Device and method for detecting nanosecond laser damage process based on pump-probe technology

Abstract

A device and method for detecting nanosecond laser damage processes based on pump-probe technology. The device comprises: a first digital delay signal generator, a second digital delay signal generator, a third digital delay signal generator, a detection laser that generates femtosecond or picosecond pulses, a pump laser that generates nanosecond high-energy pulses, a first shutter, a second shutter, a focusing lens, a highly reflective mirror, a detection signal receiving device, and a computer. This method uses the pulse signal output by the first digital delay signal generator as a reference to trigger subsequent digital delay signal generators, which output frequency-varying signals to delay the output pulses of the detection laser and the pump laser, respectively. Shutter control is then combined to extract precisely delayed pump and detection pulses. This method reduces hardware requirements, enabling longer delays while avoiding the site and component requirements associated with optical path delays, simplifying the device's complexity and operational difficulty.

Description

Technical Field

[0001] The present invention relates to pump detection technology, in particular to a device and method for realizing time-resolved measurement of optical element damage process based on pump lasers and detection lasers with different repetition rates. Background Art

[0002] Advances in laser technology are placing increasing demands on the resistance of optical components to laser damage. Using time-resolved pump-probe technology to capture the dynamics of damage is crucial for clarifying laser damage mechanisms and guiding improvements in the damage resistance of optical components. The basic principle of pump-probe technology is to use a pulsed laser beam as the pump light to excite the material and a separate pulsed laser beam as the probe light. During the pump-light irradiation of the material, the probe light passes through the region of the material exposed by the pump light before entering a detection signal receiving device such as a CCD, enabling time-resolved measurement of the damage process in the irradiated region. Pump-probe technology allows for the investigation of the microscopic mechanisms and physical processes of the interaction between intense lasers and materials. Temporal resolution and delay control accuracy are two of the most important technical specifications. Without considering the delay jitter between the pump and probe beams, the temporal resolution of the information obtained by the system depends primarily on the pulse width of the probe beam. By sequentially varying the delay between the probe and pump beams, while ensuring the repeatability of each ultrafast event, and when the delay covers the entire dynamic damage process, complete information on laser-induced material damage can be obtained.

[0003] In current pump-probe experiments, the relative delay between the pump pulse and the probe pulse is primarily achieved through electrical and optical delays. Electrical delay requires two lasers: one for generating the pump pulse and the other for generating the probe pulse. Synchronizing the two lasers to achieve a fixed relative delay is a major challenge. Optical delay involves splitting the same laser to produce two beams, achieving synchronization between the pump and probe pulses. However, the delay between the pump and probe pulses is achieved through the optical path difference, which requires a longer optical path for longer delays. Due to experimental site limitations, the relative delay between the two laser pulses can only be controlled within a small range.

[0004] In experiments studying laser-induced damage in optical components, damage analysis based on pump-probe technology requires a relatively short pulse width of the probe light, which necessitates two light sources and presents synchronization issues. Since signal synchronization and delay between two lasers with the same repetition frequency are easy to achieve, and high delay control accuracy can be achieved, the two lasers generating the pump and probe light often have the same repetition frequency. However, under existing conditions in many laboratories, the available pump and probe lasers have different repetition frequencies, making it difficult to ensure the accuracy of delay control between the pump and probe light, making it difficult for researchers to use pump-probe technology to achieve time-resolved measurement of laser-induced material damage processes. Achieving precise synchronization and delay between pump and probe lasers with different repetition frequencies is of great significance to the development of pump-probe technology. It will lower the threshold for laser parameter requirements for time-resolved pump-probe technology, making the implementation of time-resolved pump-probe technology more convenient. Summary of the Invention

[0005] To address the deficiencies of the prior art, the present invention proposes a device and method for detecting nanosecond laser damage processes based on pump-probe technology for pump lasers and probe lasers with different repetition rates.

[0006] The technical solutions of the present invention are as follows:

[0007] A device for detecting nanosecond laser damage processes based on pump-probe technology is characterized in that the device includes: a first digital delay signal generator, a second digital delay signal generator, a third digital delay signal generator, a detection laser that generates femtosecond or picosecond pulses, a pump laser that generates nanosecond high-energy pulses, a first shutter, a second shutter, a focusing lens, a high-reflection mirror, a detection signal receiving device and a computer.

