[Show abstract][Hide abstract] ABSTRACT: A suitable femtosecond (fs) laser system can provide a broad band comb of stable optical frequencies and thus can serve as
an rf/optical coherent link. In this way we have performed a direct comparison of the 1S—2S transition in atomic hydrogen at 121 nm with a cesium fountain clock, built at the LPTF/Paris, to reach an accuracy of 1.9×10-14. The same comb-line counting technique was exploited to determine and recalibrate several important optical frequency standards.
In particular, the improved measurement of the Cesium D1 line is necessary for a more precise determination of the fine structure constant. In addition, several of the best-known
optical frequency standards have been recalibrated via the fs method. By creating an octave-spanning frequency comb a single-laser
frequency chain has been realized and tested.
[Show abstract][Hide abstract] ABSTRACT: We review advances in optical precision spectroscopy of atomic hydrogen achieved at Garching and Paris since the first symposium
on the Hydrogen Atom at Pisa in 1988. The work at Garching has been focused on measurements of the 1S—2S and 2S—4S two-photon transitions in atomic hydrogen and on the isotope shift between hydrogen and deuterium. The Paris experiments
have been directed at the 1S—3S and 2S—nS/nD transitions. A general least squares adjustment combining different measurements yields the currently most precise values
for the Rydberg constant and the Lamb shift of the 1S ground state.
[Show abstract][Hide abstract] ABSTRACT: Absolute frequency measurements of a transportable optical frequency standard based on a He-Ne/CH4 laser at lambda = 3.39 mum stabilized on the central 7-6 component of the hyperfine structure of the F2(2) methane absorption line were made. For the first time, two different phase-coherent frequency chains based on the femtosecond comb technology and a transportable cesium fountain clock were used in the experiment.
[Show abstract][Hide abstract] ABSTRACT: A frequency comparison and an absolute frequency measurement of iodine stabilized frequency-doubled Nd:YAG lasers at 532 nm has been performed at the Max-Planck-Institute for Quantum Optics. Two independent I2-stabilized laser systems, one assembled at the Institute of Laser Physics, Novosibirsk, Russia, the other at the Physikalisch-Technische Bundesanstalt, Braunschweig, Germany were investigated. Using a phase-coherent frequency chain, the absolute frequency of the I2-stabilized lasers has been compared to a CH4-stabilized He–Ne laser at 3.39 μm which has been calibrated against an atomic cesium fountain clock. A new value for the R(56)32-0:a10 component, recommended by the Comit International des Poids et Mesures for the realization of the meter [Metrologia 30 (1993/1994) 523; Metrologia 36 (1999) 211], has been obtained with reduced uncertainty. Improved absolute frequency values of the R(56)32-0 and P(54)32-0 iodine absorption lines together with the hyperfine line separations are presented.
Lecture Notes in Physics 06/2001; 192(3-6-192):263-272. DOI:10.1016/S0030-4018(01)01190-7
[Show abstract][Hide abstract] ABSTRACT: We report on an absolute frequency measurement of the 1S-2S two-photon transition frequency in atomic hydrogen. In our experiment, we have directly linked the transition frequency to a cesium atomic clock. A careful analysis of the spectroscopic line-shape by means of a theoretical model allowed the determination of the line center to about 1/100 of the linewidth, yielding a value for the 1S-2S transition frequency of 2 466 061 413 187 103(46) Hz. .
[Show abstract][Hide abstract] ABSTRACT: Single laser-cooled ions stored in radiofrequency traps are the atomic systems which allow the high- est resolution in optical or microwave spectroscopy. A narrow transition in such an ion can serve as a reference for a frequency standard of extremely high accuracy and stability. In view of this application we study the 5 s 2 1 S 0 -5 s 5 p 3 P 0 clock transition in a single trapped 115 In + ion at a wavelength of 237 nm (1). This transition is highly immune to systematic frequency shifts. A frequency control at the millihertz level is expected leading to a residual relative uncertainty at the level of 10 -18 . For realizing the standard it is necessary to compare its abso- lute frequency to other known frequencies, at best to the present primary frequency standard, the cesium atomic clock. We report on the comparison of the In + clock transition to a methane-stabilized He-Ne laser at 3.39 μ m. This laser was calibrated before the measurement against an atomic cesium fountain clock. A frequency gap of 37 THz at the fourth harmonic of the He-Ne standard was bridged by a frequency comb generated by a mode- locked femtosecond laser. The frequency of the clock transition was determined to 1267402452899.92 (0.23) kHz where the accuracy of the measurement is limited by the uncertainty of the He-Ne standard.
