Nonlinear phenomena pulsed observations

A large number of papers has appeared on the subject of excimer laser exposure of polymer films (16-21). Most of these have dealt with the phenomenon of photoablation. A few have observed intensity dependent photochemistry (22,23). The latter authors were concerned with the effect of exposure intensity on resist development characteristics. The utility of nonlinear photochemistry for image modification has not been explored except in our earlier communication, in which strongly nonlinear irreversible bleaching was observed for KrF laser irradiation of acridine/PMMA films with lOnsec pulses (5). 

Thermal lensing contribution to the measured nonlinear optical properties. If the pulse duration is longer than the characteristic time of the heat diffusion in the medium, or if this time is itself longer than the delay between successive pulses, material heating may lead to an observable transient thermal lens phenomenon [120, 165, 212, 218, 219], This can show itself, in experiments, with characteristics similar to those of a pure (electronic) Kerr effect. There have been some attempts to extract the respective values of the thermal and electronic contributions to y from z-scan measurements [136, 160, 165, 166, 175, 220], However, de Nalda et al. proved later that this method was not reliable enough to get quantitative results [219],... 

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