Excimer laser induced electrical conductivity in polyimide: Applications to engineering, physics, and applied science

Various aspects of the interaction of excimer laser pulses and polyimide were investigated, focusing on low fluences where laser induced electrical conductivity is observed.;Multiple shot excimer ablation of polyimide was investigated, and at fluences between 20 mJ/cm;The optical properties of the laser irradiated surface were also studied with regard to a transient decrease in reflectivity that is observed during and in the first few tens of nanoseconds after irradiation. Pump probe experiments using electronically delayed probe pulses were performed and measurements of reflectivity, transmissivity and scattering were made under identical conditions. The results, a decrease in reflectivity and scattering with a simultaneous increase in transmissivity, imply a transient refractive index phenomenon during the first 150 ns after excimer irradiation.;A nonlinear current-voltage relation was observed near the critical point of the laser induced metal-insulator transition. The crossover behavior from nonlinear to linear regimes was studied in detail and interpreted in terms of a percolation theory of binary conductor-insulator mixtures. The nonlinearity and the crossover can, for the first time, be described simultaneously in terms of a new theory of space charge limited currents on percolation clusters.