the generated fluctuation signals can reach 50% of the amplitude of the measured signal. Summary of the Invention

[0004] The object of the present invention is to provide a method for testing the radiation damage of an optical switch, aiming at the problems of the existing technology. The device involved in this method consists of a picosecond pulsed laser, a beam expander, a deflecting mirror, a focusing mirror, an optical energy meter, an optical switch test board, a high-voltage DC power supply, a capacitor, an attenuator, an oscilloscope, a grounding terminal, a positive terminal, a first coaxial cable, a limit bottom plate, a fixture table, a high-voltage cable, a third coaxial cable, an optical slit, a second coaxial cable, an optical switch device, and a coaxial cable interface; the optical switch test board adopts a coaxial structure and simplifies the circuit structure at the same time, so that the electromagnetic interference of the electrical circuit is small and the signal transmission damage is low. Adjusting the focusing mirror and the optical slit can change the optical energy intensity and the spot size of the pulsed laser, and the optical energy intensity of the pulsed laser is monitored by an optical energy meter to achieve precise control of the optical path. The oscilloscope collects the pulsed signal on the attenuator, and the key performance parameters of the optical switch such as the on-resistance, rise time, fall time, half-peak width, and load peak power can be obtained through calculation. It meets the requirements of the irradiation damage effect test of the optical switch. It overcomes the existing test problems such as poor repeatability and low accuracy of the optical switch test.

[0005] A method for testing the radiation damage of an optical switch according to the present invention, the device involved in this method consists of a picosecond pulsed laser (1), a beam expander (2), a deflecting mirror (3), a focusing mirror (4), an optical switch test board (5), a high-voltage DC power supply (6), a capacitor (7), an attenuator (8), an oscilloscope (9), a grounding terminal (10), a positive terminal (11), a first coaxial cable (12), a limit bottom plate (13), a fixture table (14), a high-voltage cable (15), a third coaxial cable (16), an optical slit (17), a second coaxial cable (18), an optical switch device (19), and a coaxial cable interface (20), and an optical energy meter (21); the output laser of the picosecond pulsed laser (1) increases the spot through the beam expander (2), and then passes through the deflecting mirror (3) and the focusing mirror (4) to change the optical path and focus the spot at the same time, and finally the spot size is precisely controlled through the optical slit (17); the optical energy intensity is measured by the optical energy meter (21); the picosecond pulsed laser (1) is connected to the oscilloscope (9) through the first coaxial cable (12), the attenuator (8) is connected to the oscilloscope (9) through the second coaxial cable (18), the high-voltage DC power supply (6) is connected to the optical switch test board (5) through the high-voltage cable (15), the optical switch test board (5) is connected to the attenuator (8) through the third coaxial cable (16), and the optical switch test board (5) is placed and fixed on the fixture table (14); the optical switch test board (5) consists of an optical switch device (19), a capacitor (7), a grounding terminal (10), a positive terminal (11), a limit bottom plate (13), and a coaxial cable interface (20); the capacitor (7) is welded between the grounding terminal (10) and the positive terminal (11), and both ends of the optical switch device are connected to the positive terminal (11) and the coaxial cable interface (20). The specific operation is carried out according to the following steps:

[0006] a. Fix the photoconductive switch test board (5) on the fixture table (14). Connect one end of the high-voltage cable to the high-voltage output of the high-voltage DC power supply, and the other end to the positive terminal (11) on the photoconductive switch test board (5). Connect the grounding terminal (10) to the ground wire. Connect the coaxial cable interface of the photoconductive switch test board (5) to the input of the attenuator through the third coaxial cable (19). Connect the oscilloscope (9) to the photoelectric output of the picosecond laser (1) and the output of the attenuator (8) through the first coaxial cable (12) and the second coaxial cable (18) respectively. Set the output impedance of the input channel of the oscilloscope (9) to 50 ohms, and the attenuation multiple to the attenuation value of the attenuator (8). Select an attenuation multiple of 50 dB. Check the connection of these wires again. Then, turn on the picosecond laser (1) and adjust the deflecting mirror (3) so that the laser beam focusing position is at the window position of the photoconductive switch test board (5).

