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 threshold 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 measurements from low intensities to 100 GW/cm(2) showed that two-photon absorption is the dominant nonlinearity in this range and the two-photon absorption coefficient was measured to be (1.6+/-0.3) cm/GW. In the intensity regime above threshold (>1 TW/cm(2)), however, low ablation rates indicate strong absorption by laser induced free carriers. The dynamics of diamond ablation was investigated time-resolved using pump probe transmission and pulse pair ablation measurements. Ablation with short pulses at 248 MI is also compared to ablation with 15 ns pulses at 193 nm. (C) 1995 American Institute of Physics.