Th. Udem

Max Planck Institute of Quantum Optics, Arching, Bavaria, Germany

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Publications (139)533.44 Total impact

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    ABSTRACT: We demonstrate the generation of broadband, visible astronomical frequency combs with flattened spectral envelopes. The flat-top region of the spectrum ranges from about 450 to 730 nm, at mode spacings of 18 and 25 GHz.
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    ABSTRACT: Waveform-stabilized laser pulses have revolutionized the exploration of the electronic structure and dynamics of matter by serving as the technological basis for frequency-comb and attosecond spectroscopy. Their primary sources, mode-locked titanium-doped sapphire lasers and erbium/ytterbium-doped fibre lasers, deliver pulses with several nanojoules energy, which is insufficient for many important applications. Here we present the waveform-stabilized light source that is scalable to microjoule energy levels at the full (megahertz) repetition rate of the laser oscillator. A diode-pumped Kerr-lens-mode-locked Yb:YAG thin-disk laser combined with extracavity pulse compression yields waveform-stabilized few-cycle pulses (7.7[thinsp]fs, 2.2 cycles) with a pulse energy of 0.15[thinsp][mu]J and an average power of 6[thinsp]W. The demonstrated concept is scalable to pulse energies of several microjoules and near-gigawatt peak powers. The generation of attosecond pulses at the full repetition rate of the oscillator comes into reach. The presented system could serve as a primary source for frequency combs in the mid infrared and vacuum UV with unprecedented high power levels.
    Nature Communications 05/2015; 6. DOI:10.1038/ncomms7988 · 11.47 Impact Factor
  • G Almog · M Scholz · W Weber · P Leisching · W Kaenders · Th Udem ·
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    ABSTRACT: We report on the development and characterization of continuous, narrow-band, and tunable laser systems that use direct second-harmonic generation from blue and green diode lasers with an output power level of up to 11.1 mW in the mid-ultraviolet. One of our laser systems was tuned to the mercury 61 S 0 → 63 P 1 intercombination line at 253.7 nm. We could perform Doppler-free saturation spectroscopy on this line and were able to lock our laser to the transition frequency on long time scales.
    The Review of scientific instruments 03/2015; 86(3):033110. DOI:10.1063/1.4915501 · 1.61 Impact Factor
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    ABSTRACT: We investigate a new scheme for astronomical spectrograph calibration using the laser frequency comb at the Solar Vacuum Tower Telescope on Tenerife. Our concept is based upon a single-mode fiber channel, that simultaneously feeds the spectrograph with comb light and sunlight. This yields nearly perfect spatial mode matching between the two sources. In combination with the absolute calibration provided by the frequency comb, this method enables extremely robust and accurate spectroscopic measurements. The performance of this scheme is compared to a sequence of alternating comb and sunlight, and to absorption lines from Earth's atmosphere. We also show how the method can be used for radial-velocity detection by measuring the well-explored 5-minute oscillations averaged over the full solar disk. Our method is currently restricted to solar spectroscopy, but with further evolving fiber-injection techniques it could become an option even for faint astronomical targets.
    New Journal of Physics 02/2015; 17(2). DOI:10.1088/1367-2630/17/2/023048 · 3.56 Impact Factor
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    ABSTRACT: We describe a novel method for providing geometrical on-axis access to an optical enhancement resonator through an on-axis aperture at one of its mirrors. A superposition of transverse modes in a stable degenerate resonator is used to form a field distribution which avoids the aperture and therefore exhibits small loss. Upon propagation in the resonator the modes acquire a different phase, and an on-axis intensity maximum is formed at a different position. We call this a quasi-imaging resonator, because it is related to imaging in the sense that a hole in the field distribution, exacted by the aperture, is reproduced after a resonator round trip.
