Abstract

Impact ionization is one of the processes of electron transport under extremely high fields. Previous measurements are limited by the dielectric breakdown up to 10⁷ V/cm with a static electric field. With ultrashort lasers, however, we are able to measure the ionization coefficient up to 2.8 × 10⁸ V/cm for the first time. We utilized the optical breakdown of normally transparent optical materials, such as fused silica, to study this ionization phenomona. Through the nonlinear photon-matter interaction (electron avalanche process or multiphoton ionization), a plasma is generated at the focal spot and laser energy is deposited in the material.

© 1994 Optical Society of America