NONLINEAR EXCITONIC OPTICAL-ABSORPTION IN GASB

We have measured the saturation of optical absorption in GaSb at wavelengths close to the band gap, and have determined the nonlinear absorption (α2) and refraction (n2) coefficients. At liquid-helium temperature a sharp free-exciton absorption line is observed which saturates with increasing incident laser intensity; we obtain values ∥α2∥=70 cm W-1 and ∥n 2∥≊0.2 cm2 kW-1. At room temperature we do not observe a well-defined exciton; saturation of the residual interband absorption occurs at much higher intensity, and it is found to be obscured by strong thermal effects