Th. Udem

Publications (54)196.95 Total impact

• Source

  Available from: Ronald Holzwarth

  Article: Nonlinear amplification of side-modes in frequency combs

  R. A. Probst, T. Steinmetz, T. Wilken, H. Hundertmark, S. P. Stark, G. K. L. Wong, P. St. J. Russell, T. W. Hänsch, R. Holzwarth, Th. Udem
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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. · 3.59 Impact Factor
• Source

  Available from: ipv6.ppk.itb.ac.id

  Article: A 920-kilometer optical fiber link for frequency metrology at the 19th decimal place.

  K Predehl, G Grosche, S M F Raupach, S Droste, O Terra, J Alnis, Th Legero, T W Hänsch, Th Udem, R Holzwarth, H Schnatz
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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. · 31.20 Impact Factor
• Article: Frequency dependence of the fixed point in a fluctuating frequency comb

  D.R. Walker, Th. Udem, Ch. Gohle, B. Stein, T.W. Hänsch
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  ABSTRACT: We report measurements of the response of a Kerr-lens mode-locked Ti:sapphire frequency comb to pump power modulation. For each setting of the laser, the comb expands and contracts about a particular fixed point in frequency. We measured this fixed point and found that it is within 8% of our frequency comb’s center. In addition, we found that as we shift the comb’s center frequency, the fixed point follows to some extent. It follows that modulating the pump power mostly affects the comb’s group velocity, i.e., the repetition rate.
  Applied Physics B 04/2012; 89(4):535-538. · 2.19 Impact Factor
• Article: Femtosecond optical frequency combs

  Th. Udem, R. Holzwarth, Th. Hänsch
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  ABSTRACT: A laser frequency comb allows the conversion of the very rapid oscillations of visible light of some 100’s of THz down to frequencies that can be handled with conventional electronics. This capability has enabled the most precise laser spectroscopy experiments yet that allowed to test quantum electrodynamics, to determine fundamental constants and to search for possible slow changes of these constants. Using an optical frequency reference in combination with a laser frequency comb has made it possible to construct all optical atomic clocks, that are now outperforming even the best cesium atomic clocks. In future direct frequency comb spectroscopy might enable high resolution laser spectroscopy in the extreme ultraviolet for the first time. Frequency combs are also used to calibrate astronomical spectrographs and might reach an accuracy that is sufficient to observe the expansion of the universe in real time.
  The European Physical Journal Special Topics 04/2012; 172(1):69-79. · 1.56 Impact Factor
• Source

  Available from: Thomas Kuehl

  Article: Comment on: “Lorentz violation in high-energy ions” by Santosh Devasia

  G. Saathoff, S. Reinhardt, R. Holzwarth, T. W. Hänsch, Th. Udem, D. Bing, D. Schwalm, A. Wolf, S. Karpuk, G. Huber, C. Novotny, B. Botermann, C. Geppert, W. Nörtershäuser, T. Kühl, T. Stöhlker, G. Gwinner
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  ABSTRACT: In an article “Lorentz violation in high-energy ions” by S. Devasia published in this Journal [EPJ C 69, 343 (2010)], our recent Doppler shift experiments on fast ion beams are reanalyzed. Contrary to our analysis, Devasia concludes that our results provide an “indication of Lorentz violation”. We argue that this conclusion is based on a fundamental misunderstanding of our experimental scheme and reiterate that our results are in excellent agreement with Special Relativity.
  European Physical Journal C 04/2012; 71(3):1-2. · 3.63 Impact Factor
• Article: Sub-milliKelvin spatial thermometry of a single Doppler cooled ion in a Paul trap

  S. Knünz, M. Herrmann, V. Batteiger, G. Saathoff, T. W. Hänsch, Th. Udem
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  ABSTRACT: We report on observations of 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 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.
  03/2012;
• Source

  Available from: menlosystems.com

  Article: 14 GHz visible supercontinuum generation: calibration sources for astronomical spectrographs.

