Thomas Elsaesser

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

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Publications (529)1382.78 Total impact

  • Biswajit Guchhait · Yingliang Liu · Torsten Siebert · Thomas Elsaesser
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    ABSTRACT: DNA oligomers are studied at 0% and 92% relative humidity, corresponding to N < 2 and N > 20 water molecules per base pair. Two-dimensional (2D) infrared spectroscopy of DNA backbone modes between 920 and 1120 cm−1 maps fluctuating interactions at the DNAsurface. At both hydration levels, a frequency fluctuation correlation function with a 300 fs decay and a slow decay beyond 10 ps is derived from the 2D lineshapes. The fast component reflects motions of DNA helix, counterions, and water shell. Its higher amplitude at high hydration level reveals a significant contribution of water to the fluctuating forces. The slow component reflects disorder-induced inhomogeneous broadening.
    No preview · Article · Jul 2016 · Structural Dynamics
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    ABSTRACT: Nonlinear dynamics of continuous-wave pumped regenerative amplifiers operating at 2 μm are investigated. At repetition rates near 1 kHz, three different operation regimes are observed, including stable regular, chaotic, and subharmonic dynamics. Numerical simulations reproduce this behavior in a quantitative way. In particular, we find stable periodic doubling regimes in which every other seed pulse experiences high gain. Exploiting a narrow parameter window beyond the onset of chaos enables operation of a high-gain picosecond Ho:YLF regenerative amplifier which delivers up to 16 mJ picosecond pulses at 2050 nm. Energy fluctuations of the 700 Hz pulse train are as low as 0.9% rms.
    No preview · Article · Jan 2016 · Laser & Photonics Review
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    ABSTRACT: A 2.051-mu m laser source delivering picosecond pulses with energies as high as 34 mJ at a 1 kHz repetition rate is reported. The main amplifier system is based on Ho:YLF and consists of a regenerative amplifier (RA) and a single-pass booster amplifier running at room temperature. The continuous-wave pumped, high-gain RA produces pulse trains with up to 10-mJ energy when operating in a stable periodic doubling regime. The recorded complete RA bifurcation diagram agrees well with our numerical simulations. At the highest pulse energy after the booster amplifier the pulse-to-pulse fluctuations are as low as 0.9% rms. Pulse compression is performed up to the 10-mJ level resulting in a duration of 37 ps. (C) 2015 Optical Society of America
    No preview · Article · Dec 2015 · Optics Express
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    ABSTRACT: Single-spatial mode lasers emitting at 980 nm are studied during continuous-wave long-term operation and ultra-high power short-term operation (stress-test) up to 13.5 W. We find that both tests eventually activate the same degradation mechanism, namely internal catastrophic optical damage. In the case of ultra-high power operation, we show that the mechanism that initializes this effect is a lateral widening of the optical mode, resulting in increased absorption outside the waveguide. Defects formed during long-term aging may eventually lead to the same effect. Stress testing allows for activation of several degradation mechanisms in a device one after the other and for distinguishing between mechanisms induced by aging and independent ones. Stress tests could pave the way toward more time-efficient testing, e.g., for comparison of different technology variants in development.
    No preview · Article · Nov 2015 · Journal of Lightwave Technology
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    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.
    No preview · Article · Sep 2015 · Physical Review Letters
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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.
    No preview · Article · Aug 2015 · Physical Review B
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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.
    No preview · Article · Jul 2015 · Optics Letters
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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.
    No preview · Article · Jul 2015 · Semiconductor Science and Technology
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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.
    Full-text · Article · Jun 2015 · The Journal of Physical Chemistry B
  • 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.
    No preview · Article · Jun 2015 · The Journal of Chemical Physics
  • 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.
    No preview · Article · Jun 2015 · Optics Express
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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.
    No preview · Article · May 2015
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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.
    No preview · Article · Mar 2015 · The Journal of Chemical Physics
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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.
    No preview · Article · Mar 2015 · Proceedings of SPIE - The International Society for Optical Engineering
  • 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.
    No preview · Article · Mar 2015 · Proceedings of SPIE - The International Society for Optical Engineering
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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.
    Full-text · Article · Mar 2015 · Structural Dynamics
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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.
    Full-text · Article · Feb 2015 · Optica
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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$/s}$.
    Full-text · Article · Jan 2015 · Physical Review B
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    ABSTRACT: We review the photogalvanic effect (PGE) in poled media as a ratchet type directed transport of photogenerated carriers in the absence of other external bias. We demonstrate that besides the perturbative regime involving multiphoton absorption which has exclusively been addressed previously, the PGE can also proceed through field induced tunneling, also termed dynamic Zener tunneling. The demonstration was done in a high optical gap crystal, the ferroelectric LiNbO3, with intense short THz pulses using two dimensional THz spectroscopy.
    No preview · Article · Jan 2015 · Romanian Reports in Physics
  • 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.
    No preview · Article · Dec 2014 · Chemie in unserer Zeit

Publication Stats

11k Citations
1,382.78 Total Impact Points

Institutions

  • 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