Ethanol-assisted ablation of silicon and germanium by temporally shaped femtosecond pulses

A surprising phenomenon can be discovered by using femtosecond double-pulse ablation of silicon and germanium in ethanol. The ablation areas present an oscillation increase phenomenon when the pulse delay increases from 200 fs to 1 ps in the fluence range of 0.5–0.6 J∕cm2. In contrast, the ablation areas exhibit an oscillation decrease phenomenon as the pulse delay increases when the laser fluence F < 0.5 J∕cm2, which is consistent with the results of the experiment in air. It is considered that the adjustment of the photon–electron coupling efficiency by pulse train technology plays an important role in the ablation process.