  S P Stark, T Steinmetz, R A Probst, H Hundertmark, T Wilken, T W Hänsch, Th Udem, P St J Russell, R Holzwarth
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  ABSTRACT: We report the use of a specially designed tapered photonic crystal fiber to produce a broadband optical spectrum covering the visible spectral range. The pump source is a frequency doubled Yb fiber laser operating at a repetition rate of 14 GHz and emitting sub-5 pJ pulses. We experimentally determine the optimum core diameter and achieve a 235 nm broad spectrum. Numerical simulations are used to identify the underlying mechanisms and explain spectral features. The high repetition rate makes this system a promising candidate for precision calibration of astronomical spectrographs.
  Optics Express 08/2011; 19(17):15690-5. · 3.59 Impact Factor
• Article: Hydrogen-deuterium isotope shift: From the 1S-2S-transition frequency to the proton-deuteron charge-radius difference

  U.D. Jentschura, A. Matveev, C.G. Parthey, J. Alnis, R. Pohl, Th. Udem, N. Kolachevsky, T.W. Hänsch
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  ABSTRACT: We analyze and review the theory of the hydrogen-deuterium isotope shift for the 1S-2S transition, which is one of the most accurately measured isotope shifts in any atomic system, in view of a recently improved experiment. A tabulation of all physical effects that contribute to the isotope shift is given. These include the Dirac binding energy, quantum electrodynamic effects, including recoil corrections, and the nuclear-size effect, including the pertaining relativistic and radiative corrections. From a comparison of the theoretical result Δfth=670 999 566.90(66)(60) kHz (exclusive of the nonrelativistic nuclear-finite-size correction) and the experimental result Δfexpt=670 994 334 605(15) Hz, we infer the deuteron-proton charge-radius difference 〈r2〉d-〈r2〉p=3.820 07(65) fm2 and the deuteron structure radius rstr=1.975 07(78) fm.
  Phys. Rev. A. 04/2011; 83(4).
• Source

  Available from: Thomas Kuehl

  Article: Comment on "Missing Transverse-Doppler Effect in Time-Dilation Experiments with High-Speed Ions"

  G. Saathoff, S. Reinhardt, R. Holzwarth, T W Hänsch, Th. Udem, D. Bing, D. Schwalm, A Wolf, S. Karpuk, G Huber, C. Novotny, B. Botermann, C. Geppert, W. Nörtershäuser, T Kühl, T. Stöhlker, G. Gwinner
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  ABSTRACT: In an article "Missing Transverse-Doppler Effect in Time-Dilation Experiments with High-Speed Ions" by S. Devasia [arXiv:1003.2970v1], our recent Doppler shift experiments on fast ion beams are reanalyzed. Contrary to our analysis, Devasia concludes that our results provide an "indication of Lorentz violation". We argue that this conclusion is based on a fundamental misunderstanding of our experimental scheme and reiterate that our results are in excellent agreement with Special Relativity.
  02/2011;
• Article: Injection locking of a trapped-ion phonon laser.

  S Knünz, M Herrmann, V Batteiger, G Saathoff, T W Hänsch, K Vahala, Th Udem
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  ABSTRACT: We report on injection locking of optically excited mechanical oscillations of a single, trapped ion. The injection locking dynamics are studied by analyzing the oscillator spectrum with a spatially selective Fourier transform technique and the oscillator phase with stroboscopic imaging. In both cases we find excellent agreement with theory inside and outside the locking range. We attain injection locking with forces as low as 5(1)×10{-24}  N so this system appears promising for the detection of ultraweak oscillating forces.
  Physical Review Letters 07/2010; 105(1):013004. · 7.37 Impact Factor
• Article: Two-photon direct frequency comb spectroscopy with chirped pulses

