High contrast D1_{1} line electromagnetically induced transparency in nanometric-thin rubidium vapor cell

Electromagnetically induced transparency (EIT) on atomic D$_{1}$ line of rubidium is studied using a nanometric-thin cell with atomic vapor column length in the range of L= 400 - 800 nm. It is shown that the reduction of the cell thickness by 4 orders as compared with an ordinary cm-size cell still allows to form an EIT resonance for $L= \lambda$ ($\lambda =794$ nm) with the contrast of up to 40%. Remarkable distinctions of EIT formation in nanometric-thin and ordinary cells are demonstrated. Despite the Dicke effect of strong spectral narrowing and increase of the absorption for $L=$ $\lambda /2$, EIT resonance is observed both in the absorption and the fluorescence spectra for relatively low intensity of the coupling laser. Well resolved splitting of the EIT resonance in moderate magnetic field for $L=$ $\lambda$ can be used for magnetometry with nanometric spatial resolution. The presented theoretical model well describes the observed results.Comment: Submitted to Applied Physics B: Lasers and Optics, 9 pages, 10 figure

Physico-mathematical model for determining the direction in space to point sources of gamma radiation using spherical absorber

Physico-mathematical model for determining the direction in space to point sources of gamma radiation using a spherical absorber was developed. CdTe detectors of appropriate sizes are placed in the regular pyramid tops under absorber. The physico-mathematical model allowed, taking into account the exponential attenuation of gamma radiation by the absorber, to find the distance from the location of any CdTe sensor to the surface of sphere in any direction in space. Calculated information and signal received from the detectors, correlate to each other. The ratios found depend on the angle to the source of gamma radiation and represent the ratio of transmittance coefficients for four sensors. A methodology for locating the developed device in space, which allowed to obtain dependence of the calculated ratios from the angle in space for θ = 90° and φ from 0° to 360° in increments of 15° was proposed. Each direction in space corresponds to a set of six respective ratios

Peculiarities of plasma fluctuations during RF heating in Uragan-3M torsatron by means of two alfven waves

Three wave interaction has been observed in experiments on Uragan-3M torsatron. Two RF antennas with frequencies Ω1 and Ω2 were used simultaneously for plasma production and heating. Plasma was probed by microwaves, these allowed to study reflection of microwaves at almost whole plasma radius. Spectral analysis of reflected microwaves showed an existence of plasma density fluctuation with frequency Ω1 – Ω2. The suppression of plasma low frequencies was observed, when the plasma oscillation with Ω1 – Ω2 frequency has appeared. Microwaves probing of these fluctuations is the useful tool for studies of their influence on plasma behavior and possibly RF power absorption profile.Трьоххвильова взаємодія спостерігалась в експериментах на торсатроні Ураган-3М. Дві ВЧ антени з частотами Ω1 і Ω2 одночасно використовувались для створення і нагріву плазми, яка зондувалась мікрохвилями, місце відбиття яких перекривало майже весь радіус. При спектральному аналізі відбитих НВЧ сигналів виявлені флуктуації густини плазми з частотою Ω1 – Ω2. При появі коливань з частотою Ω1 – Ω2 спостерігалось пригнічення НЧ флуктуацій. Мікрохвильове зондування є корисним засобом для вивчення їх впливу на поведінку плазми та, можливо, для відтворення профілю поглинання ВЧ потужності.Трехволновое взаимодействие наблюдалось в экспериментах на торсатроне Ураган-3М. Две ВЧ антенны с частотами Ω1 и Ω2 одновременно использовались для создания и нагрева плазмы, которая зондировалась микроволнами, место отражения которых перекрывало почти весь радиус. При спектральном анализе отраженных СВЧ сигналов обнаружены флуктуации плотности плазмы с частотой Ω1 – Ω2. При появлении колебаний на частоте Ω1 – Ω2 наблюдалось подавление НЧ флуктуаций. Микроволновое зондирование является полезным средством для изучения их влияния на поведение плазмы и, возможно, для воссоздания профиля поглощения ВЧ мощности

