Level Rate Equation Model Research Articles

The Influence of Gain Compression Factor on Dynamical Properties of Single Level InAs/GaAs Quantum Dot Lasers

In this paper, by representing a single level rate equation model for InAs/GaAs quantum dot lasers and computations by fourth-order Runge–Kutta method some characteristics of the output laser are considered. The change of photon number in time and current and also the output power versus current with different gain compression factors are investigated for lasing from ground state (GS). Afterwards, the response function of small signal modulation for ground state in constant current but different gain compressions is surveyed. At last, we find an optimum value for gain compression factor in lasing from GS.

Analysis of the effects of temperature and the electric field on quantum cascade laser characteristics

The effects of temperature and the electric field on the characteristics of a quantum cascade laser (QCL) have been investigated theoretically. A complete three level rate equation model considering all the scattering events has been proposed. The analytical expression for the threshold current density has been derived and the effects of temperature and the electric field are examined. The rate equation model is further used to analyze the population and photon number dynamics present within the cavity of a QCL and the effects of temperature and the electric field on the laser dynamics are investigated numerically.

On the applicability of a few level rate equation model to the determination of exciton versus biexciton kinetics in quasi-zero-dimensional structures

Hereby, we present a few level rate equation model in a context of the interpretation of excitation power dependent exciton and biexciton emission intensity from single quantum-dot-like structures. We emphasize that it not only allows identifying the excitonic and biexcitonic emission from one quasi-zero-dimensional object, but gives also an insight into the kinetics of the carriers confined in the system (both the internal dynamics of the exciton within its fine structure and the relative exciton to biexciton lifetimes ratio), the regime of the confinement itself and the importance of the higher energy levels occupation. Eventually, there are presented and discussed examples of the rate equation model application for an analysis of the experimental data for several kinds of epitaxial nanostructures.

Exciton kinetics and few particle effects in self-assembled GaAs-based quantum dashes

We report on the emission properties of single molecular-beam-epitaxially grown InGaAs/GaAs quantum dashes. Supported by a few level rate equation model it has been revealed a decreased exciton to biexciton radiative lifetimes ratio being a fingerprint of a weak carrier confinement. Furthermore, a biexciton sideband, connected with the Coulomb interaction of quantum dash biexciton with excitons confined in the wetting layer (WL), has been observed in photoluminescence (PL). Both the effects have found a confirmation in direct measurements of PL decay times, including long radiative lifetimes of the WL states which appeared to have a localized character.

Quantum Dashes and Quantum Rods: Optical Properties and Application Prospects

There are reported the optical properties of novel quasi-zero-dimensional semiconductor structures obtained by self-assembly during the molecular beam epitaxy process. The studies has been focused on strongly asymmetric systems, called quantum dashes, quantum rods or columnar quantum dashes, and their potential applications in light sources or amplifiers for telecommunication and data transmission or single photon sources and other quantum electrodynamics based emitters. There is discussed the linear polarization degree of the edge emission of the columnar structures with respect to their potential for a polarization independent semiconductor optical amplifier at 1.55 μm. Additionally, there have been analyzed the photoluminescence spectra of single quantum dashes and single quantum rods in order to detect the exciton/biexciton emission, determine the biexciton binding energy and predict the exciton to biexciton radiative lifetimes ratio basing on a few level rate equation model.

Exciton and biexciton emission from a single InAs/InP quantum dash

Molecular beam epitaxy grown InAs/InGaAlAs/InP quantum dashes designed for the 1.5 μm range were investigated by microphotoluminescence spectroscopy. The exciton and biexciton emission from a single quantum dash was detected revealing a biexciton binding energy of about 0.4 meV. The dependence of the photoluminescence intensity versus the excitation power density was determined and analyzed using the three level rate equation model, which allowed to confirm that the observed lines originate from the same single quantum dash.

