Polarization modulation by vanadium dioxide on metallic substrates

Vanadium dioxide (VO2) undergoing phase transition is known alters the polarization state of light in reflection owing to large changes in complex refractive indices. While this effect is promising for optical modulation applications, the usual VO2 films on dielectric substrates tend to offer limited tunability for polarization modulation. In this paper, we show that metallic under-layers greatly enhance the performance by widening the spectral range and include visible wavelengths, by increasing the polarization modulation amplitude, and by widening the range of workable incidence angles. The imaginary part of the refractive index in the metallic layer is found to increase the relative phase shifts between s- and p-components of polarization as well as increasing the reflectance

Ice, body checks and slap shot tricks

Intellectual Muscle: University Dialogues for the Vancouver 2010 Games was developed by Vancouver 2010 and the University of British Columbia Continuing Studies in collaboration with universities across Canada and The Globe and Mail.Non UBCUnreviewedOthe

Coherent control of photocurrent in bulk semiconductors

grantor: University of TorontoCoherent control of photocurrent via interband transitions in bulk semiconductors is proposed and demonstrated in GaAs. A Fermi's Golden Rule approach is used to calculate the overall transition rate for simultaneous single- and two-photon excitation in direct band gap semiconductors using phase-related beams at frequencies $\omega$ and 2$\omega$, with \hbar\omega, where E\sb{g} is the band gap energy. The calculation is carried out to obtain the current generation rate as a function of the beams' intensity, polarization and frequency; numerical results are given for GaAs. Coherent control of photocurrent is demonstrated using picosecond and femtosecond laser pulses on GaAs at room temperature. By integrating the current in a metal-semiconductor-metal (MSM) device, peak current densities as high as 20 mA$\mu$m\sp{-2} are measured using phase-related 100 fs pulses at 1550 and 775 nm from an optical parametric generator. Carrier densities of {\sim}10\sp{18} cm\sp{-3} are achieved during the process, but carrier-carrier scattering does not seem to significantly affect the current decay time. Non-degenerate coherent control is also demonstrated with three beams of different frequency such that \omega\sb1 + \omega\sb2 = \omega\sb3 and \hbar\omega\sb1\not=\hbar\omega\sb2. Low-temperature grown GaAs is found to be more suitable for current integration than normally-grown GaAs because the former has a shorter carrier lifetime which prevents the MSM device from discharging during the time between pulses.Ph.D