Abstract

We have studied, experimentally and theoretically, the liquid-solid morphologies^1,2 induced by the interaction of plane-polarized cw 10.6-µm laser radiation with silicon on a sapphire substrate. The experiments were performed at normal incidence, with silicon thicknesses ranging from 0.5 to 2 µm. Near the melt threshold, the large difference in optical properties of liquid and solid semiconductor drives an instability breaking the translational symmetry of the surface. The initial morphology of the nonuniform melting consists of lamellae structures, e.g., microscopic solid islands in a liquid background, which then evolve into a steady-state periodic arrangement of liquid and solid with increasing laser intensity. The structures have been studied using real-time microscopy and optical diffraction techniques. A key phenomenon in the evolution and maintenance of these surface structures is interference shielding, whereby existing liquid regions electromagnetically shield surrounding regions of solid, hindering further local melting. There is a strong competition in this process between the orientation of induced structure and the polarization of the incident field. A simple theory which exploits an analogy with the Ising model of disorder—order phase transitions is discussed.

© 1985 Optical Society of America