Laser heat treatments driven by integrated beams: role of irradiation nonuniformities

An analysis is given of how nonuniformities in the laser beam intensity tra nslate into variations on the induced temperature distribution on an irradi ated sample. The study involves materials with different thermal conductivi ties. By use of a reshaped irradiating beam obtained with a multifaceted in tegrating mirror, a three-dimensional numerical calculation allows us to es tablish both surface and in-depth temperature distributions. The results sh ow that in the case of materials such as glass (i.e., with low thermal cond uctivity) large thermal gradients occur both on the surface and in depth du ring irradiation. However, the lateral heat flow is high enough to strongly reduce the surface gradients as soon as the laser irradiation ends. Conver sely, in good thermal conductors such as nickel, the laser intensity nonuni formities induce a thermal peaking of the surface with lateral thermal grad ients that are by no means negligible. Experimental evidence during laser g lass polishing that confirms the numerical assessments are also provided. ( C) 1999 Optical Society of America. OCIS codes: 140.3390, 140.6810, 160.275 0, 140.3300, 220.5450, 120.6660.