Nonlinear reflection from polymer surfaces during femtosecond ultraviolet photoablation

The sub-picosecond response of the surface reflectivity of different polymers during ablation was measured using a pump-and-probe technique. Ablation was generated by a 0.5 ps duration KrF excimer laser. The time-dependent reflectivity of the surfaces was measured by a 496 nm, 0.5 ps long, low power laser. It showed an up to 4-fold increase from the unirradiated sample to a maximum of 94% within less than a picosecond and with a few picoseconds falltime. The spectrum of the ultraviolet light reflected from the spot is blue-shifted and exhibits more than three times the bandwidth of the incident radiation.