Two different regimes in a V-type three-level atom trapped in an optical cavity

In this paper two different behaviors of a V-type three-level atom which is driven by a classical field in an optical cavity are shown. We show that the behavior of an atom depends on the values of the critical photon number. The system treatment for large enough values of the critical photon number is described by the semiclassical laser theory. In contrast, for small enough values of the critical photon number, the system shows new quantum properties. In the former case, it is shown that the system performs like a conventional laser and in the latter one, the system acts as an effective two-level model. The behaviors of the system are investigated both in the semiclassical approximation and full quantum theory. For comparing the results, computer simulations are implemented.     

Effects of cavity damping on the entanglement for a three-level atomic system

Based on the master equation for the density matrix, the dynamics of the entanglement of the three-level atom interacting with single-mode field in a finite-Q cavity are studied. It was found that the cavity damping leads to growing entropy and a strong degradation of the entanglement, therefore the coherence loss and entanglement is very sensitive to any change in the cavity damping parameter.     

Optical force and friction of a V-type three-level atom in a driven high-Q cavity

A model is presented to calculate the optical force and friction for a three-level atom in a V-type configuration in a weakly driven high-finesse cavity. Analytical expressions for the force and friction are derived using Heisenberg equations. It is demonstrated that the cooling rate can be increased by one order of magnitude over that of a two-level atomic system, which would stimulate further experimental investigations.     

Phase-change heat transfer of single/hybrid nanoparticles-enhanced phase-change materials over a heated horizontal cylinder confined in a square cavity

The melting process of a nano-enhanced phase-change material is investigated in a square cavity with a hot cylinder located in the middle of the cavity in the presence of both single and hybrid nanoparticles. The dimensionless partial differential equations are solved numerically using the Galerkin finite element method using a grid with 6000 quadrilateral elements. The effects of the volume fraction of nanoparticles, the Fourier number, the thermal conductivity parameter, and the viscosity parameters are studied. The results show that the solid-liquid interface and the liquid fraction are significantly affected by the volume fraction of nanoparticles and the thermal conductivity parameter. Additionally, it is found that the melting rate is much larger when the Fourier number changes between 0 and 0.5 and a further increase in the Fourier number causes a reduction in the rate of the melting.     

Time evolution of entanglement and bistability of two coupled quantum dots in a driven cavity

Abstract

The time evolution of entanglement between two quantum dots (QDs) trapped inside a cavity driven by a coherent quantized field is studied. In the presence of dissipation, entanglement shows many interesting features such as sudden death and revival, and finite steady state value after sudden death. We also investigate dependence of entanglement on dot variables and its relation to bistability. It is found that entanglement vanishes when the cavity field intensity approaches the upper branch of the bistability curve. When the cavity is driven by a modulated field in the presence of dissipation, it can periodically generate entanglement, which is much larger than the maximum value attained in the steady-state for this system but the dots are never fully entangled.     

The effects of a finite pulse time in the flash thermal diffusivity method

After a brief review of the finite pulse time effects in flash thermal diffusivity measurements, an analytical expression for an exponential shape pulse was determined using the Green function method. The results were compared with those obtained by Larson and Koyama. It was found that, using the Larson and Koyama equation, when the dimensionless time is equal to zero, the dimensionless temperature rise V cannot reach zero, and when _p, the time characterizing the dimensionless pulse, approaches 1/n ² (n=1,2,3,...), a large error of _1/2 will result. These contradictions have been resolved by the present work. In other respects, both sets of results concurred. The results are compared with the triangular pulse and are discussed.     

The control of spontaneous emission from a three-level atom in an anisotropic photonic crystal with two asymmetric bands

We theoretically investigate the spontaneous emission light of an excited three-level atom embedded in an anisotropic photonic crystal with two asymmetric bands. The property of spontaneous emission relating to the atomic position in a unit cell of the crystal is described with a position-dependent phase difference. The atomic transition in free space can be manipulated by the other associated transition coupling to photonic crystal. The result shows that the spontaneous emission spectra are effectively shifted and tuned by the atomic position-dependent phase, which results in the asymmetric distribution of the photonic density of states between two bands, and the increasing band can push the emitted light towards the other band. The physical process can be further illuminated through analyzing the emitted field in photonic crystal. The result perhaps offers an interesting route towards tunable photonic devices.     

