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We have observed quantum interference currents by exciting exciton transitions in GaAs quantum wells. A phase shift of the current occurs when tuning the exciting photon energy from the heavy hole to the light hole exciton transition.
We demonstrate fabrication of the first AlN-waveguide-based intersubband transition device. The device can operate at 1.3 mum, confirmed with the new waveguide-coupling measurement method. The intersubband absorption saturation in the device is also successfully demonstrated.
We demonstrate a muW-level broadly tunable THz source based on parametric down-conversion in orientation-patterned GaAs pumped by femtosecond pulses from a Tm-doped fiber laser. Generated THz powers should be scalable to mW-levels with this approach.
We demonstrate efficient generation of narrow-bandwidth THz waveforms in optically-contacted multi-layer and orientation-patterned GaAs, using optical rectification of 2-4 mum, 100-fs pump pulses. THz waveforms were directly measured using two-color time-domain spectroscopy.
Recovery of electrons from excited neutral donor states in GaAs is time-resolved using a novel optical readout technique and pulsed terahertz excitation. Long (0.1-1 mus) 2P state lifetimes are measured at various magnetic fields.
We report lasing of optically pumped Ga(AsNP)/GaP multiple quantum-well structures grown pseudomorphically on GaP substrate. A distinct threshold behaviour is observed at both cryogenic and room temperature; modal gain of up to 20 cm-1 is determined.
The spectral width of terahertz emission from ion-implanted terahertz emitters increases with ion damage, owing to ultrafast carrier capture. Carrier dynamics simulations reinforce these findings. Optical-pump, terahertz-probe experiments confirm the sub-picosecond lifetimes of these materials.
Terahertz (THz) radiation from p-type (100) InAs was investigated using time domain spectroscopy. Azimuthal angle dependence measurements and the ambipolar mobility theory suggest the dominant THz radiation mechanism to be that of the surge current.
The feasibility of using femtosecond laser micro-machining to create Gallium Arsenide (GaAs) quasi-phasematched devices from single GaAs wafers is investigated. We describe machining of the structure and details of the machining quality achievable in GaAs.
Ballistic pure spin currents generated via quantum interference in the absorption of femtosecond pulses are demonstrated to produce transverse ballistic Hall pure charge currents and vice versa via spin-dependent asymmetric scattering processes.
Femtosecond two-color pump-probe experiments on intersubband absorption spectra of electrons in a GaN/AlN superlattice show distinct spectral holes unraveling both the homogeneous broadening contribution and the underlying optical phonon progression.
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