Transmission behaviors of single mode hollow metallic waveguides dedicated to mid-infrared nulling interferometry

This paper reports the characterization of hollow metallic waveguides (HMW) to be used as single-mode wavefront filters for nulling interferometry in the 6-20 microns range. The measurements presented here were performed using both single-mode and multimode conductive waveguides at 10.6 microns. We found propagation losses of about 16dB/mm, which are mainly due to the theoretical skin effect absorption in addition to the roughness of the waveguide metallic walls. The input and output coupling efficiency of our samples has been improved by adding tapers to minimize the impedance mismatch. A proper distinction between propagation losses and coupling losses is presented. Despite their elevate propagation losses, HMW show excellent spatial filtering capabilities in a spectral range where photonics technologies are only emerging.Comment: This paper was published in Optics Express and can be found at http://www.opticsinfobase.org/abstract.cfm?URI=oe-15-26-1800

On-chip spectro-detection for fully integrated coherent beam combiners

This paper presents how photonics associated with new arising detection technologies is able to provide fully integrated instrument for coherent beam combination applied to astrophysical interferometry. The feasibility and operation of on-chip coherent beam combiners has been already demonstrated using various interferometric combination schemes. More recently we proposed a new detection principle aimed at directly sampling and extracting the spectral information of an input signal together with its flux level measurement. The so-called SWIFTS demonstrated concept that stands for Stationary-Wave Integrated Fourier Transform Spectrometer, provides full spectral and spatial information recorded simultaneously thanks to a motionless detecting device. Due to some newly available detection principles considered for the implementation of the SWIFTS concept, some technologies can even provide photo-counting operation that brought a significant extension of the interferometry domain of investigation in astrophysics . The proposed concept is applicable to most of the interferometric instrumental modes including fringe tracking, fast and sensitive detection, Fourier spectral reconstruction and also to manage a large number of incoming beams. The paper presents three practical implementations, two dealing with pair-wise integrated optics beam combinations and the third one with an all-in-one 8 beam combination. In all cases the principles turned into a pair wise baseline coding after proper data processing.Comment: 12 pages, 6 figures, part of the Optics Express special issue dedicated to Astrophotonic

M-lines characterization of selenide and telluride waveguides for mid-infrared interferometry

Nulling interferometry is an astronomical technique that combines equal wavefronts to achieve a deep rejection ratio of an on-axis star, and that could permit to detect Earth-like planets in the mid-infrared band 5 -- 20 microns. Similarly to what is done in the near-infrared, high frequencies spatial filtering of the incoming beams can be achieved using single-mode waveguides operating in the mid-infrared. An appreciable reduction of the instrumental complexity is also possible using integrated optics (IO) devices in this spectral range. The relative lack of single-mode guided optics in the mid-infrared has motivated the present technological study to demonstrate the feasibility of dielectric waveguides functioning at longer wavelengths. We propose to use selenide and telluride components to pursue the development of more complex IO functions.Comment: accepted in OSA Optics Express, 11 pages, 4 figure

First fringes with an integrated-optics beam combiner at 10 um - A new step towards instrument miniaturization for mid-infrared interferometry

Observations at mas-resolution scales and high dynamic range hold a central place in achieving, for instance, the spectroscopic characterization of exo-Earths or the detailed mapping of their protoplanetary disc birthplace. Ground or space-based multi-aperture infrared interferometry is a promising technique to tackle these goals. But significant efforts still need to be undertaken to achieve a simplification of these instruments if we want to combine the light from a large number of telescopes. Integrated-optics appears as an alternative to the current conventional designs, especially if its use can be extended to a higher number of astronomical bands. This article reports for the first time the experimental demonstration of the feasibility of an integrated-optics approach to mid-infrared beam combination for single-mode stellar interferometry. We have fabricated a 2-telescope beam combiner prototype integrated on a substrate of chalcogenide glasses, a material transparent from 1 to 14 um. We have developed laboratory tools to characterize the modal properties and the interferometric capabilities of our device. We obtain fringes at 10 um and measure a mean contrast V=0.981 \pm 0.001 with high repeatability over one week and high stability over 5h. We show experimentally - as well as on the basis of modeling considerations - that the component has a single-mode behavior at this wavelength, which is essential to achieve high-accuracy interferometry. From previous studies, the propagation losses are estimated to 0.5 dB/cm for such components. We also discuss possible issues that may impact the interferometric contrast. The IO beam combiner performs well at 10. We also anticipate the requirement of a better matching between the numerical apertures of the component and the (de)coupling optics to optimize the total throughput. The next step foreseen is the achievement of wide-band interferograms.Comment: Accepted in A&A; 7 pages; 7 figure