    Journal of optics 02/2015; 17(2). DOI:10.1088/2040-8978/17/2/025609 · 2.06 Impact Factor
  • D. C. Yost · A Matveev · E. Peters · A Beyer · T. W. Haensch · Th. Udem ·
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    ABSTRACT: Quantum interference arising from spontaneous emission, or cross-damping, is an important yet frequently overlooked systematic in precision spectroscopy experiments which aim to determine a transition frequency with an uncertainty smaller than the natural linewidth. Here, we calculate the effects of such interference in two-photon frequency-comb spectroscopy using a perturbative approach and by integration of the density matrix equations. We then apply these techniques to the two-photon spectroscopy of the hydrogen 1S-3S transition currently being performed in our group. Depending on the detection geometry, we find distortions of the line shapes which can lead to systematic errors of similar to 1 kHz if such interference effects are ignored in the data analysis. This result is independent of whether a cw laser or frequency comb is used for the excitation. Finally, we propose a time-dependent detection scheme which, when used in conjunction with frequency-comb excitation, can mitigate the line distortions arising from such interference.
    Physical Review A 07/2014; 90(1-1). DOI:10.1103/PhysRevA.90.012512 · 2.81 Impact Factor
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    ABSTRACT: The solar spectrum is a primary reference for the study of physical processes in stars and their variation during activity cycles. In Nov 2010 an experiment with a prototype of a Laser Frequency Comb (LFC) calibration system was performed with the HARPS spectrograph of the 3.6m ESO telescope at La Silla during which high signal-to-noise spectra of the Moon were obtained. We exploit those Echelle spectra to study the optical integrated solar spectrum . The DAOSPEC program is used to measure solar line positions through gaussian fitting in an automatic way. We first apply the LFC solar spectrum to characterize the CCDs of the HARPS spectrograph. The comparison of the LFC and Th-Ar calibrated spectra reveals S-type distortions on each order along the whole spectral range with an amplitude of +/-40 m/s. This confirms the pattern found by Wilken et al. (2010) on a single order and extends the detection of the distortions to the whole analyzed region revealing that the precise shape varies with wavelength. A new data reduction is implemented to deal with CCD pixel inequalities to obtain a wavelength corrected solar spectrum. By using this spectrum we provide a new LFC calibrated solar atlas with 400 line positions in the range of 476-530, and 175 lines in the 534-585 nm range. The new LFC atlas improves the accuracy of individual lines by a significant factor reaching a mean value of about 10 m/s. The LFC--based solar line wavelengths are essentially free of major instrumental effects and provide a reference for absolute solar line positions. We suggest that future LFC observations could be used to trace small radial velocity changes of the whole solar photospheric spectrum in connection with the solar cycle and for direct comparison with the predicted line positions of 3D radiative hydrodynamical models of the solar photosphere.
    Astronomy and Astrophysics 10/2013; 560. DOI:10.1051/0004-6361/201322324 · 4.38 Impact Factor
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    ABSTRACT: We demonstrate the generation of broad spectra with a flat intensity distribution from originally highly structured supercontinua, obtained with femtosecond pulses in a photonic crystal fiber. This is accomplished by truncating the spectra at a constant level using a liquid crystal based spatial light modulator. The technique is useful for astronomical spectrograph calibration using frequency combs, where it allows to equalize the optical power of the calibration lines. This enables an improved calibration accuracy by maximizing each line’s signal-to-noise ratio.
    SPIE Optical Engineering + Applications; 09/2013
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    ABSTRACT: To compare the increasing number of optical frequency standards, highly stable optical signals have to be transferred over continental distances. We demonstrate optical-frequency transfer over a 1840-km underground optical fiber link using a single-span stabilization. The low inherent noise introduced by the fiber allows us to reach short term instabilities expressed as the modified Allan deviation of 2×10^{-15} for a gate time τ of 1 s reaching 4×10^{-19} in just 100 s. We find no systematic offset between the sent and transferred frequencies within the statistical uncertainty of about 3×10^{-19}. The spectral noise distribution of our fiber link at low Fourier frequencies leads to a τ^{-2} slope in the modified Allan deviation, which is also derived theoretically.
