Abstract

We report the first pulsewidth study of the various bulk phase transitions of crystalline silicon (c-Si) induced by ultrashort pulses of λ = 1 μm laser radiation from 4 - 260 ps in duration. In particular, we find a continuous reduction in the single shot melting threshold, E_TH, for c-Si from 2.7 ± 0.3 J/cm^-2 for 225 ps pul ses to 0.6 ± 0.1 J/cm^-2 for 6 ps pul ses. Although pulses longer than 30 ps induce bulk melting followed by recrystallization, pulses of 10 ps duration or less can actually produce an amorphized layer on the c-Si, contrary to published expectations [1]. Additionally, we find that, in all cases where a phase change occurs, periodic ripple patterns are formed even for pulses as short as 4 ps. This reduces the proposed minimum irradiation time of 20 ps [2] required to form these structures on c-Si.

© 1984 Optical Society of America