Thomas Elsaesser

Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, Berlín, Berlin, Germany

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Publications (521)1375.74 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Longitudinal bulk plasmons in an n-doped ZnO layer system are studied by two-color femtosecond pump-probe spectroscopy in the midinfrared. The optical bulk plasmon resonance identified in linear reflectivity spectra undergoes a strong redshift and a limited broadening upon intraband excitation of electrons. The nonlinear changes of plasmon absorption decay on a time scale of 2 ps and originate from the intraband redistribution of electrons. Theoretical calculations explain the plasmon redshift by the transient increase of the ensemble-averaged electron mass and the concomitantly reduced plasma frequency in the hot electron plasma. The observed bulk plasmon nonlinearity holds strong potential for applications in plasmonics.
    Physical Review Letters 09/2015; 115(14). DOI:10.1103/PhysRevLett.115.147401 · 7.51 Impact Factor
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    ABSTRACT: We present an approach for controlling quantum coherences in condensed matter by interaction with a nonresonant optical control field. Coherent intersubband (IS) excitations of electrons in GaAs/AlGaAs quantum wells are manipulated by a strong nonresonant terahertz (THz) field as demonstrated by phase-resolved two-color two-dimensional spectroscopy. In the linear regime of IS response, we observe a THz-induced enhancement of the midinfrared (MIR) IS absorption and a dispersive perturbed free induction decay caused by a THz-induced blueshift of the IS polarization. In the regime of IS Rabi oscillations, the THz field causes pronounced phase shifts of the coherently emitted MIR field, while the IS Rabi frequency remains unaffected. Such behavior is accounted for by a full solution of the Maxwell-Bloch equations, treating the THz and MIR fields without approximations. Our control scheme paves the way for THz control of IS emitters and holds potential for an extension to other systems. © 2015 American Physical Society.
    Physical Review B 08/2015; 92(8). DOI:10.1103/PhysRevB.92.085306 · 3.74 Impact Factor
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    ABSTRACT: Electric-field transients covering the extremely wide frequency range from 0.5 to 26 THz are generated in the organic nonlinear crystal 4-N,N-dimethylamino-4<sup>'</sup>-N<sup>'</sup>-methylstilbazolium 2,4,6-trimethylbenzenesulfonate (DSTMS). Parametric difference frequency mixing within the spectrum of 25-fs amplified pulses centered at 800 nm provides a highly stable broadband output with an electric-field amplitude of up to several hundred kilovolts/cm. The high stability of the terahertz pulse parameters allows for sensitive phase-resolved broadband spectroscopy of optically thick crystalline samples.
    Optics Letters 07/2015; 40(14):3404-7. DOI:10.1364/OL.40.003404 · 3.29 Impact Factor
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    ABSTRACT: Catastrophic optical damage (COD) in 450 nm emitting InGaN/GaN diode lasers is artificially provoked by applying single sub-microsecond current pulses of increasing amplitude. Studying a batch of devices in which COD does not represent the main degradation mode, we find that COD is a ‘hot’ process. It becomes re-ignited in subsequent pulses. During the process, the spatial filamentation changes abruptly and the outer appearance of the damage pattern is predominantly created within the initial pulse. The process can cause material ejection out of the front facet as shown by thermography.
    Semiconductor Science and Technology 07/2015; 30(7). DOI:10.1088/0268-1242/30/7/072001 · 2.19 Impact Factor
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    ABSTRACT: The vibrational modes of the deoxyribose-phosphodiester backbone moiety of DNA and their interactions with the interfacial aqueous environment are addressed with two-dimensional (2D) infrared spectroscopy on the femto- to picosecond time scale. Beyond the current understanding in the harmonic approximation, the anharmonic character and delocalization of the backbone modes in the frequency range from 900 to 1300 cm(-1) are determined with both diagonal anharmonicities and inter-mode couplings of the order of 10 cm(-1). Mediated by the inter-mode couplings, energy transfer between the backbone modes takes place on a picosecond time scale, parallel to vibrational relaxation and energy dissipation into the environment. Probing structural dynamics noninvasively via the time evolution of the 2D lineshapes, limited structure fluctuations are observed on a 300 fs time scale of low-frequency motions of the helix, counterions, and water shell. Structural disorder of the DNA-water interface and DNA-water hydrogen bonds are, however, preserved for times beyond 10 ps. The different interactions of limited strength ensure ultrafast vibrational relaxation and dissipation of excess energy in the backbone structure, processes which are important for the structural integrity of hydrated DNA.
