Published: Jan 1986
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We review our experimental and theoretical work on surface transformations produced on amorphous and crystalline semiconductors and metals by single or multiple ultrashort laser pulses. In addition to melting and vaporization, two phenomena have attracted our attention: the formation of surface ripples and transformations due to repetitive subthreshold illumination.
A detailed theoretical model that explains successfully the formation and the major properties of the surface ripples has been developed and we illustrate the agreement by many examples. However, we also present experimental results which suggest that to describe the interaction between the incident beam and the surface diffracted waves, a perturbative approach is not always sufficient. A phenomenological explanation is presented for these nonstandard ripples.
Repetitive subthreshold illumination can produce the same surface transformations as single pulse illumination above threshold. We present universal growth curves and determine a safe level for multiple shot exposure in various materials. Our results are compared to several models, including accumulation of plastic deformation, creation of microcrystallites, and the early stages of ripple formation.