Spatial redistribution of energy in a nanosecond laser pulse by an organicoptical limiter

The spatial redistribution of energy resulting from the interaction between a near-diffraction-limited nanosecond laser pulse and the nonlinear absorb ing optical limiting dye silicon naphthalocyanine is described, for what is to our knowledge the first time, in an optical geometry that is likely to be found in practical applications. For input fluences above that required for nonlinear absorption but below that for bubble growth, a plane wave or Gaussian spatial input evolves unexpectedly to a sharp central spike and a well-defined outer ring. The observed energy redistribution is thought to r ely on a combination of nonlinear processes, since a pure absorptive proces s alone cannot explain the profiles presented. A model involving nonlinear absorption and nonlinear refraction qualitatively reproduces the observed s patial profiles. It is clear from the results that the performance of optic al limiting dyes in representative optical geometries, even at fluences wel l below that required for bubble growth, cannot be described solely by nonl inear absorption. OCIS codes: 140.3360, 140.3380, 140.6810, 160.4890, 160.4 760, 190.4400.