G. Tränkle

Ferdinand-Braun-Institut, Berlín, Berlin, Germany

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Publications (303)411.34 Total impact

  • Source
    A Kaltenbach · R Bege · K Paschke · G Tränkle
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    ABSTRACT: Picosecond laser pulses in the visible spectral range are of great interest for many applications, ranging from material to bio-physical science. Especially for fluorescence lifetime imaging there is a high demand on freely triggerable laser sources with portable dimensions which emit in the yellow spectral range from 550 nm to 590 nm. Due to the lack of suitable material compositions for direct emission in this spectral range nonlinear frequency conversion of gain-switched semiconductor lasers becomes a key technique to satisfy these specifications. In this work we present highly efficient frequency doubling of 1116 nm picosecond pulses generated in a distributed Bragg reflector ridge waveguide diode laser (DBR-RWL) by gain-switching. The converted 558 nm pulses exhibit a pulse power of 0.7 W. To our knowledge, this is the highest output power of such a laser device at this wavelength so far The DBR-RWL consists of an AlGaAs-GaAs structure with an InGaAs double quantum well in its active region [1]. The asymmetrical embedding of the active region into the waveguide core is well suited to gain high single pulse power with the gain-switching method [2]. The average output power of the fundamental 1116 nm radiation was limited to 4.3 mW to avoid excessive trailing pulses. The fundamental pulses exhibit a FWHM of 60 ps and contain an energy of 95 pJ. Frequency doubling is realized in a magnesium doped periodically poled lithium niobate (PPLN) ridge-waveguide crystal. The crystal has a length of 7 mm and a quasi phase-matching temperature of 39°C. Fig. 1 Pulse shapes of the (a) fundamental radiation and (b) the second harmonic radiation at a repetition frequency of 40 MHz Fig. 2 Efficiency of the SHG process at 40 MHz. Fig. 1 shows both the pulse shapes of (a) the fundamental and (b) the second harmonic radiation. The fundamental pulse shows explicit trailing pulses which are largely suppressed in the conversion process. The 558 nm second harmonic (SH) pulses show a FWHM of 50 ps and contain an energy of 35 pJ which is 95 % of the total energy. The dependence of the SH pulse power on the pump pulse power is shown in Fig. 2. The SH pulse power follows very well the theoretical SH to pump power dependence í µí±ƒ SHG = í µí¼ • í µí±ƒ pump • tanh 2 √í µí¼ • í µí¼‚ • í µí±ƒ pump • í µí±™ 2 , with transmission τ, crystal length l and normalized conversion efficiency η, which is determined to be 169 %/W-1 cm-2. At a repetition frequency of 40 MHz an SH average output power of 1.5 mW and a SH pulse power of 0.7 W could be obtained. Together with the good beam quality this device is well suited for the mentioned applications. At the conference we will present more details on the investigations on the second harmonic radiation characteristics such as spectral and spatial properties. We will also present results on the performance of the micro integration of this concept.
    CLEO/Europe-EQEC 2015, Munich; 06/2015
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    ABSTRACT: Wavelength stabilized diode laser light sources are requested for several applications. Beside this, some applications need also a wavelength alternating operation. In the case of absorption spectroscopy, e.g. for DIAL, a switching between wavelengths with large and small absorption coefficient is needed or in the case of Raman spectroscopy a spectral shift of about 10 cm-1 is needed to apply shifted excitation Raman difference spectroscopy (SERDS) to distinguish between Raman lines and disturbing backgrounds like natural or artificial light, scattering or fluorescence.