[Show abstract][Hide abstract] ABSTRACT: The absolute frequency of the In(+) 5s(2) (1)S(0)5s5p (3)P(0) clock transition at 237 nm was measured with an accuracy of 1.8 parts in 10(13). Using a phase-coherent frequency chain, we compared the (1)S(0)(3)P(0) transition with a methane-stabilized HeNe laser at 3.39 microm, which was calibrated against an atomic cesium fountain clock. A frequency gap of 37 THz at the fourth harmonic of the HeNe standard was bridged by a frequency comb generated by a mode-locked femtosecond laser. The frequency of the In(+) clock transition was found to be 1,267,402,452,899.92 (0.23) kHz, the accuracy being limited by the uncertainty of the HeNe laser reference. This result represents an improvement in accuracy of more than 2 orders of magnitude over previous measurements of the line and now stands as what is to our knowledge the most accurate measurement of an optical transition in a single ion.s.
[Show abstract][Hide abstract] ABSTRACT: For more than a century, precise optical spectroscopy of atoms and molecules has played a central role in the discovery of the laws of quantum physics, in the determination of fundamental constants, and in the realization of standards for time, frequency, and length. The advent of highly monochromatic tunable lasers and techniques for nonlinear Doppler-free spectroscopy in the early seventies had a dramatic impact on the field of precision spectroscopy [1, 2]. Today, we are able to observe extremely narrow optical resonances in cold atoms or single trapped ions, with resolutions ranging from 10-,to 10-,, so that it might ultimately become possible to measure the line center of such a resonance to a few parts in 10,. Laboratory experiments searching for slow changes of fundamental constants would then reach unprecedented sensitivity. A laser locked to a narrow optical resonance could serve as a highly stable oscillator for a future all-optical atomic clock that can satisfy the growing demands of optical-frequency metrology, fiber optical telecommunication, or navigation. However, until recently there was no reliable optical "clockwork" available that could provide a link between optical frequencies of hundreds of THz and the microwave fre-quency of current atomic clocks based on the 9 GHz hyperfine resonance in atomic cesium. (*) http://www. mpq. mpg. de c Societ`a Italiana di Fisica
[Show abstract][Hide abstract] ABSTRACT: We have used the comb of optical frequencies emitted by a mode-locked laser as a ruler to measure frequency differences of
up to 45.2 THz between two laser signals. We have shown that the modes are distributed uniformly in frequency space within
the experimental limit of 3.0 parts in 1017, and that the mode separation equals the pulse repetition rate within an experimental limit of 6.0 parts in 1016. We have used this comb to bridge a frequency mismatch of 18.4 THz for an absolute optical frequency measurement of the cesium
1 line at 335 THz (895 nm) by comparison with the fourth harmonic of a methane-stabilized He-Ne Laser at 88.4THz (3.39 m).
Bridging a frequency gap of 45.2THz, we could demonstrate for the first time a new type of frequency chain that is based on
the measurement of frequency differences between laser harmonics. With this type of apparatus we have also measured the absolute
frequency of the hydrogen 1S 2S transition at 2466 THz (121 nm) in a direct comparison with the output signal from a commercial cesium atomic clock.
[Show abstract][Hide abstract] ABSTRACT: We have performed an absolute optical frequency measurement of the cesium D2 line at 352 THz (852 nm). This frequency is an important scaling parameter in atomic interferometry. The D2 line has been compared with the fourth harmonic of a methane stabilized He-Ne laser at 88.4 THz (3.39 μm). A frequency mismatch of 1.78 THz between 4×88.4 THz=354 THz and the D2 line was bridged with an optical frequency comb generator. We find fD2=351725718.50(11) MHz for the hyperfine centroid, improving previous results by almost two orders of magnitude.
Physical Review A 08/2000; 62(3). DOI:10.1103/PhysRevA.62.031801 · 2.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report on an absolute frequency measurement of the hydrogen 1S-2S two-photon transition in a cold atomic beam with an accuracy of 1.8 parts in 10(14). Our experimental result of 2 466 061 413 187 103(46) Hz has been obtained by phase coherent comparison of the hydrogen transition frequency with an atomic cesium fountain clock. Both frequencies are linked with a comb of laser frequencies emitted by a mode locked laser.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate a versatile new technique that provides a phase coherent link between optical frequencies and the radio frequency domain. The regularly spaced comb of modes of a mode-locked femtosecond laser is used as a precise ruler to measure a large frequency gap between two different multiples (harmonics or subharmonics) of a laser frequency. In this way, we have determined a new value of the hydrogen 1S-2S two-photon resonance, f(1S-2S) = 2 466 061 413 187.29(37) kHz, representing now the most accurate measurement of an optical frequency.
