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- ItemHigh-power diode lasers with in-situ-structured lateral current blocking for improved threshold, efficiency and brightness(Bristol : IoP Publ., 2022) Elattar, M.; Brox, O.; Della Casa, P.; Mogilatenko, A.; Maaßdorf, A.; Martin, D.; Wenzel, H.; Knigge, A.; Weyers, M.; Crump, P.We present high-power GaAs-based broad-area diode lasers with a novel variant of the enhanced self-aligned lateral structure ‘eSAS’, having a strongly reduced lasing threshold and improved peak conversion efficiency and beam quality in comparison to their standard gain-guided counterparts. To realize this new variant (eSAS-V2), a two-step epitaxial growth process involving in situ etching is used to integrate current-blocking layers, optimized for tunnel current suppression, within the p-Al0.8GaAs cladding layer of an extreme-triple-asymmetric epitaxial structure with a thin p-side waveguide. The blocking layers are thus in close proximity to the active zone, resulting in strong suppression of current spreading and lateral carrier accumulation. eSAS-V2 devices with 4 mm resonator length and varying stripe widths are characterized and compared to previous eSAS variant (eSAS-V1) as well as gain-guided reference devices, all having the same dimensions and epitaxial structure. Measurement results show that the new eSAS-V2 variant eliminates an estimated 89% of lateral current spreading, resulting in a strong threshold current reduction of 29% at 90 μm stripe width, while slope and series resistance are broadly unchanged. The novel eSAS-V2 devices also maintain high conversion efficiency up to high continuous-wave optical power, with an exemplary 90 μm device having 51.5% at 20 W. Near-field width is significantly narrowed in both eSAS variants, but eSAS-V2 exhibits a wider far-field angle, consistent with the presence of index guiding. Nonetheless, eSAS-V2 achieves higher beam quality and lateral brightness than gain-guided reference devices, but the index guiding in this realization prevents it from surpassing eSAS-V1. Overall, the different performance benefits of the eSAS approach are clearly demonstrated.
- ItemSpectral linewidth vs. Front facet reflectivity of 780 nm DFB diode lasers at high optical output power(Basel : MDPI AG, 2018) Nguyen, T.-P.; Wenzel, H.; Brox, O.; Bugge, F.; Ressel, P.; Schiemangk, M.; Wicht, A.; Tien, T.Q.; Tränkle, G.The influence of the front facet reflectivity on the spectral linewidth of high power DFB (distributed feedback) diode lasers emitting at 780 nm has been investigated theoretically and experimentally. Characterization of lasers at various front facet reflections showed substantial reduction of the linewidth. This behavior is in reasonable agreement with simulation results. A minimum linewidth of 8 kHz was achieved at an output power of 85 mW with the laser featuring a front facet reflectivity of 30%. The device with a front facet reflectivity of 5% reached the same linewidth value at an output power of 290 mW.
- ItemHigh-brightness broad-area diode lasers with enhanced self-aligned lateral structure(Bristol : IOP Publ., 2020) Elatta, M.; Brox, O.; Della Casa, P.; Maaßdorf, A.; Martin, D.; Wenzel, H.; Knigge, A.; Crump, P.Broad-area diode lasers with increased brightness and efficiency are presented, which are fabricated using an enhanced self-aligned lateral structure by means of a two-step epitaxial growth process with an intermediate etching step. In this structure, current-blocking layers in the device edges ensure current confinement under the central stripe, which can limit the detrimental effects of current spreading and lateral carrier accumulation on beam quality. It also minimizes losses at stripe edges, thus lowering the lasing threshold and increasing conversion efficiency, while maintaining high polarization purity. In the first realization of this structure, the current block is integrated within an extreme-triple-asymmetric epitaxial design with a thin p-doped side, meaning that the distance between the current block and the active zone can be minimized without added process complexity. Using this configuration, enhanced self-aligned structure devices with 90 µm stripe width and 4 mm resonator length show up to 20% lower threshold current, 21% narrower beam waist, and slightly higher (1.03 ) peak efficiency in comparison to reference devices with the same dimensions, while slope, divergence angle and polarization purity remain almost unchanged. These results correspond to an increase in brightness by up to 25%, and measurement results of devices with varying stripe widths follow the same trend. © 2020 The Author(s). Published by IOP Publishing Ltd.