[0007] b. Turn on the high-voltage DC power supply (6) to provide high voltage to the photoconductive switch test board (5) through the high-voltage cable (15). Adjust the voltage to 5 - 6 kV. Under this voltage drop, fine-tune the deflecting mirror (3) so that the laser irradiates the best trigger area on the surface of the photoconductive switch test board (5) to maximize the peak value collected by the oscilloscope (9). Record and save the laser and load pulse signals at this time. Use the optical power meter (21) to measure the light intensity at 5 cm behind the optical slit (17). Move the optical power probe of the optical power meter (21) out through the moving platform at 5 cm to measure. The light intensity measurement positions before and after are the same, and record the light intensity and the amplification voltage of the picosecond pulse laser. After the measurement, remove the optical power probe. If a focusing lens is used, adjust the position of the focusing lens to change the spot size and light intensity. If an adjustable optical slit is used, accurately adjust the spot size with an accuracy of 0.001 mm. Measure the pulse signals under two different voltage biases under this light intensity condition. The voltage range is 1 kV - 7 kV, and measure and save once every 1 kV interval. When saving, select the signal with the smallest difference between the photoelectric signals of the picosecond laser before and after. This measured value is used as the initial value of the photoconductive switch.

[0008] c. Keep the optical path basically unchanged, remove the photoconductive switch test board (5), and conduct the irradiation experiment. During the irradiation process, provide a bias to the irradiated photoconductive switch test board (5) through the DC high-voltage power supply (6). After the irradiation is completed, fix the photoconductive switch test board (5) on the fixture table (14) and conduct the parameter measurement after irradiation. First, adjust the light intensity and the amplification voltage of the picosecond laser defined in step b to ensure that the difference from the initial value condition is less than 0.01% to be an effective measurement. Set the amplification voltage of the picosecond laser (1) and adjust the rotation knob on the deflecting mirror (3), that is, adjust the required light intensity at a fixed position.

[0009] d. Measure two groups of pulse signals under different biases, with the voltage range from 1 kV to 7 kV, and save the measurement results once every 1 kV interval; the oscilloscope (9) saves the signal data, and calculates the on-resistance, rise time, fall time, half-peak width, and load peak power at this dose through existing calculation methods.

[0010] e. Repeat step c - step d to complete the data acquisition and calculation at each dose point.

[0011] In the test method for radiation damage of a photoconductive switch described in the present invention, the photoconductive switch test board in this method includes a microstrip circuit board and a limiting bottom plate, which are fixed together with the limiting bottom plate by screws on the grounding terminal and grounded as a whole. The holes on the microstrip circuit board are used to weld the packaged photoconductive switch test board, and a 2nF capacitor is connected between the grounding terminal and the positive terminal to provide a voltage drop for the photoconductive switch test board through capacitor charging and discharging. This can prevent the transient pulse current from burning out the high-voltage DC power supply. The output of the photoconductive switch test board adopts a 50-ohm microstrip structure with a coaxial cable interface.

[0012] The voltage coverage range of the high-voltage DC power supply is 0 - 10 kV. The high-voltage DC power supply provides a high voltage to the photoconductive switch test board to be measured through a high-voltage cable. The DC high-voltage output line is connected to the positive terminal of the photoconductive switch test board, and the grounding of the high-voltage DC power supply is connected to the grounding terminal of the photoconductive switch test board and then connected to the ground wire. The output of the photoconductive switch test board is connected to the input terminal of the attenuator through a coaxial cable. Insulating gel is used to isolate all exposed joints in contact with air to avoid air discharge due to contact with air, signal loss, and safety threats. The impedance of the attenuator is 50 ohms, and the output of the attenuator is connected to the oscilloscope through a second coaxial cable. The pulse signal on the attenuator is captured by the oscilloscope in a single-shot trigger mode. The collected pulse signal is in the ps magnitude, has a very high bandwidth, and the pulse peak is very high. For a general sampling resistor, its resistance value will change under the conditions of high bandwidth and high peak value. Moreover, general voltage probes are limited by bandwidth and have low precision in measuring picosecond signals. Using a broadband attenuator can avoid these problems.

