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/I_sat)^−1/2, where I_sat = 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.

© 1989 Optical Society of America