Time resolved four-wave mixing technique to measure the ultrafast coherent dynamics in semiconductor optical amplifiers

A femtosecond four-wave mixing technique is used to measure the ultrafast coherent dynamics of the optical polarization in semiconductor optical amplifiers. A heterodyne detection scheme enables us to measure a background-free quasi-degenerate four-wave mixing signal even without spatial separation of the pump and probe beam. First results indicate that the polarization dephasing time close to the transparency point is on the order of 100 fs. (C) 1996 American Institute of Physics.