    Physical Review Letters 09/2013; 111(11):110801. DOI:10.1103/PhysRevLett.111.110801 · 7.51 Impact Factor
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    ABSTRACT: Coherently enhancing laser pulses in a passive cavity provides ideal conditions for high-order harmonic generation in a gas, with repetition rates around 100 MHz (refs 1,2,3). Recently, extreme-ultraviolet radiation with photon energies of up to 30 eV was obtained, which is sufficiently bright for direct frequency-comb spectroscopy at 20 eV (ref. 4). Here, we identify a route to scaling these radiation sources to higher photon energies. We demonstrate that the ionization-limited attainable intracavity peak intensity increases with decreasing pulse duration. By enhancing nonlinearly compressed pulses of an Yb-based laser and coupling out the harmonics through a pierced cavity mirror, we generate spatially coherent 108 eV (11.45 nm) radiation at 78 MHz. Exploiting the full potential of the demonstrated techniques will afford high-photon-flux ultrashort-pulsed extreme-ultraviolet sources for a number of applications in science and technology, including photoelectron spectroscopy, coincidence spectroscopy with femtosecond to attosecond resolution5, 6 and characterization of components and materials for nanolithography7.
    Nature Photonics 07/2013; 7(8):608-612. DOI:10.1038/nphoton.2013.156 · 32.39 Impact Factor
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    ABSTRACT: We investigate how suppressed modes in frequency combs are modified upon frequency doubling and self-phase modulation. We find, both experimentally and by using a simplified model, that these side-modes are amplified relative to the principal comb modes. Whereas frequency doubling increases their relative strength by 6 dB, the growth due to self-phase modulation can be much stronger and generally increases with nonlinear propagation length. Upper limits for this effect are derived in this work. This behavior has implications for high-precision calibration of spectrographs with frequency combs used for example in astronomy. For this application, Fabry-P´erot filter cavities are used to increase the mode spacing to exceed the resolution of the spectrograph. Frequency conversion and/or spectral broadening after non-perfect filtering reamplify the suppressed modes, which can lead to calibration errors.
    Optics Express 05/2013; 21(10):11670. DOI:10.1364/OE.21.011670 · 3.49 Impact Factor
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    ABSTRACT: We present two major advances of enhancement-cavity-based high-order harmonic generation (HHG). First, the generated extreme ultraviolet (XUV) radiation is coupled out collinearly through an on-axis opening in the mirror following the HHG focus. This minimizes the interaction of both the fundamental and the intracavity generated ra diation with the output coupler while simultaneously enabling a large enhancement and an output coupling efficiency that increases with the harmonic order. Second, we use the nonlinearly compressed pulses of an Yb-based laser to drive intracavity HHG allowing for a unique power regime combining short pulses with high average powers. Together, these advances overcome fundamental limitations of current enhancement cavity setups and extend intracavity HHG towards higher photon energies. In a proof-of-principle experiment we use a 3-kW and 78-MHz train of 54-fs to generate and couple out coherent sub-20 nm radiation.
    The European Physical Journal Conferences 03/2013; 41:10023-. DOI:10.1051/epjconf/20134110023
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    ABSTRACT: Following the development of the laser frequency comb which led to the 2005 Nobel Prize in Physics, we began investigating the possibility of using this novel technology for precise and accurate spectrograph calibration. A programme was begun, aimed at demonstrating the capabilities of laser frequency combs (LFC) when coupled to an astronomical spectrograph. In the last three years we have tested an LFC connected to HARPS at the 3.6-metre telescope in La Silla, the most precise spectrograph available. Here we show the very promising results obtained so far, and outline future activities, including the provision of an LFC system for routine operation with HARPS, to be offered to the community in the near future.
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    ABSTRACT: Laser frequency combs (LFC) provide a direct link between the radio frequency (RF) and the optical frequency regime. The comb-like spectrum of an LFC is formed by exact equidistant laser modes, whose absolute optical frequencies are controlled by RF-references such as atomic clocks or GPS receivers. While nowadays LFCs are routinely used in metrological and spectroscopic fields, their application in astronomy was delayed until recently when systems became available with a mode spacing and wavelength coverage suitable for calibration of astronomical spectrographs. We developed a LFC based calibration system for the high-resolution echelle spectrograph at the German Vacuum Tower Telescope (VTT), located at the Teide observatory, Tenerife, Canary Islands. To characterize the calibration performance of the instrument, we use an all-fiber setup where sunlight and calibration light are fed to the spectrograph by the same single-mode fiber, eliminating systematic effects related to variable grating illumination.
