Impact of amplified spontaneous emission on carrier density formeasurement of optical nonlinearities in GaAs/AlGaAs multiple quantumwells

It is shown that amplified spontaneous emission (ASE) can affect the measurement of nonlinear optical properties in semiconductors through its reduction of the excess carrier density. When the optical excitation area is large, lateral ASE can reduce the carriers within a much shorter period of time than the normal carrier lifetime. Just after ASE is over, the time-integrated surface photoluminescence signal may be used as a measure of the carrier density, which is the carrier density experienced by an ns probe in ps pump experiments. When the excited carrier density is at 10²⁰ cm^-3, surface ASE is also possible and is observed, even with small spot sizes