Measurement of Photo-induced Charge Distribution in Seeded Second Harmonic Generation by Charge-Selective Etching in Glasses

Abstract

Ever since the discovery of efficient second harmonic generation (SHG) in centro symmetric optical fibers [1-4] and bulk glasses [5,6], many researchers, through experimental and theoretical work, have investigated this problem in the hopes of developing models to explain the mechanism behind this unexpected effect. Much of the work focused on the mechanism responsible for producing a quasi-phase matched effective χ(2) in these materials. Models such as the creation of a semi-permanent dc electric field via optical rectification field [7], charge organization by light controlled transport effects [8], and most recently, directional photo-ionization [9] were proposed to explain this phenomenon. Although these models were successful in explaining the mode symmetries of the radiated second harmonic light at high encoding intensity regimes, no one had been successful in directly measuring the charge distribution responsible for second harmonic generation in glasses. Work by Dominic and Feinberg [10] used an SHG mapping technique where they focused a probe beam onto a seeded area of a SK5 glass sample and inferred its charge distribution from the radiated SHG power. Their study supported the dipolar distribution predicted by directional photo-ionization model at high encoding intensities, but did not address the strong mode symmetry violation at low encoding intensities previously reported by Driscoll and Lawandy [11].