[0013] After the laser passes through the deflection mirror and the focusing mirror in sequence, the light intensity per unit area is increased, making the laser energy distribution more uniform. Then, the spot size is precisely controlled through the optical slit, which can improve the accuracy of the measurement results. The focusing mirror can increase the power density, and the optical slit can adjust the spot size, but it cannot change the power density. The voltage provided by the high-voltage DC power supply causes the electron-hole pairs generated by the laser in the photoconductive switch to be instantaneously collected at both ends of the electrode, generating a transient current pulse with a current peak as high as several hundred A. This pulse signal can be collected by the oscilloscope after passing through the attenuator. The collected voltage signal is the pulse voltage signal on the load, and the waveform data is saved. Through calculation, the on-resistance, rise time, fall time, half-peak width, and load peak power of the device under the specified trigger conditions can be obtained. In addition, the photoelectric signal output of the picosecond pulsed laser is connected to the oscilloscope, and the laser signal when the photoconductive switch is turned on each time can be collected, and precise screening can be carried out to ensure the trigger accuracy.

[0014] A method for testing the radiation damage of a photoconductive switch according to the present invention. The method for calculating the parameters of the photoconductive switch is as follows:

[0015] (1) Method for calculating the load peak power:

[0016]

[0017] In Equation (1), P PCSS is the load peak power, V MAX is the peak value of the load pulse collected by the oscilloscope, and the resistance value R of the attenuator 1 = 50 Ω;

[0018] (2) Method for calculating the on-resistance of the photoconductive switch:

[0019]

[0020] In Equation (2), R on is the on-resistance of the photoconductive switch, V S is the output voltage of the high-voltage DC source, V MAX is the peak value of the load pulse collected by the oscilloscope, and the resistance value R of the attenuator 1 = 50 Ω;

[0021] (3) Method for calculating the rise time:

[0022] t LH = t MAX -t left，low

[0023] t LH is the rise time of the photoconductive switch, t MAXIt is the time corresponding to the value obtained by multiplying the peak value of the load pulse signal by 90%. If there is no exactly equal value, select the time of the first point on the left that is closest as t MAX 。t left，low is the time corresponding to the value obtained by multiplying the peak value of the load pulse signal by 10% during the pulse rising stage. If there is no exactly equal value, select the time of the first point on the left that is closest as t left，low ;

[0024] (4) Falling time calculation method:

[0025] t HL =t right，low -t MAX

[0026] t HL is the falling time of the photoconductive switch, t MAX is the time corresponding to the value obtained by multiplying the peak value of the load pulse signal by 90%. If there is no exactly equal value, select the time of the first point on the right that is closest as t MAX 。t left，low is the time corresponding to the value obtained by multiplying the peak value of the load pulse signal by 10% during the pulse falling stage. If there is no exactly equal value, select the time of the first point on the right that is closest as t left，low ;

[0027] (5) Calculation method of full width at half maximum:

[0028] t FWHM =t right，half -t left，half

[0029] t FWHM is the full width at half maximum of the photoconductive switch, t right，half is the time corresponding to the point at half of the peak value during the pulse falling stage. Select the point closest to half of the peak value. t left，half is the time corresponding to the point at half of the peak value during the pulse rising stage. Select the point closest to half of the peak value.

[0030] The beneficial effects of the present invention compared with the prior art are as follows:

[0031] The microstrip structure of the photoconductive switch test board improves the anti-electromagnetic interference ability, and the microstrip line achieves good impedance matching with the attenuator, oscilloscope, and third coaxial cable; the circuit structure is simple, yet it suppresses the interference of parasitic capacitance and inductance; for high voltages, air breakdown and flashover phenomena may occur at any time. By using a special insulating anti-arc gel to cover the exposed high-voltage interfaces and transmission lines, such phenomena can be completely avoided, improving the loop stability;

[0032] The circuit is simplified by removing ordinary resistors whose resistance values change under high-current pulses, with the order of magnitude of the change being much larger than the dozens of Ω of the on-resistance. At the same time, sampling resistors (CVRs) with insufficient bandwidth accuracy are avoided, and a high-bandwidth attenuator is directly used to reduce the power of the pulse signal without loss of the signal frequency. High-precision sampling of ps-level and kV-level pulse signals is achieved. The optical path adjustment method using a focusing mirror and an adjustable optical slit is applicable to a variety of complex test situations. Combining with the photoelectric output signals of an optical energy meter and a picosecond pulsed laser, it can accurately monitor the light intensity irradiating on the surface of the photoconductive switch, and can accurately control the laser intensity and spot size of the irradiation. Furthermore, repeated measurement of the pulse signals excited by each light intensity at a fixed spot position is realized. The repeated measurement accuracy can reach 0.1%. In addition, changes in the conduction pulse waveform caused by changes in other conditions (such as defect energy levels introduced by irradiation) can be detected.