- ItemImproving the stability of distributed-feedback tapered master-oscillator power-amplifiers(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2009) Tronciu, Vasile Z.; Lichtner, Mark; Radziunas, Mindaugas; Bandelow, U.; Wenzel, H.We report theoretical results on the wavelength stabilization in distributed-feedback master-oscillator power-amplifiers which are compact semiconductor laser devices capable of emitting a high brilliance beam at an optical power of several Watts. Based on a traveling wave equation model we calculate emitted optical power and spectral maps in dependence on the pump of the power amplifier. We show that a proper choice of the Bragg grating type and coupling coefficient allows to optimize the laser operation, such that for a wide range of injection currents the laser emits a high intensity continuous wave beam.
- ItemImpact of the capture time on the series resistance of quantum-well diode lasers(Bristol : IOP Publ., 2020) Boni, A.; Wünsche, H.J.; Wenzel, H.; Crump, P.Electrons and holes injected into a semiconductor heterostructure containing quantum wells are captured with a finite time. We show theoretically that this very fact can cause a considerable excess contribution to the series resistivity and this is one of the main limiting factors to higher efficiency for GaAs based high-power lasers. The theory combines a standard microscopic-based model for the capture-escape processes in the quantum well with a drift-diffusion description of current flow outside the quantum well. Simulations of five GaAs-based devices differing in their Al-content reveal the root-cause of the unexpected and until now unexplained increase of the series resistance with decreasing heat sink temperature measured recently. The finite capture time results in resistances in excess of the bulk layer resistances (decreasing with increasing temperature) from 1 mΩ up to 30 mΩ in good agreement with the experiment. © 2020 The Author(s). Published by IOP Publishing Ltd.
- ItemVerbundvorhaben Femto-Diode, Teilvorhaben: Halbleiterkomponenten für kompakte Femtosekunden-Laserstrahlquellen : Projekt-Abschlussbericht ; Projekt FBH 9140, HaFemLas ; Abschlussbericht: 1.10.2004 - 30.09.2007(Hannover : Technische Informationsbibliothek (TIB), 2008) Klehr, Andreas; Zorn, Martin; Weyers, M.; Erbert, G.; Fricke, J.; Knauer, A.; Pittroff, W.; Staske, R.; Wenzel, H.; Zeimer, U.[no abstract available]
- 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.
- ItemFörderschwerpunkt Laser 2000: Grundlegende Untersuchungen zur hochgenauen, berührungslosen laserinterferometrischen Messung großer Längen im Maschinenbau, Teilvorhaben: Grundlegende Untersuchungen leistungsstarker durchstimmbarer Halbleiterlaserdioden : Schlußbericht(Berlin : Ferdinand-Braun-Institut, 2000) Erbert, G.; Brugge, F.; Fechner, I.; Fredrich, D.; Gielow, M.; Hofmann, L.; Klehr, A.; Klein, A.; Krause, A.; Knauer, A.; Olschewsky, R.; Oster, A.; Rechenberg, I.; Ressel, P.; Sebastian, J.; Selent, R.; Smirnitzki, V.; Tessaro, T.; Thiemann, M.; Thies, A.; Vogel, K.; Wenzel, H.; Weyers, M.; Würfel, J.; Wochatz, P.[no abstract available]
- ItemFörderschwerpunkt NOVALAS : Grundlegende Untersuchungen zur Technologie von Hochleistungsdiodenlasern, Teilvorhaben: Hochleistungsdiodenlaser auf der Basis von Al-freien Quantengräben und Wellenleitern im Wellenlängenbereich 800 - 1000 nm ; Schlussbericht(Berlin : Ferdinand-Braun-Institut, 2001) Erbert, G.; Beister, G.; Brade, P.; Fechner, I.; Fredrich, D.; Fricke, J.; Gielow, M.; Hülsewede, R.; Klein, A.; Krause, A.; Knauer, A.; Maege, J.; Pittroff, W.; Olschewsky, R.; Rechenberg, I.; Ressel, P.; Sebastian, J.; Selent, R.; Staske, R.; Schulze, H.; Sumpf, B; Tessaro, T.; Vogel, K.; Wenzel, H.; Wiechmann, S.; Weyers, M.; Würfel, J.; Wochatz, P.[no abstract available]
- ItemErforschung und Realisierung von innovativen hybridintegrierten Diodenlaser-Komponenten und Systemen (INDILAS), Teilvorhaben: Halbleiterkomponenten zur Erzeugung von definierten optischen ps-Impulsfolgen hoher Brillanz auf der Basis modengekoppelter Laser (KomodLa) : InDiLAS/KoModLa ; Schlussbericht ; Laufzeit des Vorhabens: 01.06.2009 - 31.05.2012(Hannover : Technische Informationsbibliothek (TIB), 2012) Erbert, G.; Klehr, A.; Schwertfeger, S.; Wenzel, H.; Liero, A.; Hoffmann, T.[no abstract available]