Complex direct comb spectroscopy with a virtually imaged phased array

LetterAbstract not availableSarah K. Scholten, James D. Anstie, Nicolas Bourbeau Hébert, Richard T. White, Jérôme Genest, and Andre N. Luite

Electromagnetic form factors of charged and neutral kaons in an extended vector-meson-dominance model

A model is developed for electromagnetic form factors of the charged and neutral K-mesons. The formalism is based on ChPT Lagrangians with vector mesons. The form factors, calculated without fitting parameters, are in a good agreement with experiment for space-like and time-like photon momenta. Contribution of the two-kaon channels to the muon anomalous magnetic moment a_\mu is calculated.Comment: 23 pages, 11 figures, accepted for publication in Eur. Phys. J.

Ultrahigh-resolution direct-frequency-comb spectrometer

At low pressures, molecular spectra typically exhibit a large number of very narrow absorption features spread across a relatively wide spectral bandwidth. In order to obtain an accurate estimate of the line shapes, widths, and depths of these absorption features it is a requirement that one performs spectroscopy that is both densely spaced and high resolution across the entire spectral range. Here we demonstrate an approach that delivers on this need: it makes use of an optical frequency comb as the light source along with an optical filter cavity and a dispersive spectrometer to acquire high-resolution spectra with dense spectral sampling. The technique has the potential to acquire spectra with a resolution limit imposed solely by the frequency stability of the comb. As a proof of concept we measure the absorption spectrum of acetylene with a 7.86-MHz spectral spacing over 3.4-THz (25 nm) spectral range. This represents more than 430 000 individual spectral measurements, which are each individually free from the instrumentation broadening that limits conventional spectrometers. Using this spectrum, we extract the thermodynamic properties (temperature, pressure, and molecular density) of the gas sample with high accuracy and precision while simultaneously performing gas compositional analysis.Faisal Karim, Sarah K. Scholten, Christopher Perrella and Andre N. Luite

Experimental and Theoretical Study of Dynamic Polarizabilities in the 5S1/2–5D5/2 Clock Transition in Rubidium-87 and Determination of Electric Dipole Matrix Elements

The interaction between light and an atom causes perturbations in the atom’s energy levels, known as the light shift. These light shifts are a key source of inaccuracy in atomic clocks, and can also deteriorate their precision. We present a study of light shifts and associated dynamic polarizabilities for a two-photon atomic clock based on the 5S1/2–5D5/2 transition in rubidium-87 over the range 770–800 nm. We determine experimental and theoretical values for a magic wavelength in this range and the electric dipole (E1) matrix element for the 5P3/2–5D5/2 transition. We find a magic wavelength of 776.179(5) nm (experimental) and 776.21 nm (theoretical) in the vicinity of the 5P3/2–5D5/2 resonance, and the corresponding reduced E1 matrix element 1.80(6)ea0 (experimental) and 1.96(15)ea0 (theoretical). These values resolve a previous discrepancy between theory and experiment.Rhona Hamilton, Benjamin M. Roberts, Sarah K. Scholten, Clayton Locke, Andre N. Luiten, Jacinda S.M. Ginges, and Christopher Perrell

Small-scale oxygen distribution patterns in a coral reef

One mechanism giving fleshy algae a competitive advantage over corals during reef degradation is algal-induced and microbially-mediated hypoxia (typically less than 69.5 µmol oxygen L−1). During hypoxic conditions oxygen availability becomes insufficient to sustain aerobic respiration in most metazoans. Algae are more tolerant of low oxygen conditions and may outcompete corals weakened by hypoxia. A key question on the ecological importance of this mechanism remains unanswered: How extensive are local hypoxic zones in highly turbulent aquatic environments, continuously flushed by currents and wave surge? To better understand the concert of biological, chemical, and physical factors that determine the abundance and distribution of oxygen in this environment, we combined 3D imagery, flow measurements, macro- and micro-organismal abundance estimates, and experimentally determined biogenic oxygen and carbon fluxes as input values for a 3D bio-physical model. The model was first developed and verified for controlled flume experiments containing coral and algal colonies in direct interaction. We then developed a three-dimensional numerical model of an existing coral reef plot off the coast of Curaçao where oxygen concentrations for comparison were collected in a small-scale grid using fiberoptic oxygen optodes. Oxygen distribution patterns given by the model were a good predictor for in situ concentrations and indicate widespread localized differences exceeding 50 µmol L-1 over distances less than a decimeter. This suggests that small-scale hypoxic zones can persist for an extended period of time in the turbulent environment of a wave- and surge- exposed coral reef. This work highlights how the combination of three-dimensional imagery, biogenic fluxes, and fluid dynamic modeling can provide a powerful tool to illustrate and predict the distribution of analytes (e.g., oxygen or other bioactive substances) in a highly complex system