[0033] Due to the overall compact and streamlined optical path and circuit, the portability is very high, and it can be applied to a variety of irradiation tests and other photoconductive switch tests. Moreover, it is simple to build, has a high degree of integration, is more convenient to operate, and has a very broad promotion space.

[0034] Therefore, the conditions for pre- and post-measurement can be made consistent, the test results under the same conditions differ very little, and the accuracy can reach 0.1%. High-precision, high-repeatability, and strong anti-interference performance tests of photoconductive switches are achieved. The method described in the present invention can collect signals within a 10 GHz bandwidth under the combined action of high voltage, strong laser, etc., the signals are stable, and electromagnetic interference can be shielded. Signal changes caused by radiation damage can be detected, with high sensitivity. While meeting the requirements of high-precision pulse signal testing, the circuit and optical path structures are streamlined, and the integration degree is improved. Description of the Drawings

[0035] Figure 1 It is a schematic diagram of the composition of the test device for radiation damage of the photoconductive switch of the present invention.

[0036] Figure 2 It is the equivalent optical path and circuit diagram of the present invention.

[0037] Figure 3 It is a schematic diagram of the structure of the photoconductive switch test board of the present invention.

[0038] In the figure, picosecond pulsed laser 1, beam expander 2, deflection mirror 3, focusing mirror 4, photoconductive switch test board 5, high-voltage DC power supply 6, capacitor 7, attenuator 8, oscilloscope 9, ground terminal 10, positive terminal 11, first coaxial cable 12, limit bottom plate 13, fixture table 14, high-voltage cable 15, third coaxial cable 16, optical slit 17, second coaxial cable 18, photoconductive switch device 19, coaxial cable interface 20, optical energy meter 21. Detailed Embodiments

[0039] The present invention will be described in detail with reference to the accompanying drawings and embodiments, but the present invention is not limited thereto.

[0040] A test method for radiation damage of an optical switch according to the present invention. The device involved in this method consists of a picosecond pulse laser 1, a beam expander 2, a deflection mirror 3, a focusing mirror 4, an optical switch test board 5, a high-voltage DC power supply 6, a capacitor 7, an attenuator 8, an oscilloscope 9, a ground terminal 10, a positive terminal 11, a first coaxial cable 12, a limit bottom plate 13, a fixture table 14, a high-voltage cable 15, a third coaxial cable 16, an optical slit 17, a second coaxial cable 18, an optical switch device 19, a coaxial cable interface 20, and an optical energy meter 21. The output laser of the picosecond pulse laser 1 can change the spot size and light intensity through the beam expander 2. If an adjustable optical slit 17 is used, the spot size can be accurately adjusted with an accuracy of 0.001 mm. The optical energy intensity is measured using the optical energy meter 21. The picosecond pulse laser 1 is connected to the oscilloscope 9 through the first coaxial cable 12, and the attenuator 8 is connected to the oscilloscope 9 through the second coaxial cable 18. The high-voltage DC power supply 6 is connected to the optical switch test board 5 through the high-voltage cable 15, and the optical switch test board 5 is connected to the attenuator 8 through the third coaxial cable 16. The optical switch test board 5 is placed and fixed on the fixture table 14. The optical switch test board 5 consists of an optical switch device 19, a capacitor 7, a ground terminal 10, a positive terminal 11, a limit bottom plate 13, and a coaxial cable interface 20. The capacitor 7 is welded between the ground terminal 10 and the positive terminal 11, and both ends of the optical switch device 19 are connected to the positive terminal 11 and the coaxial cable interface 20. The specific operation is carried out according to the following steps:

[0041] a. Fix the optical switch test board 5 on the fixture table 14. Connect one end of the high-voltage cable 15 to the high-voltage output terminal of the high-voltage DC power supply, and the other end to the positive terminal 11 on the optical switch test board 5. Connect the ground terminal 10 to the ground wire. The coaxial cable interface 20 of the optical switch test board 5 is connected to the input of the attenuator 8 through the third coaxial cable 16. The oscilloscope 9 is connected to the photoelectric output of the picosecond laser 1 and the output of the attenuator 8 through the first coaxial cable 12 and the second coaxial cable 18 respectively. Set the output impedance of the input channel of the oscilloscope 9 to 50 ohms, and the attenuation multiple to the attenuation value of the attenuator 8. Select an attenuation multiple of 50 dB. Check the connection of these wires again, turn on the picosecond pulse laser 1, and adjust the deflection mirror 3 so that the laser beam focusing position is at the window position of the optical switch test board 5.