    CLEO/Europe-EQEC 2015, Munich; 06/2015
  • Martin Maiwald · André Müller · Bernd Sumpf · Götz Erbert · Günther Tränkle
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    ABSTRACT: We present the capability of shifted excitation Raman difference spectroscopy (SERDS) under ambient daylight. A dual-wavelength diode laser emitting at 785 nm is used as the excitation light source. The monolithic diode laser provides more than 110 mW in cw operation. Both excitation lines show an emission width ≤0.2 cm<sup>-1</sup> and a spectral distance of 10 cm<sup>-1</sup> as targeted for SERDS. Polystyrene (PS) is used as the test sample and ambient daylight to generate real-world background interference. Here, a broadband background signal with narrowband absorption lines from water vapor and Fraunhofer lines from singly ionized calcium (Ca II) obscure the Raman lines of PS. SERDS clearly separates the Raman signals from the background signals with a 13-fold improvement in signal-to-background noise.
    Applied Optics 06/2015; 54(17):5520. DOI:10.1364/AO.54.005520 · 1.78 Impact Factor
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    ABSTRACT: We present micro-integrated diode laser modules operating at wavelengths of 767 and 780 nm for cold quantum gas experiments on potassium and rubidium. The master-oscillator-power-amplifier concept provides both narrow linewidth emission and high optical output power. With a linewidth (10 μs) below 1 MHz and an output power of up to 3 W, these modules are specifically suited for quantum optics experiments and feature the robustness required for operation at a drop tower or on-board a sounding rocket. This technology development hence paves the way toward precision quantum optics experiments in space.
    Applied Optics 06/2015; 54(17):5332. DOI:10.1364/AO.54.005332 · 1.78 Impact Factor
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    ABSTRACT: This work presents investigations of the dynamic behavior of short channel AlGaN/GaN HEMTs with Lg varying from 100 nm to 200 nm. Transistors were fabricated using AlGaN/GaN epitaxial structures with nominally the same GaN:Fe buffer layer and AlGaN barrier layers with different thicknesses and Al mole fractions. DC measurements of fabricated transistors showed similar performance for all epitaxial structures as well as for all L g. Dynamic I-V analysis (DIVA) revealed significant differences between transistors with different L g fabricated on the same epitaxial structure, as well as between transistors with the same L g fabricated on different epitaxial structures. Differences in the amount of drain current reduction, gm max degradation and knee voltage walkout at gate lag conditions were observed. The differences are attributed to the traps located in the area under the gate electrode. The physical mechanism of the observed phenomena was related to the interaction of several effects that influence electron mobility in the channel.
    CS Mantech 2015, Scottsdale, Arizona, USA; 05/2015
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    ABSTRACT: The thermal properties of large periphery 60 mΩ AlGaN/GaN HEMTs fabricated on Si and SiC substrates have been studied by applying pulsed Ids characterization at varying base plate temperatures and by correlating it to ANSYS simulation. At bias points being typical for power switching (linear region of I-V characteristics) the thermal properties of devices on SiC substrates show a small advantage as compared to those on Si substrates. However, if operated in the saturation region (higher value of power dissipation) at longer time pulse, GaN-on-SiC devices show a clear advantage over GaN-on-Si devices.
    Int. Conf. on Compound Semiconductor Manufacturing Technology (CS ManTech 2015), Scottsdale / USA; 05/2015
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    ABSTRACT: Two concepts of dual-wavelength 785-nm DBR ridge waveguide (RW) lasers, i.e. RW mini-arrays consisting of two DBR-RW lasers and Y-branch DBR-RW lasers, will be compared with respect to their usability as excitation light sources for shifted excitation Raman difference spectroscopy (SERDS). For both types of devices for each wavelength, output powers up to 215 mW were measured. A stable spectral distance between the laser emissions of the two resonator branches with the targeted value of 0.6 nm, i.e. 10 cm−1, is observed. In the case of the mini-array up to an output power of about 70 mW, the device shows single-mode operation. Although at higher power levels, mode hops and multi-mode operation occur, the emission width smaller than 0.15 nm still meets the requirements for Raman measurements of solids and liquids. Over the whole working range, the spectral distance between the two wavelengths is approximately constant with 0.62 nm. The near field shows two emission spots according to the dimension of the RW and their processed distance of 20 μm. The Y-branch laser shows single-mode operation up to 150 mW with a narrow spectral emission width. At higher powers also, multi-mode operation with an emission width of 0.15 nm occurs. The nearly diffraction- limited emission comes from one output aperture; the far-field emission shows a pronounced asymmetry between the two branches. Both types of devices fulfil the spectral requirements from Raman spectroscopy and SERDS up to 215 mW output power.
