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See detailParasitic interference in nulling interferometry
Matter, A.; Defrère, D.; Danchi, W. C. et al

in Monthly Notices of the Royal Astronomical Society (2013), 431(2), 1286-1295

Nulling interferometry aims to detect faint objects close to bright stars. Its principle is to produce a destructive interference along the line of sight so that the stellar flux is rejected, while the ... [more ▼]

Nulling interferometry aims to detect faint objects close to bright stars. Its principle is to produce a destructive interference along the line of sight so that the stellar flux is rejected, while the flux of the off-axis source can be transmitted. In practice, various instrumental perturbations can degrade the nulling performance. Any imperfection in phase, amplitude or polarization produces a spurious flux that leaks to the interferometer output and corrupts the transmitted off-axis flux. One of these instrumental perturbations is the crosstalk phenomenon, which occurs because of multiple parasitic reflections inside transmitting optics, and/or diffraction effects related to beam propagation along finite size optics. It can include a crosstalk of a beam with itself, and a mutual crosstalk between different beams. This can create a parasitic interference pattern, which degrades the intrinsic transmission map - or intensity response - of the interferometer. In this context, we describe how this instrumental effect impairs the performance of a Bracewell interferometer. A simple formalism is developed to derive the corresponding modified intensity response of the interferometer, as a function of the two parameters of interest: the crosstalk level (or contamination rate) and the phase shift between the primary and secondary - parasitic - beams. We then apply our mathematical approach to a few scientific cases, both analytically and using the GENIESIM simulation software, adapted to handle coherent crosstalk. Our results show that a coherent crosstalk level of about 1 per cent implies a 20 per cent drop of the signal-to-noise ratio at most. Careful attention should thus be paid to reduce the crosstalk level inside an interferometric instrument and ensure an instrumental stability that provides the necessary sensitivity through calibration procedures. [less ▲]

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See detailMatisse
Lopez, B.; Lagarde, S.; Wolf, S. et al

in Moorwood, 1 (Ed.) Science with the VLT in the ELT Era (2009)

MATISSE is foreseen as a mid-infrared spectro-interferometer combining the beams of up to four UTs/ATs of the Very Large Telescope Interferometer (VLTI). MATISSE will measure closure phase relations and ... [more ▼]

MATISSE is foreseen as a mid-infrared spectro-interferometer combining the beams of up to four UTs/ATs of the Very Large Telescope Interferometer (VLTI). MATISSE will measure closure phase relations and thus offer an efficient capability for image reconstruction in the L, M and N bands of the mid-infrared domain. [less ▲]

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See detailMATISSE Science Cases
Wolf, S.; Lopez, B.; Jaffe, W. et al

in Moorwood, A. (Ed.) Science with the VLT in the ELT Era (2009)

MATISSE is foreseen as a mid-infrared spectro-interferometric instrument combining the beams of up to four UTs/ATs of the Very Large Telescope Interferometer (VLTI). MATISSE will measure closure phase ... [more ▼]

MATISSE is foreseen as a mid-infrared spectro-interferometric instrument combining the beams of up to four UTs/ATs of the Very Large Telescope Interferometer (VLTI). MATISSE will measure closure phase relations and thus offer an efficient capability for image reconstruction. In addition to this, MATISSE will open 2 new observing windows at the VLTI: the L and M band in addition to the N band. Furthermore, the instrument will offer the possibility to perform simultaneous observations in separate bands. MATISSE will also provide several spectroscopic modes. In summary, MATISSE can be seen as a successor of MIDI by providing imaging capabilities in the mid-infrared domain (for a more detailed description of MATISSE see Lopez et al., these proceedings). [less ▲]

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