A Simple Model of Gain Saturation in Homogeneously CW Lasers with Distributed Losses

Abstract

A simple approximate method for the analysis of two-mirror lasers including longitudinal electric field dependence, distributed loss and point losses at the mirrors is presented. Two kinds of the approximate expression are obtained with the help of the energy theorem and the threshold field approximation which require only a programmable calculator for appropriate calculation. They relate the normalized small signal gain in the active medium to laser parameters and they are found to be in a good agreement with exact solutions. A stable optical resonator and a homogeneously broadened medium is assumed.     

Optical bistability and multistability driven by external magnetic field in a dielectric slab doped with nanodiamond nitrogen vacancy centres

Abstract

The theoretical investigation of controlling the optical bistability (OB) and optical multistability (OM) in a dielectric medium doped with nanodiamond nitrogen vacancy centres under optical excitation are reported. The shape of the OB curve from dielectric slab can be tuned by changing the external magnetic field and polarization of the control beam. The effect of the intensity of the control laser field and the frequency detuning of probe laser field on the OB and OM behaviour are also discussed in this paper. The results obtained can be used for realizing an all-optical bistable switching or development of nanoelectronic devices.     

Optical Bistability and Reversed Switching Effect in a Three-photon Resonant Medium

We have developed, ab initio, a theory for the interaction of coherent laser light in three-photon resonance with two effective levels of a multilevel atom. The theory is developed to consider the optical bistability of homogeneously broadened, three-photon, resonant multilevel atoms inside a ring cavity. It is shown that optical bistable behaviour in the fundamental and the generated third harmonic can be obtained using, for example, Na atoms. The device may be useful in constructing two-channel, optical bistable switches. In certain nonlinear regimes it may be possible to obtain reversed switching between the fundamental and the third harmonic bistability.     

Electron-tunneling study of the fluxoid structure in thin superconducting films

We have studied by electron tunneling the subcritical gapless behavior of superconductingIn Bi thin films in a perpendicular magnetic field. The variation of the initial slope of the tunneling characteristics with field gives quantitative information on the variation of the pair potential and allows a comparison with the various existing models. We confirmed the important contribution of the macroscopic screening currents in the films due to the large demagnetizing effects for this geometry. We also found that the effect of the decrease of the microscopic screening currents of the vortex structure for very thin film was largely compensated by the increasing role of the inhomogeneous field distribution outside the sample.     

Laser Instabilities and Chaos in Inhomogeneously Broadened Dense Media

Abstract

We study numerically the effects of local-field corrections originating from near dipole—dipole interactions on the dynamics of a single mode, inhomogeneously broadened laser. Our analysis is based on a set of generalized Maxwell–Bloch equations in which the inhomogeneous nature of gain broadening is accounted for by introducing two new dynamical variables and a single parameter that governs the extent of inhomogeneous broadening. Our results show that local-field effects occurring in a dense gain medium reduce the range of continuous wave operation and lead to instabilities and chaos at much lower pumping levels.     

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.     

Cooperative Effects on Transient Spectral Hole Burning

Abstract

The nonlinear optical susceptibility is calculated for a system of two closely located bound excitons by treating the test field as a perturbation in pump-probe experiments. The effect of photon trapping on the spectral hole burning is found to be dramatic in the transient regime for both on-resonance and off-resonance pumping.     

Motional Sidebands in the Microwave Spectra of Ions in an Rf Trap

Abstract

The atomic motion of an ion in an rf trap adds sidebands to the ion's hyperfine transitions, shifted and broadened by the space charge. Sidebands and carrier depend differently on the microwave polarization, which is determined by observing microwave spectra with the orientation of the dc magnetic field varied. This phenomenon is caused by dc amplitude and phase modulation of the microwave radiation that is partially reflected inside the trap.     

Space-time laser instabilities in homogeneously broadened dense media

Abstract

We investigate the space-time dynamics of a homogeneously broadened single-mode laser when local field correction (LFC) is taken into account. We demonstrate that the Maxwell—Bloch equations modified by LFC admit travelling-wave solutions, as when LFC is not taken into account. Their stability is discussed and compared to the case without LFC.     

Simple theory of microwave induced transparency in atomic and molecular systems

Abstract

In recent years the idea of electromagnetically induced transparency in atomic systems using a microwave coupling field has been discussed. We present theoretical work on how this may be achieved in both Doppler systems, and by extension in non-Doppler broadened systems. By considering the specific example of atomic rubidium we demonstrate the feasibility and practical difficulties of such an experiment. By considering systems with appropriate rotational-vibration structure we conclude that microwave induced transparency in gas vapours is more readily achievable in molecular systems.     

Optical bistability in metal-insulator-metal plasmonic waveguide with nanodisk resonator containing Kerr nonlinear medium

We numerically investigate the optical bistability effect in the metal-insulator-metal waveguide with a nanodisk resonator containing a Kerr nonlinear medium. It is found that the increase of the refractive index, which is induced by enhancing the incident intensity, can cause a redshift for the resonance wavelength. The local resonant field excited in the nanodisk cavity can significantly increase the Kerr nonlinear effect. In addition, an obvious bistability loop is observed in the proposed structure. This nonlinear structure can find important applications for all-optical switching in highly integrated optical circuits.     