[Show abstract][Hide abstract] ABSTRACT: Summary form only given. The periodic pulse train emitted by a
modelocked femtosecond laser can be viewed in the frequency domain as a
comb of equidistant modes spaced by the pulse repetition rate. This
broad frequency comb can be used like a ruler to phase coherently
measure large differences between laser frequencies. With our Kerr-lens
mode-locked Ti:sapphire laser (pulselength 73 fs, Coherent Inc., model
Mira 900) we have shown that the modes of the femtosecond frequency comb
are distributed uniformly in frequency space within the experimental
Lasers and Electro-Optics, 2000. (CLEO 2000). Conference on; 02/2000
[Show abstract][Hide abstract] ABSTRACT: We have shown that the modes of a femtosecond mode-locked laser
are distributed uniformly in frequency space and can be used like a
ruler to measure large optical frequency differences. To measure
absolute optical frequencies we use nonlinear optics for the conversion
into a large frequency interval. Unlike the complex harmonic frequency
chains used in the past this new approach uses only a few laser sources
(ideally just one) and is nevertheless capable of measuring almost any
optical frequency with the same set up. We applied the new technique to
determine the absolute frequencies of the cesium D<sub>1</sub> line at
335 THz, of several components in I<sub>2</sub> around 563 THz, the
</sup>P<sub>0</sub> transition at 1267 THz and the hydrogen 1S-2S
transition at 2466 THz
[Show abstract][Hide abstract] ABSTRACT: We have determined the frequency of the a1 component of the P(54)32-0 transition of molecular iodine with an estimated relative standard uncertainty below 1·10-11 using a phase-coherent optical frequency chain from the CH4 frequency standard to the visible. This allows the realisation of the meter by visible frequencies with an uncertainty reduced by more than one order of magnitude compared to previous measurements (1999)
[Show abstract][Hide abstract] ABSTRACT: Summary form only given. The reciprocal relationship between time and frequency implies that a single short laser pulse has a broad spectrum. A pulse circulating inside a laser cavity or the periodic pulse train if a mode-locked laser, however, can be described as a coherent superposition of discrete laser modes. This frequency-domain comb of modes is now providing an elegant and universal solution to the long challenging problem of how to measure the frequency of light. In a Kerr-lens mode-locked Ti:sapphire laser, each mode is injection locked by modulation sidebands of the other modes via a nonlinear refractive index. Any mode must follow this collective dictate and oscillate in precise lock-step, or it will suffer high round trip losses in a properly designed cavity. We have demonstrated experimentally that the teeth of such a frequency comb are precisely equally spaced to within a few parts in 1018, and that their spacing is exactly given by the pulse repetition rate.
[Show abstract][Hide abstract] ABSTRACT: Solar eclipses have been reported to have a strange influence on the behaviour of atomic clocks and pendulums, which has been attributed to some unknown feature of gravity. Here we correct this idea after being unable to detect any anomalous changes in the relative rates of three types of atomic clock, based on the ground-state hyperfine transitions of hydrogen, rubidium and caesium, during the solar eclipse of 11 August 1999 over central Europe.
[Show abstract][Hide abstract] ABSTRACT: We have stabilized the modes of a comb of optical frequencies emitted by a mode-locked femtosecond-laser and used it as a ruler to measure differences of up to 45.2 THz between laser frequencies in a new type of frequency chain. Directly converting optical to radio frequencies, we have used it for an absolute frequency measurement of the 1S–2S transition in the hydrogen atom. Here, an intuitive model of the comb's properties is given and essential techniques for its stabilization and efficient detection of beat signals are presented.
[Show abstract][Hide abstract] ABSTRACT: We have measured the absolute frequency of the 115In+ 5s21S0–5s5p3P0 clock transition at 236.5 nm with an accuracy of 3.3 parts in 1011. For this measurement, a frequency synthesis chain was used which links the indium clock transition to a methane-stabilized He–Ne laser at 3.39 μm and a Nd:YAG laser at 1064 nm whose second harmonic was locked to a hyperfine component in molecular iodine. A frequency gap in the chain of 1.43 THz at 850 nm was bridged with the help of an optical frequency comb generator. The frequency of the 115In+ clock transition was determined to 1267402452914(41) kHz, where the accuracy is limited by the uncertainty of the iodine reference. This measurement represents an improvement of more than three orders of magnitude in accuracy compared to previous measurements of the line.