A5012132573- Advanced Frequency and Time Standards
- Atomic and Subatomic Physics Research
- Cold Atom Physics and Bose-Einstein Condensates
- Advanced Fiber Laser Technologies
- Spectroscopy and Laser Applications
- Scientific Measurement and Uncertainty Evaluation
- Cardiovascular Syncope and Autonomic Disorders
- Quantum optics and atomic interactions
- Quantum, superfluid, helium dynamics
- Quantum Information and Cryptography
- Laser Design and Applications
- Advanced Fiber Optic Sensors
- Analytical Chemistry and Sensors
- Mechanical and Optical Resonators
- Atomic and Molecular Physics
- Atmospheric Ozone and Climate
- Photonic Crystal and Fiber Optics
- Semiconductor Lasers and Optical Devices
- Solid State Laser Technologies
- Gas Sensing Nanomaterials and Sensors
- Advanced Electrical Measurement Techniques
- Photonic and Optical Devices
- Capital Investment and Risk Analysis
- Advanced Measurement and Metrology Techniques
- Hemodynamic Monitoring and Therapy
National Physical Laboratory
2010-2024
Imperial College London
2005-2013
Teddington Memorial Hospital
2012
University of Colorado Boulder
2001-2004
National Institute of Standards and Technology
2000-2004
Imperial Valley College
2004
Max Planck Institute for Nuclear Physics
1998
Microwave atomic clocks have been the de facto standards for precision time and frequency metrology over past 50 years, finding widespread use in basic scientific studies, communications, navigation. However, with its higher operating frequency, an clock based on optical transition can be much more stable. We demonstrate all-optical referenced to 1.064-petahertz of a single trapped 199Hg+ ion. A clockwork mode-locked femtosecond laser provides output pulses at 1-gigahertz rate that are...
The frequency comb created by a femtosecond mode-locked laser and microstructured fiber is used to phase coherently measure the frequencies of both Hg+ Ca optical standards with respect SI second. We find transition be f(Hg) = 1 064 721 609 899 143(10) Hz f(Ca) 455 986 240 494 158(26) Hz, respectively. In addition unprecedented precision demonstrated here, this work precursor all-optical atomic clocks based on standards. Furthermore, when combined previous measurements, we no time variations...
We search for transient variations of the fine structure constant using data from a European network fiber-linked optical atomic clocks. By searching coherent in recorded clock frequency comparisons across network, we significantly improve constraints on constant. For example, constrain variation alpha to <5*10^-17 transients duration 10^3 s. This analysis also presents possibility dark matter, mysterious substance hypothesised explain galaxy dynamics and other astrophysical phenomena that...
Abstract We present a new framework to study the time variation of fundamental constants in model-independent way. Model independence implies more free parameters than assumed previous studies. Using data from atomic clocks based on 87 Sr, 171 Yb + and 133 Cs, we set bounds controlling fine-structure constant, α , electron-to-proton mass ratio, µ . consider variations timescales ranging minute almost day. In addition, use our results derive some tightest limits date parameter space models...
We present a novel microfabricated optical cavity, which combines very small mode volume with high finesse. In contrast to other micro-resonators, such as microspheres, the structure we have built gives atoms and molecules direct access high-intensity part of field mode, enabling them interact strongly photons in cavity for purposes detection quantum-coherent manipulation. Light couples directly out resonator through an fibre, avoiding need sensitive coupling optics. This renders...
Abstract The detection of variations fundamental constants the Standard Model would provide us with compelling evidence new physics, and could lift veil on nature dark matter energy. In this work, we discuss how a network atomic molecular clocks can be used to look for such unprecedented sensitivity over wide range time scales. This is precisely goal recently launched QSNET project: A measuring stability constants. will include state-of-the-art clocks, but also develop next-generation highly...
We describe the performance characteristics and frequency measurements of two high-accuracy high-stability laser-cooled atomic standards. One is a 657-nm (456-THz) reference using magneto-optically trapped Ca atoms, other 282-nm (1064-THz) based on single Hg/sup +/ ion confined in an RF-Paul trap. A femtosecond mode-locked laser combined with nonlinear microstructure fiber produces broad stable comb optical modes that used to measure frequencies lasers locked The measurement system...
We present a cooling method that should be generally applicable to atoms with narrow optical transitions. This technique uses velocity-selective pulses drive towards zero-velocity dark state and then quenches the excited increase rate. demonstrate this of quenched narrow-line by reducing 1-D temperature sample neutral 40Ca atoms. velocity select cool 1S0(4s2) 3P1(4s4p) 657 nm intercombination line quench 1S0(4s5s) at 553 nm, which increases rate eight-fold. Limited only available quenching...
Abstract A full evaluation of the uncertainty budget for ytterbium ion optical clock at National Physical Laboratory (NPL) was performed on electric octupole (E3) <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mrow/> <mml:mn>2</mml:mn> </mml:msup> <mml:msub> <mml:mtext>S</mml:mtext> <mml:mn>1</mml:mn> <mml:mo>/</mml:mo> </mml:mrow> </mml:msub> <mml:mo>→</mml:mo> <mml:mtext>F</mml:mtext> <mml:mn>7</mml:mn> </mml:math> transition. The...