[0042] b. Turn on the high-voltage DC power supply 6 and output high voltage through the high-voltage cable 15 to provide high voltage for the photoconductive switch test board 5. Adjust the voltage to 5 - 6 kV. Under this voltage drop, by finely adjusting the deflecting mirror 3, make the laser irradiate the optimal triggering area on the surface of the photoconductive switch test board 5 to maximize the peak value collected by the oscilloscope 9. Record and save the laser and load pulse signals at this time. Use an optical power meter to measure the light intensity at a position 5 cm after passing through the optical slit 17. Move the optical power probe out through the moving platform at the 5 cm position to measure. The light intensity measurement positions before and after are the same, and record the light intensity and the amplification voltage of the picosecond pulse laser 1. After the measurement is completed, remove the optical power probe. If the focusing lens 4 is used, adjust the position of the focusing lens 4 to change the spot size and light intensity. If the adjustable optical slit 17 is used, the spot size can be accurately adjusted with an accuracy of 0.001 mm. Measure the pulse signals under two different voltage biases under this light intensity condition. The voltage range is 1 kV - 7 kV, and measure and save once every 1 kV interval. When saving, select the signal with the smallest difference between the photoelectric signals before and after the picosecond pulse laser 1. This measured value is used as the initial value of the photoconductive switch;

[0043] c. Keep the optical path basically unchanged, remove the photoconductive switch test board 5, and conduct the irradiation experiment. During the irradiation process, provide a bias for the irradiated photoconductive switch test board 5 through the DC high-voltage power supply 6. After the irradiation is completed, fix the photoconductive switch test board 5 on the fixture table 14 and conduct the parameter measurement after irradiation. First, adjust the light intensity and the amplification voltage of the picosecond pulse laser 1 defined in step b to ensure that the difference from the initial value condition is less than 0.01% before it can be used as an effective measurement. Set the amplification voltage of the picosecond pulse laser 1 and adjust the rotation knob on the deflecting mirror 3, that is, adjust the required light intensity at a fixed position;

[0044] d. Measure two groups of pulse signals under different biases. The voltage range is 1 kV - 7 kV, and measure and save once every 1 kV interval. The oscilloscope 9 saves the signal data and calculates the on-resistance, rise time, fall time, half-peak width, and load peak power at this dose through the existing calculation method;

[0045] e. Repeat steps c - d to complete the data acquisition and calculation at each dose point;

[0046] As Figure 1 shown, the photoconductive switch test board 5 includes a microstrip circuit board and a limit bottom plate. As Figure 3As shown, the microstrip circuit board is fixed on the limit base plate by screws and grounded as a whole. The microstrip circuit board includes an optical switch device 19, a capacitor 7, a ground terminal 10, a positive terminal 11, and a coaxial cable interface 20. The holes on the microstrip circuit board are used for welding the packaged optical switch. A 2nF capacitor 7 is connected between the ground terminal 10 and the positive terminal 11. The capacitor 7 charges and discharges to provide a voltage drop for the optical switch, avoiding the high-voltage DC power supply 6 from being burned by transient pulse current. The output of the optical switch test board 5 adopts a 50-ohm microstrip structure with a coaxial cable interface 20 to convert the microstrip circuit into a coaxial output;

[0047] The voltage coverage range of the high-voltage DC power supply 6 is 0 - 10 kV. The high-voltage DC power supply 6 provides a high voltage for the optical switch to be tested through a high-voltage cable. The DC high-voltage output line is connected to the positive terminal 11 of the optical switch test board 5, and the ground of the high-voltage DC power supply 6 is connected to the ground terminal 10 of the optical switch test board 5 and then connected to the ground wire; the output of the optical switch test board 5 is connected to the input end of the attenuator 8 through a coaxial cable. Insulating gel is used to isolate all exposed joints in contact with the air to avoid air discharge during contact with the air, signal loss, and safety threats; the impedance of the attenuator 8 is 50 ohms. The output of the attenuator 8 is connected to the oscilloscope 9 through a coaxial cable. The pulse signal on the attenuator 8 is captured by the oscilloscope 9 in a single-shot trigger mode; the collected pulse signal is in the ps magnitude, has a very high bandwidth, and the pulse peak value is very high. For a normal sampling resistor, its resistance value will change under the conditions of high bandwidth and high peak value; moreover, the voltage probe is limited by bandwidth and has low accuracy in measuring picosecond signals. Using a broadband attenuator 9 can avoid these problems;