Astrophotonics: a new era for astronomical instruments

Astrophotonics lies at the interface of astronomy and photonics. This burgeoning field -- now formally recognized by the optics community -- has emerged over the past decade in response to the increasing demands of astronomical instrumentation. Early successes include: (i) planar waveguides to combine signals from widely spaced telescopes in stellar interferometry; (ii) frequency combs for ultra-high precision spectroscopy to detect planets around nearby stars; (iii) ultra-broadband fibre Bragg gratings to suppress unwanted background; (iv) photonic lanterns that allow single-mode behaviour within a multimode fibre; (v) planar waveguides to miniaturize astronomical spectrographs; (vi) large mode area fibres to generate artificial stars in the upper atmosphere for adaptive optics correction; (vii) liquid crystal polymers in optical vortex coronographs and adaptive optics systems. Astrophotonics, a field that has already created new photonic capabilities, is now extending its reach down to the Rayleigh scattering limit at ultraviolet wavelengths, and out to mid infrared wavelengths beyond 2500nm.Comment: 5 pages, Editorial for the Focus Issue on Astrophotonics (Optics Express); all 12 papers are free to air at http://www.opticsinfobase.org/oe/Issue.cf

Novel mRNA-specific effects of ribosome drop-off on translation rate and polysome profile

IS and MCR were supported by the Biotechnology and Biological Sciences Research Council (BBSRC) (http://www.bbsrc.ac.uk) BB/N017161/1. IS was supported by the Biotechnology and Biological Sciences Research Council (BBSRC) (http://www.bbsrc.ac.uk) BB/I020926/1. PB and MCR were supported by the Scottish Universities Life Sciences Alliance (SULSA) (http://www.sulsa.ac.uk). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewedPublisher PD

Image potential states as quantum probe of graphene interfaces

Image potential states (IPSs) are electronic states localized in front of a surface in a potential well formed by the surface projected bulk band gap on one side and the image potential barrier on the other. In the limit of a two-dimensional solid a double Rydberg series of IPSs has been predicted which is in contrast to a single series present in three-dimensional solids. Here, we confirm this prediction experimentally for mono- and bilayer graphene. The IPSs of epitaxial graphene on SiC are measured by scanning tunnelling spectroscopy and the results are compared to ab-initio band structure calculations. Despite the presence of the substrate, both calculations and experimental measurements show that the first pair of the double series of IPSs survives, and eventually evolves into a single series for graphite. Thus, IPSs provide an elegant quantum probe of the interfacial coupling in graphene systems.Comment: Accepted for publication in New Journal of Physic

Wavelength-scale stationary-wave integrated Fourier-transform spectrometry

Spectrometry is a general physical-analysis approach for investigating light-matter interactions. However, the complex designs of existing spectrometers render them resistant to simplification and miniaturization, both of which are vital for applications in micro- and nanotechnology and which are now undergoing intensive research. Stationary-wave integrated Fourier-transform spectrometry (SWIFTS)-an approach based on direct intensity detection of a standing wave resulting from either reflection (as in the principle of colour photography by Gabriel Lippmann) or counterpropagative interference phenomenon-is expected to be able to overcome this drawback. Here, we present a SWIFTS-based spectrometer relying on an original optical near-field detection method in which optical nanoprobes are used to sample directly the evanescent standing wave in the waveguide. Combined with integrated optics, we report a way of reducing the volume of the spectrometer to a few hundreds of cubic wavelengths. This is the first attempt, using SWIFTS, to produce a very small integrated one-dimensional spectrometer suitable for applications where microspectrometers are essential