Direct frequency comb measurements of absolute optical frequencies and population transfer dynamics

A phase-stabilized femtosecond laser comb is directly used for high-resolution spectroscopy and absolute optical frequency measurements of one- and two-photon transitions in laser-cooled \rb atoms. Absolute atomic transition frequencies, such as the 5S$_{1/2}$ F=2 \ra 7S$_{1/2}$ F"=2 two-photon resonance measured at 788 794 768 921(44) kHz, are determined without \textit{a priori} knowledge about their values. Detailed dynamics of population transfer driven by a sequence of pulses are uncovered and taken into account for the measurement of the 5P states via resonantly enhanced two-photon transitions.Comment: 5 pages, 4 figures, submitte

AC electric trapping of neutral atoms

We study the dynamic behavior of ultracold neutral atoms in a macroscopic ac electric trap. Confinement in such a trap is achieved by switching between two saddle-point configurations of the electric field. The gradual formation of a stably trapped cloud is observed and the trap performance is studied versus the switching frequency and the symmetry of the switching cycle. Additionally, the electric field in the trap is mapped out by imaging the atom cloud while the fields are still on. Finally, the phase-space acceptance of the trap is probed by introducing a modified switching cycle. The experimental results are reproduced using full three-dimensional trajectory calculations.Comment: 10 pages, 13 figures, updated version, added journal referenc

Trapping of Rb atoms by ac electric fields

We demonstrate trapping of an ultracold gas of neutral atoms in a macroscopic ac electric trap. Three-dimensional confinement is obtained by switching between two saddle-point configurations of the electric field. Stable trapping is observed in a narrow range of switching frequencies around 60 Hz. The dynamic confinement of the atoms is directly visualized at different phases of the ac switching cycle. We observe about 10^5 Rb atoms in the 1 mm^3 large and several microkelvins deep trap with a lifetime of approximately 5 s.Comment: 4 pages, 4 figures; updated version, added journal referenc

Phase-Coherent Multilevel Two-Photon Transitions in Cold Rb Atoms: Ultrahigh-Resolution Spectroscopy via Frequency-Stabilized Femtosecond Laser

A two-photon transition in cold Rb atoms will be probed with a phase-coherent wide bandwidth femtosecond laser comb. Frequency domain analysis yields a high-resolution picture where phase coherence among various transition pathways through different intermediate states produces interference effects on the resonantly enhanced transition probability. This result is supported by the time domain Ramsey interference effect. The two-photon transition spectrum is analyzed in terms of the pulse repetition rate and carrier frequency offset, leading to a cold-atom-based frequency stabilization scheme for both degrees of freedom of the femtosecond laser

High resolution atomic coherent control via spectral phase manipulation of an optical frequency comb

Sem informaçãoWe demonstrate high resolution coherent control of cold atomic rubidium utilizing spectral phase manipulation of a femtosecond optical frequency comb. Transient coherent accumulation is directly manifested by the enhancement of signal amplitude and spectral resolution via the pulse number. The combination of frequency comb technology and spectral phase manipulation enables coherent control techniques to enter a new regime with natural linewidth resolution. © 2006 The American Physical Society.We demonstrate high resolution coherent control of cold atomic rubidium utilizing spectral phase manipulation of a femtosecond optical frequency comb. Transient coherent accumulation is directly manifested by the enhancement of signal amplitude and spectral resolution via the pulse number. The combination of frequency comb technology and spectral phase manipulation enables coherent control techniques to enter a new regime with natural linewidth resolution.We demonstrate high resolution coherent control of cold atomic rubidium utilizing spectral phase manipulation of a femtosecond optical frequency comb. Transient coherent accumulation is directly manifested by the enhancement of signal amplitude and spectral resolution via the pulse number. The combination of frequency comb technology and spectral phase manipulation enables coherent control techniques to enter a new regime with natural linewidth resolution.961514Sem informaçãoSem informaçãoSem informaçãoUdem, Th., Holzwarth, R., Hänsch, T.W., (2002) Nature (London), 416, p. 233. , NATUAS. 0028-0836. 10.1038/416233aCundiff, S.T., Ye, J., (2003) Rev. Mod. Phys., 75, p. 325. , RMPHAT 0034-6861 10.1103/RevModPhys.75.325Marian, A., (2004) Science, 306, p. 2063. , SCIEAS 0036-8075 10.1126/science.1105660Marian, A., (2005) Phys. Rev. Lett., 95, p. 023001. , PRLTAO 0031-9007 10.1103/PhysRevLett.95.023001Diddams, S.A., (2001) Science, 293, p. 825. , SCIEAS 0036-8075 10.1126/science.1061171Ye, J., Ma, L.-S., Hall, J.L., (2001) Phys. Rev. Lett., 87, p. 270801. , PRLTAO 0031-9007 10.1103/PhysRevLett.87.270801Holman, K.W., (2005) Opt. Lett., 30, p. 1225. , OPLEDP 0146-9592 10.1364/OL.30.001225Jones, R.J., (2005) Phys. Rev. Lett., 94, p. 193201. , PRLTAO 0031-9007 10.1103/PhysRevLett.94.193201Gohle, C., (2005) Nature (London), 436, p. 234. , NATUAS 0028-0836 10.1038/nature03851Kuklinski, J.R., (1989) Phys. Rev. A, 40, p. 6741. , PLRAAN 1050-2947 10.1103/PhysRevA.40.6741Broers, B., Van Linden Van Den Heuvell, H.B., Noordam, L.D., (1992) Phys. Rev. Lett., 69, p. 2062. , PRLTAO 0031-9007 10.1103/PhysRevLett.69.2062Meshulach, D., Silberberg, Y., (1998) Nature (London), 396, p. 239. , NATUAS 0028-0836 10.1038/24329Balling, P., Maas, D.J., Noordam, L.D., (1994) Phys. Rev. A, 50, p. 4276. , PLRAAN 1050-2947 10.1103/PhysRevA.50.4276Chatel, B., (2003) Phys. Rev. A, 68, p. 041402. , PLRAAN 1050-2947 10.1103/PhysRevA.68.041402Oron, D., (2002) Phys. Rev. Lett., 88, p. 063004. , PRLTAO 0031-9007 10.1103/PhysRevLett.88.063004Salzmann, W., (2006) Phys. Rev. A, 73, p. 023414. , PLRAAN 1050-2947 10.1103/PhysRevA.73.023414Felinto, D., Acioli, L.H., Vianna, S.S., (2004) Phys. Rev. A, 70, p. 043403. , PLRAAN 1050-2947 10.1103/PhysRevA.70.043403Martinez, O.E., (1987) IEEE J. Quantum Electron., 23, p. 59. , IEJQA7 0018-9197 10.1109/JQE.1987.1073201Yoon, T.H., (2001) Phys. Rev. A, 63, p. 011402. , PLRAAN 1050-2947 10.1103/PhysRevA.63.011402Vala, J., (2001) Phys. Rev. A, 63, p. 013412. , PLRAAN 1050-2947 10.1103/PhysRevA.63.013412We thank funding support from ONR, NSF, and NIST

