Enhancement and suppression of spatial splitting four-wave mixing in atomic medium

We experimentally report on the evolution from singly-dressed to doubly-dressed four-wave mixing (FWM) process by controlling the powers of the probe, the pump and the dressing fields respectively. The differences in the enhancement and the suppression of FWM signal between the two-level and cascade three-level atomic systems are observed and explained by the multi-dressed effect theoretically. Both the x direction and the y direction spatial splittings of the degenerate-FWM (DWFM) beams are obtained. We also investigate the switch between the enhancement and the suppression of the DWFM signals and between its spatial splittings in x direction and y direction. The spatial splittings in x direction and y direction can be controlled by the relative position and the intensity of the involved laser beams. Such a study can be useful for optimizing the efficiency of the FWM process and providing potential applications in spatial signal processing.     

Resonantly enhanced continuous-wave four-wave mixing with spontaneously generated coherence in a five-state cold atomic medium

Using Schroedinger-Maxwell formalism, we propose and analyse a continuous-wave four-wave mixing (FWM) scheme for the generation of coherent light in a five-state double-A atomic system with or without spontaneously generated coherence (SGC) based on electromagnetically induced transparency (EIT). We derive the corresponding explicit analytical expressions for the generated FWM field under the steady-state condition. The influence of hyperfine sublevel and SGC effect on the amplitude of the generated FWM field is predicted in detail via the derived analytical expressions. We also give a brief discussion on the experimental realization of the proposed scheme.     

Determination of quasi-elastic coefficients of intermolecular interaction in associates of fatty acids and their perfluorine derivatives

Kuzbass State Technical University, 28 Vesennyaya Str., Kemerovo, 650026, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 6, pp. 58–61, November–December, 1995.     

Coherent forward four-wave mixing of ultrashort radiation pulses in a resonant medium

Forward four-wave mixing (FFWM) of ultrashort light pulses is considered theoretically under their coherent propagation in a resonant-absorbing medium. Nonlinear equations describing FFWM are obtained and studied and it is shown that the energy exchange between pulses of exact resonance may lead to the enhancement of weak radiation. The influence of input radiation parameters and interaction geometry on the FFWM characteristics has been studied.     

Photon statistics of pulse-pumped four-wave mixing in fiber with weak signal injection

We study the photon statistics of pulse-pumped four-wave mixing in fibers with weak coherent signal injection by measuring the intensity correlation functions of individual signal and idler fields. The experimental results show that the intensity correlation function of individual signal(idler) field g_(s(i))~(2) decreases with the intensity of signal injection. After applying narrow band filter in signal(idler) band, the value of g_(s(i))~(2) decreases from 1.9 ± 0.02(1.9 ± 0.02) to 1.03 ± 0.02(1.05 ± 0.02) when the intensity of signal injection varies from 0 to 120 photons/pulse. The results indicate that the photon statistics changes from Bose–Einstein distribution to Poisson distribution. We calculate the intensity correlation functions by using the multi-mode theory of four-wave mixing in fibers. The theoretical curves well fit the experimental results.Our investigation will be useful for mitigating the crosstalk between quantum and classical channels in a dense wavelength division multiplexing network.     

Multi-mode ground state interaction terms in C60-based electron donor-acceptor complexes

Quantum-chemical testing of donor-acceptor properties of binary molecular complexes, related to the singlet state, is suggested as QCh calculations of studied systems and their constituents by using both spin-nondependent (RHF) and spindependent (UHF) versions of the exploited computational tool. The avoided crossing of intermolecular interaction terms of neutral moleculesE _int (A ⁰ B ⁰) and molecular ionsE _int (A ⁺ B ⁻) causes a multi-mode character of the ground state term. The dependence of D-A complex properties on the type of the term, space positions of the term minimum, and the interrelation of the corresponding energies are discussed. The suggested approach has been applied to binary complexes C₆₀+X (X=TAE, TDAE, DMMA, COANP, 2Li, Mg).     

Spectrum of the Y=2 pentaquarks

Based on an assumed mass formula for the spectrum of the Y=2 pentaquarks, where the chromo-magnetic interaction plays an important role, and identifying the lightest state with the Θ⁺(1540), we predict a spectrum in good agreement with the few I=0 and I=1 candidates proposed in the past.     

Stability and bistability of stationary states in four-wave interaction in a photorefractive medium

The stability of stationary states is investigated analytically and numerically for various four-wave mixing schemes in a photorefractive medium with nonlocal nonlinear response when recorded with a translucent grating. Bistability is indicated for a number of four-wave-mixing schemes and the conditions for its existence are indicated.Quantum-Radiophysics Division, Plasma-Phenomena-Theory Sector, Lebedev Physics Institute. Translated from Preprint No. 138 of the Lebedev Physics Institute, Academy of Sciences of the USSR, Moscow, 1989.     

双光子共振非简并四波混频测量钡原子里德伯态碰撞展宽中的伴线研究

研究了采用双光子共振非简并四波混频技术测量原子里德伯态碰撞展宽时出现的伴线现象, 测量了不同缓冲气压下的钡原子里德伯态6snd ¹D₂ (n=16, 22, 36) 的四波混频谱线, 研究了伴线随主量子数n 的变化曲线以及伴线信号强度随缓冲气压压强的变化曲线, 分析了伴线对NFWM谱线的线宽的影响, 发现考虑伴线对四波混频谱线线宽的贡献, 可以对NFWM模型下测量到的碰撞展宽系数进行修正.     

Phase-matching analysis of four-wave mixing induced by modulation instability in a single-mode fiber

Four-wave mixing induced by modulation instability in a single-mode fiber is analyzed from the phase-matching point of view. For the two-channel transmission, a method is proposed to select the four-wave-mixing-induced sidebands, which is based on the proper use of a continuous-wave and a pulse as light sources. We find that a mass of sidebands are generated in the modulation instability resonance region, and the power of the sideband increases with not only the peak power of the pump pulse but also the continuous-wave power which acts as a seed. The research will provide guidance for fiber communication and sensing systems using wavelength division multiplexing technology.     

The effective absorption cross-section of thermal neutrons in a medium containing strongly or weakly absorbing centres

The structure of a heterogeneous system influences diffusion of thermal neutrons. The thermal-neutron absorption in grained media is considered in the paper. A simple theory is presented for a two-component medium treated as grains embedded in the matrix or as a system built of two types of grains (of strongly differing absorption cross-sections). A grain parameter is defined as the ratio of the effective macroscopic absorption cross-section of the heterogeneous medium to the absorption cross-section of the corresponding homogeneous medium (consisting of the same components in the same proportions). The grain parameter depends on the ratio of the absorption cross-sections and contributions of the components and on the size of grains. The theoretical approach has been verified in experiments on prepared dedicated models which have kept required geometrical and physical conditions (silver grains distributed regularly in Plexiglas). The effective absorption cross-sections have been measured and compared with the results of calculations. A very good agreement has been observed. In certain cases the differences between the absorption in the heterogeneous and homogeneous media are very significant. A validity of an extension of the theoretical model on natural, two-component, heterogeneous mixtures has been tested experimentally. Aqueous solutions of boric acid have been used as the strongly absorbing component. Fine- and coarse-grained pure silicon has been used as the second component with well-defined thermal-neutron parameters. Small and large grains of diabase have been used as the second natural component. The theoretical predictions have been confirmed in these experiments.