SUBPICOSECOND ULTRAVIOLET-LASER ABLATION OF DIAMOND - NONLINEAR PROPERTIES AT 248 NM AND TIME-RESOLVED CHARACTERIZATION OF ABLATION DYNAMICS

Ablation of diamond by short UV pulses is reported. The ablation thres hold for 500 fs pulses at 248 nm was found to be 0.6 J/cm(2) (equal to a peak intensity of 1.1 TW/cm(2)). Intensity-dependent transmission m easurements from low intensities to 100 GW/cm(2) showed that two-photo n absorption is the dominant nonlinearity in this range and the two-ph oton absorption coefficient was measured to be (1.6+/-0.3) cm/GW. In t he intensity regime above threshold (>1 TW/cm(2)), however, low ablati on rates indicate strong absorption by laser induced free carriers. Th e dynamics of diamond ablation was investigated time-resolved using pu mp probe transmission and pulse pair ablation measurements. Ablation w ith short pulses at 248 MI is also compared to ablation with 15 ns pul ses at 193 nm. (C) 1995 American Institute of Physics.