Nonlinear electronic line shape determination in Yb3+-doped phosphate glass

Nonlinear refraction spectroscopy has been performed in Yb3+-doped phosphate glass to determinate the line shape of real and imaginary parts of n2 (n2' and n2"). The n2' spectrum presented an asymmetric feature due to the interference of resonant and nonresonant contributions, where the nonresonant term arises from the polarizability difference between excited and ground states (delta alpha). The measurements were performed in the transient regime to determine population dynamics and the pump saturation intensity at 975 nm (peak of the absorption spectrum). Because of the small quantum defect of Yb3+, we estimated that the magnitude of the thermal lens effect is approximately 20 times smaller than the population lens effect, caused by n2.