We show theoretically that interband transitions in a bulk semiconductor via coherent one-and twophoton absorption leads to the formation of an electrical current whose direction is controlled by the relative phase of the beams. The phenomenon can occur in centrosymmetric and noncentrosymmetric materials; easily measurable currents are predicted for GaAs under realistic experimental conditions.

We demonstrate room temperature coherent generation and control of a directional photocurrent in bulk GaAs via simultaneous one-and two-photon interband absorption processes using phase-related 1 ps or 175 fs pulses at 0.775 and 1.55 mm. Electrical currents generated in low-temperature-grown (LT) and normal bulk GaAs are collected via gold electrodes. Current densities as high as 3 nA͞mm 2 in LT-GaAs are measured for injected carrier densities as low as 10 14 cm 23 and for peak irradiances of 18 MW cm 22 (1.550 mm) and 3 kW cm 22 (0.775 mm).

It is theoretically shown that discrete nonlinear surface waves are possible in waveguide lattices. These self-trapped states are located at the edge of the array and can exist only above a certain power threshold. The excitation characteristics and stability properties of these surface waves are systematically investigated.

High-quality colloidal crystal multilayers were fabricated from aqueous solutions by the vertical deposition method. The effect of the evaporation temperature on the crystalline quality of colloidal crystals was carried out. It is found that with the increase of the evaporation temperature, the colloidal crystal shows an increasing tendency towards equilibrium face-centered-cubic phase, and the resulted sample also shows few dislocations and vacancies when the balance in the processes of nucleus formation, particle transport, and crystallization can be kept. However, with the further increase of the evaporation temperature (above 55 °C), a vast amount of defects appear in the crystal because the fast water evaporation rate, which results in a fast crystal growth rate, will spoil the balance. Optical measurements correspond well to the microstructure results.