The FIREBall-2 Instrument Model (FIREBallIMO) is a piece of software simulating the optical behaviour of the Multi-Object Two-Curved Schmidt Slit Spectograph of FIREBall-2 (Faint Intergalactic Redshifted Emission BALLoon), a balloon-borne telescope (40 km in alt.) designed to perform a direct detection of the faint Circum Galactic Medium (CGM) in emission around low-z galaxies. The spectrograph has been optimized to operate in a narrow UV band [195-225] nanometers, the so-called atmospheric sweet spot, where the sky background presents no emission lines and can be considered approximately at, a value of 500 continnum units, seen through an optical transmission of 50% at an atmospheric pressure of 3 millibars. This paper gives an overview of the software current modular architecture after a year of productive effort (in terms of parametric model space definition, associated data cubes generation and digital processing) starting from the instrument initial optical model designed under Zemax software to the final 2D-detected image. A special emphasis is put on the design of a cython-wrapped driver able to retrieve dense ray-sampled PSFs out of the Zemax box efficiently. The optical mappings and distortions from the sky to the spectrograph's entrance slit plane and from the sky to the detection plane are presented, as well as some end-to-end simulations leading to Signal-to-Noise Ratio estimates computed on artificial point-like or extended test sources.
Interferometry beam combiners that use optical waveguides, i.e. optical fibers or integrated optics, become popular in optical interferometry because of their flexibility, but also in the case of single-mode waveguide because of their properties of spatial filtering that increases the accuracy of interferometric measurement in an atmosphere-perturbed environment. However we know very little
about the way the electric field propagates and even less about the
correlation between the different beams of an optical interferometer. In this paper, we present in this paper an analysis of single mode optical waveguides in the framework of stellar interferometry. We first analyze the output electric field using
radiated modes and show that the rejection rate we can derive in the
case of nulling interferometry depends on many parameters, including the flux integration radius and the force of the aberrations. Secondly, since the interferometric equation can be interpreted in terms of carrying wave that carries respectively the optical power received by each telescope and the coherent power between two telescopes, we show that the interferometric equation involves a quantity called the modal visibilities which is not equal to the object visibility. The relationship between the two visibilities and the behaviour in the presence of atmosphere are also presented.
We present a summary of the global system analysis that led to the current definition of the AMBER instrument. AMBER is a near infrared multi-beam combiner for the Very Large Telescope Interferometer. This analysis goes through the following issues: atmospheric systematics including atmospheric turbulence and dispersion, analysis of single mode optical fibers, photometry calibration, spectral dispersion, background noise, data reduction and calibration steps.
We present the design and realization of the AMBER data simulator. This tool provides the AMBER team with: (1) a way to test the performance and sensitivity of AMBER wrt. external parameters (e.g., observed source magnitude, AO correction); (2) a means to validate proposed visibility retrieval algorithms; and (3) a mean to obtain realistic data flows to test and implement the AMBER data reduction software.
Optical fibers are now often used in long baseline interferometry because they offer spatial filtering which leads to better accuracy in presence of atmospheric turbulence. Although this property is now well-known and spatial filtering used at various interferometers (IOTA, PTI, ...) and planned for upcoming facilities (VLTI/AMBER, Keck), the underlying physics of spatial filtering is far from being understood. For example up to now, nobody has been able to theoretically predict in which conditions the use of spatial filters improves the quality of the measures. In this paper, we study the propagation of the light through different spatial filters (pinhole, step index fibers) and given preliminary theoretical prediction for the domain of superiority of spatial filtering. We show that for typical observations in the near-infrared with large telescopes corrected by a 64-actuators adaptive optics system, the spatial filtering always provide a better signal-to-noise ratio than the direct coupling of the light.
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