Accurate measurement of large optical frequency differences with a mode-locked laser

Udem, Th.; Reichert, J.; Holzwarth, Ronald; Hänsch, Theodor W.

doi:10.1364/ol.24.000881

Cited by 378 publications

(131 citation statements)

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“…The recent introduction of phase-stabilized, widebandwidth frequency combs based on modelocked femtosecond lasers has provided a direct connection between these two domains (3,4). Many laboratories have constructed frequency combs that establish optical frequency markers directly linked to a microwave or optical standard, covering a variety of spectral intervals.…”

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confidence: 99%

United Time-Frequency Spectroscopy for Dynamics and Global Structure

Marian

Stowe

Lawall

et al. 2004

Science

264

195

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Ultrashort laser pulses have thus far been used in two distinct modes. In the time domain, the pulses have allowed probing and manipulation of dynamics on a subpicosecond time scale. More recently, phase stabilization has produced optical frequency combs with absolute frequency reference across a broad bandwidth. Here we combine these two applications in a spectroscopic study of rubidium atoms. A wide-bandwidth, phase-stabilized femtosecond laser is used to monitor the real-time dynamic evolution of population transfer. Coherent pulse accumulation and quantum interference effects are observed and well modeled by theory. At the same time, the narrow linewidth of individual comb lines permits a precise and efficient determination of the global energy-level structure, providing a direct connection among the optical, terahertz, and radio-frequency domains. The mechanical action of the optical frequency comb on the atomic sample is explored and controlled, leading to precision spectroscopy with an appreciable reduction in systematic errors.Ultrashort laser pulses have given a remarkably detailed picture of photophysical dynamics. In studies of alkali atoms (1) and diatomics (2) in particular, coherent wave packet motion has been observed and even actively controlled. However, the broad bandwidth of these pulses has prevented a simultaneous high-precision measurement of state energies. At the expense of losing any direct observation or control of coherent dynamics, precision spectroscopy enabled by continuous wave (cw) lasers has been one of the most important fields of modern scientific research, providing the experimental underpinning of quantum mechanics and quantum electrodynamics.This trade-off between the time and frequency domains might seem fundamental, but in fact it results from pulse-to-pulse phase fluctuations in laser operation. The recent introduction of phase-stabilized, widebandwidth frequency combs based on modelocked femtosecond lasers has provided a direct connection between these two domains (3, 4). Many laboratories have constructed frequency combs that establish optical frequency markers directly linked to a microwave or optical standard, covering a variety of spectral intervals. Atomic and molecular structural information can now be probed over a broad spectral range, with vastly improved measurement precision and accuracy enabled by this absolute frequency-based approach (5). One of the direct applications is the development of optical atomic clocks (6-8). To date, however, traditional cw laserbased spectroscopic approaches have been essential to all of these experiments, with frequency combs serving only as reference rulers (9).Here we take advantage of the phasestable femtosecond pulse train to bridge the fields of high-resolution spectroscopy and ultrafast dynamics. This approach of direct frequency comb spectroscopy (DFCS) uses light from a comb of appropriate structure to directly interrogate a multitude of atomic levels and to study time-dependent quantum coherence. DFCS allows time-resol...

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confidence: 99%

United Time-Frequency Spectroscopy for Dynamics and Global Structure

Marian

Stowe

Lawall

et al. 2004

Science

264

195

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“…Kerr-lens mode-locked femtosecond lasers emit a periodic train of short pulses. The spectrum of this emission corresponds to a comb of distinct modes, that are exactly equally spaced due to the strong and fast Kerr-lens mode-coupling mechanism [1]. Any external signal with frequency ν i within the comb spectrum can be related to a suitable comb mode by detection of the beat-note frequency ∆ i ,…”

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confidence: 99%

“…The development of optical frequency comb generators based on Kerr-lens mode-locked femtosecond lasers [1,2] has enormously stimulated the field of optical frequency synthesis and metrology. Using this technique, the absolute frequencies of a number of narrow transitions in cold atoms or single stored ions such as H, Ca, Yb + or Hg + have been measured by phase-coherently linking those signals to primary cesium-clock controlled hydrogen masers [3][4][5][6].…”

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confidence: 99%

Ultraprecise Measurement of Optical Frequency Ratios

Stenger¹,

Schnatz²,

Tamm³

et al. 2002

Phys. Rev. Lett.

136

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We developed a novel technique for frequency measurement and synthesis, based on the operation of a femtosecond comb generator as transfer oscillator. The technique can be used to measure frequency ratios of any optical signals throughout the visible and near-infrared part of the spectrum. Relative uncertainties of 10 −18 for averaging times of 100 s are possible. Using a Nd:YAG laser in combination with a nonlinear crystal we measured the frequency ratio of the second harmonic νSH at 532 nm to the fundamental ν0 at 1064 nm, νSH/ν0 = 2.000 000 000 000 000 001 × (1 ± 7 × 10 −19 ).The development of optical frequency comb generators based on Kerr-lens mode-locked femtosecond lasers [1,2] has enormously stimulated the field of optical frequency synthesis and metrology. Using this technique, the absolute frequencies of a number of narrow transitions in cold atoms or single stored ions such as H, Ca, Yb + or Hg + have been measured by phase-coherently linking those signals to primary cesium-clock controlled hydrogen masers [3][4][5][6]. The measurement instabilities approached those of the hydrogen masers, indicating that neither the optical frequency standards nor the frequency combs themselves were limiting parts of the setups.Any absolute frequency measurement is finally limited by the frequency instability of the device realizing the unit of frequency, Hertz, such as a radio or microwave reference like the hydrogen maser. A possibility to avoid this limitation is the measurement of optical frequency ratios, which are unitless. Thus, frequency ratios for oscillators with better stability than that of the radio or microwave reference can be determined with smaller uncertainty than the absolute frequencies if a technique is available to realize the frequency ratio without introducing additional noise.Such a technique is the transfer oscillator concept, which has been realized with a harmonic frequency chain [7]. However, the measured frequency ratios were restricted to small integer numbers. In this Letter, we describe a novel technique based on the operation of a femtosecond frequency comb generator as a transfer oscillator. Our technique has the capability of generating arbitrary ratios of any optical frequencies throughout the visible and near-infrared part of the spectrum, while frequency fluctuations of the comb modes do not enter the measurement but cancel out.We demonstrate the superior short-term instability by two measurements: first, we measured the frequency ratio of signals from a single-Yb + -ion frequency standard [8] and from an I 2 -frequency-stabilized Nd:YAG laser [9]. Second, we used the Nd:YAG laser and measured the frequency ratio of the second harmonic at 532 nm to its fundamental at 1064 nm, thereby testing how accurately the 2:1 frequency ratio is realized by second harmonic generation. We demonstrate the capability of our technique of frequency-ratio measurements with relative uncertainty better than 10 −18 . Kerr-lens mode-locked femtosecond lasers emit a periodic train of short pulses. The...

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“…Frequency comb generators based on Kerr-lens modelocked femtosecond lasers [1,2] have dramatically simplified absolute optical frequency measurements. Such measurements of optical clock transitions in samples of cold atoms or single trapped ions mark an important step towards the realization of future optical clocks.…”

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confidence: 99%