7 research outputs found
Probing ultrafast carrier dynamics and nonlinear absorption and refraction in core-shell silicon nanowires
We investigate the relaxation dynamics of photogenerated carriers in silicon
nanowires consisting of a crystalline core and a surrounding amorphous shell,
using femtosecond time-resolved differential reflectivity and transmission
spectroscopy at photon energies of 3.15 eV and 1.57 eV. The complex behavior of
the differential transmission and reflectivity transients is the mixed
contributions from the crystalline core and the amorphous silicon on the
nanowire surface and the substrate where competing effects of state filling and
photoinduced absorption govern the carrier dynamics. Faster relaxation rates
are observed on increasing the photo-generated carrier density. Independent
experimental results on crystalline silicon-on-sapphire help us in separating
the contributions from the carrier dynamics in crystalline core and the
amorphous regions in the nanowire samples. Further, single beam z-scan
nonlinear transmission experiments at 1.57 eV in both open and close aperture
configurations yield two-photon absorption coefficient \ (~3 cm/GW) and
nonlinear refraction coefficient \ (-2.5x10^-4 cm2/GW).Comment: 6 pages, 6 figure
Photo-designed terahertz devices
Technologies are being developed to manipulate electromagnetic waves using artificially structured materials such as photonic crystals and metamaterials, with the goal of creating primary optical devices. For example, artificial metallic periodic structures show potential for the construction of devices operating in the terahertz frequency regime. Here we demonstrate the fabrication of photo-designed terahertz devices that enable the real-time, wide-range frequency modulation of terahertz electromagnetic waves. These devices are comprised of a photo-induced, planar periodic-conductive structure formed by the irradiation of a silicon surface using a spatially modulated, femtosecond optical pulsed laser. We also show that the modulation frequency can be tuned by the structural periodicity, but is hardly affected by the excitation power of the optical pump pulse. We expect that our findings will pave the way for the construction of all-optical compact operating devices, such as optical integrated circuits, thereby eliminating the need for materials fabrication processes
Effect of copper on the carrier lifetime in black silicon
Porte HP, Turchinovich D, Persheyev S, Fan Y, Rose MJ, Jepsen PU. Effect of Copper on the Carrier Lifetime in Black Silicon. Journal of Infrared, Millimeter, and Terahertz Waves. 2011;32(7):883-886