Phase optical bistability in structures with surface plasmons

A theoretical analysis is made of the phenomenon of phase optical bistability in structures with surface plasmons. It is shown that in an optical waveguide with a nonlinear layer, not only amplitude but also phase bistability may occur when p-polarized radiation is reflected from the nonlinear waveguide. Pis’ma Zh. Tekh. Fiz. 24, 60–65 (August 26, 1998)     

Optical bistability and multistability in an open ladder-type atomic system

A novel scheme is proposed for controlling the optical bistability and multistability in an atomic system. In an open ladder-type three-level atomic system, it is shown that, by adjusting the ratio between atomic injections and exit rates from the cavity, the intensity threshold of optical bistability can be controlled. The effect of incoherent pumping field and spontaneously generated coherence (SGC) on optical bistability for different values of exit rates is also discussed. It is found that SGC makes the medium phase dependent, so the optical bistability and multistability threshold can be controlled via relative phase between applied fields. Moreover, it is shown that the optical bistability can be switched to optical multistability, which is favorable for the next generation of all-optical systems and quantum networks.     

Model of Gain Saturation in A Two-mirror Laser

Abstract

An approximate method of analysis of nonlinear operation of Fabry-Perot lasers including longitudinal electric field dependence and the spatial hole burning effect is presented. The method is based on a semiclassical approach and provides an approximate expression relating the normalized small signal gain to the normalized output power and laser parameters. The influence of the spatial hole burning effect on the laser characteristics is investigated. It is shown that this effect determines the value of the optimal coupling strength, as well as causing changes in the laser characteristics.     

Model of the nonlinear operation of a laser with a gaussian mirror

Abstract

In this paper a semi-classical model of the nonlinear operation of a laser is extended to describe a laser with a Gaussian mirror. Modified nonlinear self-consistent equations including transverse and longitudinal field dependence, gain saturation, spatial hole burning and nonlinear dispersion effects are derived. With the help of an energy theorem an approximate solution for steady-state single mode operation is presented, which relates the small signal gain to the output power and the laser system characteristic parameters. The laser output power characteristics are presented for various cavity configurations, especially, revealing an influence of the Gaussian mirror parameter on the power efficiency of the laser.     

Intracavity Optical Bistability Driven by Squeezed Light from a Parametric Amplifier

Abstract

We describe the theory of optical bistability when atoms are collectively excited within the cavity of a parametric oscillator. Both optical bistability and parametric amplification can squeeze significantly the cavity-field quantum noise. When they are coupled together we find significant changes both on the mean value bistability and on the spectrum of squeezing as the parametric coupling increases. These are calculated directly from the appropriate master equation for the density matrix using a quantum distribution function (positive P) to develop Fokker—Planck and Ito equations.     

The Effect of Phase Fluctuation on Electromagnetically Induced Transparency,Inversionless Lasing and Refractive Index Enhancement in a Λ System

Abstract

The steady-state behaviour for a Λ-type, three-level atomic system has been analysed by taking into account the effect of the phase fluctuation. It is shown that, for a monochromatic driving field, even if the probe field is in resonance with the corresponding atomic transition, a large refraction index can still be generated; for a finite linewidth of the driving field, inversionless lasing and index enhancement tends to disappear. Furthermore, the linewidth prevents the transparency of the medium.     

Comparison of optical properties between ladder and lambda-type EIT medium with Er3+ ion concentration in Er3+:YAG crystal

The effect of Er³⁺ doped ion concentration on optical properties of two type three-level schemes in 35 nm Er³⁺:YAG (yttrium aluminum garnet) crystal is studied. It is found that intensity threshold of optical bistability and multistability can be changed by Er³⁺ doped ion concentration. Moreover, switching from optical multistability to optical bistability can be done differently by Er³⁺ concentration in two types of three-level schemes. The steady-state and transient behaviors of absorption, dispersion and group index of weak probe field in two schemes are also discussed. In this study, we will report an initial study on optical properties in Er³⁺:YAG crystal and propose a basis for selecting the suitable concentration to carry out experimental investigations in the future.     

Stress dependence of bistability in a zero-magnetostrictive amorphous wire

New data on the bistability of (Co₉₅Fe₅)_72.5Si_12.5B₁₅ amorphous wire are discussed in the framework of a simple model of magnetic interaction between inner core and outer shell of a wire. Experimental results are reported on the tensile stress and annealing-time dependence of switching field and remanence magnetization, for longitudinal and circular hysteresis loops. Theoretical considerations allow various scenarios of the bistability effect to be distinguished, which are helpful in our understanding of the experimental data.     

Simultaneous alignment and micropatterning of carbon nanotubes using modulated magnetic field

Abstract

We report simultaneous alignment and micropatterning of carbon nanotubes (CNTs) using a high magnetic field. It is important to prepare well-dispersed CNTs for alignment and patterning because CNT aggregation obstructs alignment. In magnetic field, highly anisotropic CNTs rotate in the direction stabilized in energy. Owing to their diamagnetic nature, CNTs suspended in a liquid medium are trapped in a weak magnetic field generated by a field modulator; meanwhile, they align to the applied strong magnetic field. The alignment has been achieved not only in polymers but also in ceramic and silicone composites.