Approximate response of a two-level system to intense multimode radiation

The rotating wave solution for a two-level atom in an intense monochromatic radiation field is extended by an approximation to the case of a multimode radiation field. Expressions for the resultant average excitation probability of the upper state are presented for rectangular and triangular pulses.     

Two-level atoms moving in strong biharmonic and monochromatic counterpropagating fields

The polarization and power spectra of radiation of two-level atoms moving in a field of biharmonic and monochromatic counterpropagating waves are computer simulated. It is shown that, as the frequencies of the counterpropagating waves are scanned with respect to the central frequency of the Doppler contour in the intensity distribution of groups of atoms moving at velocities that satisfy the resonance conditions for multiphoton transitions between quasi-energy levels, apart from well-known sub-Doppler resonances, narrow peaks appear. Such resonances should also occur for the stimulated light pressure force.     

Scheme for Preparation of the W State via Cavity QED

We put forward a scheme for preparation of an entangled multiparty W state between different modes of radiation field inside high-Q cavity QED. Our scheme is based on the interaction of a two-level atom with the cavity field with the assistance of a strong classical driving field for precalculated interaction time. In principle, the scheme can be extended to prepare an N-party W state. The required experimental techniques are within the scope of what can be obtained in the microwave cavity QED setup.     

Cyclotron mechanism of free-electron lasing without inversion

We consider one of the “paradoxical” effects of the theory of radiation and matter interaction: stimulated emission in the absence of inversion. The theory of simultaneous inversionless emission of two high-frequency waves due to their parametric interaction with ensemble of free electrons in magnetic field is developed. The analytical investigation and numerical simulation of the most interesting scheme of this two-photon interaction are presented. New effects are revealed; namely they are self-induced parametric instability of sufficiently strong waves and enhanced parametric instability in sufficiently dense electron medium.     

Coherence-controlled transparency and far-from-degenerate parametric gain in a strongly absorbing Doppler-broadened medium

An inversionless gain of anti-Stokes radiation above the oscillation threshold in an optically dense far-from-degenerate double- ? Doppler-broadened medium accompanied by Stokes gain is predicted. The outcomes are illustrated with numerical simulations applied to sodium dimer vapor. Optical switching from absorption to gain via transparency controlled by a small variation of the medium and of the driving radiation parameters, which are at a level of less than one photon per molecule, is shown.     

腔内混合态原子系统中辐射场的压缩效应

本文应用熵最大原理，假定腔内二能级原子起初就没有关于系统所处态的任何信息，研究了腔内原子与腔场相互作用的压缩行为，得出了原子初始处于任意统计混合态下，当初始激发足够强时，辐射场将产生极其接近于纯态情况在相同激发时的强压缩现象的重要结果，同时还讨论了产生压缩的混态范围。     

Effect of cavity dissipation on the emission spectrum of an atom interacting with a field in the dispersive approximation

The emission spectrum of a two-level atom interacting dispersively with a single mode radiation field in the dissipative cavity is investigated. A general expression for the emission spectrum is derived. The numerical results for the initial field in coherent state are calculated. It is found that the spectrum structure is influenced significantly by the cavity damping constant \kappa , and the spectrum structure is dependent on the interaction time T when the cavity dissipation is present. Only one peak located at Ω_a appears in the atomic spectra for larger T.     

Observation of the Rabi oscillation of light driven by an atomic spin wave

Coherent conversion between a Raman pump field and its Stokes field is observed in a Raman process with a strong atomic spin wave initially prepared by another Raman process operated in the stimulated emission regime. The oscillatory behavior resembles the Rabi oscillation in atomic population in a two-level atomic system driven by a strong light field. The Rabi-like oscillation frequency is found to be related to the strength of the prebuilt atomic spin wave. High conversion efficiency of 40% from the Raman pump field to the Stokes field is recorded and it is independent of the input Raman pump field. This process can act as a photon frequency multiplexer and may find wide applications in quantum information science.     

Nonstationary theory of polarized light pulse propagation through a four-level resonant medium with allowance for nonlinear complex refractive index of medium

Nonstationary theory of polarized light pulse propagation through the medium with resonant transition 1/2 -1/2 is developed with taking into account complexity of the medium nonlinear refractive index. The theory is developed based on the irreducible tensor formalism which allows diagonalizing relaxations matrix and introducing effective decay times associated with the population relaxation, as well as relaxation of coherence between magnetic sublevels of the resonant system. It is shown that as a result of interference of magnetic sublevels in the polarized radiation field the inversionless amplification of radiation occurs due to optical pumping process. The dependence of inversionless amplification on the line broadening and resonance detuning is studied.     