[0048] The laser output by the picosecond pulse laser 1 increases the light spot size after passing through the beam expander 2. After being adjusted by the deflection mirror 3 and the focusing mirror 4, the light intensity per unit area is increased, making the laser energy distribution more uniform. Then, the optical slit 17 is used to precisely control the light spot size, which can improve the measurement accuracy; the focusing mirror 4 can increase the power density, and the optical slit 17 can adjust the light spot size but cannot change the power density; when the voltage provided by the high-voltage DC power supply 6 causes the electrons and holes generated by the laser in the optical switch to be instantaneously collected at both ends of the electrode, a transient current pulse is generated, and the current peak value is as high as several hundred A; this pulse signal can be collected by the oscilloscope 9 after passing through the attenuator 8. The collected voltage signal is the pulse voltage signal on the load, and the waveform data is saved; through calculation, the on-resistance, rise time, fall time, half-width at half maximum, and load peak power of the device under the specified trigger conditions can be obtained; in addition, the optoelectronic output signal of the picosecond pulse laser 1 is connected to the oscilloscope 9, and the laser signal when the optical switch is triggered to conduct each time can be collected, and precise screening can be performed to ensure the trigger accuracy;

[0049] Test steps:

[0050] Step 1: a. Fix the photoconductive switch test board 5 on the fixture table 14. Connect one end of the high-voltage cable to the high-voltage output terminal of the high-voltage DC power supply, and the other end to the positive terminal 11 on the photoconductive switch test board 5. Connect the grounding terminal 10 to the ground wire. Connect the coaxial cable interface 20 of the photoconductive switch test board 5 to the input of the attenuator 8 through the third coaxial cable 16. Connect the oscilloscope 9 to the photoelectric output of the picosecond laser 1 and the output of the attenuator 8 through the first coaxial cable 12 and the second coaxial cable 18 respectively. Set the output impedance of the input channel of the oscilloscope 9 to 50 ohms, and the attenuation multiple to the attenuation value of the attenuator 8. Select an attenuation multiple of 50 dB. Check the connection of these wires again. Turn on the picosecond laser 1 and adjust the deflection mirror 3 so that the laser beam focusing position is at the window position of the photoconductive switch test board 5.

[0051] Step 2: Turn on the switching power supply of the high-voltage DC power supply 6 and preheat it for 10 minutes to ensure stable voltage output. Turn on the high-voltage output switch of the high-voltage DC power supply 6 to provide high voltage to the photoconductive switch test board 5. Adjust the voltage to 5 - 6 kV. Because the signal is relatively stable under a relatively high voltage drop, at this voltage drop, fine-tune the deflection mirror 3 so that the laser irradiates the optimal trigger area on the surface of the photoconductive switch test board 5, which is manifested as the maximum peak collected by the oscilloscope 9. Record and save the laser and load pulse signals at this time. Use an optical power meter to measure the light intensity at 5 cm after passing through the optical slit 17. Move the optical power probe out through the moving platform at 5 cm to measure. The positions of the measured light intensities before and after are the same, and record the light intensity and the amplification voltage of the picosecond pulse laser 1. After the measurement, remove the optical power probe. If using a focusing lens 4, adjust the position of the focusing lens 4 to change the spot size and light intensity. If using an adjustable optical slit 17, the spot size can be accurately adjusted with a precision of 0.001 mm. Measure the pulse signals under two different voltage biases under this light intensity condition. The voltage range is 1 kV - 7 kV, and measure and save once every 1 kV interval. When saving, select the signal with the smallest difference between the front and back of the laser photoelectric signal. This measured value is used as the initial value of the photoconductive switch device 19.

