Modeling the imaging process in optical stellar interferometers

Abstract

Abstract. Optical interferometers on the ground, like ESO's Very Large Telescope Interferometer (VLTI) and the Keck Interferometer, and in space, like the InfraRed Space Interferometer (IRSI/Darwin) and the Space Interferometry Mission (SIM), will bring a major breakthrough in optical and near-infrared high angular resolution astronomy at the beginning of the next millennium. These instruments are complex systems with an exceptionally interdisciplinary character involving active/adaptive optics, structural mechanics, control engineering, electronics and various environmental disturbances (e.g. atmospheric turbulence and absorption, wind, seismic noise). For their design and development an approach from two sides is appropriate: laboratory testbeds are used for experimental investigations while numerical modeling tools perform an End-to-End instrument simulation. We have developed a set of numerical modeling tools to simulate the dynamic imaging process of an interferometer. The time-dependent point spread function (PSF) mainly characterizes the imaging performance of the instrument. It is computed by an optomechanical model. Based on the knowledge of the PSF the image of an incoherently radiating extended object is computed using a Fourier optical method. This article describes the modeling approach including an extension to more than two interferometric beams. Some results of simulations on the VLTI as a representative example are shown.

Integrated modeling for stellar interferometry: motivation, development strategy, and practical usage

“…Once the dynamic response to a point source is known, the observation of extended objects can be treated in the spatial frequency domain using two-dimensional signal theory (Fourier optics). 4 The diagram only shows a single closed loop of the controlled optical signal flow representative for several, partially nested loops in a practical implementation. The model of the control loop(s) forms the comprehensive framework for integration of all subsystem models in different disciplines (optics, mechanical structure, sensors, actuators, disturbances).…”

Michelson wide-field stellar interferometry: principles and experimental verification

“…The shape of the mirror depends on the baseline and on the pointing direction, and it must be determined during the observation, as the entrance pupil varies with hour angle. 10 This paper is organized as follows: in Section 2 we derive the equation for the OPD as a function of the position in the field. We have adopted here the celestial coordinates that are commonly used in astronomical observations.…”

Diffraction losses in ground-based optical interferometers

“…The impact of these effects for long‐baseline interferometry was first investigated by Tango & Twiss (1974), and has subsequently been addressed by a number of authors (Bagnuolo 1988; Colavita 1990; Hrynevych 1992; Schöller, Wilhelm & Koehler 2000). An important shortcoming of these studies has been the lack of a detailed treatment of the effects of the atmospherically perturbed wavefront profiles of the interfering beams.…”