Emission Spectrum from Two Atoms in Bell States in a Cavity

By means of time-evolution operator, the emission spectrum from two two-level entangled atoms in Bell states interacting with a single-mode cavity field in the Fock state has been studied in the paper. The physical spectrum expression of radiation emitted by the atoms is given out for each Bell state. In general, the spectrum shows the symmetrical multi-peak structure and the symmetrical three-peak structure with the strong optical input. Bell states composed of two identical atoms can be partially distinguished in view of the characterizations of their emission spectrum.     

原子间的偶极相互作用对其在腔场中辐射谱的影响

研究了两个通过偶极-偶极力关联的两能级原子在单模腔场中的辐射谱,发现原子间偶极-偶极力的贡献;使辐射谱偏离关于中心频率的对称性.对真空场和强场情况作了细致的讨论.     

Effect of the Doppler broadening on the nonlinear amplification of a polarized wave that propagates in a resonant medium without population inversion

The general nonlinear stationary theory of propagation of an elliptically polarized pulse that resonantly interacts with the 1/2-1/2 transition is developed taking into account relaxation processes. It is shown that interference of magnetic sublevels in the field of polarized radiation that optically pumps atoms results in inversionless amplification of radiation. Taking into account the Doppler broadening of spectral lines shows that there exists a certain optimal length of the resonant medium along which the radiation that emerges from the medium is maximally amplified.     

激光等离子体光丝中太赫兹频谱的调控

研究了双色激光场激发空气成丝产生太赫兹辐射频谱的变化规律.实验观察到随驱动光功率和光丝长度增加,太赫兹光谱主要发生红移的现象.分析表明,由于等离子体密度的增加,太赫兹辐射的趋肤深度减小,等离子体吸收主导了红移的发生.在光丝足够短的条件下,趋肤深度远大于光丝长度,从而产生等离子体振荡主导的太赫兹辐射光谱蓝移.本研究为超快宽带太赫兹辐射的频谱调控提供了新思路.     

Emission Spectrum Property of Modulated Atom-Field Coupling System

The emission spectrum of a two-level atom interacting with a single mode radiation field in the case of periodic oscillation coupling coefficient is investigated. A general expression for the emission spectrum is derived. The numerical results for the initial field in pure number stare are calculated. It is found that the effect of the coupling coefficient modulation on the spectral structure is very obvious in the case of a low modulation frequency and larger amplitude when the initial field is vacuum, which is potentially useful for exploring a modulated light source.     

Emission Spectrum Property of Modulated Atom-Field Coupling System

The emission spectrum of a two-level atom interacting with a single mode radiation field in the case of periodic oscillation coupling coefficient is investigated.A general expression for the emission spectrum is derived.The numerical results for the initial field in pure number stare are calculated.It is found that the effect of the coupling coefficient modulation on the spectral structure is very obvious in the case of a low modulation frequency and larger amplitude when the initial field is vacuum,which is potentially useful for exploring a modulated light source.     

Transmission of a light pulse by a nonlinear medium

Resonance interaction is considered for a pulse of monochromatic radiation in a medium of phthalocyanin type, on the basis of a two-level model. The change in pulse width and height are deduced, as is the degree of bleaching.     

"两原子-双模腔场"系统的腔场谱

研究了存在偶极相互作用的两等同原子与双模腔场共振相互作用双光子过程的腔场谱,研究发现,当两模初态都为光子数态或相干态时,两模腔场谱之间有很强的相互影响,在两模场强相同时,两划的光谱结构也相同,且在强场下呈现三峰结构;当两模初态场强不同时,较强的一模出现简单的单峰结构,而较弱模光谱中三峰的距离随另一模光子数的增加而增大。当两模均为压缩真空态时,在强场下得到经典共振荧光谱,且两模腔场谱之间的相互影响很弱。     

Effects of Dipole Interaction on Emission Spectra of Atoms in Two-Photon Processes

We study the interaction of a pair of coupling two-level atoms with a single mode of the radiation field in an ideal cavity via two-photon resonant transition and/or degenerate Ramancoupled processes.In particular, we consider the emission spectra for both two-photon processes. The effects of atomic coupling are analyzed and the properties of emission spectra for large photon number of the cavity-mode are discussed.     

由灰体辐射场驱动的二能级原子的发射谱

给出了与灰体辐射场相互作用的二能级原子发射谱的一般公式,研究了入射场的光子数分布、腔体吸收系数、系统温度和原子偶极矩对原子发射谱的影响. 关键词：