[0052] Step 3: Keep the optical path basically unchanged, remove the photoconductive switch test board 5, and conduct the irradiation experiment. During the irradiation process, a bias can be provided to the irradiated photoconductive switch test board 5 through the DC high-voltage power supply 6. Shield other electrical components on the photoconductive switch test board 5 except the photoconductive switch device 19. After the irradiation is completed, fix the photoconductive switch test board 5 on the fixture table 14 and conduct the parameter measurement after irradiation. First, adjust the light intensity and the amplification voltage of the picosecond pulse laser 1 defined in Step 2 to ensure that the difference from the initial value condition is less than 0.01% before it can be used as an effective measurement. Set the amplification voltage of the picosecond pulse laser 1 and adjust the rotation knob of the deflection mirror 3 to adjust the required light intensity at a fixed position.

[0053] Step 4: Measure two groups of pulse signals under different biases, with the voltage range from 1 kV to 7 kV, and save the measurement once every 1 kV interval; Oscilloscope 9 saves the signal data, and calculates the on-resistance, rise time, fall time, half-peak width, and load peak power at this dose through the existing calculation method;

[0054] Step 5: Repeat Step 3 - Step 4 to complete the data acquisition and calculation at each dose point;

[0055] The parameter calculation process is as follows:

[0056] (1) Load peak power calculation method:

[0057]

[0058] In the above formula, V MAX is the load pulse peak collected by the oscilloscope, and the resistance value R 1 of the attenuator = 50 Ω;

[0059] (2) Photoconductive switch on-resistance calculation method:

[0060]

[0061] In the above formula, V S is the output voltage of the high-voltage DC source, V MAX is the load pulse peak collected by the oscilloscope, and the resistance value R 1 of the attenuator = 50 Ω;

[0062] (3) Rise time calculation method:

[0063] t LH = t MAX - t left，low

[0064] In the above formula, t LH is the rise time of the photoconductive switch, t MAX is the time corresponding to 90% of the peak value of the load pulse signal. If there is no exactly equal value, select the time of the leftmost first point closest to it as t MAX . t left，low is the time corresponding to 10% of the peak value of the load pulse signal in the pulse rising stage. If there is no exactly equal value, select the time of the leftmost first point closest to it as t left，low ;

[0065] (4) Fall time calculation method:

[0066] t HL = t right，low - t MAX

[0067] In the above formula, t HL is the fall time of the photoconductive switch, and t MAX is the time corresponding to the value obtained by multiplying the peak value of the load pulse signal by 90%. If there is no exactly equal value, select the time of the first point on the right that is closest as t MAX . t left，low is the time corresponding to the value obtained by multiplying the peak value of the load pulse signal by 10% during the pulse fall stage. If there is no exactly equal value, select the time of the first point on the right that is closest as t left，low .

[0068] (5) Calculation method of the full width at half maximum:

[0069] t FWHM = t right，half - t left，half

[0070] In the above formula, t FWHM is the full width at half maximum of the photoconductive switch, t right，half is the time corresponding to the point that is half of the peak value during the pulse fall stage, and select the point closest to half of the peak value; t left，half is the time corresponding to the point that is half of the peak value during the pulse rise stage, and select the point closest to half of the peak value;

[0071] The parameter calculation results of the embodiments are shown in Table 1:

[0072] Table 1 Test Results of Embodiment Parameters

[0073]

[0074]

[0075] It can be seen from Table 1 that: the test ability of the present invention covers the key performance parameters of the photoconductive switch, with a wide measurement range and high measurement accuracy. In particular, the test stability and repeatability are high, and the differences between multiple measurement results are very small, so that the test data eliminates the accidental errors introduced by factors such as light spot and light intensity, and solves the problem of large measurement deviation before and after the photoconductive switch. The test results can reflect the influence of the damage introduced by radiation on the conduction performance of the photoconductive switch, and the test data has extremely high credibility, which is not possessed by most other photoconductive switch test methods.

