Coherent preparation by laser light of quantum states of atoms and molecules can lead to quantum interference in the amplitudes of optical transitions. In this way the optical properties of a medium can be dramatically modified, leading to electromagnetically induced transparency and related effects, which have placed gas-phase systems at the center of recent advances in the development of media with radically new optical properties. This article reviews these advances and the new possibilities they offer for nonlinear optics and quantum information science. As a basis for the theory of electromagnetically induced transparency the authors consider the atomic dynamics and the optical response of the medium to a continuous-wave laser. They then discuss pulse propagation and the adiabatic evolution of field-coupled states and show how coherently prepared media can be used to improve frequency conversion in nonlinear optical mixing experiments. The extension of these concepts to very weak optical fields in the few-photon limit is then examined. The review concludes with a discussion of future prospects and potential new applications.

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Electromagnetically induced transparency : Optics in coherent media

We review the field of cavity optomechanics, which explores the interaction between electromagnetic radiation and nano- or micromechanical motion This review covers the basics of optical cavities and mechanical resonators, their mutual optomechanical interaction mediated by the radiation pressure force, the large variety of experimental systems which exhibit this interaction, optical measurements of mechanical motion, dynamical backaction amplification and cooling, nonlinear dynamics, multimode optomechanics, and proposals for future cavity quantum optomechanics experiments In addition, we describe the perspectives for fundamental quantum physics and for possible applications of optomechanical devices

Cavity Optomechanics

The status of experimental tests of general relativity and of theoretical frameworks for analyzing them is reviewed and updated. Einstein’s equivalence principle (EEP) is well supported by experiments such as the Eotvos experiment, tests of local Lorentz invariance and clock experiments. Ongoing tests of EEP and of the inverse square law are searching for new interactions arising from unification or quantum gravity. Tests of general relativity at the post-Newtonian level have reached high precision, including the light deflection, the Shapiro time delay, the perihelion advance of Mercury, the Nordtvedt effect in lunar motion, and frame-dragging. Gravitational wave damping has been detected in an amount that agrees with general relativity to better than half a percent using the Hulse-Taylor binary pulsar, and a growing family of other binary pulsar systems is yielding new tests, especially of strong-field effects. Current and future tests of relativity will center on strong gravity and gravitational waves.

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The Confrontation Between General Relativity and Experiment

A topical review of numerical and experimental studies of supercontinuum generation in photonic crystal fiber is presented over the full range of experimentally reported parameters, from the femtosecond to the continuous-wave regime. Results from numerical simulations are used to discuss the temporal and spectral characteristics of the supercontinuum, and to interpret the physics of the underlying spectral broadening processes. Particular attention is given to the case of supercontinuum generation seeded by femtosecond pulses in the anomalous group velocity dispersion regime of photonic crystal fiber, where the processes of soliton fission, stimulated Raman scattering, and dispersive wave generation are reviewed in detail. The corresponding intensity and phase stability properties of the supercontinuum spectra generated under different conditions are also discussed.

Supercontinuum generation in photonic crystal fiber

Electromagnetically induced transparency is a technique for eliminating the effect of a medium on a propagating beam of electromagnetic radiation EIT may also be used, but under more limited conditions, to eliminate optical self‐focusing and defocusing and to improve the transmission of laser beams through inhomogeneous refracting gases and metal vapors, as figure 1 illustrates The technique may be used to create large populations of coherently driven uniformly phased atoms, thereby making possible new types of optoelectronic devices