    The Journal of Physical Chemistry B 06/2015; 119(30). DOI:10.1021/acs.jpcb.5b04499 · 3.30 Impact Factor
  • Thomas Elsaesser · Klaus Reimann · Michael Woerner ·
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    ABSTRACT: Intense terahertz (THz) electric field transients with amplitudes up to several megavolts/centimeter and novel multidimensional techniques are the key ingredients of nonlinear THz spectroscopy, a new area of basic research. Both nonlinear light-matter interactions including the non-perturbative regime and THz driven charge transport give new insight into the character and dynamics of low-energy excitations of condensed matter and into quantum kinetic phenomena. This article provides an overview of recent progress in this field, combining an account of technological developments with selected prototype results for liquids and solids. The potential of nonlinear THz methods for future studies of low-frequency excitations of condensed-phase molecular systems is discussed as well.
    The Journal of Chemical Physics 06/2015; 142(21):212301. DOI:10.1063/1.4916522 · 2.95 Impact Factor
  • Lorenz von Grafenstein · Martin Bock · Uwe Griebner · Thomas Elsaesser ·
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    ABSTRACT: We report a high-gain, cw-pumped regenerative amplifier which is based on Ho-doped crystals and seeded by a versatile broadband source emitting between 2050 and 2100 nm. The regenerative amplifier is implemented in a chirped-pulse amplification system operating at room temperature. Using Ho:YLF as gain medium, 1.1 mJ pulses with a 50 ps pulse duration and a 10 kHz repetition rate are generated at 2050 and 2060 nm, corresponding to an average power of 11 W. Using the same seed source, a 10 kHz Ho:YAG regenerative amplifier at 2090 nm is studied in the same configuration. In all cases the regenerative amplifier parameters are chosen to operate in a tunable single-energy regime without instabilities.
    Optics Express 06/2015; 23(11):14744. DOI:10.1364/OE.23.014744 · 3.49 Impact Factor
  • C. Somma · D. Morrill · G. Folpini · K. Reimann · M. Woerner · T. Elsaesser · K. Biermann ·
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    ABSTRACT: Using fully phase-resolved two-dimensional terahertz spectroscopy we study coherent intersubband Rabi oscillations in GaAs quantum wells. A strong terahertz field modifies particularly the phase of the nonlinearly emitted field during the Rabi oscillation.
  • Rene Costard · Tobias Tyborski · Benjamin P. Fingerhut · Thomas Elsaesser ·
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    ABSTRACT: Phosphate vibrations serve as local probes of hydrogen bonding and structural fluctuations of hydration shells around ions. Interactions of H2PO−4 ions and their aqueous environment are stud- ied combining femtosecond 2D infrared spectroscopy, ab-initio calculations, and hybrid quantum- classical molecular dynamics (MD) simulations. Two-dimensional infrared spectra of the symmet- ric (νS(PO−2)) and asymmetric (νAS(PO−2)) PO−2 stretching vibrations display nearly homogeneous lineshapes and pronounced anharmonic couplings between the two modes and with the δ(P-(OH)2) bending modes. The frequency-time correlation function derived from the 2D spectra consists of a predominant 50 fs decay and a weak constant component accounting for a residual inhomogeneous broadening. MD simulations show that the fluctuating electric field of the aqueous environment induces strong fluctuations of the νS(PO−2) and νAS(PO−2) transition frequencies with larger fre- quency excursions for νAS(PO−2). The calculated frequency-time correlation function is in good agreement with the experiment. The ν(PO−2) frequencies are mainly determined by polarization contributions induced by electrostatic phosphate-water interactions. H2PO−4 /H2O cluster calculations reveal substantial frequency shifts and mode mixing with increasing hydration. Predicted phosphate- water hydrogen bond (HB) lifetimes have values on the order of 10 ps, substantially longer than water-water HB lifetimes. The ultrafast phosphate-water interactions observed here are in marked contrast to hydration dynamics of phospholipids where a quasi-static inhomogeneous broadening of phosphate vibrations suggests minor structural fluctuations of interfacial water.