Electromagnetic modeling of active silicon nanocrystal waveguides

In this paper we propose an electromagnetic analysis of active silicon nano-crystal (Si-nc) waveguide devices. To account for the nonlinearity in the active medium we introduce a four level rate equation model whose parameters are based on experimentally reported material properties. The electromagnetic polarization serves to couple the quantum mechanical and electromagnetic behavior within the ADE-FDTD scheme. The developed modeling tool is used to simulate waveguide amplifiers, enhanced spontaneous emission microcavities, and the temporal lasing dynamics of active Si-nc based devices.

Temperature-related performance of Yb 3+ :YAG disc lasers and optimum design for diamond cooling

In this paper the temperature-related performances of the Yb3+:YAG disc laser has been investigated based on quasi-three level rate equation model. A compact diamond window cooling scheme also has been demonstrated. In this cooling scheme, laser disc is placed between two thin discs of single crystal synthetic diamond, the heat transfer from Yb3+:YAG to the diamond, in the direction of the optical axis, and then rapidly conducted radically outward through the diamond to the cooling water at the circumference of the diamond/Yb3+:YAG assembly. Simulation results show that increasing the thickness of the diamond and the overlap-length (between diamond and water) decreases the disc temperature. Therefore a 0.3?0.5?mm thick diamond window with the overlap-length of 1.5?2.0?mm will provide acceptable cost effective cooling, e.g., with a pump intensity of 15?kW/cm2 and repetitive rate of 10?Hz, to keep the maximum temperature of the lasing disc below a reasonable value (310K), the heat exchange coefficient of water should be about 3000 W/m2K.

Wavelength Dependence of the Non-Linear Transmission of Hitci Using the Z-Scan Technique

AbstractThe excited state properties of dyes become important under intense illumination of a short laser pulse. The pulse induces a significant population in an excited state which will have different absorptive properties, this causes a change in absorption of the incident pulse within its duration. An increase in absorption arises from molecules in an excited state having an absorption greater than the corresponding ground state.The z-scan technique has been used to measure the induced absorption of a carbocyanine dye 1,1′,3,3,3′,3′- Hexamethylindtricarbocyanine Iodide (HITCI) for laser pulses of different wavelengths. An optical parametric oscillator pumped by the third harmonic of a Q-switched Nd:YAG laser was used. Z-scans were taken at a number of different wavelengths between 460 and 630 nm. Data is presented which shows the spectral region where induced absorption occurs. An eight level rate equation model is used to predict the non-linear behaviour and to fit to the experimental data, good correlation is found between the model and data.

Coherence effects in light-induced drift

The occurrence of black resonances in light-induced drift in a Na-Xe mixture is demonstrated experimentally. On the D 1 a strong effect on the drift velocity is observed, whereas on the D 2 line the effect is less pronounced. This difference is explained in terms of excited state hyperfine structure. The effect is described with a four level rate-equation model, in which the influence of the ground-state coherence has been included. A sign reversal of the light-induced drift velocity at the black resonance is predicted for small laser bandwidths.

Collisional effects on laser-induced fluorescence measurements of hydroxide concentrations in a combustion environment 2: Effects for v′ = 1 excitation

A full vibrational–rotational level rate equation model has been used to investigate the application of laser-induced fluorescence techniques to number density measurements of hydroxide in a combustion environment. The extent of deviation of the population in the laser-pumped vibrational and rotational levels from the-two-level model prediction, due to collisional exchange mechanisms, was investigated for a range of pressures, temperatures, laser powers, and collisional exchange rates.

Collisional effects on laser-induced fluorescence measurements of hydroxide concentrations in a combustion environment 1: Effects for v′ = 0 excitation

A full vibrational–rotational level rate equation model has been used to investigate the application of laser-induced fluorescence techniques to number density measurements of hydroxide in a combustion environment. The extent of deviation of the population in the laser-pumped vibrational and rotational levels from the-two-level model prediction, due to collisional exchange mechanisms, was investigated for a range of pressures, temperatures, laser powers, and collisional exchange rates.