H. Tajalli

Subwavelength atom localization via amplitude and phase control of the absorption spectrum-II

Mostafa Sahrai, Habib Tajalli, Kishore T. Kapale, ∗ and M. Suhail Zubairy Department of Physics, Tabriz University, Tabriz, Iran Quantum Computing Technologies Group, Jet Propulsion Laboratory, California Institute of Technology, Mail Stop 126-347, 4800 Oak Grove Drive, Pasadena, California 91109-8099 Institute for Quantum Studies and Department of Physics, Texas A&M University, College Station, TX 77843-4242

The effects of the incoherent pumping field on the phase control of group velocity

This paper studies the effects of the incoherent pumping field and the spontaneously generated coherence (SGC) on the phase control of group velocity. The effects of a relative phase between probe and coupling fields on the absorption and the dispersion are then discussed. It is shown that the phase dependence of the group velocity not only depends on the existence of the SGC, but also depends on the existence of the incoherent pump field. We show that for the weak probe field, and in the presence of SGC, the existence of the incoherent pump field is a necessary condition for the phase control of the dispersion, the absorption and the group index.

Effects of surfactants on the molecular aggregation of rhodamine dyes in aqueous solutions

The aggregative properties of rhodamine 6G (R6G) and rhodamine B (RB) in aqueous solutions of cationic and anionic surfactants were studied using the absorption and fluorescence spectroscopic methods. The dye-surfactant interactions in aqueous and surfactant solutions were also studied. The spectroscopic studies were extended in order to determine the effect of molecular structure of the surfactants on the aggregative behavior of the rhodamine dyes. The aggregate structures and the nature of the interacting pairs in these dyes were discussed using the exciton theory.

PHOTONIC TRANSMISSION SPECTRA IN ONE-DIMENSIONAL FIBONACCI MULTILAYER STRUCTURES CONTAINING SINGLE-NEGATIVE METAMATERIALS

We investigate the transmission properties of the Fibonacci quasiperiodic layered structures consisting of a pair of double positive (DPS), epsilon-negative (ENG) or/and mu-negative (MNG) materials. It is found that there exist the polarization-dependent transmission gaps which are invariant with a change of scaling and insensitive to incident angles. Analytical methods based on transfer matrices and efiective medium theory have been used to explain the properties of transmission gaps of DPS-MNG, DPS-ENG and ENG- MNG Fibonacci multilayer structures.

Switching from normal to anomalous dispersion via coherent field

This paper investigates the group velocity of a probe field in a four-level atomic system. It is shown that switching from positive to negative dispersion can be achieved just by the intensity of the coupling field. Superluminal light propagation in the system at stake is accompanied by reduced absorption to make sure that the probe field is not attenuated as it passes through the medium.

Substituent and solvent effects on the photo-physical properties of some coumarin dyes

Absorption and fluorescence spectra of three coumarin dyes with various substituents and alkyl groups have been recorded in solvents in the range of 200-730 nm. The photo-physical behavior of dissolved dye depends on the nature of its environment, i.e. the solvatochromic behaviors of coumarin dyes and solvent/solute hydrogen bonding interactions can be analyzed by means of linear solvation energy relationships concept proposed by Kamlet and Taft. The intensity, shape, and maximum wavelength of the absorption and fluorescence band of these dyes in solution depend strongly on the solvent-solute interactions and solvent nature. Hydrogen bonding interactions (specific solute-solvent interactions) between these dye-solvent complex and dipolarity/polarizability (non-specific solute-solvent interactions) control reorientation of solvent molecules around the dye.

Highly sensitive electrochemiluminescence detection of p53 protein using functionalized Ru–silica nanoporous@gold nanocomposite

A simple, rapid response time and ultrahigh sensitive electrochemiluminescence (ECL) immunosensor based on Ru(bpy)3(2+)doped silica doped AuNPs (Ru-Si@Au nanocomposite) was developed for detection of p53 protein, a well-known tumor suppressor. The immunosensor was constructed using biotinylated capture antibody, immobilized on the glassy carbon electrode (GCE) using streptavidin modified-gold nanoparticles/thiolated graphene oxide, followed by its conjugation with the Ru-silica@Au nanocomposite labeled secondary antibody to form a sandwich-type immunocomplex. The use of Ru-Si@Au nanocomposites led to a remarkable increase in the ECL intensity and, thus, the sensitivity of the method. Under the optimized conditions, the linear range of the proposed p53 immunosensor was found between 0.2 and 200 pM with a calculated limit of detection of 22.8 fM. The selectivity and reproducibility of the immunosensor was also investigated and the results showed high specificity and great stability in detecting of p53. Moreover, the ECL immunosensor was successfully applied for quantification of p53 protein in the human spiked serum samples and more importantly in the human normal and cancer skin fibroblast cells showing much satisfactory result compared with the ELISA method. The proposed immunosensor reported herein offers a considerable potential in early detection of cancer and clinical diagnosis and provides a new platform for biomarker detection.

Anisotropic media effect on the dipole moment of some coumarin dyes.

The ground state (μ(g)) and the excited state (μ(e)) dipole moments of two coumarin laser dyes, C500 and C503, were studied at room temperature in various solvents, viz., aprotic solvents, alcohols and liquid crystals at 298 K. We report dipole moment of laser dyes in different anisotropic (liquid crystals) and isotropic environments. The dipole moments values in different media help to investigate environment effects on the molecular dipole moment and provide a straightforward method for comparing their properties. Ground and excited state dipole moments of coumarin dyes were evaluated by means of solvatochromic shift method. It was observed that dipole moment values of excited states (μ(e)) were higher than corresponding ground state values (μ(g)), indicating a substantial redistribution of the π-electron densities in a more polar excited state for the dyes investigated.

Measurement of the Wigner function of a cavity field via Autler-Townes spectroscopy

We show that the Wigner fuction of a cavity field can be constructed from the spontaneous emission spectrum in driven three-level atomic systems. We consider two configurations, the upper- and lower-level couplings, in which the driving field is the quantized field inside a cavity. In the proposed method, the Wigner function of the driving field is recovered in a straightforward manner, without much mathematical manipulation of the experimental data, from the spontaneous emission spectra.

Tunable Metamaterials Made of Graphene-Liquid Crystal Multilayers

The dispersion properties of an anisotropic metamaterial composed of periodic stacking of graphene-liquid crystal layers are investigated in the far-infrared region. It is represented that this structure is able to show both the elliptic and hyperbolic dispersions using the tunable properties of the graphene and liquid crystal. The switching between two dispersion phases via control of the temperature, voltage and external electric fleld is studied. It is shown that this switching can be used to control of the transmission and re∞ection at the interface of the metamaterial and air.