Experimental studies and thermal modelling of 1064-and 532-nm Nd:YVO4 micro-laser ablation of polyimide

Experiments and thermal modelling of polyimide ablation using the fundamental 1064-nm emission from a 20-kHz nanosecond diode-pumped solid-state Nd: YVO4 micro-laser are described and compared with findings for the 532-nm doubled output. For exposures restricted to short pulse trains, it is found that micron-scale-size ablation features can be defined with this laser, even though polyimide films have weak absorption at 1064 nm and relatively weak absorption at 532 nm. There is evidence at both wavelengths of an incubation effect, driven by thermal modification of the polymer and, with long-term exposure at 1064 nm, Raman micro-spectroscopy reveals a progressive growth of predominantly amorphous carbon in the ablation site. Calculations of the temperature rise produced in the polymer by exposure to a high-repetition-rate pulse train are described that aid an understanding of the thermal aspects of the interaction at the two wavelengths.