Pierre J. Lena

10-μm interferometry on the VLTI with the MIDI instrument : a preview

We describe principles, design and present status of MIDI, the mid-infrared interferometric instrument for the VLTI, which is planned to come into operation at the ESO Very Large Telescope Interferometer during the second half of 2001.

Fibered large interferometer on top of Mauna Kea: OHANA, the optical Hawaiian array for nanoradian astronomy

The Mauna Kea site houses two eight-meter and two ten-meter class telescopes which will soon by fully operational. In addition to other existing large telescopes already available, the Mauna Kea summit offers a unique opportunity to build a large optical and infrared interferometer in the northern hemisphere with both the highest angular resolution and the highest sensitivity. We discuss the possibility to recombine with single-mode fibers this array whose large telescopes will all be equipped with adaptive optics facilities. We show the tremendous potential of this instrument for astrophysics and how complementary it is to other large arrays now under construction.

OHANA Phase III: scientific operation of an 800-meter Mauna Kea interferometer

Once the proof of concept of the OHANA Array has been demonstrated, the Phase II capabilities can be put into regular science operation, and the OHANA facility can be upgraded to extend interferometric operation to include all of the telescopes of the OHANA Consortium member observatories. This will constitute the Phase III of OHANA. The technical developments required will be relatively straight-forward. Longer fiber sets will be procured (fiber losses are not a limiting factor at the OHANA scale). An enhanced delay line capability will be needed in order to exploit longer baselines with good sky coverage and ample super-synthesis (several compact, multi-pass long optical delay concepts are under investigation). The scheduling and operation modes of an instrument such as OHANA present interesting opportunities and complications. We envision a place for both collaborative consortium science, based on mutual allocation of facility access, and PI-driven access, based on telescope access exchange between consortium members. The most potentially successful mode of operation would imply a community driven model, open to proposals from the different time allocation comittees. This poster looks at possible methods of allocation and operation, inspired by the UKIRT infrared survey (UKIDSS), the European VLBI, and the very interesting possibility of a Mauna Kea telescope time exchange scheme. The issue of data property is of course intimately tied with the proposal/operation system, and means of data availability and distribution are discussed, along with data interpretation tools, which may be modeled on existing systems such as the ISC at Caltech or the JMMC in France. when weighed against the UV coverage, the potential science and the uniqueness of this project, all these issues are worth an in depth study. Discussions are starting as to an OHANA Operation Committee, the goal of which would be to discuss, define and eventually carry out operational modes. The goal, of course, is for the Operation Committee to handle the details of multi-telescope scheduling in a way that will be transparent to the scientist who merely seeks the observational results.

Multistage fiber optic delay line for astronomical interferometry

In fiber optic Fourier transform spectrometry (FTS), fiber optic double Fourier interferometry (DFI) and, probably, in single-mode fiber-linked telescope array, fiber delay lines are needed to make the system all-fiber optic, which will results in many advantages. Fiber-stretching operation has been demonstrated to be one method in which a piece of fiber is stretched mechanically to generate optical path difference (OPD). Nevertheless, this fiber-stretching operation has two drawbacks. First, it introduces additional polarization and dispersion effects, both of which are stretching state and wavelength dependent. Second, in practive, its maximum delay is limited. In this paper, we describe a new type of fiber delay line in which the fiber-stretching device (we call it OPD generator) is used to generate continuous OPD, and, OPD stores made of optical switch and two segments fibers having different lengths are employed to save and release the OPD that the OPD generator produces. The main advantages of this kind of fiber delay line are: 1) dispersion in the OPD stores may be minimized because the fiber in an OPD store is free of external strain, and polarization effect can be eliminated; 2) fiber-stretching operation will introduce less dispersion and polarization effects; hence 3) large optical delay may be obtained with shorter fiber. At the same time, performance of this kind of delay line is analyzed and the characteristics are discussed.

Interferometric connection of large telescopes at Mauna Kea

We present and discuss the possibility to coherently couple several (up to seven) large telescopes located on the Mauna Kea summit, in order to obtain interferometric capabilities at visible and infrared wavelengths. The advent of adaptive optics and single mode optical fibers allows the use of telescopes which were not built for interferometric use. The diameter of the telescopes, the orientations and lengths of potential baselines can lead to impressive performances in terms of sensitivity and angular resolution, with a negligible site impact.

DOUBLE FOURIER INTERFEROMETRY WITH IR SINGLE-MODE FIBER OPTICS

Abstract An implementation of double Fourier interferometry with IR single-mode, all-fiber optics is described, in which the optical path difference modulations and beam combinations are performed within waveguides. A laboratory prototype is presented, and the first experimental results that prove the validity of the concept.