    Applied Physics B 05/2015; 120(2):261-269. DOI:10.1007/s00340-015-6133-x · 1.86 Impact Factor
  • N Ruhnke · A Müller · B Eppich · R Güther · M Maiwald · B Sumpf · G Erbert · G Tränkle
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    ABSTRACT: We demonstrate a compact system for single-pass frequency doubling of high-power GaN diode laser radiation. The deep UV laser light at 222.5 nm is generated in a β-BaB<sub>2</sub>O<sub>4</sub> (BBO) crystal. A high-power GaN external cavity diode laser (ECDL) system in Littrow configuration with narrowband emission at 445 nm is used as pump source. At a pump power of 680 mW, a maximum UV power of 16 μW in continuous-wave operation at 222.5 nm is achieved. This concept enables a compact diode laser-based system emitting in the deep ultraviolet spectral range.
    Optics Letters 05/2015; 40(9):2127-2129. DOI:10.1364/OL.40.002127 · 3.29 Impact Factor
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    ABSTRACT: A self-optimizing approach to intra-cavity spectral shaping of external cavity mode-locked semiconductor lasers using edge-emitting multi-section diodes is presented. An evolutionary algorithm generates spectrally resolved phase- and amplitude masks that lead to the utilization of a large part of the net gain spectrum for mode-locked operation. Using these masks as a spectral amplitude and phase filter, a bandwidth of the optical intensity spectrum of 3.7 THz is achieved and Fourier-limited pulses of 216 fs duration are generated after further external compression.
    Optics Express 04/2015; 23(8). DOI:10.1364/OE.23.009710 · 3.49 Impact Factor
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    ABSTRACT: We present a compact, ultra-narrow-linewidth semiconductor laser based on a 780 nm distributed feedback diode laser optically self-locked to a mode of an external monolithic confocal Fabry-Perot resonator. We characterize spectral properties of the laser by measuring its frequency noise power spectral density. The white frequency noise levels at 5 Hz2/Hz above a Fourier frequency as small as 20 kHz. This noise level is more than five orders of magnitude smaller than the noise level of the same solitary diode laser without resonant optical feedback, and it is three orders of magnitude smaller than the noise level of a narrow linewidth, grating-based, extended-cavity diode laser. The corresponding Lorentzian linewidth of the laser with resonant optical feedback is 15.7 Hz at an output power exceeding 50 mW.
    Optics Express 04/2015; 23(8). DOI:10.1364/OE.23.009705 · 3.49 Impact Factor
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    ABSTRACT: Recently, high-power broad-area laser diodes based on GaN with output powers beyond 1 W have become available. However, their broad spectral emission limits their applicability. Due to a lack of internal grating technology for GaN devices, narrowband emission with several hundreds of milliwatts in the blue-green spectral range has not been achieved with laser diodes thus far. In this work, a high-power external cavity diode laser (ECDL) system at 445 nm is presented. The system is based on a commercially available broad-area GaN laser diode and a surface diffraction grating in Littrow configuration for optical feedback. Using this configuration an output power of 400 mW with a reduced spectral emission bandwidth of 20 pm (FWHM) with a side-mode suppression ratio larger than 40 dB is obtained. With the above presented optical output power and narrowband laser emission at 445 nm, the ECDL is well suited as a pump light source for nonlinear frequency conversion into the deep ultraviolet spectral range.
