Laser Interaction with Semiconductors and Superconductors.

The optical properties of CdS_ {rm x}Se_{rm 1-x} doped glasses were investigated by absorption and photoluminescence. From these studies, quantum confinement effects were exhibited along with amorphous-semiconductor -like behavior. By combining the absorption spectra and the photoluminescence, a band diagram near the energy gap was given. The recombination lifetime and the photoluminescence spectra of these materials were found to be strongly dependent on the pumping laser intensity. In the time domain, two decay components corresponding to recombination of the excitons and free carriers were obtained. The recombination lifetime varied from 5 ns to 10 ps corresponding to a pump intensity range from 100 kW/cm^2 to 25 MW/cm^2 at 4 K. It was also found that long-term exposure of the glass to high-intensity laser pulses produced a permanent reduction of the free carriers lifetime. In the frequency domain, two spectral features corresponding to two different recombination mechanisms were identified. Next, optical quality thin films of CdS _{rm x}Se_ {rm 1-x} were grown by laser evaporation deposition for various values of x. The structure characteristics and optical properties of these thin films were studied. It was found that the films are highly oriented with a c axis perpendicular to the surface, and are optically smooth and homogeneous. An empirical relationship CdS-CdSe was obtained. An amplified spontaneous emission was also observed pumped by a laser. Direct laser writing was used on high T _{rm c} superconducting films to study their electrical properties as well as for device fabrication. With such a patterning system, superconducting strips as narrow as 0.6 μm wide were fabricated on mirror-like Y-Ba-Cu-O thin films on various substrates. Laser patterning had no effect on the T_{rm c} and J_{rm c} until the lines were <1 μm wide. The 0.6 mum-wide strip showed some degradation of T_{rm c} and J_{rm c}. The critical current densities for these patterned lines were measured to be ~ 6 times 10^5 A/cm^2 at 77 K. Finally, high Tc superconducting thin film optical and infrared detectors were fabricated and studied at different wavelengths. (Abstract shortened with permission of author.).