[0008] The T0 output terminal of the first digital delay signal generator is respectively connected to the EXT TRIG input terminal of the second digital delay signal generator and the EXT TRIG input terminal of the third digital delay signal generator, the A output terminal of the first digital delay signal generator is connected to the input terminal of the first shutter, the B output terminal of the first digital delay signal generator is connected to the input terminal of the second shutter, the A output terminal of the second digital delay signal generator is connected to the input terminal of the detection laser, and the A output terminal of the third digital delay signal generator is connected to the input terminal of the pump laser. The output light of the pump laser is sequentially converged by the second shutter and the focusing lens and then irradiated to the test sample. The output light of the detection laser is reflected by the high-reflection mirror after passing through the first shutter to form reflected light;

[0009] The reflected light is parallel to and close to the irradiated area of the test sample, and is received by the detection signal receiving device, so as to detect the nanosecond laser damage process on the front surface of the test sample; or;

[0010] The reflected light is made to irradiate the rear surface of the test sample at a certain angle, and after being reflected by the test sample, is received by the detection signal receiving device for detecting the nanosecond laser damage process on the rear surface of the test sample.

[0011] Using the pulse signal output by the first digital delay signal generator as a reference signal for the second digital delay signal generator and the third digital delay signal generator to achieve synchronization between the output signals of the second digital delay signal generator and the third digital delay signal generator;

[0012] The output pulse delay of the detection laser and the pump laser is achieved by frequency conversion of the second digital delay signal generator and the third digital delay signal generator, and the extraction of precisely delayed pump pulses and detection pulses is achieved by controlling the shutter opening and closing time.

[0013] A method for detecting nanosecond laser damage processes based on pump-probe technology specifically comprises the following steps:

[0014] ① Setting the output terminal T0 of the first digital delay signal generator to output a pulse signal of a fixed frequency, wherein the pulse signal is the input reference signal of the second digital delay signal generator and the third digital delay signal generator; wherein the delay between the reference signal and the output light of the detection laser is t1, and the delay between the reference signal and the output light of the pump laser is t2;

[0015] ② Setting the A output terminal of the second digital delay signal generator to output a pulse signal with a repetition frequency of mHz, and setting the A output terminal of the third digital delay signal generator to output a pulse signal with a repetition frequency of nHz; wherein mHz is the operating frequency of the detection laser, and nHz is the operating frequency of the pump laser;

[0016] ③ Setting the signal delay of the output terminal of the second digital delay signal generator A relative to its EXT TRIG input terminal to t2-t1+T, if the time T=0, the probe pulse and the pump pulse are synchronized and irradiate the test sample at the same time; if the time T is a negative value, the probe pulse precedes the pump pulse; if the time T is a positive value, the probe pulse lags behind the pump pulse;

[0017] ④ Setting the delay of channel A of the first digital delay signal generator to t1-t3 and the delay of channel B to t2-t4, the two shutters can select the synchronously irradiated pump pulse and detection pulse and block the remaining pulses; wherein the response delay of the first shutter is t3 and the response delay of the second shutter is t4;

[0018] ⑤ Clamp the test sample, adjust the pump beam irradiation position and the detection beam irradiation direction and position according to the test requirements, and install the detection signal receiving device at an appropriate position according to the parameters of the detection signal receiving device;

[0019] ⑥ Turning on the detection laser and the pump laser, setting the first shutter and the second shutter to an external control mode, starting the first digital delay signal generator to emit a periodic pulse signal, and the detection signal receiving device can collect the detection signal and transmit it to the computer for storage and processing;

[0020] ⑦ Move the test sample position, and the delay time T is changed to T1, T2, T3, T4, ..., T according to the actual measurement requirements. n , repeat step ⑥; where T1 <T2<T3<T4<…<T n ;

[0021] ⑧ The delay time T collected by the computer in step ⑦ is T1, T2, T3, T4, ..., T n By splicing the detection information, the complete time-resolved information of the laser damage of the test sample can be obtained.

[0022] The technical effects of the present invention are:

[0023] ① The present invention utilizes the fixed-frequency pulse signal output by the first digital delay signal generator as the reference signal for different digital delay signal generators, thereby realizing laser synchronization and delay of laser pulses output by any laser with different frequencies, which greatly expands the application convenience and scope of application of the pump-probe technology.

[0024] ② The delay between the pump pulse and the detection pulse is achieved by setting the signal delay signal generator, which not only can achieve a delay of nearly infinite length, but also avoids the disadvantages of traditional optical path delay, such as complex optical path structure, high adjustment accuracy requirements and large site occupation area. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the device for detecting nanosecond laser damage process on the front surface of optical components.

[0026] Figure 2 It is the diffraction pattern of the plasma generated at different times during the nanosecond laser damage process after being detected by the laser.

