Controlling the optical bistability in a Λ-type atomic system via incoherent pump field

We investigated optical bistability (OB) and the absorption properties of a weak probe field in a three-level Λ-type atomic system confined in a unidirectional ring cavity via incoherent pump field. We found that the threshold of OB and the probe field absorption can be controlled by the rate of incoherent pump field. No laser field was used in the pumping processes.     

Enhancing Kerr nonlinearity via quantum interference from incoherent pumping

The effect of quantum interference from incoherent pump field on the Kerr nonlinearity of V- and Lambda-type three-level systems is investigated. It is found that enhanced Kerr nonlinearity can be obtained via quantum interference of incoherent pump field. It is also demonstrated that the enhanced Kerr nonlinearity is located in the reduced-absorption region. The enhancement of Kerr nonlinearity is attributed mainly to the presence of extra atomic coherence induced by quantum interference from incoherent pump field.     

Incoherent pump influence on the transient gain in a V-type system with spontaneously generated coherence

We study the influence of the incoherent pump field on the transient response of a three-level V-type system with two near-degenerate excited states. In this system due to interaction of the field with the vacuum an interference term appears, the spontaneously generated coherence term. We find that due to the incoherent pump the transient proprieties of the atomic system can be significantly modified. The enhancement of the transient gain can be obtained for proper values of the rate of the incoherent pump field and relative phase between the two fields.     

Dynamical switching and memory via incoherent pump assisted optical bistability

We analyze the dynamical behavior of all-optical switching and memory based on tunable optical bistability in a three-level Λ-type atomic system driven by a probe field circulating in an optical ring cavity, a coherent coupling field and an incoherent pump field outside cavity. Owing to the incoherent pump process, the absorption and Kerr nonlinearity near the atomic resonance change dramatically as a result of varied population distribution and atomic coherence, and then the switch-up and switch-down thresholds, as well as the width (or area) of bistable curve, can be manipulated effectively. By tuning the intensity of either coherent coupling field or incoherent pump field, we can make the system output flip between the lower and upper branches of different bistable hysteresis loops while the cavity input keeps to a constant value. Accordingly, all-optical switching and memory can be implemented via dynamical control of the bistable behavior under the assistance of incoherent pump. The proposed scheme can find potential applications in all-optical communication and computation.     

用双光源相位共轭型非相干光时间延迟简并四波混频测量超快速过程

本文提出用双光源相位共轭型非相干光时间延迟简并四波混频测量失相时间和布居弛豫时间的理论,并对其应用进行了讨论.     

Modifying spontaneous emission via interferences from incoherent pump fields

The spontaneous emission spectrum is evaluated from the doublet of a 4-level atomic system. Excitation from the ground state of the closed system is supplied solely by two incoherent pump fields with one involving the doublet states; i.e., no laser fields are involved at any stage of the problem. We find that the interference which arises due to the incoherent pump field induces substantial modifications of the spontaneous emission spectrum. In particular, the occurrence of a narrow spectral feature is shown to be quite sensitive to the incoherent pump-induced interference.     

非相干泵浦过程对光学双稳的影响

研究了低能级偶极子的非相干泵浦过程环形腔中双稳行为的影响，结果表明，耦合系统的双稳机制为非相干泵浦过程的干涉性，双稳迟滞环与非相干泵浦场有严格的对应关系，在一定条件下，甚至出现多稳态，可以利用非相干泵浦的干步性能控制光学双稳。     

Electromagnetically Induced Grating Without Absorption Using Incoherent Pump

We propose a scheme for creating electromagnetically induced grating in a four-level double- Λ atomic system driven by a coupling field and an incoherent pump field. Owing to the incoherent pumping process, large refractivity accompanied with vanishing absorption or even gain across the probe field can be built up in the atoms, thus phase grating or gain-phase grating, which diffracts a probe light into different directions, can be formed with the help of a standing-wave coupling field. The diffraction efficiency of the gratings can be tuned by the coupling field intensity and the incoherent pump rate, hence the proposed gratings should be suitable for beam splitter and optical switching in optical communication and networking.     

