The temporal and spatial evolution of femtosecond laser-induced phase transitions and ablation on single-crystalline silicon carbide (SiC) were investigated via pump-probe microscopy in air on a time scale from approximately 100 fs to 1 ns. The largest reflectivity change was observed between 300 fs and 1 ps after excitation, which is due to free carrier generation, and the Drude model calculations indicated that the maximum free electron density was greater than 3.3 × 1021 cm−3. After a few picoseconds, there was direct evidence of the production of a rarefaction wave propagating towards the bulk, whose propagation velocity was estimated to be 3286 m/s. At delay times between a few hundreds of picoseconds and 1 ns, characteristic transient ring patterns were clearly observed and were related to the optical interference of the probe laser pulse reflected at the front surface of the ablating layer and at the interface of the non-ablating substrate. The estimated expansion velocity of the ablation front in 6H–SiC was found to be comparable to or slower than those reported for other semiconductors and dielectrics.

中文翻译：

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飞秒激光诱导单晶碳化硅熔化和烧蚀的超快泵浦探针显微成像

通过在空气中的泵浦探针显微镜在大约 100 fs 到 1 ns 的时间尺度上研究了飞秒激光诱导相变和烧蚀在单晶碳化硅 (SiC) 上的时间和空间演变。在激发后 300 fs 和 1 ps 之间观察到最大的反射率变化，这是由于自由载流子的产生，Drude 模型计算表明最大自由电子密度大于 3.3 × 1021 cm-3。几皮秒后，有直接证据表明产生了向大块传播的稀疏波，其传播速度估计为 3286 m/s。在几百皮秒和 1 ns 之间的延迟时间，清晰地观察到特征瞬态环形图案，并且与在烧蚀层的前表面和非烧蚀基板的界面处反射的探针激光脉冲的光学干涉有关。发现 6H-SiC 中烧蚀前沿的估计膨胀速度与其他半导体和电介质报道的膨胀速度相当或更慢。