Electromagnetically Induced Transparency

sensitive detection techniques. Typical near-IR transition line strengths of to cmpl have been measured. The BRD enables this high sensitivity without the need for highfrequency modulation approaches, yet maintaining sensitivities equivalent to those obtained with FM techn iq~es .~ ,~ The operational, electronic, and mechanical simplifications afforded by room-temperature, near-IR lasers (versus cryogenic mid-IR lasers) in combination with the BRD circuit will allow detection limits of a few ppm/meter in standard atmospheric pressure, room temperature air. Higher sensitivity will be achieved by use of compact multi-pass cells. The initial investigations of the application of near-IR diode laser absorption spectroscopy to the detection ofVOCs have concentrated on the recording of Fourier transform infrared (FTIR) spectra of the species of interest. Because the near-IR transitions are typically orders of magnitude weaker than the mid-IR transitions, there are few references available in the spectroscopic literature. Figure 1 is an example FTIR spectrum of methanol in the 1.34 to 1.44 micron region. This spectrum was recorded at a neat methanol pressure of 5.2 torr, with an absorption pathlength of 5 meters achieved by use of a white cell. Similar spectra of additional VOCs have been recorded to quantify the wavelengths and strengths of the absorption transitions. These spectra are used as guides for the application of diode laser absorption spectroscopy. During this talk we will also present preliminary diode laser absorption spectra of VOCs. These spectra are recorded with use of DFB and external-cavity diode laser systems. We will report on absorption strengths and potential interferences for the identification of optimum spectral regions for the development of compact, electro-optic, VOC sensors. 1. P. C. D. Hobbs, SPIE Laser Noise 1376, 216-221 (1990). 2. M. G. Allen, K. L. Carleton, S . J. Davis, W. J. Kessler, K. R. McManus, presented at the 25th Plasmadynamics and Laser Conference, A I M paper 94-2433 (1 994). M. G. Allen, K. L. Carleton, S. J. Davis, W. J. Kessler, C. E. Otis, D. A. Palombo, D. M. Sonnenfroh, Appl. Opt. 34, No. 18, 3240-3249 (1995). 3.

High-precision mid-infrared spectrometer using diode-pumped difference-frequency generation in PPLN

Optical frequencies of the hyperfine components of the D2 line in 133Cs are determined using high-resolution spectroscopy and a femtosecond laser frequency comb The achieved frequency uncertainties are <10 kHz, which is 10 times better than previous results

Precise frequency measurements of 6s 2S1/2 -6p 2P3/2 transition in 133Cs atomic beam using a femtosecond laser frequency comb

At the previous Symposium on Frequency Standards and Metrology, H. Katori proposed using IS0 ---->3pO transitions in alkaline earth like atoms to make high performance optical clocks based on large numbers of neutral atoms tightly confined in an optical lattice. 1 This proposal was based on the use of Sr atoms, as were the initial experiments.24 In 2004 Porsev et al. proposed the use of the analogous transition in Yb at 578 nm,5 and we have been developing lattice clocks based on Yb over the past four years. While there are considerable similarities between the Sr and Yb atomic systems, there are also some important differences. Most significantly, Yb has an

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THE Yb OPTICAL LATTICE CLOCK

We present results on optical atomic clocks based on lasers stabilized to optical transitions (in Ca and Hg/sup +/) and whose frequencies are phase-coherently divided down to the microwave domain with a spectrally-broadened mode-locked fs-laser.

Frequency metrology with optical clocks: comparison of the Ca and Hg/sup +/ clock transitions

Center-frequency drift in diode lasers can be reduced by stabilizing the laser to an optical cavity with a low bandwidth feedback loop that acts on the injection current Resonant optical feedback from a confocal or ring cavity can reduce high frequency noise, yielding linewidths in the 10 kHz range With either an optical or an electronic lock to a cavity, the laser's wavelength is restricted to those regions that can be reached by temperature and current tuning of the solitary diode; this can be extended to full coverage by means of an extended cavity with a frequency-selective component, such as a diffraction grating

Leo W. Hollberg

Papers

High-precision mid-infrared spectrometer using diode-pumped difference-frequency generation in PPLN

Precise frequency measurements of 6s 2S1/2 -6p 2P3/2 transition in 133Cs atomic beam using a femtosecond laser frequency comb

THE Yb OPTICAL LATTICE CLOCK

Frequency metrology with optical clocks: comparison of the Ca and Hg/sup +/ clock transitions

Diode laser stabilization