[Show abstract][Hide abstract] ABSTRACT: The refractive index of coherently driven rubidium vapour is experimentally investigated in a three-level cascade configuration using a selective reflection technique. The maximum measured resonant change in the refractive index is Δn 0.1. The selective reflection is accompanied by a four-wave-mixing process that can reach ~90% efficiency.
Full-text · Article · Dec 2010 · Journal of Modern Optics
[Show abstract][Hide abstract] ABSTRACT: 10 GHz optical pulses are generated by line-by-line phase compensation on an optical frequency comb. Residual pulse timing jitter les 10 fs and high power signals at harmonics up to 80 GHz are measured.
[Show abstract][Hide abstract] ABSTRACT: Optical filtering of a stabilized 1 GHz optical frequency comb produces a 20 GHz comb with approximately 40 nm bandwidth (FWHM) at 960 nm. Use of a low-finesse Fabry-Pérot cavity in a double-pass configuration provides a broad cavity coupling bandwidth (Deltalambda/lambda approximately 10%) and large suppression (50 dB) of unwanted modes. Pulse durations shorter than 40 fs with less than 2% residual amplitude modulation are achieved.
[Show abstract][Hide abstract] ABSTRACT: We use a Fabry-Perot cavity to optically filter the output of a Ti:sapphire frequency comb to integer multiples of the original 1 GHz mode spacing. This effectively increases the pulse repetition rate, which is useful for several applications. In the case of low-noise microwave signal generation, such filtering leads to improved linearity of the high-speed photodiodes that detect the mode-locked laser pulse train. The result is significantly improved signal-to-noise ratio at the 10 GHz harmonic with the potential for a shot-noise limited single sideband phase noise floor near -168 dBc/Hz.
[Show abstract][Hide abstract] ABSTRACT: We describe the development and latest results of an optical lattice
clock based on neutral Yb atoms, including investigations based on both
even and odd isotopes. We report a fractional frequency uncertainty
below 10-15 for 171Yb.
[Show abstract][Hide abstract] ABSTRACT: The phase noise of a 20 GHz picosecond optical pulse train generated by a modulator-based optical frequency comb generator is analysed. The residual timing jitter is 10 fs for Fourier frequencies from 10 Hz to 10 MHz. Photodetection of the optical pulse train provides millimetre-wave signals with similarly low residual jitter at 40, 60, and 80 GHz with applicable powers of 7.5, 10.5, and 13 dBm, respectively.
Preview · Article · Mar 2009 · Electronics Letters
[Show abstract][Hide abstract] ABSTRACT: Femtosecond mode-locked lasers are used to transfer the high stability of cw optical frequency references to electronic oscillators/synthesizers and generate microwave signals with exceptional frequency stability, low timing jitter and low phase-noise.
[Show abstract][Hide abstract] ABSTRACT: We report an uncertainty evaluation of an optical lattice clock based on
the S01↔P03 transition in the bosonic
isotope Yb174 by use of magnetically induced spectroscopy. The
absolute frequency of the S01↔P03 transition
has been determined through comparisons with optical and microwave
standards at NIST. The weighted mean of the evaluations is
ν(Yb174)=518294025309217.8(0.9)Hz . The uncertainty due to systematic
effects has been reduced to less than 0.8Hz , which represents
1.5×10-15 in fractional frequency.
Full-text · Article · May 2008 · Physical Review A
[Show abstract][Hide abstract] ABSTRACT: We report an uncertainty evaluation of an optical lattice clock based on the (1)S(0) <-> (3)P(0), transition in the bosonic isotope (174)Yb by use of magnetically induced spectroscopy. The absolute frequency of the (1)S(0) <-> (3)P(0) transition has been determined through comparisons with optical and microwave standards at NIST. The weighted mean of the evaluations is nu((174)Yb)=518 294 025 309 217.8(0.9) Hz. The uncertainty due to systematic effects has been reduced to less than 0.8 Hz, which represents 1.5 X 10(-15) in fractional frequency.
No preview · Article · May 2008 · Physical Review A
[Show abstract][Hide abstract] ABSTRACT: We present an experimental study of the lattice-induced light shifts on the (1)S(0) --> (3)P(0) optical clock transition (nu(clock) approximately 518 THz) in neutral ytterbium. The "magic" frequency nu(magic) for the 174Yb isotope was determined to be 394 799 475(35) MHz, which leads to a first order light shift uncertainty of 0.38 Hz. We also investigated the hyperpolarizability shifts due to the nearby 6s6p(3)P(0) --> 6s8p(3)P(0), 6s8p(3)P(2), and 6s5f(3)F(2) two-photon resonances at 759.708, 754.23, and 764.95 nm, respectively. By measuring the corresponding clock transition shifts near these two-photon resonances, the hyperpolarizability shift was estimated to be 170(33) mHz for a linear polarized, 50 microK deep, lattice at the magic wavelength. These results indicate that the differential polarizability and hyperpolarizability frequency shift uncertainties in a Yb lattice clock could be held to well below 10(-17).
Full-text · Article · Mar 2008 · Physical Review Letters
[Show abstract][Hide abstract] ABSTRACT: We report the technical aspects of the optical-to-microwave comparison for our recent measurements of the optical frequency
of the mercury single-ion frequency standard in terms of the SI second as realized by the NIST-F1 cesium fountain clock. Over
the course of six years, these measurements have resulted in a determination of the mercury single-ion frequency with a fractional
uncertainty of less than 7×10-16, making it the most accurately measured optical frequency to date. In this paper, we focus on the details of the comparison
techniques used in the experiment and discuss the uncertainties associated with the optical-to-microwave synthesis based on
a femtosecond laser frequency comb. We also present our most recent results in the context of the previous measurements of
the mercury single-ion frequency and arrive at a final determination of the mercury single-ion optical frequency: f(Hg+)=1 064 721 609 899 145.30(69) Hz.
