Dynamical control of atoms with polarized bichromatic weak field

We propose ultranarrow dynamical control of population oscillation (PO) between ground states through the polarization content of an input bichromatic field. Appropriate engineering of classical interference between optical fields results in PO arising exclusively from optical pumping. Contrary to the expected broad spectral response associated with optical pumping, we obtain subnatural linewidth in complete absence of quantum interference. The ellipticity of the light polarizations can be used for temporal shaping of the PO leading to generation of multiple sidebands even at low light level.Comment: 5 Pages, 5 Figure

Beyond Quantum interference and Optical pumping: invoking a Closed-loop phase

Atomic coherence effects arising from coherent light-atom interaction are conventionally known to be governed by quantum interference and optical pumping mechanisms. However, anisotropic nonlinear response driven by optical field involves another fundamental effect arising from closed-loop multiphoton transitions. This closed-loop phase dictates the tensorial structure of the nonlinear susceptibility as it governs the principal coordinate system in determining, whether the light field will either compete or cooperate with the external magnetic field stimulus. Such a treatment provides deeper understanding of all magneto-optical anisotropic response. The magneto-optical response in all atomic systems is classified using closed-loop phase. The role of quantum interference in obtaining electromagnetically induced transparency or electromagnetically induced absorption in multi-level systems is identified

Non-linear dynamics of double-cavity optical bistability of three-level ladder system

We present non-linear dynamical features of two-photon double-cavity optical bistability exhibited by a three level ladder system in the mean field limit. The system exhibits a hump like feature in the lower branch of the bistable response, wherein a new region of instability develops. The system displays a range of dynamical features varying from normal stable switching, periodic self-pulsing to a period-doubling route to chaos. The inclusion of two competing cooperative atom-field couplings leads to such rich nonlinear dynamical behavior. We provide a domain map that clearly delineates the various regions of stability that will aid the realization of any desired dynamics. We also present bifurcation diagram and the associated supporting evidence that clearly identifies the period-doubling route to chaos, which occurs at low input light levels.Comment: 7 Pages, 9 figures. Feedback is welcom

Coherent control of the refractive index using optical bistability

Refractive index and absorption experienced by a probe field propagating through a three-level atomic medium can be effectively manipulated by the bistable behavior of a control field. The probe field couples the lower transition of the atom in ladder configuration and experiences normal or anomalous dispersion depending on the control field being in the upper or lower bistable state, respectively. We also obtain nonlinear dynamical instability in the form of periodic self-pulsing as the lower bistable branch becomes unstable, quite unlike earlier demonstrations of unstable regime in the upper branch. Consequently, the susceptibility experienced by the probe field varies periodically in time dictated by the control field self-pulsing.Comment: comments can be sent to [email protected]

Optical instabilities in three-level lambda and V system inside double-cavity

We obtain optical instabilities in all-optical bistable systems arising from competing cooperative pathways at low input light levels. In particular for three-level atomic systems in the lambda and V configuration interacting with two independent cavity modes, we identify the necessary conditions related to the incoherent pathways required to obtain instabilities. The instabilities arise when atomic states involved in the bistable transition are leaky and have substantial population, where the incoherent processes adversely affect the cooperative behavior of the atomic ensemble.Comment: Comments can be sent to [email protected]

Negative and positive hysteresis in double-cavity optical bistability in three-level atom

We present novel hysteretic behaviour of a three-level ladder atomic system exhibiting double-cavity optical bistability in the mean-field limit. The two fields coupling the atomic system experience feedback via two independent, unidirectional, single mode ring cavities and exhibit cooperative phenomena, simultaneously. The system displays a range of rich dynamical features varying from normal switching to self pulsing and a period-doubling route to chaos for both the fields. We focus our attention to a new hump like feature in the bistable curve arising purely due to cavity induced inversion, which eventually leads to negative hysteresis in the bistable response. This is probably the only all-optical bistable system that exhibits positive as well as negative bistable hysteresis in different input field intensity regimes. For both the fields, the switching times, the associated critical slowing down, the self-pulsing characteristics, and the chaotic behaviour can be controlled to a fair degree, moreover, all these effects occur at low input light levels.Comment: 5 Pages, 3 figures. Feedback is welcom

Enhanced propagation of photon density waves in random amplifying media

We demonstrate enhanced wave-like character of diffuse photon density waves (DPDW) in an amplifying random medium. The amplifying nature makes it contingent to choose the wave solution that grows inside the amplifying medium, and has a propagation vector pointing opposite to the growth direction. This results in negative refraction of the DPDW at an absorbing-amplifying random medium interface as well as the possibility of supporting "anti"-surface-like modes at the interface. A slab of amplifying random medium sandwiched between two absorbing random media supports waveguide resonances that can be utilized to extend the imaging capabilities of DPDW.Comment: 13 pages, 3 figures; Submitted to Optics Letter

Controlling propagation of spatial coherence for enhanced imaging through scattering media

It is known that a spatially partially coherent light field produces better imaging contrast compared to a spatially coherent field and that the contrast increases as the spatial coherence length of the field becomes smaller. The transverse spatial coherence length of most spatially partially coherent fields increases upon propagation. As a result, the field produces progressively decreasing image quality at subsequent transverse planes. By controlling the propagation of spatial coherence, we demonstrate enhanced image quality at different transverse planes along the propagation direction through a scattering medium. Using a source with propagation-invariant spatial coherence function, we report experimental observations of imaging different transverse planes with equal contrast over a significant distance. Furthermore, we generate a spatially partially coherent source that can be tailored to have minimum-possible transverse coherence area at the plane of the object to be imaged, and using this source, we demonstrate imaging spatially separated transverse planes with maximum possible image contrast

Switching a plasma-like metamaterial via embedded resonant atoms exhibiting electromagnetically induced transparency

We theoretically demonstrate control of the plasma-like effective response of a metamaterial composed of aligned metallic nanorods when the electric field of the incident radiation is parallel to the nanorods. By embedding this metamaterial in a coherent atomic/molecular medium, for example silver nanorod arrays submerged in sodium vapor, we can make the metamaterial transmittive in the forbidden frequency region below its plasma frequency. This phenomenon is enabled by having Lorentz absorbers or other coherent processes like stimulated Raman absorption in the background medium which provide a large positive dielectric permittivity in the vicinity of the resonance, thereby rendering the effective permittivity positive. In particular, processes such as electromagnetically induced transparency are shown to provide additional control to switch and tune the new transmission bands.Comment: 9 pages, 3 figure

Efficient generation of propagation-invariant spatially-stationary partially coherent fields

We propose and demonstrate a novel method for generating propagation-invariant spatially-stationary fields in a controllable manner. Our method relies on producing incoherent mixtures of plane waves using planar primary sources that are spatially completely uncorrelated. The strengths of the individual plane waves in the mixture decide the exact functional form of the generated coherence function. We use LEDs as the primary incoherent sources and experimentally demonstrate the effectiveness of our method by generating several spatially-stationary fields, including a new type, which we refer to as the "region-wise spatially-stationary field." We also experimentally demonstrate the propagation-invariance of these fields, which is an extremely interesting and useful property of such fields. Our work should have important implications for applications that exploit the spatial coherence properties either in a transverse plane or in a propagation-invariant manner, such as correlation holography, wide-field OCT, and imaging through turbulence