Single crystal ZnO nanowires are synthesized and configured as field-effect transistors. Photoluminescence and photoconductivity measurements show defect-related deep electronic states giving rise to green-red emission and absorption. Photocurrent temporal response shows that current decay time is significantly prolonged in vacuum due to a slower oxygen chemisorption process. The photoconductivity of ZnO nanowires is strongly polarization dependent. Collectively, these results demonstrate that ZnO nanowire is a remarkable optoelectronic material for nanoscale device applications.
Acousto-optic interaction in optical fiber is examined from the perspective of copropagating optical and acoustic vortex modes. Calculation of the acousto-optic coupling coefficient between different optical modes leads to independent conservation of spin and orbital angular momentum of the interacting photons and phonons. We show that the orbital angular momentum of the acoustic vortex can be transferred to a circularly polarized fundamental optical mode to form a stable optical vortex in the fiber carrying orbital angular momentum. The technique provides a useful way of generating stable optical vortices in the fiber medium.
We demonstrate a multi-functional optical trap capable of trapping, motion control, position sensing and fluorescence detection of chemically treated polystyrene beads, using off-the-shelve optical components. It consists of two collinearly aligned single-mode fibers separated by a spacing of 130-170mum for trapping, another single-mode fiber for probing/pumping and a fourth multi-mode fiber for optical detection. The fibers are mounted either on V-grooved Si or PDMS platforms fabricated using microfabrication and molding techniques, respectively. The result represents an important milestone towards a functional integrated trapping platform.
Photoluminescence (PL) at 77 K is used to study tensile stress variations in chemically etched stripes of a 3-μm-thick GaAs film grown on Si substrate. The etched patterns consist of 1-mm-long stripes with widths ranging from 100 to 4 μm and 4 μm by 4 μm squares. We observed monotonic shift of PL peaks towards shorter wavelength for decreasing stripe width. In particular, when the width of the stripe is less than 7 μm, tensile stress is essentially uniaxial as evident from the magnitude of shift in PL peaks. The polarization characteristics of the PL spectra of these uniaxially stressed stripes are investigated and found to agree well with theoretical predictions.
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