    SPIE Photonics West 2015, San Francisco; 03/2015
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    ABSTRACT: Thick AlxGa1−xN layers were grown by hydride vapor phase epitaxy on hexagonally patterned sapphire substrates. Non-c-planar growth is found inside the etched honeycombs which in part hinders coalescence of the c-plane AlGaN layer growing on top of the ridges. From X-ray diffraction, electron backscatter diffraction and scanning electron microscopy, the orientations of the parasitic crystallites were identified as {11–22} and {1–103} AlGaN growing on m-plane sapphire sidewalls as well as c-plane oriented AlGaN growing on n-plane sidewall facets which are located in the corners of the combs. According to the geometry of parasitic crystallites, it is further observed, that the semipolar growth occurring on sapphire m-plane sidewalls does not hinder the coalescence of c-plane AlGaN growing on top of the ridges, whereas fast propagation of parasitic crystallites nucleating on n-plane sidewall facets leads to delayed layer coalescence.
    Journal of Crystal Growth 03/2015; 414. DOI:10.1016/j.jcrysgro.2014.10.010 · 1.70 Impact Factor
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    ABSTRACT: High power broad-area diode lasers are the most efficient source of optical energy, but cannot directly address many applications due to their high lateral beam parameter product BPP = 0.25 × ΘL95% × W95% (ΘL95% and W95% are emission angle and aperture at 95% power content), with BPP > 3 mm×mrad for W95%~90μm. We review here progress within the BRIDLE project, that is developing diode lasers with BPP < 2 mm×mrad for use in direct metal cutting systems, where the highest efficiencies and powers are required. Two device concepts are compared: narrow-stripe broad-area (NBA) and tapered lasers (TPL), both with monolithically integrated gratings. NBAs use W95% ~ 30 μm to cut-off higher order lateral modes and reduce BPP. TPLs monolithically combine a single mode region at the rear facet with a tapered amplifier, restricting the device to one lateral mode for lowest BPP. TPLs fabricated using ELoD (Extremely Low Divergence) epitaxial designs are shown to operate with BPP below 2mm×mrad, but at cost of low efficiency (<35%, due to high threshold current). In contrast, NBAs operate with BPP < 2 mm×mrad, but maintain efficiency >50% to output of > 7 W, so are currently the preferred design. In studies to further reduce BPP, lateral resonant anti-guiding structures have also been assessed. Optimized anti-guiding designs are shown to reduce BPP by 1 mm×mrad in conventional 90 μm stripe BA-lasers, without power penalty. In contrast, no BPP improvement is observed in NBA lasers, even though their spectrum indicates they are restricted to single mode operation. Mode filtering alone is therefore not sufficient, and further measures will be needed for reduced BPP.
    Photonics West 2015, San Francisco; 03/2015
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    ABSTRACT: Variation of the H2 fraction in the carrier gas affects partial pressures and homogeneity of the species at the growth front. Changing the H2:N2 ratio thus requires readjustment of the flows of the reacting species to keep the V/III ratio at the growth front constant. In this paper the complex effect of the carrier gas composition, i.e., the H2 + N2 mixture on optical and structural properties of GaN films grown by hydride vapor phase epitaxy (HVPE) is studied. With constant input flows of the main reactants but different H2 fractions in each experiment, good morphology was observed only in a small parameter window. Partial pressures at the growth front were calculated using a commercial virtual reactor simulation tool. After readjustment of the growth species partial pressures to those which previously provided good morphology, it became possible to achieve higher growth rates, comparable morphologies, and widths of the rocking curves (FWHM) for a wide range of hydrogen fractions (0–70%). Further flow pattern correction enabled growth of 1 mm thick layers for 40–75% H2 in the carrier gas. The results of the study allow to find optimal conditions for HVPE growth of thick GaN layers when scaling up from 2 to 3 in. substrate diameter.