Beta decay of the axially asymmetric ground state of 192Re

The β decay of 75192Re117, which lies near the boundary between the regions of predicted prolate and oblate deformations, has been investigated using the KEK Isotope Separation System (KISS) in RIKEN Nishina Center. This is the first case in which a low-energy beam of rhenium isotope has been successfully extracted from an argon gas-stopping cell using a laser-ionization technique, following production via multi-nucleon transfer between heavy ions. The ground state of 192Re has been assigned Jπ=(0−) based on the observed β feedings and deduced logft values towards the 0+ and 2+ states in 192Os, which is known as a typical γ-soft nucleus. The shape transition from axial symmetry to axial asymmetry in the Re isotopes is discussed from the viewpoint of single-particle structure using the nuclear Skyrme-Hartree-Fock model

Submonolayer Quantum Dots for High Speed Surface Emitting Lasers

We report on progress in growth and applications of submonolayer (SML) quantum dots (QDs) in high-speed vertical-cavity surface-emitting lasers (VCSELs). SML deposition enables controlled formation of high density QD arrays with good size and shape uniformity. Further increase in excitonic absorption and gain is possible with vertical stacking of SML QDs using ultrathin spacer layers. Vertically correlated, tilted or anticorrelated arrangements of the SML islands are realized and allow QD strain and wavefunction engineering. Respectively, both TE and TM polarizations of the luminescence can be achieved in the edge-emission using the same constituting materials. SML QDs provide ultrahigh modal gain, reduced temperature depletion and gain saturation effects when used in active media in laser diodes. Temperature robustness up to 100 °C for 0.98 μm range vertical-cavity surface-emitting lasers (VCSELs) is realized in the continuous wave regime. An open eye 20 Gb/s operation with bit error rates better than 10−12has been achieved in a temperature range 25–85 °Cwithout current adjustment. Relaxation oscillations up to ∼30 GHz have been realized indicating feasibility of 40 Gb/s signal transmission

Formation of ITB in the vicinity of rational surfaces in the Uragan-3M torsatron

It was shown that there is the possibility of ITB formation in the vicinity of rational surfaces in a torsatron magnetic configuration. The formation of ITB is accompanied by fast change of plasma poloidal rotation velocity, radial electric field and its shear and the decrease of plasma density fluctuations. After the ITB formation the transition to the improved plasma confinement takes place. The transition stars when electron temperature in the region of rational surfaces is sufficient to satisfy the condition υTe/uei>>2πR0 (here υTe is electron thermal velocity and uei is the frequency of ion – electron collisions, and R0 is the major radius of the torus). Such a regime can be maintained during the whole duration of RF discharge without any disturbances.Показано, що існує можливість формування внутрішнього теплового бар’єру (ВТБ) в плазмі ВЧ розряду в околиці раціональних поверхонь в торсатронній магнітній конфігурації. Формування ВТБ супроводжується бистрими змінами швидкості полоідального обертання плазми, радіального електричного поля и його шира і зменшенням флуктуацій густини плазми поблизу раціональних поверхонь. Після формування ВТБ спостерігається перехід в режим поліпшеного утримання плазми. Час переходу зменшується із збільшенням ВЧ потужності нагріву.Показано, что имеется возможность формирования внутреннего теплового барьера (ВТБ) в плазме ВЧ разряда в окрестности рациональных поверхностей в торсатронной магнитной конфигурации. Формирование ВТБ сопровождается быстрыми изменениями скорости полоидального вращения плазмы, радиального электрического поля и его шира и уменьшением флуктуаций плотности плазмы вблизи рациональных поверхностей. После формирования ВТБ наблюдается переход в режим улучшенного удержания плазмы. Время перехода сокращается с увеличением ВЧ мощности нагрева

Energy Exchange Between Laser Pulses in Atomic Medium with a Closed Excitation Contour

In this work we investigate propagation of two laser pulses in the optically dense atomic medium (three-level Λ -system) in the case of a closed excitation contour. The closed excitation contour is created by additional microwave radiation which interacts with the low-frequency transition of the Λ -system. Two cases are considered: when the pulse duration is more and less then lifetime of the excited atomic level. It is shown that the propagation of the pulses depends on the relative phase of the fields. When the relative phase is zero, the pulses energy is absorbed linearly. When the relative phase is π / 2, the pulses exchange energy between each other