Simultaneous electromagnetically induced transparency and absorption in thermal atomic medium

A three-level lambda system driven by multicolor control, pump, and probe fields is investigated. The pump and probe fields are derived from the same laser with opposite propagating directions. Due to the Doppler effect, the zero group-velocity atoms face bichromatic fields, while other atoms face trichromatic fields. The atomic medium shows distinct characteristics and exhibits simultaneous electromagnetically induced transparency(EIT) and electromagnetically induced absorption(EIA) at two frequencies. EIT and EIA peaks have a fixed relationship with frequency, which is determined by the Doppler shifts.     

四能级原子系统中电磁感应吸收的相位控制

在以三个电偶极跃迁构成简并N型四能级系统中,利用密度矩阵方程计算了介质对探测场的吸收,研究了激光场拉比相位对吸收的影响.结果表明:介质对探测场的吸收和放大取决于控制场和信号场的拉比相位,且吸收和放大随控制场、信号场的拉比相位改变而作周期性变化,周期为2π;而探测场的拉比相位变化对吸收没有影响.同时,控制场、信号场拉比相位对吸收的影响是相同的,而且拉比相位主要影响原子相干,对原子布居影响不大.     

四能级原子系统中非线性电磁感应吸收的理论研究

在n型四能级原子系统中,研究了电磁感应吸收的非线性理论.结果表明:探测光的拉比频率和衰减分配系数A影响非线性吸收,进而影响介质吸收.当探测光光强较弱时,介质吸收和线性吸收一致,均表现为电磁感应吸收特征;当探测光光强增大时,介质吸收和线性吸收不再一致,介质吸收曲线将会呈现出烧孔现象;当探测光光强增大到控制光(或信号光)光强时,介质吸收表现出很大的增益现象.同时,非线性吸收受到衰减分配系数A的影响,即使在探测场很弱的条件下,随着A值的减小,介质吸收由电磁感应吸收现象表 关键词： 电磁感应吸收 非线性吸收 增益现象 n型四能级原子系统     

Low-frequency stimulated emission and induced absorption in a three-level atom

Investigations of the motion of conventional negative ions (electron bubbles) in He II under pressures above 11 bar have provided the only means of measuring the Landau critical velocity for roton creation,v _L, and for studying supercritical dissipation at higher velocities. Earlier work on roton creation is reviewed and it is pointed out that there is still no generally agreed explanation of the fact that the rotons seem to be emitted from the moving ionin pairs; nor is it known why the matrix element characterising the pair emission process should decrease rapidly with pressure. The possibility of studying these phenomena through use either of the fast ion (whose nature remains unknown), or of selected ions from the large variety of species that can be injected into He II by the recently developed technique of laser ablation, is discussed.     

Low-frequency stimulated emission and induced absorption in a three-level atom

We consider the excitation spectra of a bichromatically driven three-level atom in the lambda configuration and in the low-frequency domain. These dynamically induced spectra occur when the excitation fields operate at low intensities and are neither one- nor two-photon resonant with the various transitions of the system.     

Electromagnetically induced transparency and electromagnetically induced absorption in Y-type system

The propagation of a probe field through a four-level Y-type atomic system is described in the presence of two additional coherent radiation fields, namely, the control field and the coupling field. An expression for the probe response is derived analytically from the optical Bloch equations under steady state condition to study the absorptive properties of the system under probe field propagation through an ensemble of stationary atoms as well as in a Doppler broadened atomic vapor medium. The most striking result is the conversion of electromagnetically induced transparency(EIT) into electromagnetically induced absorption(EIA) as we start switching from weak probe regime to strong probe regime. The dependence of this conversion on residual Doppler averaging due to wavelength mismatch is also shown by choosing the coupling transition as a Rydberg transition.     

Decoherence of electromagnetically induced transparency in atomic vapor

We report characterization of electromagnetically induced transparency (EIT) resonances in the D1 line of (87)Rb under various experimental conditions. The dependence of the EIT linewidth on the power of the pump field was investigated at various temperatures for the ground states of the lambda system associated with different hyperfine levels of the atomic 5S(1/2) state as well as magnetic sublevels of the same hyperfine level. Strictly linear behavior was observed in all cases. A theoretical analysis of our results shows that dephasing in the ground state is the main source of decoherence, with population exchange playing a minor role.     

五能级原子系统中的多重电磁感应透明

利用半经典理论,研究了在相干外场驱动下的倒三脚架型原子系统的吸收性质.数值计算结果表明:通过调节相干场的Rabi频率,该系统可以呈现出三重、双重、单重电磁感应透明;在三重电磁感应透明中,透明窗的位置可以通过调节相干场的失谐量来进行控制,而且透明点的位置可连续地变化,即在一定范围内存在一系列连续频率的探测光无吸收地通过介质.最后,在缀饰态表象中对上述现象给出了解释.     