    physica status solidi (b) 03/2015; 252(5). DOI:10.1002/pssb.201451609 · 1.49 Impact Factor
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    ABSTRACT: Third harmonic 355nm picosecond pulses are generated by sum frequency mixing in a periodically poled magnesium doped stoichiometric lithium tantalate (PPMgSLT) crystal. The third harmonic generation is based on the 1064nm radiation of a gain-switched distributed feedback (DFB) diode laser which is amplified by a two-stage fiber amplifier. The diode laser is freely triggerable at variable repetition rates up to 80MHz and provides optical pulses of 65 ps FWHM duration and pulse energies in the range of 5 pJ. The 355nm third harmonic generation is realized in a two-step conversion process. First, the 1064nm fundamental radiation is frequency-doubled to 532 nm, afterwards both frequencies are mixed in the PPMgSLT crystal to 355 nm. The UV-radiation shows a pulse width of 60 ps, a good beam profile and stable pulse energy over a wide range of repetition rates by proprietary pump power management. At 355nm a pulse peak power of 5.3W was achieved with 192W pulse peak power of the fundamental radiation.
    SPIE Photonics West, San Francisco, USA; 02/2015
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    ABSTRACT: The application of shifted excitation Raman difference spectroscopy (SERDS) using a dual wavelength distributed Bragg reflector (DBR) diode laser at 785 nm will be presented. Both excitation wavelengths necessary for SERDS provide an optical power of more than 160 mW in continuous wave operation. Raman experiments are carried out and demonstrate the suitability of the excitation light source for SERDS. Moreover, a dual-wavelength master-oscillator power amplifier diode laser system is presented. The diode laser system reaches optical powers larger 750 mW while the spectral properties of the dual-wavelength laser remain unchanged
    Proceedings of SPIE - The International Society for Optical Engineering 02/2015; 9313:9313=Y. DOI:10.1117/12.2080922 · 0.20 Impact Factor
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    ABSTRACT: Semiconductor based sources which emit high-power spectrally stable nearly diffraction-limited optical pulses in the nanosecond range are ideally suited for a lot of applications, such as free-space communications, metrology, material processing, seed lasers for fiber or solid state lasers, spectroscopy, LIDAR and frequency doubling. Detailed experimental investigations of 975 nm and 800 nm diode lasers based on master oscillator power amplifier (MOPA) light sources are presented. The MOPA systems consist of distributed Bragg reflector lasers (DBR) as master oscillators driven by a constant current and ridge waveguide power amplifiers which can be driven DC and by current pulses. In pulse regime the amplifiers modulated with rectangular current pulses of about 5 ns width and a repetition frequency of 200 kHz act as optical gates, converting the continuous wave (CW) input beam emitted by the DBR lasers into a train of short optical pulses which are amplified. With these experimental MOPA arrangements no relaxation oscillations in the pulse power occur. With a seed power of about 5 mW at a wavelength of 973 nm output powers behind the amplifier of about 1 W under DC injection and 4 W under pulsed operation, corresponding to amplification factors of 200 (amplifier gain 23 dB) and 800 (gain 29 dB) respectively, are reached. At 800 nm a CW power of 1 W is obtained for a seed power of 40 mW. The optical spectra of the emission of the amplifiers exhibit a single peak at a constant wavelength with a line width < 10 pm in the whole investigated current ranges. The ratios between laser and ASE levels were > 50 dB. The output beams are nearly diffraction limited with beam propagation ratios M2lat ∼ 1.1 and M2ver ∼ 1.2 up to 4 W pulse power.
