High contrast D1_{1} line electromagnetically induced transparency in nanometric-thin rubidium vapor cell

Electromagnetically induced transparency (EIT) on atomic D$_{1}$ line of rubidium is studied using a nanometric-thin cell with atomic vapor column length in the range of L= 400 - 800 nm. It is shown that the reduction of the cell thickness by 4 orders as compared with an ordinary cm-size cell still allows to form an EIT resonance for $L= \lambda$ ($\lambda =794$ nm) with the contrast of up to 40%. Remarkable distinctions of EIT formation in nanometric-thin and ordinary cells are demonstrated. Despite the Dicke effect of strong spectral narrowing and increase of the absorption for $L=$ $\lambda /2$, EIT resonance is observed both in the absorption and the fluorescence spectra for relatively low intensity of the coupling laser. Well resolved splitting of the EIT resonance in moderate magnetic field for $L=$ $\lambda$ can be used for magnetometry with nanometric spatial resolution. The presented theoretical model well describes the observed results.Comment: Submitted to Applied Physics B: Lasers and Optics, 9 pages, 10 figure

Insulator-metal transition in biased finite polyyne systems

A method for the study of the electronic transport in strongly coupled electron-phonon systems is formalized and applied to a model of polyyne chains biased through metallic Au leads. We derive a stationary non equilibrium polaronic theory in the general framework of a variational formulation. The numerical procedure we propose can be readily applied if the electron-phonon interaction in the device hamiltonian can be approximated as an effective single particle electron hamiltonian. Using this approach, we predict that finite polyyne chains should manifest an insulator-metal transition driven by the non-equilibrium charging which inhibits the Peierls instability characterizing the equilibrium state.Comment: to appear at EPJ

Hyperspectral multimodal CARS microscopy in the fingerprint region

A simple scheme for multimodal coherent anti-Stokes Raman scattering (CARS) microscopy is based on the spectral focusing of ultrafast-oscillator-derived pump/probe light and synchronous photonic crystal fiber (PCF) fiber-generated broadband Stokes light. To date, such schemes allowed rapid hyperspectral imaging throughout the CH/OH high frequency region (2700-4000 cm-1). Here we extend this approach to the middle (1640-3300 cm-1) and fingerprint regions (850-1800 cm-1) of the Raman spectrum. Our simple integrated approach to rapid hyperspectral CARS microscopy in the fingerprint region is demonstrated by applications to label-free multimodal imaging of cellulose and bulk bone, including use of the phosphate resonance at 960 cm-1. \ua9 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Peer reviewed: YesNRC publication: Ye

Spatial-spectral coupling in hyperspectral CARS microscopy image formation

Hyperspectral coherent anti-Stokes Raman scattering (CARS) microscopy has provided an imaging tool for extraction of 3-dimensional volumetric information, as well as chemically-sensitive spectral information. These techniques have been used in a variety of different domains including biophysics, geology, and material science. The measured CARS spectrum results from interference between the Raman response of the sample and a non-resonant background. We have collected four dimensional data sets (three spatial dimensions, plus spectra) and extracted Raman response from the CARS spectrum using a Kramers-Kronig transformation. However, the three dimensional images formed by a CARS microscope are distorted by interference, some of which arises because of the Gouy phase shift. This type of interference comes from the axial position of the Raman resonant object in the laser focus. We studied how the Gouy phase manifests itself in the spectral domain by investigating microscopic diamonds and nitrobenzene droplets in a CARS microscope. Through experimental results and numerical calculation using finite-diference time-domain (FDTD) methods, we were able to demonstrate the relationship between the spatial configuration of the sample and the CARS spectral response in three dimensional space. \ua9 2013 Copyright SPIE.Peer reviewed: YesNRC publication: Ye