Cooling Considerations for the Long Length HVDC Cables Cryostat within BEST PATHS Project

HVDC cables have been identified as the preferred solution for future pan-European grids for the transmission over long distances of the large power produced by renewable energy farms which are generally located far for the consumption places. The European project Best Paths has been launched to identify the remaining barriers and propose some innovative solutions to achieve such envisioned grids. As superconductivity offers very attractive and efficient solutions vision studies for long-distance superconducting power transmission lines are conducted. The superconducting technology under study is based on the MgB$_{2}$ conductor cooled with one-phase liquid hydrogen. A flexible cryostat with 15 to 25 K core cooling and with additional shield cooling using liquid nitrogen or hydrogen gas is required. For long length cables the limiting parameters are the cryostat heat load and the pressure drop. The calculation results show the interdependencies of the maximum length between neighboring cooling sections with the heat load on shield and core, mass flows and pressure drop, enthalpy change, viscosity, friction factors and cryostat geometry. The calculations are carried out for different fluid options and diameters, and the corresponding results are presented and discussed

MgB2-Based MVDC Superconducting Power Cable in Liquid Hydrogen for Hybrid Energy Distribution

The combination of liquid hydrogen and superconducting cables presents a unique opportunity to distribute both hydrogen and bulk electricity in the same infrastructure. In particular, liquid hydrogen around 20 K is ideally suited for cooling the MgB 2 superconductor, resulting in a compact power cable that also leaves sufficient place for the hydrogen flow. Such a hybrid system operating in the MVDC range at 25 kV and 20 kA constitutes one of the main goals of the European project SCARLET. After a description of the rationale and benefits of the electricity – hydrogen system, various possible applications and a first distribution system are presented. Furthermore, the different cable components already designed are discussed along with the research challenges and general strategy for the development.MgB2-Based MVDC Superconducting Power Cable in Liquid Hydrogen for Hybrid Energy DistributionacceptedVersio

SCARLET – A European Effort to Develop HTS and MgB2 Based MVDC Cables

Superconducting cables have been proven in a variety of pilot projects and utility installations, demonstrating several of their advantages, including compact size and low energy losses, which can make the technology economically attractive for certain applications. It is clear though that different applications impose different requirements and challenges, but also opportunities for the cables. An interesting application is high-power DC transfer at medium voltage (MVDC). The high-current capability of the superconductor allows for a reduction in voltage while maintaining or increasing the power transfer level. In this way, one MVDC superconducting cable can replace one or more conventional high-voltage DC cables. In the European project SCARLET (Superconducting cables for sustainable energy transition), two types of MVDC cables will be developed, one based on HTS and one on MgB2 materials. Additionally, protection requirements will be considered, including the development of a modular DC fault current limiter for 10 kA. A main motivation for the development is the elimination of costly high-voltage converter stations when going from high to medium voltage, e.g., for offshore wind power plants. Another feature is the combined hydrogen and electricity transmission from generation sites to industry or mobility end users. This paper describes the superconducting MVDC cable concept as well as the main challenges and research needed to develop and type test the cables.SCARLET – A European Effort to Develop HTS and MgB2 Based MVDC CablesacceptedVersio