    The Journal of Chemical Physics 03/2015; 142(21):212406. DOI:10.1063/1.4914152 · 2.95 Impact Factor
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    ABSTRACT: Pulsed operation of standard 980-nm emitting single-spatial-mode high power diode lasers at multi-watt power levels is studied. Primary emission, short wavelength infrared emission, as well as the spatio-temporal evolution of the near field are recorded. This approach allows for the determination of the operation parameters during which single-mode operation is maintained. This gives limits of safe operation far beyond the standard specifications as well as information about the relevant degradation mechanisms in this regime. Reference experiments with a set of long-term operated devices reveal gradual aging signatures and the starting points of the relevant aging processes become detectable. They are compared with those obtained from the devices operated under pulsed conditions.
    Proceedings of SPIE - The International Society for Optical Engineering 03/2015; 9348. DOI:10.1117/12.2075896 · 0.20 Impact Factor
  • Martin Hempel · Jens W. Tomm · Fangyu Yue · Mauro Bettiati · Thomas Elsaesser ·
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    ABSTRACT: The infrared emission from 980-nm single-mode high power diode lasers is analyzed in the wavelength range from 0.8 to 7.0 μm. A pronounced short-wavelength infrared (SWIR) emission band with a maximum at 1.3 μm is found to originate from defect states located within the waveguide of the devices. The SWIR intensity is verified to represent a measure of the non-equilibrium carrier concentration in the waveguide, allowing for non-destructive waveguide mapping in spatially resolved detection schemes. The potential of this approach is demonstrated by measuring spatially resolved profiles of SWIR emission and correlating them with mid-wavelength infrared thermal emission along the cavity of devices undergoing repeated catastrophic optical damage. The enhancement of SWIR emission in the damaged parts of the cavity is due to a locally enhanced carrier density in the waveguide and allows for in situ analysis of the damage patterns. Moreover, spatial resolved SWIR measurements are a promising tool for device inspecting even in low-power operation regimes.
    Proceedings of SPIE - The International Society for Optical Engineering 03/2015; 9382:93821G. DOI:10.1117/12.2075859 · 0.20 Impact Factor
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    ABSTRACT: The interaction of intense femtosecond pulses with metals allows for generating ultrashort hard x-rays. In contrast to plasma theories, tunneling from the target into vacuum is introduced as electron generation step, followed by vacuum acceleration in the laser field and re-entrance into the target to generate characteristic x-rays and Bremsstrahlung. For negligible space charge in vacuum, the Kα flux is proportional to the incident intensity and the wavelength squared, suggesting a strong enhancement of the x-ray flux by mid-infrared driving pulses. This prediction is in quantitative agreement with experiments on femtosecond Cu Kα generation.
    Structural Dynamics 03/2015; 2(2):024102. DOI:10.1063/1.4915485
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    ABSTRACT: Third-order optical nonlinearities play a vital role for the generation and characterization of ultrashort optical pulses. One particular characterization method is frequency-resolved optical gating, which can be based on a large variety of third-order nonlinear effects. Any of these variants presupposes an instanta- neous temporal response, as it is expected off resonance. In this paper we show that resonant excitation of the third harmonic gives rise to surprisingly large decay times, which are on the order of the duration of the shortest oscillator pulses generated to date. To this end, we measured interferometric third-harmonic frequency-resolved optical gating traces in TiO2 and SiO2, corroborating polarization decay times up to 6.5 fs in TiO2. This effect is among the fastest effects observed in ultrafast spectroscopy. Numerical solutions of the time-dependent Schrödinger equation are in excellent agreement with experimental observations. Our work (experiments and simulations) corroborates that a noninstantaneous polarization decay may appear in the presence of a 3-photon resonance. In turn, pulse generation and characterization in the ultraviolet may be severely affected by this previously unreported effect.
