Slow Light in Doppler Broadened Two level Systems

We show that the propagation of light in a Doppler broadened medium can be slowed down considerably eventhough such medium exhibits very flat dispersion. The slowing down is achieved by the application of a saturating counter propagating beam that produces a hole in the inhomogeneous line shape. In atomic vapors, we calculate group indices of the order of 10^3. The calculations include all coherence effects.Comment: 6 pages, 5 figure

A Strategy for Structuring and Reporting a Read-Across Prediction of Toxicity

Category formation, grouping and read across methods are broadly applicable in toxicological assessments and may be used to fill data gaps for chemical safety assessment and regulatory decisions. In order to facilitate a transparent and systematic approach to aid regulatory acceptance, a strategy to evaluate chemical category membership, to support the use of read-across predictions that may be used to fill data gaps for regulatory decisions is proposed. There are two major aspects of any read-across exercise, namely assessing similarity and uncertainty. While there can be an over-arching rationale for grouping organic substances based on molecular structure and chemical properties, these similarities alone are generally not sufficient to justify a read-across prediction. Further scientific justification is normally required to justify the chemical grouping, typically including considerations of bioavailability, metabolism and biological/mechanistic plausibility. Sources of uncertainty include a variety of elements which are typically divided into two main issues: the uncertainty associated firstly with the similarity justification and secondly the completeness of the read-across argument. This article focuses on chronic toxicity, whilst acknowledging the approaches are applicable to all endpoints. Templates, developed from work to prepare for the application of new toxicological data to read-across assessment, are presented. These templates act as proposals to assist in assessing similarity in the 50 context of chemistry, toxicokinetics and toxicodynamics as well as to guide the systematic characterisation of uncertainty both in the context of the similarity rationale, the read across data and overall approach and conclusion. Lastly, a workflow for reporting a read-across prediction is suggested

General analysis of type I second-harmonic generation with elliptical Gaussian beams

One can enhance second-harmonic generation in angle-tuned crystals by focusing the fundamental to an elliptical waist in the crystal. We present a general analysis for type I phase-matched uniaxial and biaxial crystals that will find particular application in the generation of harmonics from diode lasers

Combined trap for laser-stimulated recombination

We present a combined Paul-Penning trap to study CO2-laser stimulated recombination of protons and electrons. The trap is located in the center of an optical resonator for 11 mu m radiation. In this manner the available laser intensity is enhanced for stimulated recombination to the n=11 state of hydrogen

Towards laser spectroscopy of antihydrogen

The development of the first continuous coherent source at 121.56 nm is described. Radiation at this wavelength of Lyman-alpha can be used for laser-cooling of antihydrogen on the strong 1S-2P transition. It also opens up a possibility for precision spectroscopy that requires just a few antihydrogen atoms

Generation of continuous coherent radiation at Lyman-alpha and 1S-2P Spectroscopy of atomic hydrogen

Continuous coherent radiation from wavelengths from 121 to 123 nm in the vacuum ultraviolet (VUV) was generated by four-wave sum-frequency mixing in mercury vapor. A yield of 20 nW at Lyman-alpha (121.57 nm) was achieved. We describe the experimental setup in detail and present a calculation of the nonlinear susceptibility, the phase-matching integral, and the VUV yield. The Lyman-alpha beam was used to perform 1S-2P spectroscopy in a cold beam of atomic hydrogen. Linewidths of only 120 MHz were observed, which is close to the natural linewidth