Educação matemática pela arte
Gusmão, Lucimar Donizete
2013-08-28
Search results
90 records were found.
The significance of nuclear spin polarisation in time-resolved optical studies of III–V semiconductors is addressed. Electron Larmor beats in pump-probe reflectivity from a GaAs/AlGaAs quantum well show Overhauser shift of 0.7 T due to accumulated nuclear polarisation I/I=0.065. This leads to precision values of electron g-factor, elucidates nuclear spin pumping and diffusion mechanisms in quantum wells and informs discussion of implications for spin-electronics and transport.
The influence of quantum confinement and built-in strain on conduction-electron g factors in lattice-matched GaAs/Al0.35Ga0.65As and strained-layer In0.11Ga0.89As/GaAs quantum wells is investigated for well widths between 3 and 20 nm. The magnitude, sign, and anisotropy of the g factors were obtained from quantum beats due to Larmor precession of electron spins in time-resolved, polarization-sensitive, pump-probe reflection at 10 K in magnetic fields applied along and at 45° to the growth axis. Slowly varying shifts of precession frequency, due to buildup of nuclear polarization in the samples over ∼1 h and equivalent to up to 0.5 T, occurred for fixed circular pump polarization and oblique applied fields. These Overhauser shifts confirmed the sign of the g factors and were eliminated by modulation of pump polarization to give precise ...
The significance of nuclear spin polarisation in time-resolved optical
studies of III-V semiconductors is addressed. Electron Larmor beats in
pump-probe reflectivity from a GaAs/AlGaAs quantum well show Overhauser shift
of 0.7 T due to accumulated nuclear polarisation /I=0.065. This leads to
precision values of electron g-factor, elucidates nuclear spin pumping and
diffusion mechanisms in quantum wells and informs discussion of implications
for spin-electronics and transport.
Pulse code modulation telemetry encoder used in united kingdom satellite-c experiments
Ultrafast optical methods are used to study low temperature nuclear spin polarisation and electron spin precession and relaxation in an oblique magnetic field in undoped GaAs/AlGaAs quantum wells. We find that electron localisation dramatically extends electron spin relaxation and accelerates nuclear spin polarisation which is manifest as a large time-dependent Overhauser shift in electron Larmor precession frequency. Nuclear polarisation is a two-stage process, which we suggest involves contact hyperfine interaction at electron localisation centres and nuclear spin diffusion to the remaining nuclei of the sample. Special samples are used to investigate nuclear spin diffusion through the barriers, which is found to be an order of magnitude slower than within the wells, consistent with extra dipolar and quadrupolar disorder in the alloy.
We derive the analytical condition for eigenwaves in terms of nonlocal optical susceptibilities of media with nonlocal response. A wave picture of the recently observed effect of nonreciprocal polarization plane rotation that is due to gyrotropic linear dichroism is discussed
Comment: 4 pages, 3 figures, to appear in Phys. Rev. Letters
A simple diode-pumped, Q-switched fibre laser is reported based on large mode area ytterbium-doped fibre capable of producing pulses with a high beam quality (M2=1.1), a duration of ~40 ns and energies as high as 1.2 mJ at a repetition rate of 10 kHz. This combination of desirable beam qualities makes the source attractive for a range of industrial applications currently serviced by conventional bulk crystal/glass based Q-switched laser systems.
We have demonstrated a diode pumped 1.2mJ, 37ns Q-switched laser with good mode quality, operating at ~1075nm with a repetition rate of 10kHz, utilizing a ytterbium doped LMA fiber.
We investigate the performance of a gain-switched picosecond laser diode operating at 1.06 μm when either injection- or self- seeded. We conclude that the much simpler self-seeding arrangement leads to no degradation of performance.
