Phase-sensitive detection of Bragg scattering at 1D optical lattices

We report on the observation of Bragg scattering at 1D atomic lattices. Cold atoms are confined by optical dipole forces at the antinodes of a standing wave generated by the two counter-propagating modes of a laser-driven high-finesse ring cavity. By heterodyning the Bragg-scattered light with a reference beam, we obtain detailed information on phase shifts imparted by the Bragg scattering process. Being deep in the Lamb-Dicke regime, the scattered light is not broadened by the motion of individual atoms. In contrast, we have detected signatures of global translatory motion of the atomic grating.Comment: 4 pages, 4 figure

Direct Measurement of intermediate-range Casimir-Polder potentials

We present the first direct measurements of Casimir-Polder forces between solid surfaces and atomic gases in the transition regime between the electrostatic short-distance and the retarded long-distance limit. The experimental method is based on ultracold ground-state Rb atoms that are reflected from evanescent wave barriers at the surface of a dielectric glass prism. Our novel approach does not require assumptions about the potential shape. The experimental data confirm the theoretical prediction in the transition regime.Comment: 4 pages, 3 figure

Ultra-cold atoms in an optical cavity: two-mode laser locking to the cavity avoiding radiation pressure

The combination of ultra-cold atomic clouds with the light fields of optical cavities provides a powerful model system for the development of new types of laser cooling and for studying cooperative phenomena. These experiments critically depend on the precise tuning of an incident pump laser with respect to a cavity resonance. Here, we present a simple and reliable experimental tuning scheme based on a two-mode laser spectrometer. The scheme uses a first laser for probing higher-order transversal modes of the cavity having an intensity minimum near the cavity's optical axis, where the atoms are confined by a magnetic trap. In this way the cavity resonance is observed without exposing the atoms to unwanted radiation pressure. A second laser, which is phase-locked to the first one and tuned close to a fundamental cavity mode drives the coherent atom-field dynamics.Comment: 7 pages, 7 figure

Dimensional Crossover in Bragg Scattering from an Optical Lattice

We study Bragg scattering at 1D optical lattices. Cold atoms are confined by the optical dipole force at the antinodes of a standing wave generated inside a laser-driven high-finesse cavity. The atoms arrange themselves into a chain of pancake-shaped layers located at the antinodes of the standing wave. Laser light incident on this chain is partially Bragg-reflected. We observe an angular dependence of this Bragg reflection which is different to what is known from crystalline solids. In solids the scattering layers can be taken to be infinitely spread (3D limit). This is not generally true for an optical lattice consistent of a 1D linear chain of point-like scattering sites. By an explicit structure factor calculation we derive a generalized Bragg condition, which is valid in the intermediate regime. This enables us to determine the aspect ratio of the atomic lattice from the angular dependance of the Bragg scattered light.Comment: 4 pages, 5 figure

New algorithm for energy dispatch scheduling of grid-connected solar photovoltaic system with battery storage system

Purpose. In last decade the problem of energy management system (EMS) for electric network has received special attention from academic researchers and electricity companies. In this paper, a new algorithm for EMS of a photovoltaic (PV) grid connected system, combined to an storage system is proposed for reducing the character of intermittence of PVs power which infect the stability of electric grid. In simulation model, the PV system and the energy storage system are connected to the same DC bus, whereas EMS controls the power flow from the PV generator to the grid based on the predetermined level of PV power. In the case where the PV power is less than the predefined threshold, energy is stored in the batteries banc which will be employed in the peak energy demand (PED) times. Otherwise, it continues to feed the principal grid. The novelty of the proposed work lies in a new algorithm (smart algorithm) able to determine the most suitable (optimal) hours to switching between battery, Solar PVs, and principal grid based on historical consumption data and also determine the optimal amount of storage energy that be injected during the peak demand. Methods. The solution of the problem was implemented in the Matlab R2010a Platform and the simulation conducted on Laptop with a 2.5 GHz processor and 4 GB RAM. Results. Simulation results show that the proposed model schedules the time ON/OFF of the switch in the most optimal way, resulting in absolute control of power electric path, i.e. precise adaptation at the peak without compromising consumers comfort. In addition, other useful results can be directly obtained from the developed scheme. Thus, the results confirm the superiority of the proposed strategy compared to other improved techniques.Мета. В останнє десятиліття проблемі системи енергоменеджменту (СЕМ) для електричної мережі приділялася особлива увага з боку науковців та електроенергетичних компаній. У цій роботі пропонується новий алгоритм для СЕМ фотоелектричної (ФЕ) системи, підключеної до мережі, об'єднаної з системою накопичення енергії для зменшення характеру переривчастості потужності ФЕ системи, що впливає на стабільність електричної мережі. У розрахунковій моделі ФЕ система та система накопичення енергії підключені до однієї і тієї ж шини постійного струму, тоді як СЕМ керує потоком потужності від ФЕ генератора до мережі на основі заздалегідь визначеного рівня потужності ФЕ. У тому випадку, коли потужність ФЕ менше заздалегідь визначеного порогу, енергія накопичується в батареях акумуляторів, що буде використано в часи пікового попиту на енергію. В іншому випадку ФЕ продовжує живити основну мережу. Новизна запропонованої роботи полягає в новому алгоритмі (розумному алгоритмі), здатному визначити найбільш підходящі (оптимальні) години для перемикання між акумулятором, сонячними ФЕ та основною мережею на основі даних про історію споживання, а також визначити оптимальну величину енергії накопичення, що вводиться під час пікового попиту. Методи. Розв‘язання задачі було реалізовано на платформі Matlab R2010a, а моделювання проведено на ноутбуці з процесором 2,5 ГГц та 4 ГБ оперативної пам'яті. Результати. Результати моделювання показують, що запропонована модель найоптимальніше планує час увімкнення/вимкнення вимикача, що призводить до абсолютного контролю потужності шляху електроенергії, тобто точної адаптації на піку без шкоди для комфорту споживачів. Крім того, з розробленої схеми можна безпосередньо отримати інші корисні результати. Таким чином, результати підтверджують перевагу запропонованої стратегії порівняно з іншими вдосконаленими методами

Cooperative Scattering by Cold Atoms

We have studied the interplay between disorder and cooperative scattering for single scattering limit in the presence of a driving laser. Analytical results have been derived and we have observed cooperative scattering effects in a variety of experiments, ranging from thermal atoms in an optical dipole trap, atoms released from a dark MOT and atoms in a BEC, consistent with our theoretical predictions.Comment: submitted for special issue of PQE 201