Atom—Field Correlations in the Weak-Excitation Limit of Absorptive Optical Bistability

We calculate the steady-state and first-order time varying atom—field correlation functions in the weak-excitation limit of absorptive optical bistability from a linearized theory of quantum fluctuations. We formulate a Fokker—Planck equation in the positive P representation following the phase-space analysis in [H. J. Carmichael, Phys. Rev. A 33, 3262 (1986)], which is suitable for the determination of cross-correlations as it does not resort to adiabatic elimination. Special emphasis is placed on the limit of collective strong coupling as attained from a vanishing photon-loss rate. We compare to the cavity-transmission spectrum with reference to experimental results obtained for macroscopic dissipative systems, discussing the role of anomalous correlations arising as distinct nonclassical features.

     

The photon-ion merged-beams experiment PIPE at PETRA III—The first five years

The Photon-Ion Spectrometer at PETRA III—in short, PIPE—is a permanently installed user facility at the "Variable Polarization XUV Beamline" P04 of the synchrotron light source PETRA III operated by DESY in Hamburg, Germany. The careful design of the PIPE ion-optics in combination with the record-high photon flux at P04 has lead to a breakthrough in experimental studies of photon interactions with ionized small quantum systems. This short review provides an overview over the published scientific results from photon-ion merged-beams experiments at PIPE that were obtained since the start of P04 operations in 2013. The topics covered comprise photoionization of ions of astrophysical relevance, quantitative studies of multi-electron processes upon inner-shell photoexcitation and photoionization of negative and positive atomic ions, precision spectroscopy of photoionization resonances, photoionization and photofragmentation of molecular ions, and of endohedral fullerene ions.     

Comparison of level discrimination, increment detection, and comodulation masking release in the audio- and envelope-frequency domains

In general, the temporal structure of stimuli must be considered to account for certain observations made in detection and masking experiments in the audio-frequency domain. Two such phenomena are (1) a heightened sensitivity to amplitude increments with a temporal fringe compared to gated level discrimination performance and (2) lower tone-in-noise detection thresholds using a modulated masker compared to those using an unmodulated masker. In the current study, translations of these two experiments were carried out to test the hypothesis that analogous cues might be used in the envelope-frequency domain. Pure-tone carrier amplitude-modulation (AM) depth-discrimination thresholds were found to be similar using both traditional gated stimuli and using a temporally modulated fringe for a fixed standard depth (ms = 0.25) and a range of AM frequencies (4-64 Hz). In a second experiment, masked sinusoidal AM detection thresholds were compared in conditions with and without slow and regular fluctuations imposed on the instantaneous masker AM depth. Release from masking was obtained only for very slow masker fluctuations (less than 2 Hz). A physiologically motivated model that effectively acts as a first-order envelope change detector accounted for several, but not all, of the key aspects of the data.     

VEGFR-2 targeted cellular delivery of doxorubicin by gold nanoparticles for potential antiangiogenic therapy

We report a novel gold nanobioconjugate system that achieves targeted delivery of the small molecule drug doxorubicin to endothelial cells using anti-VEGFR-2 antibody conjugated gold nanoparticles (GNPs). The reported nanobioconjugate system combines the inherent ability of GNPs to undergo high levels of derivatization with the precision of antibody recognition of a cell surface antigen. Transmission electron microscopy (TEM) and surface-enhanced Raman spectroscopy (SERS) confirmed intracellular presence of the GNPs. Using a VEGFR-2 expressing cell line and a cell line that is negative for the receptor, in combination with competition assay we established the cell specific targeted delivery of the nanobioconjugate. The nanobioconjugate system described here may have potential drug delivery applications for antiangiogenic cancer therapy.     

Bose-Einstein condensate coupled to a nanomechanical resonator on an atom chip

We theoretically study the coupling of Bose-Einstein condensed atoms to the mechanical oscillations of a nanoscale cantilever with a magnetic tip. This is an experimentally viable hybrid quantum system which allows one to explore the interface of quantum optics and condensed matter physics. We propose an experiment where easily detectable atomic spin flips are induced by the cantilever motion. This can be used to probe thermal oscillations of the cantilever with the atoms. At low cantilever temperatures, as realized in recent experiments, the backaction of the atoms onto the cantilever is significant and the system represents a mechanical analog of cavity quantum electrodynamics. With high but realistic cantilever quality factors, the strong coupling regime can be reached, either with single atoms or collectively with Bose-Einstein condensates. We discuss an implementation on an atom chip.     

Random walks on inhomogeneous lattices

For lattices with two kinds of points (black and white), distributed according to a translation-invariant joint probability distribution, we study statistical properties of the sequence of consecutive colors encountered by a random walker moving through the lattice. The probability distribution for the single steps of the walk is considered to be independent of the colors of the points. Several exact results are presented which are valid in any number of dimensions and for arbitrary probability distributions for the coloring of the points and the steps of the walk. They are used to derive a few general properties of random walks on lattices containing traps.Presented at the Symposium on Random Walks, Gaithersburg, MD, June 1982.     

Spectroscopic Properties and Laser Induced Fluorescence Determination of Some Endocrine Disrupting Compounds

This work presents spectroscopic properties of some Endocrine Disrupting Compounds (EDCs), frequently found in food and in natural water. Studied molecules belong to the groups of phenolic and phthalate EDCs. In a first part, we have examined their absorption and fluorescence properties. Fluorescence emission wavelengths are about 300 nm for phenolic compounds and 360 nm for phtalate compounds; main excitation wavelengths being comprised between 210 nm and 230 nm. Fluorescence lifetimes measured are short (about 4 ns) and the fluorescence quantum yield has been determined. In a second part, to avoid the time consuming solvent extraction step, an analytical application to evaluate the performance of a direct analysis by laser induced fluorescence spectroscopy of ECDs traces in tap water and in raw water is presented. Good detection limits have been obtained, i.e.: 0.35 μg.L⁻¹ of chlorophenol in tap water, which are always lower than the reported Predictive Non Efficient Concentration (PNEC).     

Vibrational relaxation study in 4-chloroacetophenone

Vibrational relaxation process has been emerged as a useful tool in probing the nature of solute solvent interactions in liquid phase. The Laser Raman techniques have been used to study the vibrational and rotational frequencies of molecules, which provide detailed information about the dynamic processes involved in liquids. Raman spectra of C=O stretching mode of 4-chloroacetophenone dissolved in acetonitrile and chlorobenzene have been recorded as a function of solvent concentration ranging from 10% to 90% concentration at room temperature. The 4-chloroacetophenone is a molecule having wide application in manufacture of drugs, perfumes and cosmetics. This study may provide useful information about the vibrational relaxation mechanisms in liquid solutions at molecular level. The Laser Raman components were determined and the spectra were analyzed at different solvent concentrations. The theoretical models have been tested and compare with the experimental results.     

Improving the efficiency of thin film tandem solar cells by plasmonic intermediate reflectors

Thin film tandem solar cells made of amorphous and microcrystalline silicon provide renewable energy at the benefit of low material consumption. As a drawback, these materials do not posses the high carrier mobilities of their crystalline counterpart which limits the feasible material thickness. For maintaining the light absorption as high as possible, photon management is required. Here we show that metallic nanodiscs that sustain localized plasmon polaritons can increase the efficiency of such solar cells if they are incorporated into the dielectric intermediate reflector separating the top and the bottom cell. We provide quantitative estimates for the possible absorption enhancement of optimized bi-periodic nanodiscs that are feasible for fabrication. Emphasis is also put on discussing the impact of obliquely incident sun light on the solar cell performance.