Effect of irreversible atomic relaxation on resonance fluorescence,absorption, and stimulated emission

Even for a single isolated constituent of matter, a recent generalization of quantum mechanics, called quantum thermodynamics, postulates the existence of new nonmechanical individual states, not contemplated within conventional quantum mechanics, for which the time evolution is governed by a novel nonlinear equation of motion, which entails an irreversible, energy-preserving internal redistribution mechanism of relaxation towards stable equilibrium. For a single two-level atom interacting with the quantum electromagnetic field, we show that such irreversible internal redistribution mechanism entails interesting corrections to the conventional quantum electrodynamic predictions on absorption, resonance fluorescence, and stimulated emission. For a two-level atom driven near resonance by a nearly monochromatic laser beam, we estimate the corrections implied on the spectral distribution of resonance fluorescence and on the absorption and stimulated emission line shape. We submit that our predictions call for further high-resolution studies of atom-field interactions. For example, the value or a lower bound to the value of the only unknown constant of the theory, namely, the internal redistribution time constant, can only be established by a quantitative experimental study.     

Zeeman transitions in deuterium atoms induced by ultra-relativistic electrons

We present data showing hyperfine transitions in an atomic deuterium beam induced by the (476 MHz) radio-frequency field of a 704 MeV electron beam in a storage ring. A polarized deuterium beam, produced in an atomic beam source, was crossed with a stored electron beam and analyzed with a Breit--Rabi polarimeter. Electron-beam induced transitions were singled out by injecting different combinations of hyperfine states. Transition probabilities as high as 70% were measured at large currents (~ 100 mA). All possible deuterium transitions for a radio-frequency of 476 MHz were observed. In addition, a 1--6 transition resulting from the first harmonic (952 MHz) was observed. The effects of these transitions are of general importance for the polarized internal target technique applied in nuclear and particle physics experiments. The data are reasonably described by numerical estimates. The observed mechanism can be exploited to create nuclear polarized atoms when injecting electron polarized atoms with no net nuclear polarization into a storage cell. However, when nuclear polarized atoms are injected, care should be taken to avoid this mechanism, since it would result in depolarization of the atoms. The studies enabled us to choose the magnetic guide field during our spin-dependent electron--deuteron scattering experiments, such that electron-beam induced depolarizing effects were avoided. This revised version was published online in July 2006 with corrections to the Cover Date.     

光学-射频双光子耦合作用下的电磁诱导透明和电磁诱导吸收

在通常的Λ型三能级系统中,光学耦合场和探测场分别激发两个不同的光学跃迁,探测吸收谱呈现电磁诱导透明(EIT)特性.若将此系统拓展为光学-射频双光子耦合场和探测场共同作用下的准Λ型四能级系统,探测吸收谱呈现电磁诱导吸收(EIA)和EIT两种特性.通过求解系统的密度矩阵方程,分析了EIA和EIT的产生条件,并给出了相应的缀饰态解释.研究结果表明,在准Λ型四能级系统中,光学耦合场对EIA和EIT的形成起决定作用,共振时出现EIA,非共振时出现EIT,而且EIA和EIT的线宽随着光学耦合场拉比频率的增大而增加. 关键词： 电磁诱导透明 电磁诱导吸收 射频场 光学耦合场     

From electromagnetically induced transparency to absorption in planar optical metamaterials

We theoretically investigate the classical analog of electromagnetically induced transparency （EIT） and electromagnetically induced absorption （EIA） in a planar metamaterial at optical frequency, which origi- hates from destructive and constructive interference between dark and radiative elements. The metama- terial consists of two coupled resonators with different geometries. An EIT-like transparent window with low absorption is observed and found to be strongly affected by resonant states of the resonators. The transition between the EIT and EIA is achieved by changing the split width and coupling distance. The absorption is enhanced up to 2.5 times compared with the dipolar case. The excitation of the dark mode is very important for EIT- and EIA-like responses of the proposed metamaterial. The EIT and EIA phenom- ena offer a potential method for manipulating electromagnetic response in metamaterial-based devices.     

Normal modes for electromagnetically induced transparency in the presence of off-resonance transitions

Electromagnetically induced transparency in ideal Λ atoms involves lossless propagation for paired fields with locked phase difference. Coupled equations for atomic and field vectors are solved to demonstrate that such a normal-mode propagation is stable against perturbations produced by off-resonance transitions, which can be present in real atoms.     

Two-dimensional vector solitons in a cold atomic gas via electromagnetically induced transparency

We investigate the formation and propagation of vector vortex solitons (VSs) and unipolar solitons (USs) in a cold coherent atomic gas with a Bessel lattice (BL). The system considered is a gas with a tripod level configuration. Owing to the big enhancement of Kerr nonlinearity contributed by the electromagnetically induced transparency (EIT), a weak vector vortex soliton can be effectively formed with ultraslow propagation velocity. We also demonstrate that the characteristics of two-dimensional VSs and USs can be controlled and manipulated by adjusting the parameters of BL. Results obtained may be useful for designing all-optical switches at low light levels.     

Optical storage with electromagnetically induced transparency in a dense cold atomic ensemble

We experimentally investigate optical storage with electromagnetically induced transparency in a dense cold (85)Rb atomic ensemble. By varying the optical depth (OD) from 0 to 140, we observe that the optimal storage efficiency has a saturation value of 50% as OD>50. Our result is consistent with that obtained from hot vapor cell experiments.