Picosecond Plasma Dynamics and All‐Optical Data Processing

Using time resolved pulse and probe spectroscopy, the transmission modulation of CdSe platelets is investigated under excitation and generation of a dense electron–hole plasma. Induced absorption is related to exciton screening, band‐gap renormalisation, and energy relaxation in a high density electron–hole plasma. These investigations exhibit also interest from the point of view of optical signal processing because an all‐optical picosecond inverter gate and more generally a many input NOR gate can be built based on the induced absorption which occurs in the presence of a dense electron–hole plasma. The operation of such device is described and discussed in relation with the possible development of optical coprocessors (compatible with a parallel processing of data) and especially in relation with the critical problem of associating and cascading optical NOR gates. A first step is reported toward cascadable picosecond NOR gates by demonstrating the possible operation of an all‐optical inverter gate which uses an intermediate frequency doubling of the output signal. This implies that a cascadable all‐optical NOR gate operating in an effective one‐wavelength mode is possible. Experiments are carried out at liquid nitrogen temperature. The operation wavelength is around 673 nm in CdSe. The switching energy of the NOR gate is 30 μJ/cm 2 per pulse at 337 nm.