CHIRP-CONTROLLED ULTRAFAST OPTICAL NONLINEARITIES IN SEMICONDUCTORS

We experimentally demonstrate that the differential transmission (DT) response of bulk semiconductors excited well above the band edge can b e manipulated by chirping of the broadband excitation and readout puls es. In particular, the maximum transmission change in spectrally integ rated DT experiments can be modified on the 20 fs time scale. Spectral ly resolved DT studies explain this chirp dependence. Depending on the sign of the chirp, positive or negative DT contributions at low or hi gh photon energies are probed with varying efficiency around zero time delay. These results demonstrate that chirp can become an additional degree of freedom for the optimization of device performance in ultraf ast all-optical switching. (C) 1998 American Institute of Physics. [S0 003-6951(98)00147-8].