Controlling Metamaterial Resonances with Light

We investigate the use of coherent optical fields as a means of dynamically controlling the resonant behaviour of a variety of composite metamaterials, wherein the metamaterial structures are embedded in a dispersive dielectric medium. Control and switching is implemented by coherently driving the resonant permittivity of the embedding medium by applied optical radiation. The effect of embedding Split ring resonators (SRR) in a frequency- dispersive medium with Lorentz-like dispersion or with dispersion engineered by electromagnetic induced transparency (EIT), is manifested in the splitting of the negative permeability band, the modified (frequency-dependent) filling fractions and dissipation factors. The modified material parameters are strongly linked to the resonant frequencies of the medium, while for an embedding medium exhibiting EIT, also to the strength and detuning of the control field. The robustness of control against the deleterious influence of dissipation associated with the metallic structures as well as the inhomogeneous broadening due to structural imperfections is demonstrated. Studies on plasmonic metamaterials that consist of metallic nanorods arranged in loops and exhibit a collective magnetic response at optical frequencies are presented. Control and switching in this class of plasmonic nanorod metamaterials is shown to be possible, for example, by embedding these arrays in a Raman active liquid like CS$_2$ and utilizing the Inverse Raman Effect.Comment: 9 pages, 9 figure

Development of validated stability indicating assay method for simultaneous estimation of Diclofenac Sodium and Misoprostol in their combined dosage form

A Stability indicating Reverse-Phase liquid chromatographic method for the simultaneous estimation of DF and MP was developed. The chromatographic assay involves the use of Hi Q C18 W, 150 x 4.6mm, 5m column with a simple mobile phase composition of Acetonitrile and HPLC Grade water in the ratio of 70:30%v/v at a flow rate of 1mL/min with U.V detection at wavelength of 220 nm. The method showed good linearity in the concentration range of 50-100 ?g/mL for DF and 0.20-0.40 ?g/mL for MP. The proposed method was also successfully applied to 20 tablets of marketed formulation (Arthotec). The developed method was successfully validated as per the ICH guidelines for following parameters. Accuracy, precision, repeatability, ruggedness, robustness, system suitability tests, etc. The RSD for Intra-day and Inter-day precision was found to be 0.96-1.85, 1.02-1.83 For DF and 0.55-0.59, 0.59-0.63 for MP. The average percentage recoveries for DF were found to be 90.83, 99.74, 100.21 and for MP it was found to be 100.83, 98.94, 99.72. which was in good agreement with labeled amount of Pharmaceutical formulation. The stability indicating capacity was tested by accelerated degradation of marketed formulation in acidic (0.1 N HCl), basic (0.1 N NaOH), Neutral (water), Oxidative (3% H 2 O 2 ), Thermal (60 0 C), Sunlight exposure

Gain without population inversion in V-type systems driven by a frequency-modulated field

We obtain gain of the probe field at multiple frequencies in a closed three-level V-type system using frequency modulated pump field. There is no associated population inversion among the atomic states of the probe transition. We describe both the steady-state and transient dynamics of this system. Under suitable conditions, the system exhibits large gain simultaneously at series of frequencies far removed from resonance. Moreover, the system can be tailored to exhibit multiple frequency regimes where the probe experiences anomalous dispersion accompanied by negligible gain-absorption over a large bandwidth, a desirable feature for obtaining superluminal propagation of pulses with negligible distortion.Comment: 10 pages + 8 figures; To appear in Physical Review