Laser Induced Periodic Surface Structure
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H.M. VAN DRIEL, JEFF F. YOUNG AND J.E. SIPE Department of Physics and Erindale College, University of Toronto, ario, Canada M5S IA7
Toronto, Ont-
ABSTRACT Laser induced periodic surface structure can be understood as a universal phenomenon which occurs when high intensity pulses are absorbed near the surThe phenomenon occurs on metals, semiconductors face of solids or liquids. and insulators because of the interference between the incident pulse and an This scattered field may be enhanced by the induced "radiation remnant". existence of true surface modes such as surface plasmons or phonon-polaritons but this is not essential. The universality characteristics include beam polarization, since we show that circularly polarized light can induce surface ripples, with the damage structure showing a dependence on the sense of rotation. We also present time resolved results of the formation of the ripples to illustrate the essential dynamical processes that occur.
INTRODUCTION Single, high intensity laser pulses can induce permanent or transient periodic struityges on the surfaces of solid or liquid metals, semiconductors and insulators . This effect has been observed for s and p polarized light, of different wavelengths (0.15 -11.31im), pulse widths and for various angles of incidence. This curious symmetry breaking phenomenon is of importance in various aspects of laser-material processing and, at a more fundamental level, is It of interest in revealing how coherent radiation interacts with a surface. is generally acknowledged that the periodic structures are the result of interference between the incident beam and a "surface scattered field" induced by Although various authors have suggested different forms for microroughness. 2 1 2 including pure transverse elgctromagnetic, , surface plasthe "surface w v•, , the universality of the phemon polaritons ' or surface phonon polaritons At last year's (1981) Matnomenon requires an equally univerral explanation. erials Research Society Meeting we suggested a new non-radiative surface field structure, which we called a radiation remnant, that could account for the universal characteristics. These fields, which in general have a longitudinal comRonent, propagate along the surface while their 5 a~plitude falls off as They are associated with x-3I2, where x is the distance from a line source. ' discontinuities in the derivatives of a response function rather than with the pole singularities characteristics of true propagating electromagnetic modes. These new field structures exist on materials of arbitrary dielectric constant and occur in addition to any true surface modes which may exist such as surface polaritons. These radiation remnants show a formal similarity to "lateral waves" in such diverse areas as total internal reflection of light17 and "ground radio waves" 1 8 . We have developed a detailed universal theory 9 which takes into account the radiation remnant fields using a new variational princiThis theory accounts for all ple to calculate the surface field structure
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