  S. Reinhardt, E. Peters, T. W. Hänsch, Th. Udem
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  ABSTRACT: Thanks to the high peak intensities of ultrashort pulse trains that make up an optical frequency comb, conversion to much shorter wavelengths is readily available. Therefore direct frequency comb spectroscopy may offer the possibility of extending high-resolution spectroscopy to spectral regions that are unexplored so far. In this work, we investigate the impact of a chirp, i.e., a varying frequency across the pulses, on the excitation rate obtainable with two-photon direct frequency comb spectroscopy. Using the cesium 6 2S1/2-8 2S1/2 two-photon transition at 822 nm, we show that destructive interference of various quantum paths reduces the excitation rate with the inverse of the time bandwidth product of the exciting pulses.
  Phys. Rev. A. 03/2010; 81(3).
• Article: A Peltier cooled single pass amplifier for Titanium:sapphire laser pulses

  A. Ozawa, W. Schneider, F. Najafi, T. W. Hänsch, Th. Udem, P. Hommelhoff
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  ABSTRACT: We report on a Peltier cooled single pass amplifier for high repetition rate Titanium:sapphire laser pulses. Pumped with 14 W and seeded with around 400 mW, the output reaches 1.1 W with good beam quality. This amplifier is very user-friendly, easy to maintain and set up and thus represents a device situated between more complicated liquid-nitrogen cooled amplifiers that can operate at higher pump power, and very simple near to room temperature amplifiers that can only be pumped with less power. In addition, we show the results of a finite element simulation on the temperature distribution in a liquid nitrogen cooled amplifier setup designed for highest output powers.
  Laser Physics 01/2010; 20(5):967-970. · 3.61 Impact Factor
• Article: A phonon laser

  K. Vahala, M. Herrmann, S. Kn|[uuml]|nz, V. Batteiger, G. Saathoff, T. W. H|[auml]|nsch, Th. Udem
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  ABSTRACT: Red-detuned laser pumping of an atomic resonance will cool the motion of an ion or atom. The complementary regime of blue-detuned pumping is investigated in this work using a single, trapped Mg+ ion interacting with two laser beams, tuned above and below resonance. Widely thought of as a regime of heating, theory and experiment instead show that stimulated emission of centre-of-mass phonons occurs, providing saturable amplification of the motion. A threshold for transition from thermal to coherent oscillating motion has been observed, thus establishing this system as a mechanical analogue to an optical laser—a phonon laser. Such a system has been sought in many different physical contexts.
  Nature Physics 08/2009; 5(9):682-686. · 18.97 Impact Factor
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  Available from: Guido Saathoff

  Article: Precision spectroscopy of the 3s-3p fine structure doublet in Mg+

  V. Batteiger, S. Knünz, M. Herrmann, G. Saathoff, H. A. Schüssler, B. Bernhardt, T. Wilken, R. Holzwarth, T W Hänsch, Th. Udem
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  ABSTRACT: We apply a recently demonstrated method for precision spectroscopy on strong transitions in trapped ions to measure both fine structure components of the 3s-3p transition in 24-Mg+ and 26-Mg+. We deduce absolute frequency reference data for transition frequencies, isotope shifts and fine structure splittings that are in particular useful for comparison with quasar absorption spectra, which test possible space-time variations of the fine structure constant. The measurement accuracy improves previous literature values, when existing, by more than two orders of magnitude.
  07/2009;
• Source

  Available from: nist.gov

  Article: A deep-UV optical frequency comb at 205 nm.

  E Peters, S A Diddams, P Fendel, S Reinhardt, T W Hänsch, Th Udem
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  ABSTRACT: By frequency quadrupling a picosecond pulse train from a Ti:sapphire laser at 820 nm we generate a frequency comb at 205 nm with nearly bandwidth-limited pulses. The nonlinear frequency conversion is accomplished by two successive frequency doubling stages that take place in resonant cavities that are matched to the pulse repetition rate of 82 MHz. This allows for an overall efficiency of 4.5 % and produces an output power of up to 70 mW for a few minutes and 25 mW with continuous operation for hours. Such a deep UV frequency comb may be employed for direct frequency comb spectroscopy in cases where it is less efficient to convert to these short wavelengths with continuous wave lasers.
  Optics Express 06/2009; 17(11):9183-90. · 3.59 Impact Factor
• Source

