Integrating GaAs:EL2 photodetectors and double-layer cross-slits for high-precision planar focusing in pulsed power lasers

High-power nanosecond pulse laser processing is susceptible to thermal effects, such as plasma formation and the thermally induced drift of optics, which cause a dynamic shift of the focal position. To address the problem, a novel planar focusing method is developed to improve the precision for laser focus positioning in high-power nanosecond pulse laser applications. Firstly, a planar photodetector (PPD) based on semi-insulating GaAs:EL2 was developed to improve planar focusing precision. Secondly, a novel tridimensional double-layer cruciform slit diaphragm (TCSD) was integrated to mitigate the thermal lensing effect and enhance the damage threshold. Thirdly, the key parameters of both the PPD and the TCSD have been optimized through systematic theoretical analysis. And a laser focal drift detection system is established to monitor deviations in the xy-plane. Moreover, extensive experiments on positioning resolutions have demonstrated that 31.2 mV/mm (x-direction) and 96.0 mV/mm (y-direction) are achieved. Notably, the TCSD exhibits a significantly higher damage threshold compared with conventional configurations, further confirming the robustness and precision of the system for high-intensity laser processing.