Mechanisms of enhanced laser ablation of transparent materials in photonics

Conversion efficiencies concerning the transfer of laser energy into thermal or mechanical specific internal energy on targets, both depend on material parameters and on the spectral and temporal irradiation characteristics. Investigations to be reported refer to processes governing small signal absorption at low power densities up to saturation levels, due to nonlinear optical effects at medium or high energy density values. The paper gives a survey of present achievements in this field of research. It includes results of recent investigations, carried out at the German-French Research of Saint-Louis (ISL). Particular interest in these studies was focused on the behavior of optically passive and active dielectric materials, such as those used in optronical devices, subject either to in-band, or to out-of-band laser radiation across large area surfaces. Experimental results are presented, as obtained by the use of a repetitively pulsed high average power CO 2 -laser (P average up to 15 kW) with pulsed peak powers up to about 100 MW. Suitability chosen focusing conditions provide a high flexibility concerning the available range of achievable power densities, correspondingly. Numerical simulations based on the experimental CO 2 -laser results (10.6 micrometer) allow an extrapolation towards processes and responsible mechanisms to be expected in other wavelength ranges of actually interesting high-power lasers.