Nonlinear studies of semiconductor doped glasses

Abstract

Saturation of two-photon absorption (2PA) in Corning CS-368 semiconductor doped glass has been experimentally observed via standard nonlinear transmission measurements and nonlinear refraction was observed using the newly developed "Z-scan" technique.1 We found that the saturation of the absorption for this glass follows the form α = α0(1 + I/Isat)−1/2, where Isat = 10 MW/cm2 and α0 = 4.7 cm−1 are extracted from the experimental data. At much higher irradiance levels, nonlinear absorption sets in consistent with a combination of two-photon absorption (2PA) and excited carrier absorption. A 2PA coefficient, β2 = 0.04 cm / GW was obtained for input irradiances ≃20 GW/cm2. From Z-scan measurements, the contribution to nonlinear refraction was studied. A self-defocusing nonlinearity was observed at incident irradiances ≃1 GW/cm2 giving a value of Δn = −1.5 × 10−5. This defocusing increased for higher irradiances. Theoretical studies were conducted by extending Maxwell Garnett and Mie theories to account for nonlinear [χ(3)] effects observed in several of these Corning semiconductor doped glasses. The theories predict an enhancement of the nonlinear absorption coefficient, β2, which we may or may not be observing depending on how well the particle number density of the semiconductor in glass and the actual microparticle radius is known.