Claims

1. A method for testing radiation damage of an optical switch, characterized in that The device involved in the method comprises a picosecond pulse laser (1), a beam expander (2), a deflection mirror (3), a focusing mirror (4), a photoconductive switch test board (5), a high-voltage DC power supply (6), a capacitor (7), an attenuator (8), an oscilloscope (9), a ground terminal (10), a positive terminal (11), a first coaxial cable (12), a limit bottom plate (13), a fixture table (14), a high-voltage cable (15), a third coaxial cable (16), an optical slit (17), a second coaxial cable (18), a photoconductive switch device (19), a coaxial cable interface (20), and a light energy meter (21); the output laser of the picosecond pulse laser (1) is enlarged through the beam expander (2), and then through the deflection mirror (3) and the focusing mirror (4), the light path is changed and the light spot is focused, and finally the light spot size is accurately controlled through the optical slit (17); the light energy meter (21) is used to measure the light spot size. The light energy intensity is measured; the picosecond pulse laser (1) is connected to the oscilloscope (9) through a first coaxial cable (12); the attenuator (8) is connected to the oscilloscope (9) through a second coaxial cable (18); the high-voltage DC power supply (6) is connected to the optical switch test board (5) through a high-voltage cable (15); the optical switch test board (5) is connected to the attenuator (8) through a third coaxial cable (16); the optical switch test board (5) is placed and fixed on the fixture table (14); the optical switch test board (5) is composed of an optical switch device (19), a capacitor (7), a ground terminal (10), a positive terminal (11), a limit bottom plate (13) and a coaxial cable interface (20); the capacitor (7) is welded between the ground terminal (10) and the positive terminal (11); both ends of the optical switch device are connected to the positive terminal (11) and the coaxial cable interface (20); the specific operation is performed according to the following steps: a. Fix the optical switch test board (5) on the fixture table (14), connect one end of the high-voltage cable to the high-voltage output of the high-voltage DC power supply, and connect the other end to the positive terminal (11) on the optical switch test board (5); connect the ground terminal (10) to the ground wire, connect the coaxial cable interface of the optical switch test board (5) to the input of the attenuator through the third coaxial cable (19), connect the oscilloscope (9) to the photoelectric output of the picosecond laser (1) and the output of the attenuator (8) through the first coaxial cable (12) and the second coaxial cable (18), respectively, set the output impedance of the input channel of the oscilloscope (9) to 50 ohms, the attenuation multiple to the attenuation value of the attenuator (8), and select an attenuation multiple of 50 dB; check the connection of these wires again, then turn on the picosecond laser (1), and adjust the deflection mirror (3) so that the laser beam focusing position is the window position of the optical switch test board (5); b. Turn on the high-voltage DC power supply (6) and provide high voltage to the photoconductive switch test board (5) through the high-voltage cable (15). The voltage is adjusted to 5-6 kV. Under this voltage drop, the deflection mirror (3) is fine-tuned to make the laser irradiate the optimal trigger area on the surface of the photoconductive switch test board (5). The peak value collected by the oscilloscope (9) is the largest. The laser and load pulse signals at this time are recorded and saved. Use the light energy meter (21) to measure the light intensity at 5 cm after passing through the optical slit (17). Move the light energy probe of the light energy meter (21) out through the moving platform at 5 cm, that is, It can be measured, the light intensity position measured before and after is consistent, and the light intensity and the amplification voltage of the picosecond pulse laser are recorded. After the measurement is completed, the light energy probe is removed; if a focusing mirror is used, the focusing mirror position is adjusted to change the spot size and light intensity; if an adjustable optical slit is used, the spot size is adjusted accurately with an accuracy of 0.001mm; under this light intensity condition, two groups of pulse signals under different voltage bias are measured, the voltage range is 1kV-7kV, and the measurement is saved once at an interval of 1kV; when saving, the signal with the smallest difference between the picosecond laser photoelectric signal before and after is selected to save, and this measured value is used as the initial value of the photoconductive switch; c. While keeping the optical path basically unchanged, remove the photoconductive switch test board (5) and conduct an irradiation experiment. During the irradiation process, a DC high voltage power supply (6) is used to provide a bias to the irradiated photoconductive switch test board (5). After the irradiation is completed, fix the photoconductive switch test board (5) on the fixture table (14) to measure the parameters after irradiation. First, adjust the light intensity and the amplification voltage of the picosecond laser defined in step b to ensure that the difference with the initial value condition is less than 0.01% to be used as an effective measurement, set the amplification voltage of the picosecond laser (1) and adjust the rotary knob on the deflection mirror (3), that is, adjust the required light intensity at a fixed position; d. measuring two groups of pulse signals under different biases, with a voltage range of 1 kV-7 kV, and saving the measurement once every 1 kV; using the existing calculation method to calculate the on-resistance, rise time, fall time, half-peak width and load peak power under the dose, the data of the signal saved by the oscilloscope (9); e. Repeat steps c to d to complete data collection and calculation at each dosage point.

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