[0027] Figure 3 This is a schematic diagram of a device for detecting nanosecond laser damage processes on the rear surface of an optical element. DETAILED DESCRIPTION

[0028] The present invention will be further described below with reference to examples and drawings, but the scope of protection of the invention shall not be limited thereby.

[0029] See also Figure 1 . Figure 1 This is a schematic diagram of a time-resolved detection device for plasma generated during damage to the front surface of an optical element. The first digital delay signal generator 101, the second digital delay signal generator 102, and the third digital delay signal generator 103 all use Stanford Research's product DG535, each with 4 independent output channels. The detection laser 104 uses a self-developed picosecond laser with an output pulse width of 300 to 800 ps, an output frequency of 100 Hz, and a wavelength of 1064 nm. The pump laser 105 uses a Quanta-Ray laser from Spectra-Physics, with an output wavelength of 1064 nm, a pulse width of 9 ns, a single pulse energy of up to 1.2 J, and an output frequency of 30 Hz. The test sample 112 is a high-reflection film with a 0° incidence and a reflectivity of up to 99.9% for a 1064 nm wavelength. The detection signal receiving device 110 uses a beam quality analyzer from Coherent. The time-resolved detection of plasma generated during damage to the front surface of an optical element specifically includes the following steps:

[0030] ① Set the T0 output terminal of the first digital delay signal generator 101 to output a 1 Hz pulse signal, which is the input reference signal of the second digital delay signal generator 102 and the third digital delay signal generator 103; wherein the delay between the reference signal and the output light of the detection laser 104 is t1, and the delay between the reference signal and the output light of the pump laser 105 is t2;

[0031] ② Set the A output terminal of the second digital delay signal generator 102 to output a pulse signal with a repetition frequency of 100 Hz, and set the A output terminal of the third digital delay signal generator 103 to output a pulse signal with a repetition frequency of 30 Hz; wherein 100 Hz is the operating frequency of the detection laser 104, and 30 Hz is the operating frequency of the pump laser 105;

[0032] ③ Setting the signal delay of the A output terminal of the second digital delay signal generator 102 relative to its EXT TRIG input terminal to t2-t1+T, if the time T=0, the probe pulse and the pump pulse are synchronized and irradiate the test sample 112 at the same time; if the time T is a negative value, the probe pulse precedes the pump pulse; if the time T is a positive value, the probe pulse lags behind the pump pulse;

[0033] ④ The delay of channel A of the first digital delay signal generator 101 is set to t1-t3, and the delay of channel B is set to t2-t4. Then, the two shutters can select the synchronously irradiated pump pulse and detection pulse and block the remaining pulses; wherein, the response delay of the first shutter 106 is t3, and the response delay of the second shutter 107 is t4;

[0034] ⑤ Clamp the test sample 112, adjust the pump beam irradiation position and the detection beam irradiation direction and position according to the test requirements, and install the detection signal receiving device 110 at an appropriate position according to the parameters of the detection signal receiving device 110;

[0035] ⑥ Turn on the detection laser 104 and the pump laser 106, set the first shutter 106 and the second shutter 107 to external control mode, start the first digital delay signal generator 101 to emit a periodic pulse signal, and the detection signal receiving device 110 can collect the detection signal and transmit it to the computer 111 for storage and processing;

[0036] ⑦ Move the test sample 112, and change the delay time T to 200ns, 500ns, 1000ns, and 2000ns in sequence according to actual measurement requirements, and repeat step ⑥;

[0037] ⑧ The detection information collected by the computer 111 in step ⑦ with the delay time T being 200ns, 500ns, 1000ns, and 2000ns in sequence is spliced to obtain the diffraction pattern of the plasma generated by the detection laser during the 200ns, 500ns, 1000ns, and 2000ns delay of the test sample 112 nanosecond laser damage process, as shown in FIG. Figure 2 shown.

[0038] Figure 3 This is a schematic diagram of a device for measuring the damage process of the rear surface of an optical element. Figure 1 The devices used are the same, the difference is that the detection light is reflected by the high-reflection mirror 109 and irradiates the rear surface of the test sample 112 at a certain angle. After being reflected by the test sample 112, it is received by the detection signal receiving device 110 for detecting the nanosecond laser damage process on the rear surface of the test sample 112.

