Measurement of refractive nonlinearities in GaAs above bandgap energy

We present a technique for single-beam measurement of the optical nonlinearity in GaAs for photon energies above the bandgap. We measured the real and the imaginary parts of the nonlinear refractive index of a bulk crystal by using the change in reflection of dye laser pulses (10 ns, 538 nm). The values obtained, n(2) = (7.8 ? 0.6) x 10(-8) cm(2)/W and kappa(2) = (-2.8 ? 0.7) x 10(-8) cm(2)/W, are discussed.