Papers by Keyword: Optical Gain

Abstract: Semiconductor quantum dots (QDs) exhibit significant potential for laser applications, where a thorough understanding of their optical gain properties and excitonic dynamics is crucial for performance optimization. In this study, state-resolved pump-probe transient spectroscopy was employed to investigate the optical gain and exciton dynamics in CdSe QDs. The results reveal that the gain threshold increases with pumping photon energy, attributed to the competition between surface trapping and intraband relaxation, as well as to the increased biexciton binding energy associated with higher-energy excitonic charge distributions. Notably, the biexciton binding energy reverses from negative to positive values with increasing pump energy, a transition that underpins the observed rise in gain threshold. Additionally, time-resolved decay curves demonstrate accelerated excitonic recombination at higher pump fluences, indicating a greater proportion of biexcitons relative to single excitons. These findings provide valuable insights for tailoring optical gain in quantized nanostructures and optimizing QD-based laser devices.

Abstract: The band structure and optical gain of a novel n⁺ doping tensile-strained Ge/GeSiSn quantum well are investigated by using an 8-band k·p method. The doping effect in Ge quantum well and the effect of the carrier leakage into L valley on the optical gain will also be considered. The E-k dispersion curves and optical gain spectra will be obtained and discussed.

Abstract: Effective ~1.47mm and powerful ~1.8mm infrared emissions have been observed in Tm³⁺-doped bismuth tellurite glasses with low phonon energy under the excitation of 793nm diode laser. Judd-Ofelt parameters W2 (4.65´10^-20cm²), W₄ (1.15´10^-20cm²), and W₆ (1.16´10^-20cm²) indicate a higher asymmetric and stronger covalent environment in the optical glasses. In 0.5wt% Tm³⁺-doped sample, the peak emission cross-sections of ³H₄®³F₄ and ³F₄®³H₆ transitions are derived to be 2.83´10^-21 and 6.13´10^-21cm², respectively, and the maximum gain coefficients of 0.38 and 2.21dB/cm at 1.675 (U-band edge) and 1.856mm wavelengths were anticipated in an ideal status. These results indicate the Tm³⁺-doped bismuth tellurite glasses are a promising candidate in developing S- and U-band amplifiers.

Abstract: Stimulated emission and optical gain problems are reviewed on the basis of analysis of highly photoexcited III-Nitride and ZnO wide-gap materials. Spontaneous and stimulated emission along with optical gain of these materials in UV region is analyzed. The possible mechanisms of inverted population in In-containing materials and ZnO semiconductors are discussed involving mechanisms of dense electron-hole plasma, carrier (exciton) localization, as well as various interaction processes in dense exciton gas.

Abstract: Optical characterization of molecular-beam-epitaxy-grown ZnO and MgZnO epitaxial layers on sapphire (0001) substrates is presented. The parameters such as carrier recombination time and optical gain coefficient are analyzed. Radiative recombination mechanisms of ZnO in dense quasiparticle system are discussed. The ZnO epilayers even with lower structural quality are tolerable for applications in optoelectronics as light emitters.

Abstract: The band structures and optical gain spectra of GaAsSbN/GaAs compressively strained quantum well (QW) were studied using 10-band k.p approach. We found that a higher Sb and N composition in the quantum well and a thicker well give longer emitting wavelength. The result also shows a suitable combination of Sb and N composition, and QW thickness can achieve 1.3 μm lasing. And, the optical gain spectra with different carrier concentrations will be obtained.

Abstract: According to the Harrison’s model, the level change of conduction and valence bands caused by the strain of AlInGaAs/AlGaAs quantum well (QW) was analyzed firstly. The energy level of the electron and hole in the AlInGaAs/AlGaAs strained and GaAs/AlGaAs unstrained QW were calculated, respectively. In addition, taking the lorentzian function, the linear gain of the two QWs were calculated and discussed. Contrast the gain performance of GaAs/AlGaAs QW with that of AlyInxGa1-x-yAs/AlGaAs QW, it can be found that the strained AlyInxGa1-x-yAs/AlGaAs QW material has more promising optical gain than that of the GaAs/AlGaAs QW.

Abstract: Recent reports on experimental observation of optical gain in silicon nanostructures in the visible region, performed at several laboratories all over the world, have triggered an extraordinary surge of interest in silicon lasing. However, attempts aimed at reproducing the red stimulated emission from „standard“silicon nanocrystals (sized 3-5 nm) at some other laboratories either failed, or. did not come to definite conclusions. Therefore, more detailed measurements of optical gain in a wider variety of samples containing Si nanocrystals are required in order to unravel whether or not the observation of optical gain is an intrinsic property of Si nanocrystals. We have performed a detailed study of optical gain in layers of densely packed Si nanocrystals in SiO2, prepared on the basis of porous Si, using the variable-stripe-length (VSL) method in combination with the shifted-excitation-spot (SES) method. In selected samples we have observed a distinct difference in behaviour between VSL and SES curves, indicating the occurrence of positive optical gain of ~ 24 cm-1. Preliminary reports on transport and electroluminescence measurements in thin films of SiO2 doped with porous silicon grains, prepared by spin-coating technique, are also discussed.