  Available from: Ronald Holzwarth

  Article: Testing the Stability of the Fine Structure Constant in the Laboratory

  N. Kolachevsky, A. Matveev, J. Alnis, C. Parthey, T. Steinmetz, T. Wilken, R. Holzwarth, Th. Udem, T. W. Haensch
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  ABSTRACT: In this review we discuss the progress of the past decade in testing for a possible temporal variation of the fine structure constant $\alpha$. Advances in atomic sample preparation, laser spectroscopy and optical frequency measurements led to rapid reduction of measurement uncertainties. Eventually laboratory tests became the most sensitive tool to detect a possible variation of $\alpha$ at the present epoch. We explain the methods and technologies that helped make this possible.
  05/2009;
• Article: Frequency metrology on single trapped ions in the weak binding limit: the 3s(1/2)-3p(3/2) transition in 24Mg+.

  M Herrmann, V Batteiger, S Knünz, G Saathoff, Th Udem, T W Hänsch
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  ABSTRACT: We demonstrate a method for precision spectroscopy on trapped ions in the limit of unresolved motional sidebands. By sympathetic cooling of a chain of crystallized ions, we suppress adverse temperature variations induced by the spectroscopy laser that usually lead to a distorted line profile and obtain a Voigt profile with negligible distortions. We applied the method to measure the absolute frequency of the astrophysically relevant D2 transition in single 24Mg+ ions and find 1 072 082 934.33(16) MHz, a nearly 400-fold improvement over previous results. Further, we find the excited state lifetime to be 3.84(10) ns.
  Physical Review Letters 02/2009; 102(1):013006. · 7.37 Impact Factor
• Chapter: High Resolution Wavelength Calibration: Advancements with the Laser Frequency Comb Development

  A. Manescau, C. Araujo-Hauck, L. Pasquini, M. T. Murphy, Th. Udem, T. W. Hänsch, R. Holzwarth, A. Sizmann, H. Dekker, S. D’Odorico
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  ABSTRACT: Wavelength calibration in high resolution spectroscopy is a key issue for the delivery of high quality science data. ESO and MPQ have agreed to develop a wavelength calibration unit demonstrator based on a Laser Frequency Comb, which in comparison with current standards will significantly improve calibration data. The status and next milestones are summarized.
  12/2008: pages 411-413;
• Chapter: High Harmonic Frequency Combs for High Resolution Spectroscopy

  A. Ozawa, J. Rauschenberger, Ch. Gohle, M. Herrmann, D. R. Walker, V. Pervak, A. Fernandez, A. Apolonski, R. Holzwarth, F. Krausz, T. W. Hänsch, Th Udem
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  ABSTRACT: Intracavity high harmonic generation is demonstrated in an external cavity, seeded by a Ti:sapphire mode-locked laser at a repetition rate of 10.8MHz. Harmonics up to 19th order at 43 nm were observed with plateau harmonics at the μW power level.
  12/2008: pages 843-845;
• Source

  Available from: Guido Saathoff

  Article: Frequency Metrology on single trapped ions in the weak binding limit: The 3s1/2-3p3/2 transition in 24-Mg+

  M. Herrmann, V. Batteiger, S. Knünz, G. Saathoff, Th. Udem, T W Hänsch
  [show abstract] [hide abstract]
  ABSTRACT: We demonstrate a method for precision spectroscopy on trapped ions in the limit of unresolved motional sidebands. By sympathetic cooling of a chain of crystallized ions we suppress adverse temperature variations induced by the spectroscopy laser that usually lead to a distorted line profle and obtain a Voigt profile with negligible distortions. We applied the method to measure the absolute frequency of the astrophysically relevant D2 transition in single 24-Mg+ ions and find 1072082934.33(16)MHz, a nearly 400fold improvement over previous results. Further, we find the excited state lifetime to be 3.84(10) ns. Comment: 4 pages, 5 figures
  08/2008;