Measurement of the two-photon absorption coefficient in a GaAs/AlGaAs quantum well laser

The two-photon absorption (TPA) coefficient has been measured for a single-mode GaAs/AlGaAs quantum well laser at 0.86 μm, near the lasing wavelength of 0.83 μm. Picosecond laser pulses were employed to resolve the ultrafast TPA from long-lived carrier-dependent effects. The TPA coefficient was found to be 31±6 cm GW−1, which corresponds to a value of (5.7±1.2)×10−11 esu for the imaginary part of the third-order nonlinear susceptibility. At wavelengths near the quantum well exciton, no strong resonance enhancement of the two-photon transition was observed, and the coefficient appears to be characteristic of the AlGaAs cladding layers.