Spectral evolution of an optical pattern generated by spatial modulation instability in a reorientational Kerr nonlinear medium

An experimental investigation is reported on the role of molecular reorientational nonlinearity in the spectral evolution of multifilamentation patterns induced by spatial modulation instability (MI) in a nonlinear Kerr medium. The influence of molecular reorientational Kerr nonlinear response on the spatial MI is analyzed theoretically by the standard stability analysis. The spatial MI gain spectra obtained by experimental measurements were found to agree with the theoretical derivation. In addition, by changing the launch average power, we also analyze the spatial spectral behavior of the optical pattern in such media. It is shown that, for higher launch average power, there will be secondary spatial stripes, manifesting as the original spatial modulation frequency doubling in the spatial frequency domain, which originated from the molecular reorientational Kerr nonlinearity response.     

Effect of grading in refractive index profile on Kerr nonlinear optical processes in single-mode sub-wavelength diameter optical fibre using a straightforward method

A significant effect of nature of refractive index grading in the core of sub-wavelength diameter optical fibres on their performance characteristics in single-mode region is predicted and reported, for the first time, in connection with achievement of waveguide enhancement of Kerr nonlinearity-based optical processes. The analysis is based on a straightforward approach involving Marcuse spot size formulations for single-mode graded index fibre. Our formulations and results provide useful information and insight for optimum transverse dimensions of graded index fibre together with normalized core nonlinearity coefficient corresponding to profile exponent of the power law profile and should invite attention of system designers.     

Melting of an infinite solid with a spherical cavity

The embedding technique is employed to obtain the short time exact analytical solution for the melting or solidification of an infinite body with a spherical cavity, with melting or solidification starting from the interior surface of the cavity. General cases of zero and infinite rates of ablation are considered, with particular emphasis on the Neumann problem and the case corresponding to a sudden rise of temperature. Numerical results are presented, and the validity and accuracy of the solutions are briefly discussed.     

The evolution of travelling wave-fronts in a hyperbolic Fisher model. II. The initial-value problem

In this paper an initial-value problem for a non-linear hyperbolic Fisher equation is considered in detail. The non-linear hyperbolic Fisher equation is given by

流化床CVD法制备单壁碳纳米管:反应温度与时间的影响

基于负载法Fe—MgO体系催化剂研究了化学气相沉积（CVD）法在流化床反应器中反应温度和时间对单壁碳纳米管（SWCNTs）生长的影响。通过气相色谱对尾气进行实时在线分析，获得了CH4在反应过程中的转化率随时间的变化规律。并对不同反应温度和反应时间所获产品进行了TEM、Raman和TGA等表征。结果表明，900℃是最佳的反应温度，反应温度过低会降低催化剂活性，反应温度过高则容易使催化剂过快失活。在合适的反应温度下，反应前10min催化剂的平均活性较高，能够得到较高质量的SWCNTs，10min后催化剂基本失活。     

The effect of aggregation on the nonlinear optical absorption performance of indium and gallium phthalocyanines in a solution and co-polymer host

The nonlinear optical properties (NLO) of Pcs can be modified by substituting different metal atoms into the ring or altering peripheral and axial functionalities. In this study, nonlinear optical absorption properties of tetra-substituted gallium and indium phthalocyanine complexes both in solution and polymeric film have been investigated by open aperture Z-scan measurements with nanosecond pulses at 532 nm. All investigated compounds exhibited reverse saturable absorption for both solution and film experiments. The investigated compounds in the solution showed better nonlinear optical absorption properties than polymeric films. The observed nonlinear optical absorption differences depending on the aggregation are discussed using the ultrafast dynamics and decay processes of excited states found from femtosecond pump-probe spectroscopy with white light continuum experiments.