[0039] The present invention is not limited to the above embodiments. Based on the teachings of the present invention, improvements and modifications made to the present invention by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A device for detecting nanosecond laser damage processes based on pump-probe technology, characterized in that The device comprises: a first digital delay signal generator (101), a second digital delay signal generator (102), a third digital delay signal generator (103), a detection laser (104) for generating femtosecond or picosecond pulses, a pump laser (105) for generating nanosecond high-energy pulses, a first shutter (106), a second shutter (107), a focusing lens (108), a high-reflection mirror (109), a detection signal receiving device (110), and a computer (111); The T0 output terminal of the first digital delay signal generator (101) is respectively connected to the EXT TRIG input terminal of the second digital delay signal generator (102) and the EXT The TRIG input end is connected, the A output end of the first digital delay signal generator (101) is connected to the input end of the first shutter (106), the B output end of the first digital delay signal generator (101) is connected to the input end of the second shutter (107), the A output end of the second digital delay signal generator (102) is connected to the input end of the detection laser (104), and the A output end of the third digital delay signal generator (103) is connected to the input end of the pump laser (105); the output light of the pump laser (105) is sequentially converged by the second shutter (107) and the focusing lens (108) and irradiated to the test sample (112); the output light of the detection laser (104) is reflected by the high-reflection mirror (109) after passing through the first shutter (106) to form reflected light; The reflected light is parallel to and close to the irradiation area of the test sample (112), and is received by the detection signal receiving device (110) for detecting the nanosecond laser damage process on the front surface of the test sample (112); or The reflected light is irradiated on the rear surface of the test sample (112) at a certain angle, and after being reflected by the test sample (112), is received by the detection signal receiving device (110) for detecting the nanosecond laser damage process on the rear surface of the test sample (112); Using the pulse signal output by the first digital delay signal generator (101) as a reference signal for the second digital delay signal generator (102) and the third digital delay signal generator (103), thereby achieving precise synchronization between the output signals of the second digital delay signal generator (102) and the third digital delay signal generator (103); The output pulse delay of the detection laser and the pump laser is achieved by frequency conversion of the second digital delay signal generator (102) and the third digital delay signal generator (103), and the extraction of the precisely delayed pump pulse and detection pulse is achieved by controlling the shutter opening and closing time.

2. A method for detecting nanosecond laser damage process using the nanosecond laser damage process detection device according to claim 1, characterized in that: The method comprises the following steps: ① Setting the T0 output terminal of the first digital delay signal generator (101) to output a pulse signal of a fixed frequency, wherein the pulse signal is the input reference signal of the second digital delay signal generator (102) and the third digital delay signal generator (103); wherein the delay between the reference signal and the output light of the detection laser (104) is t1, and the delay between the reference signal and the output light of the pump laser (105) is t2; ② Setting the A output terminal of the second digital delay signal generator (102) to output a pulse signal with a repetition frequency of mHz, and setting the A output terminal of the third digital delay signal generator (103) to output a pulse signal with a repetition frequency of nHz; wherein mHz is the operating frequency of the detection laser (104), and nHz is the operating frequency of the pump laser (105); ③ Setting the signal delay of the output terminal A of the second digital delay signal generator (102) relative to its EXT TRIG input terminal to t2-t1+T, if the time T=0, the detection pulse and the pump pulse are synchronized and irradiate the test sample (112) at the same time; if the time T is a negative value, the detection pulse is ahead of the pump pulse; if the time T is a positive value, the detection pulse is behind the pump pulse; ④ The delay of the A channel of the first digital delay signal generator (101) is set to t1-t3, and the delay of the B channel is set to t2-t4, so that the two shutters can select the synchronously irradiated pump pulse and detection pulse and block the remaining pulses; wherein the response delay of the first shutter (106) is t3, and the response delay of the second shutter (107) is t4; ⑤ Clamping the test sample (112), adjusting the pump beam irradiation position and the detection beam irradiation direction and position according to test requirements, and installing the detection signal receiving device (110) at a suitable position according to the parameters of the detection signal receiving device (110); ⑥ Turning on the detection laser (104) and the pump laser (105), setting the first shutter (106) and the second shutter (107) to an external control mode, starting the first digital delay signal generator (101) to emit a periodic pulse signal, and the detection signal receiving device (110) can collect the detection signal and transmit it to the computer (111) for storage and processing; ⑦ Move the test sample (112) position, and the delay time T is changed to T1, T2, T3, T4, ..., T according to the actual measurement requirements. n , repeat step ⑥; where T1 <T2<T3<T4<…<T n ; ⑧ The delay time T collected by the computer (111) in step ⑦ is T1, T2, T3, T4, ..., T n By splicing the detection information, the complete time-resolved information of the laser damage of the test sample (112) can be obtained.

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