Ablation morphology of germanium with multi-pulse femtosecond laser

Ablation morphology on germanium surface using multi-pulse femtosecond laser is reported. The SEM and laser focus give magnified views of the ablated portion. The ablation morphology shows a periodic surface structure with various laser pulses. And the formation of amorphous rings and ripples in the damage spot is discussed. The ablation threshold is 1.2 J·cm-2 and the ablation depth with single femtosecond laser pulse is about 150 nm. It is meanful for research the interaction of femtosecond laser and material, and the application of femtosecond laser in micromachining.