Sub-Poissonian radiation of a one-atom two-level laser with incoherent pumping

The quantum statistical properties of the radiation of a one-atom two-level laser with incoherent pumping are analyzed. Solution of the Liouville equation for the density operator in the basis of Fock states shows that stationary radiation from a single-mode laser with incoherent pumping can be in a squeezed (sub-Poissonian) stationary state if the rate of spontaneous decay is lower than the rate of cavity losses and the pump rate. Inside the cavity the Fano factor reaches F=0.85 (15% squeezing). Multiple squeezing (F=0.19) is possible in the transient lasing regime. Significant squeezing obtains at the cavity output; the spectral Fano factor at zero frequency is 0.36 under optimal conditions. Zh. éksp. Teor. Fiz. 115, 1210–1220 (April 1999)     

From slow to fast light in amplified negative refraction using atomic coherence assisted by an incoherent pump

We propose and demonstrate a scheme to realize large negative refraction dispersion when a probe field is amplified by cooperation between a coherent field and an incoherent pump. The probe pulse can propagate either subluminally or superluminally in the left-handed amplification medium by modulating parameters of the coherent and incoherent fields.     

Phase-matched light-induced scattering,mirrorless self-oscillation,and generation of nearly retropropagating waves in LiNbO3:Fe in “forbidden” interaction geometry

Two mutually incoherent pump waves impinging symmetrically on a LiNbO₃:Fe crystal from different faces in a plane normal to the C-axis produce chartacteristic patterns of light-induced scattering (lines and rings) and a pair of collimated waves propagating roughly in backward directions with respect to the pump waves. We show that the bright line of scattered light is in fact the mirrorless oscillation due to backward-wave four-wave mixing in the crystal with local (photovoltaic) response, while the retropropagating waves appear only because of high-order diffraction processes.     

Effects of relative phase on transient evolution in an open resonant ladder-type atomic system

In an open ladder-type resonant atomic system, variation in relative phase between probe and driving fields does not affect the transient evolution of populations, but it has remarkable effects on gain and dispersion of the probe field. No matter whether an incoherent pump is present or absent, transient and stationary gains without inversion (GWI) always can be obtained by choosing an appropriate value of the relative phase. When the incoherent pump is absent,the values of transient and stationary GWIs are much larger and the time interval required to reach the stationary value is longer than those when the incoherent pump is present. Varying the exit rate and the ratio between injection rates can obviously change the phase-dependent GWI. In addition, in the transient evolution process, the phenomenon of high dispersion (refractive index) without absorption occurs at some values of relative phase. In the corresponding closed system, the stationary GWI can be obtained by choosing an appropriate value of relative phase only when incoherent pump exists, moreover the gain is smaller than that in the open system.     

Negative refraction without absorption via both coherent and incoherent fields in a four-level left-handed atomic system

This paper attempts a probe into negative refraction without absorption by means of an incoherent pump field and a strong coherent field coupling the dense four-level atomic system. With the application of the incoherent pump field to manipulate the populations in atomic levels and the variable strong coherent field to create quantum coherence, the constraint condition of two equal transition frequencies responding to the probe field in the atomic system isn't required. And these lead to the propagation transparency and strong magnetic response of the probe field, left-handedness with vanishing absorption in the atomic system. However, an excessive coherent field intensity would increase the absorption.     

Stochastically excited waves in a 1D random medium – the mean field and power spectrum

Scalar wave propagation is examined when both the wave source and the propagation speed are random. Results are derived for the mean field and the power spectrum using the second-order Born approximation. The results depend on whether the source S(x, t) and the propagation speed c(x, t) are correlated or not. When they are uncorrelated, the mean field is zero. When they are correlated, the mean field is non-zero only when the source is non-stationary. The power spectrum is incoherent to leading order. There is a transfer of energy from lower to higher frequencies owing to wave scattering. The corresponding frequency upshift of the power profile in the (k, ω) domain is mainly caused by the cross power between the direct and the twice scattered field, which represents a second-order incoherent power contribution. The results are confirmed using a numerical solution of the wave equation where the scattered field is expanded to fifth order.     