    Optica 02/2015; 2(2):151 -157. DOI:10.1364/OPTICA.2.000151
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    ABSTRACT: Excitons play a key role for the optoelectronic properties of hybrid systems. We apply near-field scanning optical microscopy (NSOM) with a $100\,\text{-nm}$ spatial resolution to study the photoluminescence of surface excitons (SX) in a $20\,\text{nm}$ thick ZnO film capped with a monolayer of stearic acid molecules. Emission from SX, donor-bound (DX), and - at sample temperatures $T>20\,\text{K}$ - free (FX) excitons is separated in steady-state and time-resolved photoluminescence spectra. The $4\,\text{meV}$ broad smooth envelope of SX emission at $T<10\,\text{K}$ points to an inhomogeneous distribution of SX transition energies and spectral diffusion caused by diffusive SX transport on a $50\,\text{nm}$ scale with a SX diffusion coefficient of $D(T<10 K)=0.30\,\text{cm$^2$/s}$.
    Physical Review B 01/2015; 91(12). DOI:10.1103/PhysRevB.91.121415 · 3.74 Impact Factor
  • Martin Hempel · Jens Tomm · David Venables · Victor Rossin · Erik Zucker · Thomas Elsaesser ·

    Journal of Lightwave Technology 01/2015; DOI:10.1109/JLT.2015.2475605 · 2.97 Impact Factor
  • Thomas Elsaesser ·
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    ABSTRACT: Aufgrund der begrenzten Bindungsstärke von Wasserstoffbrücken unterliegen wässrige Systeme ultraschnellen strukturellen Fluktuationen im Zeitbereich zwischen 10–14 und 10–11 s. Schwingungsanregungen von Wasserstoffbrücken zerfallen ebenfalls in diesem Zeitbereich. Die mehrdimensionale Ultrakurzzeit-Infrarotspektroskopie erlaubt eine zeitaufgelöste Beobachtung dieser elementaren Dynamik in Wasser, hydratisierten DNA-Oligomeren und Phospholipiden. Neben Kopplungen zwischen Schwingungsfreiheitsgraden des hydratisierten Systems lässt sich die Wasserdynamik an Grenzflächen und im Volumen direkt aufzeichnen. Strukturelle Fluktuationen im Volumen von H2O treten im Zeitbereich zwischen 5×10–14 und 10–12 s auf, Wasserstoffbrücken werden im Takt von 10–12 s gebrochen und neu geformt. An den Grenzflächen zu DNA und Phospholipiden existieren Hydratisierungsgeometrien, die bei geringen Fluktuationen länger als 10–11 s aufrecht erhalten werden. Ein langlebiges ‘Gedächtnis’ des Wassers existiert jedoch nicht.Aqueous systems display ultrafast structural fluctuations in the time domain between 10–14 and 10–11 s, due to the limited strength of hydrogen bonds. Multidimensional ultrafast infrared spectroscopy allows for a time-resolved observation of such elementary dynamics in bulk water, DNA oligomers and phospholipids. Both the couplings of different vibrational degrees of the hydrated system and bulk water dynamics can be mapped directly. Structural fluctuations of bulk water occur in the time range between 5×10–14 and 10–12 s, the breaking and reformation of hydrogen bonds on a time scale of 10–12 s. At the interface between the water hydration shell and DNA or phospholipids, specific hydration geometries exist for periods of some 10–11 s with minor fluctuations of their structure. However, a long-lived 'memory of water' is absent.
    Chemie in unserer Zeit 12/2014; 49(1). DOI:10.1002/ciuz.201400678 · 0.26 Impact Factor
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    ABSTRACT: Ultrafast structural dynamics in the condensed phase represents a key topic of current physics, chemistry and materials science. Femtosecond hard X-ray pulses are important structure probes that have been applied in time-resolved X-ray absorption and diffraction(1-4). Optical pump/X-ray probe schemes with compact laser-driven table-top sources(5-11) have allowed for tiny changes of diffracted intensity to be measured with X-ray photon statistics, which has set the ultimate sensitivity limit(12-14). To address the strong quest for a higher X-ray flux, here we present the first hard X-ray plasma source driven by intense mid-infrared sub-100-fs pulses at 3.9 mu m. The comparably long optical period allows for accelerating electrons from the Cu target to very high kinetic energies and for generating a characteristic K alpha flux of 10(9) photons per pulse, 25 times more than with our 800 nm driver(9,10). Theoretical simulations account for the experimental results in a wide range of driving fields and predict a further enhancement of X-ray flux.
