Abstract

We present phase sensitive measurements of coherent secondary emission (CSE) from quantum well excitons at low temperatures for excitation fluences up to 8 MW/cm(2). To determine the spectral amplitude and phase of the CSE a cosinus fit method is used whereby with a stabilized interferometer a number of spectra at varying optical delay are measured. Fourier transformation leads to the field in the time domain. We have found only a weak, but temporarily smooth coherent contribution to the scattered light showing a strong dependence on temperature and laser fluence. While for low excitation the results can be described by dielectric scattering theory, taking the layer structure of the sample into account, for higher fluences strong bleaching of the excitonic contributions is observed.