Full-text · Article · Oct 2007 · Applied Physics B
[Show abstract][Hide abstract] ABSTRACT: We are interested in using a magnetic microfabricated cantilever to both magnetically trap and drive transitions in laser-cooled Rb atoms. We ascertain the feasibility and show a possible scenario for such an experiment.
[Show abstract][Hide abstract] ABSTRACT: Single-trapped-ion frequency standards based on a 282 nm transition in 199 Hg + and on a 267 nm transition in 27 Al + have been developed at NIST over the past several years. Their frequencies are measured relative to each other and to the NIST primary frequency standard, the NIST-F1 cesium fountain, by means of a self-referenced femtosecond laser frequency comb. Both ion standards have demonstrated instabilities and inaccuracies of less than 1 × 10 −16 .
Full-text · Article · Sep 2007 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: Coherent population trapping (CPT) resonances usually exhibit contrasts below 10 % when interrogated with frequency modulated lasers. We discuss a relatively simple way to increase the resonance contrast to nearly 100 % generating an additional light field through a nonlinear four-wave mixing interaction in the atomic vapor 1 . A similar method can also be used to create a beat signal at the CPT resonance frequency that can injection-lock a low-power microwave oscillator at 3.4 GHz directly to the atomic resonance 2 . This could lead to chip-scale atomic clocks (CSACs) with improved performance. Furthermore, we introduce a miniature microfabricated saturated absorption spectrometer 3 that produces a signal for locking a laser frequency to optical transitions in alkali atoms. The Rb absorption spectra are comparable to signals obtained with standard table-top setups, although the rubidium vapor cell has an interior volume of only 1 mm 3 and the volume of the entire spectrometer is around 0.1 cm 3 .
Full-text · Article · Sep 2007 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: We have designed and tested a set of five miniature nested magnetic shields constructed of high-permeability material, with external volumes for the individual shielding layers ranging from 0.01 to 2.5 cm(3). We present measurements of the longitudinal and transverse shielding factors (the ratio of external to internal magnetic field) of both individual shields and combinations of up to three layers. The largest shielding factor measured was 6 x 10(6) for a nested set of three shields, and from our results we predict a shielding factor of up to 1 x 10(13) when all five shields are used. Two different techniques were used to measure the internal field: a chip-scale atomic magnetometer and a commercially available magnetoresistive sensor. Measurements with the two methods were in good agreement.
[Show abstract][Hide abstract] ABSTRACT: We explore methods and limitations for increasing the mode spacing of a 1 GHz optical frequency comb using a Fabry-Perot filter cavity. Applications to optical and microwave waveform generation are highlighted.
[Show abstract][Hide abstract] ABSTRACT: This talk presents two different types of neutral atom optical clocks and emphasizes the systems' differences in potential performance and complexity. Approaches in attaining high stability, high accuracy, and transportable optical atomic clocks are discussed in detail.
[Show abstract][Hide abstract] ABSTRACT: We describe recent progress in the development of millimeter-scale instruments based on alkali atom vapor cells implemented with microfabrication techniques. Because of their small size and correspondingly low power requirements, these "chip-scale" atomic clocks and magnetometers have the potential to bring atomically precise instrumentation to portable, battery-operated systems such as GPS receivers, remote sensors and wireless communication devices. In addition, wafer-level processing and assembly potentially allows for very low cost per instrument if high volumes are produced.
[Show abstract][Hide abstract] ABSTRACT: We report tests of local position invariance (LPI) and constancy of fundamental constants from measurements of the frequency ratio of the 282-nm <sup>199</sup>Hg<sup>+</sup> optical clock transition to the ground-state hyperfine splitting in <sup>133</sup>Cs. Analysis of the frequency ratio, extending over six years at NIST, is used to place a limit on the fractional variation of the two clocks of less than 5.8times10<sup>-6</sup> per change in normalized solar gravitational potential, and a limit on fractional variation of the fine structure constant at alpha dot/alpha < 1.3x10<sup>-16</sup> yr<sup>-1</sup>, assuming invariance of other fundamental constants. Comparison of our results with those previously reported for the absolute optical frequency measurements of coupled <sup>171</sup>Yb<sup>+</sup> versus other constraint <sup>133</sup>Cs standard yields a coupled constraint of -0.04times10<sup>-15</sup> < alpha dot/alpha < 0.46times10<sup>-15</sup> yr<sup>-1</sup> and <sup>-</sup>2.39times10<sup>-15</sup> < d/dt In mu<sub>Cs</sub>/mu<sub>B</sub> < 0.47times10<sup>-15</sup> yr<sup>-1</sup>.
[Show abstract][Hide abstract] ABSTRACT: A wide-band power control system based on an electro-optical modulator and transimpedance amplifier has been constructed. It is capable of reducing laser intensity fluctuations to the shot noise limit over the range of Fourier frequencies from a few tens of Hz to a few MHz with the low boundary set by the light handling capacity of a photodetector and the upper boundary imposed by the spurious resonances of a given electro-optical modulator. We discuss a general approach to the design of laser intensity control system and its noise properties.