    Nature Photonics 12/2014; 8(12):927-930. DOI:10.1038/NPHOTON.2014.256 · 32.39 Impact Factor
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    R Grunwald · T Elsaesser · M Bock ·
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    ABSTRACT: Light carrying an orbital angular momentum (OAM) displays an optical phase front rotating in space and time and a vanishing intensity, a so-called vortex, in the center. Beyond continuous-wave vortex beams, optical pulses with a finite OAM are important for many areas of science and technology, ranging from the selective manipulation and excitation of matter to telecommunications. Generation of vortex pulses with a duration of few optical cycles requires new methods for characterising their coherence properties in space and time. Here we report a novel approach for flexibly shaping and characterising few-cycle vortex pulses of tunable topological charge with two sequentially arranged spatial light modulators. The reconfigurable optical arrangement combines interferometry, wavefront sensing, time-of-flight and nonlinear correlation techniques in a very compact setup, providing complete spatio-temporal coherence maps at minimum pulse distortions. Sub-7 fs pulses carrying different optical angular momenta are generated in single and multichannel geometries and characterised in comparison to zero-order Laguerre-Gaussian beams. To the best of our knowledge, this represents the shortest pulse durations reported for direct vortex shaping and detection with spatial light modulators. This access to space-time coupling effects with sub-femtosecond time resolution opens new prospects for tailored twisted light transients of extremely short duration.
    Scientific Reports 11/2014; 4:7148. DOI:10.1038/srep07148 · 5.58 Impact Factor
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    ABSTRACT: Near-field scanning optical microscopy (NSOM) is applied for analyzing GaN-based diode lasers. The measurements are carried out at the front facets of standard devices without any additional preparation. Four different schemes for luminescence and photocurrent detection are applied. The results allow for a detailed analysis of the epitaxial layer sequence, the waveguide mode, the impact of defect absorption, and efficiencies of carrier transfer into the quantum well. Moreover, the effective potential profile as formed by both layer structure and doping profile is imaged. Features being spatially separated by only 30 nm are safely resolved. Our results pave the way towards non-destructive nanoscopic analysis of wide-bandgap optoelectronic devices.
    Semiconductor Science and Technology 09/2014; 29(11):112001. DOI:10.1088/0268-1242/29/11/112001 · 2.19 Impact Factor
  • Martin Hempel · Jens W. Tomm · Fangyu Yue · Mauro A. Bettiati · Thomas Elsaesser ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Infrared emission from 980-nm single-mode high power diode lasers is recorded and analyzed in the wavelength range from 0.8 to 8.0 μm. A pronounced short-wavelength infrared (SWIR) emission band with a maximum at 1.3 μm originates from defect states located in the waveguide of the devices. The SWIR intensity is a measure of the non-equilibrium carrier concentration in the waveguide, allowing for a non-destructive waveguide mapping in spatially resolved detection schemes. The potential of this approach is demonstrated by measuring spatially resolved profiles of SWIR emission and correlating them with mid-wavelength infrared (MWIR) thermal emission along the cavity of devices undergoing repeated catastrophic optical damage. The enhancement of SWIR emission in the damaged parts of the cavity is due to a locally enhanced carrier density in the waveguide and allows for an analysis of the spatial damage patterns. The figure shows a side view of a diode laser during catastrophic degradation as recorded by a thermocamera within 5 successive current pulses. The geometry of the device is given in grayscale. The position of the laser chip is indicated by the dotted line. The thermal signatures of the internal degradation of the diode laser are overlaid in color. The bi-directional spread of the damage along the laser cavity is clearly visible.
    Laser & Photonics Review 09/2014; DOI:10.1002/lpor.201400045 · 8.01 Impact Factor

Publication Stats

11k Citations
1,375.74 Total Impact Points


  • 1994-2015
    • Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy
      Berlín, Berlin, Germany
  • 1983-2007
    • Technische Universität München
      • • Walter Schottky Institut (WSI)
      • • Faculty of Physics
      München, Bavaria, Germany
  • 2001-2004
    • Paul Drude Institute for Solid State Electronics
      Berlín, Berlin, Germany
  • 1998
    • AT&T Labs
      Austin, Texas, United States
  • 1983-1989
    • Deutsches Herzzentrum München
      München, Bavaria, Germany