基于分光延时的脉冲激光波形调节方法研究

Research on Adjustment Method of Pulsed Laser Waveform Based on Beam Splitting and Delay

脉冲激光由于具有峰值功率高、脉冲宽度窄等特点,在激光致声、激光焊接等领域中得到了广泛应用。使用特殊波形的脉冲激光,可获得比单脉冲高斯激光更加优异的应用效果,因此脉冲激光波形调节方法具有重要的应用价值。针对这一需求,提出并实验验证了一种基于分光延时的脉冲激光波形调节方法。首先对脉冲激光分光延时叠加原理进行了理论分析,设计出基于两次分光的四脉冲分光延时叠加光路,确定了产生矩形、三角形、驼峰形和双峰形脉冲激光所需的分光比与延时。然后搭建了一套基于Nd∶YAG脉冲激光器的二倍频532 nm激光的四脉冲分光延时叠加实验装置,成功获得了矩形、三角形、驼峰形和双峰形等特殊波形的脉冲激光。

Objective Pulsed lasers are widely used in many fields because of their high peak power and short pulse width.Most single-mode pulsed lasers generated by Q-switching have Gaussian waveforms.However,pulsed lasers with unique waveforms exhibit improved effects in specific applications,such as laser-induced acoustics,laser welding,laser ablation,and laser-induced breakdown spectroscopy.Two lasers are employed using a high-precision signal generator to generate a double-pulse laser.A pulsed laser with an attenuated waveform is obtained using multiple reflections.In this study,an adjustment method for pulsed laser waveforms based on beam splitting and delay is proposed.The proposed method can provide increased pulsed laser waveforms in laser-induced acoustics,laser welding,laser ablation,and laser-induced breakdown spectroscopy.Methods First,an experimental optical layout(Fig.2)based on beam splitting and delay is designed.Subsequently,a numerical simulation(Table 2 and Fig.4)is conducted for a Gaussian waveform,and the parameters required to generate superimposed pulsed lasers with rectangular,triangular,hump-shaped,and dual-peak waveforms are obtained.Finally,the 532 nm laser generated by frequency doubling of the Nd∶YAG laser enters the device.Superimposed pulsed lasers with different waveforms are obtained by varying the splitting ratio and delay.Two high-speed photodetectors and a high-speed digital oscilloscope are used to measure the waveforms of the original and superimposed pulsed lasers.Results and Discussions Superimposed pulsed lasers with rectangular,triangular,hump-shaped,and dual-peak waveforms are successfully obtained(Fig.6).The experimental results are consistent with the numerical simulation results.Because the waveform of the original laser pulse is not an ideal Gaussian waveform and the actual splitting ratio of the beam splitter is affected by the laser polarization direction,the top of the pulsed laser with a rectangular waveform is not sufficiently smooth.Subsequently,the pulsed laser with a rectangular waveform is simulated again with the waveform of the original pulsed laser,and the simulation results are consistent with the experimental results(Fig.7).This method is suitable for experiments performed under strong light but is affected by the damage threshold.If the pulsed laser energy is exceptionally high,the damage threshold can be increased via beam expansion.Conclusions This study presents a method that can flexibly adjust the pulsed laser waveform.By varying the splitting ratio and delay or increasing the numbers of beam splitters,a laser can yield superimposed pulsed lasers with different waveforms.A numerical simulation is performed,and the parameters required to generate pulsed lasers with rectangular,triangular,hump-shaped,and dual-peak waveforms are determined.Experiments are performed on the designed optical layout based on the parameters obtained from the simulation.The experimental results demonstrate that this method can yield pulsed lasers with various waveforms,such as rectangular,triangular,hump-shaped,and dual-peak waveforms,by varying the splitting ratio and delay.Because the waveform of the original pulsed laser is not an ideal Gaussian waveform and the actual splitting ratio of the beam splitter is different from the theoretical splitting ratio,the top of the pulsed laser with a rectangular waveform is not sufficiently smooth.This method provides a new special waveform pulsed laser generation scheme for laser-induced acoustics,laser welding,laser ablation,laser-induced breakdown spectroscopy,etc.