High Angular Resolution in Astrophysics

High Angular Resolution Instrumentation. An Introduction to Atmospheric Turbulence P. Lena. Design of Arrays for Ground Based Optical Interferometry S.T. Ridgway. Kilometric Baseline Interferometry P.Y. Bely. Observing with Optical/Infrared Long Baseline Interferometers J. Davis. Imaging in Interferometry O. Von der Luhe, N. Ageorges. Image Reconstruction: From Basic Notions Towards Methodological Strategies A. Lannes. Radio Interferometry S. Guilloteau. Very Long Baseline Interferometry W.D. Cotton. Laser Guide Star R. Foy. Astrophysics and High Angular Resolution. Solar-System Studies at High Angular Resolution T. Encrenaz. Circumstellar Material Around Main Sequence and Evolved Stars F. Paresce. Life on Extra-Solar Planets A. Leger. High Angular Resolution Studies of Starburst Galaxies D. Rouan. Oral Contributions. A New Detector for Wavefront Sensing in Adaptive Optics Applications A.W. Kluttig, J.L.A. Fordham. Factors Affecting the Performance of Stellar Interferometers: Application to the VLTI Error Budgets B. Koehler. Optical Interferometry and Ground-Based Astrometry after the Hipparcos Mission G.. Daigne. Improving the Natural Guide Star Magnitude Limit for Wavefront Sensing in an Open Loop System O. Esslinger, M.G. Edmunds. Dispersion Compensation and Fringe Tracking P.R. Lawson. Local Piston Detection of a Segmented Mirror Telescope with Curvature Sensing of Wavefronts Affected by Atmospheric Turbulence. Numerical Simulations J.M. Rodriguez-Ramos, J.J. Fuensalida. The First Caltech-Jodrell Bank VLBI Survey: A Morphological Classification Scheme of Powerful Radio Sources A.G. Polatidis. Adaptive Optics Imaging of the Pre-Main Sequence Star YY Orionis F. Menard, F. Malbet. Detecting Disks Around Young Stellar Objects with Infrared Interferometers F. Malbet. Detection of Circumstellar Dust Shell Around Supergiant TV Gem from Milliarcsecond Resolution Near Infrared Observations S. Ragland, et al. Combined HST and HAR Imaging and Photometry of Eruptive Binaries in Globular Cluster Cores: Based Upon Observations Taken with the William Herschel Telescope on La Palma and the Hubble Space Telescope R. Butler, et al. An Indirect Search for Low-Mass Companions to Distant Stars M.V. Sazhin, I.A. Trifalenkov.

Mid-infrared interferometry on the Chajnantor plateau: the ALIRA project

We propose here to extend ALMA toward the mid-IR wavelength band. We discuss technical aspects and show a scientific breakthrough which would come out of that extension. On the technical side, we consider in particular the following problems raised by its implementation: -Telescope coupling -Beam transportation -Optical pathlength control Alternatively, a solution using heterodyne detection could be considered. As for the scientific programs which could benefit from this proposal, we consider essentially the investigation of extrasolar planets.

Performance analyses of an infrared single-mode all-fiber-optic Fourier-transform spectrometer

Stretching one of a pair of fiber arms can be done to realize optical phase modulation for an IR single-mode all-fiber-optic Fourier-transform spectrometer (FTS). But this operation will inevitably limit the physical performance of a FTS. We study these limits theoretically and experimentally. The optical path difference (OPD) will be dispersive. At the first-order approximation, this OPD dispersion will result in a shift in the recovered spectra. The spectral resolution and the sampling distance will also be dispersive. Linear birefringence introduced when a curved fiber is stretched will affect the final spectra. This effect can be eliminated by real-time compensation and (or) by system design. Errors encountered uniquely in the all-fiber-optic FTS in the optical phase domain, such as the fiber-parameter errors, nonlinearity of the piezoelectric cylinder, and their effects on the spectra are analyzed, from which we deduce the requirements for calibration. Finally, calibration methods for optical phase modulation are discussed.

ISOCAM : an infrared camera for ISO

This paper presents the project ISOCAM for an infrared camera which will be one of the four focal plane instruments on ISO. The camera contains two optical channels, one with an InSb CID array (3 to 5 microns), the other with a Si:Ga DVR array (5 to 17 microns). Interference filters and CVFs provide spectral resolutions between 2 and 50. The optics sets the pixel field of view at 3, 6 or 12 arc second.