Pulsed laser ablation mechanisms of thin metal films

The ablation of thin films by single laser pulses is a well known technique with widespread industrial applications. Ablation occurs in a well defined power density region if a supported thin film is illuminated by a single laser pulse. In the literature there are a number of theoretical description of ablation, but a very few based on in-situ experiments. In our study we have directly visualised the ablation processes with fast photography based on application of dye laser probe pulses. The ablation of chromium and tungsten layers supported onto glass substrates with pulses of ArF excimer laser was investigated. The ablated area was illuminated by a delayed short pulse of a fluorescein dye laser or a Rhodamine6G dye laser. Snapshots of initial phase of ablation and the forthcoming material transport were recorded by an optical system and a video camera. Blowing-off mechanisms and thermo-mechanical mechanisms are considered to take place during ablation. Pressures formed during laser ablation were calculated and compared with experimental data. It was found that thermo-desorbtion of gas adsorbed on to the substrate surface, substrate material evaporation and film exfoliation by its longitudinal thermal enlargement may be acting during laser ablation of thin films.