    Proceedings of SPIE - The International Society for Optical Engineering 09/2012; 8450. DOI:10.1117/12.926224 · 0.20 Impact Factor
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    ABSTRACT: Optical clocks show unprecedented accuracy, surpassing that of previously available clock systems by more than one order of magnitude. Precise intercomparisons will enable a variety of experiments, including tests of fundamental quantum physics and cosmology and applications in geodesy and navigation. Well-established, satellite-based techniques for microwave dissemination are not adequate to compare optical clocks. Here, we present phase-stabilized distribution of an optical frequency over 920 kilometers of telecommunication fiber. We used two antiparallel fiber links to determine their fractional frequency instability (modified Allan deviation) to 5 × 10(-15) in a 1-second integration time, reaching 10(-18) in less than 1000 seconds. For long integration times τ, the deviation from the expected frequency value has been constrained to within 4 × 10(-19). The link may serve as part of a Europe-wide optical frequency dissemination network.
    Science 04/2012; 336(6080):441-4. DOI:10.1126/science.1218442 · 33.61 Impact Factor
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    ABSTRACT: We report on observations of the thermal motion of a single, Doppler-cooled ion along the axis of a linear radio-frequency quadrupole trap. We show that for a harmonic potential the thermal occupation of energy levels leads to a Gaussian distribution of the ion's axial position. The dependence of the spatial thermal spread on the trap potential is used for precise calibration of our imaging system's point spread function and sub-millikelvin thermometry. We employ this technique to investigate the laser detuning dependence of the Doppler temperature.
    Physical Review A 02/2012; 85(2):023427. DOI:10.1103/PhysRevA.85.023427 · 2.81 Impact Factor
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    ABSTRACT: Optical frequency transmission via phase-stabilized telecommunication fiber is currently the most precise technique available for disseminating frequencies. We summarize some key advances, results and applications for fiber networks spanning up to 1000 km.
    European Frequency and Time Forum (EFTF), 2012; 01/2012
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    ABSTRACT: We reference high-precision spectroscopy on atomic hydrogen measured with an uncertainty of 4×10-15 to a remote Cs-fountain clock using a 920 km actively noise-compensated fiber link.
    Lasers and Electro-Optics (CLEO), 2012 Conference on; 01/2012
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    ABSTRACT: We report the status of an experimental test of time dilation in Special Relativity. This is accomplished by simultaneously measuring the forward and backward Doppler shifts of an electronic transition of fast moving ions, using high-precision laser spectroscopy. From these two Doppler shifts both the ion velocity β = v/c and the time dilation factor &; can be derived. From measurements based on saturation spectroscopy on lithium ions stored at β = 0.03 and β = 0.06 in the TSR heavy-ion storage ring, we achieved an upper limit for a O[β 2] deviation from Special Relativity of &;. In recent measurements on a β = 0.34 Li+ beam in the ESR storage ring we used optical-optical double-resonance spectroscopy which, in combination with the TSR result, gives improved sensitivity on the O[β 4] term of &;. We discuss current limitations and possible improvements that promise an enhancement of the sensitivity by at least one order of magnitude in the future.
    Journal of Physics Conference Series 09/2011; 312(10). DOI:10.1088/1742-6596/312/10/102014

Publication Stats

7k Citations
533.44 Total Impact Points


  • 1998-2014
    • Max Planck Institute of Quantum Optics
      • Division of Laser Spectroscopy
      Arching, Bavaria, Germany
  • 2001-2005
    • Ludwig-Maximilian-University of Munich
      • Department of Physics
      München, Bavaria, Germany
  • 2003
    • National Institute of Advanced Industrial Science and Technology
      Tsukuba, Ibaraki, Japan
    • Vienna University of Technology
      • Institute of Photonics
      Vienna, Vienna, Austria
  • 2001-2002
    • National Institute of Standards and Technology
      • Time and Frequency Division
      Gaithersburg, MD, United States
  • 1998-1999
    • Tokyo Institute of Technology
      Edo, Tōkyō, Japan