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- ItemSpatially modulated broad-area lasers for narrow lateral far-field divergence(Washington, DC : Soc., 2021) Zeghuzi, Anissa; Koester, Jan-Philipp; Radziunas, Mindaugas; Christopher, Heike; Wenzel, Hans; Knigge, AndreaA novel laser design is presented that combines a longitudinal-lateral gain-loss modulation with an additional phase tailoring achieved by etching rectangular trenches. At 100 A pulsed operation, simulations predict a far-field profile with 0.3° full width at half maximum (ΘFWHM=0.3∘) where a 0.4°-wide main lobe contains 40% of the emitted optical output power (Θ40%=0.4∘). While far-field measurements of these structured lasers emitting 10 ns long pulses with 35 W peak power confirm a substantial enhancement of radiation within the central 1∘ angular range, the measured far-field intensity outside of the obtained central peak remains high.
- ItemDynamics of micro-integrated external-cavity diode lasers: Simulations, analysis and experiments(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2014) Radziunas, Mindaugas; Tronciu, Vasile Z.; Luvsandamdin, Erdenetsetseg; Kürbis, Christian; Wicht, Andreas; Wenzel, HansThis paper reports the results of numerical and experimental investigations of the dynamics of an external cavity diode laser device composed of a semiconductor laser and a distant Bragg grating, which provides an optical feedback. Due to the influence of the feedback, this system can operate at different dynamic regimes. The traveling wave model is used for simulations and analysis of the nonlinear dynamics in the considered laser device. Based on this model, a detailed analysis of the optical modes is performed, and the stability of the stationary states is discussed. It is shown, that the results obtained from the simulation and analysis of the device are in good agreement with experimental findings.
- ItemAmplifications of picosecond laser pulses in tapered semiconductor amplifiers : numerical simulations versus experiments(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2011) Tronciu, Vasile; Schwertfeger, Sven; Radziunas, Mindaugas; Klehr, Andreas; Bandelow, Uwe; Wenzel, HansWe apply a travelling wave model to the simulation of the amplification of laser pulses generated by Q-switched or mode-locked distributed-Bragg reflector lasers. The power amplifier monolithically integrates a ridge-waveguide section acting as pre-amplifier and a flared gain-region amplifier. The diffraction limited and spectral-narrow band pulses injected in to the pre-amplifier have durations between 10 ps and 100 ps and a peak power of typical 1 W. After the amplifier, the pulses reach a peak power of several tens of Watts preserving the spatial, spectral and temporal properties of the input pulse. We report results obtained by a numerical solution of the travelling-wave equations and compare them with experimental investigations. The peak powers obtained experimentally are in good agreement with the theoretical predictions. The performance of the power amplifier is evaluated by considering the dependence of the pulse energy as a function of different device and material parameters.
- ItemEfficient coupling of electro-optical and heat-transport models for broad-area semiconductor lasers(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2018) Radziunas, Mindaugas; Fuhrmann, Jürgen; Zeghuzi, Anissa; Wünsche, Hans-Jürgen; Koprucki, Thomas; Brée, Carsten; Wenzel, Hans; Bandelow, UweIn this work, we discuss the modeling of edge-emitting high-power broad-area semiconductor lasers. We demonstrate an efficient iterative coupling of a slow heat transport (HT) model defined on multiple vertical-lateral laser cross-sections with a fast dynamic electro-optical (EO) model determined on the longitudinal-lateral domain that is a projection of the device to the active region of the laser. Whereas the HT-solver calculates temperature and thermally-induced refractive index changes, the EO-solver exploits these distributions and provides time-averaged field intensities, quasi-Fermi potentials, and carrier densities. All these time-averaged distributions are used repetitively by the HT-solver for the generation of the heat sources entering the HT problem solved in the next iteration step.
- ItemMode transitions in DBR semiconductor lasers: experiments, mode analysis and simulations(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2010) Radziunas, Mindaugas; Hasler, Karl-Heinz; Sumpf, Bernd; Tien, Tran Quoc; Wenzel, HansThe paper is concerned with a general ansatz of a phenomenological evolution model for solid-solid phase transformation kinetics in steel. To model the phase transition of austenite-ferrite, -pearlite or -bainite, a first order nonlinear ordinary differential equation (ODE) is considered. The main goal of this paper is to derive certain conditions for parameters which based on data obtained from transformation diagrams. This leads to a set of independent parameters for which the inverse problem has an unique solution
- ItemMode competition in broad-ridge-waveguide lasers(Bristol : IOP Publ., 2020) Koester, J.-P.; Putz, A.; Wenzel, H.; Wünsche, H.-J.; Radziunas, M.; Stephan, H.; Wilkens, M.; Zeghuzi, A.; Knigge, A.The lateral brightness achievable with high-power GaAs-based laser diodes having long and broad waveguides is commonly regarded to be limited by the onset of higher-order lateral modes. For the study of the lateral-mode competition two complementary simulation tools are applied, representing different classes of approximations. The first tool bases on a completely incoherent superposition of mode intensities and disregards longitudinal effects like spatial hole burning, whereas the second tool relies on a simplified carrier transport and current flow. Both tools yield agreeing power-current characteristics that fit the data measured for 5-23 µm wide ridges. Also, a similarly good qualitative conformance of the near and far fields is found. However, the threshold of individual modes, the partition of power between them at a given current, and details of the near and far fields show differences. These differences are the consequence of a high sensitivity of the mode competition to details of the models and of the device structure. Nevertheless, it can be concluded concordantly that the brightness rises with increasing ridge width irrespective of the onset of more and more lateral modes. The lateral brightness W mm-1at 10 MW cm-2 power density on the front facet of the investigated laser with widest ridge (23 µm) is comparable with best values known from much wider broad-area lasers. In addition, we show that one of the simulation tools is able to predict beam steering and coherent beam coupling without introducing any phenomenological coupling coefficient or asymmetries. © 2020 The Author(s). Published by IOP Publishing Ltd.
- ItemModeling of current spreading in high-power broad-area lasers and its impact on the lateral far field divergence(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2018) Zeghuzi, Anissa; Radziunas, Mindaugas; Wenzel, Hans; Wünsche, Hans-Jürgen; Bandelow, Uwe; Knigge, AndreaThe effect of current spreading on the lateral farfield divergence of highpower broadarea lasers is investigated with a timedependent model using different descriptions for the injection of carriers into the active region. Most simulation tools simply assume a spatially constant injection current density below the contact stripe and a vanishing current density beside. Within the driftdiffusion approach, however, the injected current density is obtained from the gradient of the quasiFermi potential of the holes, which solves a Laplace equation in the pdoped region if recombination is neglected. We compare an approximate solution of the Laplace equation with the exact solution and show that for the exact solution the highest farfield divergence is obtained. We conclude that an advanced modeling of the profiles of the injection current densities is necessary for a correct description of farfield blooming in broadarea lasers.