For a neutral 40Ca-based optical frequency standard we report fractional instability of 4×10-15 in 1 s, which represents fivefold improvement over existing atomic standards. Using the technique Bordé–Ramsey spectroscopy with sample 107 trapped atoms, have resolved linewidths as narrow 200 Hz (FWHM). With colder atoms this system could potentially achieve an low 2×10-16 s. Such instabilities are important for standards and precision tests fundamental physics.
We have produced a Bose-Einstein condensate on permanent-magnet atom chip based periodically magnetized videotape. observe the expansion and dynamics of in one microscopic waveguides close to surface. The lifetime for atoms remain trapped near this dielectric material is significantly longer than above metal surface same thickness. These results illustrate suitability structures quantum-coherent preparation manipulation cold atoms.
This paper describes recent advances in the design and control of femtosecond laser combs for their use optical clocks synthesis low-noise microwave signals. The authors present a compact technically simple that directly emits broad continuum shows it can operate continuously on timescale days as phase-coherent "clockwork" an clock. They further demonstrate phase locking octave-spanning frequency comb to standard at millihertz level. As verified through heterodyne measurements with...
We describe the Sr optical lattice clock apparatus at NPL with particular emphasis on techniques used to increase reliability and minimise human requirement in its operation. Central this is a clock-referenced transfer cavity scheme for stabilisation of cooling trapping lasers. highlight several measures view towards realisation an time-scale. The contributed 502 hours data over 25 day period (84% uptime) recent measurement campaign uninterrupted periods more than 48 hours. An instability...
Concave pyramids are created in the (100) surface of a silicon wafer by anisotropic etching potassium hydroxide. High quality micromirrors then formed sputtering gold onto smooth (111) faces pyramids. These mirrors show great promise as high optical devices suitable for integration into micro-optoelectromechanical systems and atom chips. We have shown that structures this shape can be used to laser-cool hold atoms magneto-optical trap.
We present the design, construction, and characterization of longitudinal- transverse-field Zeeman slowers, based on arrays permanent magnets, for slowing thermal beams atomic Sr. The slowers are optimized operation with deceleration related to local laser intensity (by parameter ), which uses more effectively available power, in contrast usual constant mode. Slowing efficiencies up ≈18% realized compared those predicted by modelling. highlight slower, is compact, highly tunable,...
Abstract The recently concluded collaborative European project “Robust optical clocks for international timescales” (ROCIT) tackled some of the key challenges on roadmap towards a redefinition SI second. This paper gives an overview progress made improving robustness and automation verifying their uncertainty budgets through coordinated comparison campaigns. It also presents work incorporation into time scales, covering both use to steer local physical scales evaluations hydrogen masers...
We demonstrate three-dimensional (3-D) quenched narrow-line laser cooling and trapping of 40Ca. With 5 ms time we can transfer 28 % the atoms from a magneto-optic trap based on strong 423 nm line to narrow 657 clock transition (that is by an intercombination at 552 nm), thereby reducing atoms' temperature 2 millikelvin 10 microkelvin. This reduction in should help reduce overall systematic frequency uncertainty for our Ca optical standard < 1 Hz. Additional pulsed, third-stage 1-D yields...
With a fiber-broadened, femtosecond-laser frequency comb, the 76-THz interval between two laser-cooled optical standards was measured with statistical uncertainty of 2x10(-13) in 5 s , to our knowledge best short-term instability thus far reported for an measurement. One standard is based on calcium intercombination line at 657 nm, and other, mercury ion electric-quadrupole transition 282 nm. By linking this measurement known Ca frequency, we report new value Hg(+) clock improvement accuracy...
The slow electric-dipole intercombination decay of the ${2s2p}^{3}{}^{5}{S}_{2}^{o}$ level in C-like ion ${\mathrm{N}}^{+},$ which appears auroral airglow spectrum, has been optically observed from ions circulating a storage ring. A result $5.88\ifmmode\pm\else\textpm\fi{}0.03 \mathrm{ms}$ was obtained for natural lifetime this level. This represents an improvement precision by factor 10 compared to previous radio-frequency and electrostatic trap work is slight disagreement with latest...
A frequency comb is generated with a chromium-doped forsterite femtosecond laser, spectrally broadened in dispersion-shifted highly nonlinear fiber, and stabilized. The resultant evenly spaced of frequencies ranges from 1.1 to beyond 1.8 microm. was referenced simultaneously the National Institute Standards Technology's optical standard based on neutral calcium hydrogen maser that calibrated by cesium atomic fountain clock. With this we measured two references telecommunications band: one...
We describe a compact, all fiber, frequency stabilized diode laser system at 2051 nm using CO 2 gas-filled Kagome Hollow Core Fiber (HCF), capable of tuning continuously over four transitions in 12 C 16 O : R(24), R(26), R(28), and R(30).This has been designed for use future space-based atmospheric monitoring differential absorption lidar (DIAL).The fully spliced HCF gas cell is filled to kPa partial pressure we compare the observed lineshape features with those calculated HITRAN, quantify...