Opt Express. 2023 Feb 13;31(4):6877-6889. doi: 10.1364/OE.480338.
Gallium phosphide (GaP) is a widely used and promising semiconductor material for photonics devices and we suppose the ultrafast laser can be a competitive tool for GaP processing. We used an 800 nm centered femtosecond (fs) laser with a pulse duration of 50 fs to irradiate the GaP crystal. The ablation threshold was first determined, and then the ultrafast dynamics including plasma expansion, shockwave formation and propagation, and spectral evolution were acquired and analyzed. The evolution of ejected plasma in the initial stage changed from cylindrical to planar propagation with the augment of laser fluence. The study on the propagation properties of shockwaves showed that the energy of propelling shockwaves accounted for 12% to 18% of the laser pulse energy at all fluences above the ablation threshold. A prominent plasma splitting was observed at a fluence slightly higher than the threshold, and a phenomenon that the plasma protruded out of the shockwaves was also found. Finally, the transient temperature and density of electron at different fluences were calculated. The temperature difference between the plasma and the shockwave proved the heating effect of the plasma during ablation.
磷化镓（GaP）是一种广泛应用于光子学器件的有前途的半导体材料，我们假设超快激光可以成为 GaP 加工的一种有竞争力的工具。我们使用中心波长为 800nm 的飞秒（fs）激光，其脉冲持续时间为 50fs，来辐照 GaP 晶体。首先确定了消融阈值，然后获得并分析了包括等离子体膨胀、冲击波形成和传播以及光谱演化在内的超快动力学。在激光强度增加的情况下，初始阶段喷射等离子体的演化从柱形传播变为平面传播。冲击波传播特性的研究表明，在所有高于消融阈值的强度下，推动冲击波的能量占激光脉冲能量的 12%至 18%。在略高于阈值的强度下观察到明显的等离子体分裂现象，并且还发现了等离子体从冲击波中突出的现象。最后，计算了不同强度下电子的瞬态温度和密度。等离子体和冲击波之间的温差证明了在消融过程中等离子体的加热效应。
