MULTIPHOTON GENERATION OF STE IN ALPHA-SIO2 USING SUBPICOSECOND UV LASER-PULSES

Multiphoton STE generation in alpha-SiO2 was investigated in the high intensity regime (from 0.1 to a few TW cm-2) using 250 fs UV pulses, f or photon energies of 4.4 and 4 eV respectively, by monitoring the 2.8 eV luminescence of the STE. The corresponding two- and three-photon d ynamics are observed except in the 4.4 eV case, for intensities in exc ess of 0.5 TW cm-2. A theoretical study of the laser propagation, usin g a numerical solution of the Maxwell equation with non-linear terms ( representing the effects of two-photon absorption and intensity induce d self-focusing) leads us to the conclusions that propagation effects cannot account for this observation, except for the fact that it gener ates very high electron-hole pair densities (between 10(19) and 10(20) cm-3), so that interaction between neighbouring pairs could play a de cisive role in the STE generation.