<title>Thermoelectric-cooled 2Kx2K CCD imaging camera for wide-field telescopes</title>

Abstract

In this paper we describe the solutions adopted for the design and the realization of an astronomical CCD imaging system, the results achieved on a Schmidt telescope (1 degree X 1 degree Field Of View, FOV) and, as well, the images obtained on a 30 cm prototype of a really innovative wide field telescope (2 degree X 2 degree FOV), a two-mirrors Three- Reflection Telescope (TRT), adopting aspherical reflecting- only surfaces. This solution allows the correction of every aberration, removing completely the vignetting and the field- curvature on very large fields of view (FOV). The CCD camera (equipped with a Loral 2k X 2k chip), operating under 'inverted mode' (Multi-Phase-Pinned mode, MPP), shows a dark current less than 0.1 e-/min at a temperature of only 200 degrees K. This particular operational mode enables the camera to provide accurate photometry even when the CCD is not at 'conventional' cryogenic temperatures. To cool-down the CCD chip it has been designed and realized a sophisticated Thermo- Electric-Cooler (TEC), which uses a three-stage Peltier module and glycol circulating in closed circuit at minus 10 degrees Celsius as heat exchanger. This TEC can reach, in this arrangement, an operative temperature of minus 80 degrees Celsius, approaching the typical performance of usual cryogenic systems. For its small encumber and for its reliability it is especially suitable for applications in which the room available is small, such as in internal-focus telescopes (e.g. Schmidt telescopes). Finally we briefly report new CCD and telescope projects.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.