Abstract

There has been considerable interests in InSb as a nonlinear medium for the CO₂ laser due to its large nonlinearity. Optical bistability and optical switching are among some of the recent applications. The two-photon absorption of InSb has been studied extensively in the past. However, no conclusive experimental value has been established. We report here an accurate measurement of the two-photon absorption coefficient β making use of the self-defocusing effect.¹ The defocusing process is the direct result of self-phase modulation and plasma-induced refractive-index change. The self-defocusing experiment was performed at two CO₂ laser wavelengths of 10.6 and 9.6 μm. From the experimental data, the value of β can be calculated using a beam propagation computer code. It is in strong disagreement with a previous measurement.² The frequency dependence of β is consistent with a tunneling process and is not consistent with a perturbation calculation either with or without the nonparabolic band approximation.

© 1987 Optical Society of America