1,721,221 research outputs found
Spectral gain and cavity loss characterization of an optically-pumped external-cavity surface-emitting quantum well laser
No full textWe present the spectral gain and cavity loss characterisation of an optically-pumped external-cavity 1-µm surface-emitting InGaAs quantum well laser by observing the evolution of intracavity power and spontaneous emission following the uncovering of the cavity mode by an intra-cavity chopper. The smooth monotonic rise (fall) is characteristic of an external-cavity quantum well laser where the photon lifetime is approximately two orders of magnitude higher than the carrier lifetime
Electrically generated indistinguishable and entangled photon pairs
No full textWe present measurements on electrically generated photons from a quantum dot in an LED structure, showing high entanglement fidelity and two-photon interference visibility, both necessary requirements for scalable quantum communication and logic
Frequency manipulation of THz bound-to-continuum quantum-cascade lasers
No full textThe laser emission frequencies of existing designs are controlled by uniform thickness transformations. Experimental results from a total of ten wafers are presented demonstrating a predictable shift in the emission wavelength concurrent with an anticipated alteration in electrical transport. Wafers based on a design around 2.9 THz produced a frequency shift of 0.35 THz. Furthermore, a 2.5% thickness reduction in our 2-THz design saw a 0.1-THz frequency shift and changes in electrical transport predicted by simulations
Spin relaxation in GaAs/AlxGa1-xAs quantum wells
No full textSpin dynamics of photoexcited carriers in GaAs/AlxGa1-xAs quantum wells have been investigated in a wafer containing twelve different single quantum wells, allowing full investigation of well-width and temperature dependences with minimal accidental variations due to growth conditions. The behavior at low temperatures is dominated by excitonic effects, confirming results described in detail by others. Between 50 and 90 K there is a transition from excitonic to free-carrier-dominated behavior; both the temperature and time scale of the transition are in excellent agreement with a theoretical model for exciton dissociation. Above 90 K we find two-component spin decays consisting of an unresolved component (faster than 2 ps) associated with exciton dissociation and hole spin-relaxation and a longer-lived component that yields the electron spin-relaxation time. In the free-carrier regime, the electron spin-relaxation rate in wide wells follows that for bulk GaAs, which varies approximately as T2. For narrow wells the rate is approximately independent of temperature and varies quadratically with confinement energy. This behavior is consistent with dominance of the D'yakonov-Perel mechanism of electron-spin relaxation and the expected behavior of the electron mobility. The data show evidence of the influence of electron scattering by interface roughness
Fluence and polarisation dependence of GaAs based Lateral Photo-Dember terahertz emitters
Full text linkWe characterise THz output of lateral photo-Dember (LPD) emitters based on semi-insulating (SI), unannealed and annealed low temperature grown (LTG) GaAs. Saturation of THz pulse power with optical fluence is observed, with unannealed LTG GaAs showing highest saturation fluence at 1.1 ± 0.1 mJ cm-2. SI-GaAs LPD emitters show a flip in signal polarity with optical fluence that is attributed to THz emission from the metal-semiconductor contact. Variation in optical polarisation affects THz pulse power that is attributed to a local optical excitation near the metal contact
Investigation of the role of the lateral photo-Dember effect in the generation of terahertz radiation using a metallic mask on a semiconductor
No full textPulses of coherent terahertz radiation can be efficiently generated by a lateral diffusion current after ultrafast generation of photo-carriers near a metal interface on the surface of a semiconductor, this is known as the lateral photo-Dember effect. We investigate how the emission depends on the pump spot position, size, power and how it is affected by the application of an applied external bias. We study the role of the metallic mask and how it suppresses emission from the carriers diffusing under it due to a reduction of available radiation states both theoretically and experimentally.<br/
Insulator-quantum Hall transitions in two-dimensional electron gas containing self-assembled InAs dots
No full textEnergy-dependent electron-electron scattering and spin dynamics in a two-dimensional electron gas
No full textThe measurement of spin dynamics of electrons in a degenerate two-dimensional electron gas, wherein the Dyakonov–Perel mechanism is dominant, has been used to investigate the electron scattering time (tp*) as a function of energy near the Fermi energy. Close to the Fermi energy, the spin evolution is oscillatory, which indicates a quasicollision-free regime of spin dynamics. As the energy is increased, a transition to an exponential, collision-dominated spin decay occurs. The oscillation frequency and the value of tp* are extracted by using a Monte Carlo simulation method. At the Fermi energy, tp* is very close to the ensemble momentum relaxation time (tp) obtained from the electron mobility. For higher energies, tp* falls quadratically, which is consistent with the theoretical expectations for the onset of the electron-electron scattering, which is inhibited by the Pauli principle at the Fermi energy
High peak power femtosecond pulse passively mode-locked vertical-external-cavity surface-emitting laser
No full textWe report a passively mode-locked vertical-external-cavity surface-emitting laser (VECSEL) producing 335-fs near-transform-limited pulses at a repetition rate of 1 GHz with an average output power of 120 mW at a center wavelength of 999 nm. The VECSEL was optically pumped with a power of 1.85 W at a wavelength of 830 nm. The peak power of the output pulses was 315 W.<br/
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