Counterintuitive gain without inversion enhancement in pulsed fields sequence

Ultrashort pulse counterintuitive sequencing of three level lambda scheme shows five fold enhancement of the amplification without inversion on the probe transition. Introducing a short pulse weak probe field prior to the strong pump field results in an enhanced dispersion and stronger amplification on the probe field. The presence of an incoherent pump populating the upper level is crucial to the amplification. Parametric study of this effect is briefly presented.     

Control of the threshold intensity and hysteresis cycle of optical Bi(multi)stability via atomic injection and exit rates from cavity

The optical bistability (OB) and multistability (OM) in an open Λ-type three-level atomic system inside a ring cavity are investigated. It is found that the ratio of atomic injections β and the exit rates r ₀ from cavity evidently affects the threshold intensity of OB and OM. The effect of incoherent pumping field on the OB and OM of a medium is discussed. We show that the bistable behavior of the open system significantly differs from that in a corresponding closed system, especially with an increase in the incoherent pump rate. The intensity threshold is reduced in an open system but increases in a closed system. In addition, the dependence of OB and OM in an open system on spontaneously generated coherence, the relative phase the between probe and coupling fields, the coupling-field intensity, and the cooperation parameter are briefly discussed.     

Generation of coherent optical radiation by electronic means: the electro-optical parametric oscillator

We describe a novel external light control element that is capable of stabilizing both the amplitude and the frequency of an optical input field. A demanding application of this electro-optical parametric oscillator, conversion of incoherent inputs into coherent, phase-trackable outputs with small residual intensity modulation, is reported. Estimations show that commercially available light-emitting diodes have the potential to act as pump sources, although the incoherent optical input field used in these initial experiments was prepared by filtering of the coherent emission of a laser diode.     

Electrotransport in a coherent metal-hydrogen system

The growth and decay kinetics of macroscopic hydrogen density modes in single crystals of niobium excited by an applied electric field was measured. The samples were prepared in-situ as to prevent incoherent precipitations. At a low hydrogen concentration (c=0.04 H/Nb) the diffusion coefficient and the effective charge agree well with results from experiments using polycrystalline samples. At a high hydrogen concentration (c=0.28 H/Nb) the electrotransport experiments could be extended into the unstable region of the incoherent phase diagram. The spinodal temperature obtained from the concentration amplitude (350±12 K) is significantly lower than the incoherent spinodal temperature. Important difficulties in evaluating electrotransport experiments at high hydrogen concentrations are discussed.     

On the incoherent scattering of an acoustic or electromagnetic wave

A random configuration of objects in space, or a stochastically rough boundary, is considered to scatter an incident acoustic or electromagnetic wave having harmonic time dependencee ^iwt . In the case of a stochastic surface, Beckmann has compared the Kirchhoff solution with his approach, which employs random walk. The latter approach is used to demonstrate the Rayleigh-distributed amplitude of a field scattered by a very rough surface. This demonstration requires the conjecture that large standard deviations in the random phases of the scattered elementary waves result in an incoherent scattered field. Beckmann's conjecture has not been rigorously proven. However, in this paper, incoherence of the scattered field and broad distributions, over many cycles, in the phases of the elementary waves are both shown to be implied by a third condition, which is defined. Furthermore, the random phase of an incoherent field is shown to be statistically independent of its amplitude and uniformly distributed on a 2-rad interval.     

Eine kosmologische Lösung der TREDERschen Gravitationstheorie

A solution of the field equations is given for the case of an universe filled with incoherent matter (p = 0). The observable universe behaves kinematically in a good approximation like the MILNE -model but with flat subspaces t = const.