    Proceedings of SPIE - The International Society for Optical Engineering 02/2015; 9382:93821I. DOI:10.1117/12.2075652 · 0.20 Impact Factor
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    ABSTRACT: A new generation of diode-pumped high-energy-class solid-state laser facilities is in development that generate multijoule pulse energies at around 10 Hz. Currently deployed quasi-continuous-wave (QCW) diode lasers deliver average inpulse pump powers of around 300 W per bar. Increased power-per-bar helps to reduce the system size, complexity and cost per Joule and the increased pump brilliance also enables more efficient operation of the solid state laser itself. It has been shown in recent studies, that optimized QCW diode laser bars centered at 940…980 nm can operate with an average in-pulse power of > 1000 W per bar, triple that of commercial sources. When operated at pulsed condition of 1 ms, 10 Hz, this corresponds to > 1 J/bar. We review here the status of these high-energy-class pump sources, showing how the highest powers are enabled by using long resonators (4…6 mm) for improved cooling and robustly passivated output facets for high reliability. Results are presented for prototype passively-cooled single bar assemblies and monolithic stacked QCW arrays. We confirm that 1 J/bar is sustained for fast-axis collimated stacks with a bar pitch of 1.7 mm, with narrow lateral far field angle (< 12° with 95% power) and spectral width (< 12 nm with 95% power). Such stacks are anticipated to enable Joule/bar pump densities to be used near-term in commercial high power diode laser systems. Finally, we briefly summarize the latest status of research into bars with higher efficiencies, including studies into operation at sub-zero temperatures (-70°C), which also enables higher powers and narrower far field and spectra.
    Proceedings of SPIE - The International Society for Optical Engineering 01/2015; 9348:93480U-1-10. DOI:10.1117/12.2077599 · 0.20 Impact Factor
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    ABSTRACT: We present intra-cavity pulse shaping of external cavity mode-locked semiconductor lasers. In our approach, a pulse shaper utilizing a dual LC-panel spatial light modulator is used in the cavity of a mode-locked multi-quantum-well semiconductor laser to introduce spectrally resolved phase manipulation and losses to the pulse propagating in the cavity. Utilizing this, we generate pulses with broader spectra than obtained in conventional external cavity geometries without pulse shaping. The pulses can be compressed near to the transform limit using a grating compressor.
    Proceedings of SPIE - The International Society for Optical Engineering 01/2015; 9382. DOI:10.1117/12.2079040 · 0.20 Impact Factor
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    ABSTRACT: Raman lines are often superimposed by daylight, artificial light sources or fluorescence signals from the samples under study. Shifted excitation Raman difference spectroscopy (SERDS), i.e. exciting the sample alternatingly with two slightly shifted wavelengths, allows to distinguish between the Raman lines and sources of interference. In this work, monolithic dual wavelength Y-branch DBR ridge waveguide diode lasers and their application in master oscillator power amplifier (MOPA) systems at 785 nm suitable for Raman spectroscopy and SERDS will be presented. The definition of the wavelengths is made by implementing deeply-etched 10th order 500 μm long surface gratings with different periods using i-line wafer stepper lithography. Y-branch DBR lasers with a total length of 3 mm and a stripe width of 2.2 μm were manufactured and characterized. The monolithic devices reach output powers up to 215 mW with emission widths of about 20 pm. At 200 mW the conversion efficiency is 20%, i.e. the electrical power consumption is only 1 W. The spectral distance between the two laser cavities is about 0.6 nm, i.e. 10 cm-1 as targeted. The side mode suppression ratio is better than 50 dB. Amplifying these devices using a ridge waveguide amplifier
    Proceedings of SPIE - The International Society for Optical Engineering 01/2015; 9382:93821B-1-8. DOI:10.1117/12.2076259 · 0.20 Impact Factor

Publication Stats

3k Citations
411.34 Total Impact Points


  • 1970–2015
    • Ferdinand-Braun-Institut
      • Department of Optoelectronics
      Berlín, Berlin, Germany
  • 1983–2007
    • University of Technology Munich
      • • Walter Schottky Institut (WSI)
      • • Faculty of Physics
      München, Bavaria, Germany
  • 1997–1998
    • Fraunhofer Institute for Applied Solid State Physics IAF
      Freiburg, Baden-Württemberg, Germany
    • Nippon Telegraph and Telephone
      Edo, Tōkyō, Japan
  • 1986–1988
    • Universität Stuttgart
      • Institute of Physics
      Stuttgart, Baden-Württemberg, Germany
  • 1987
    • University of California, Santa Barbara
      • Department of Electrical and Computer Engineering
      Santa Barbara, California, United States