The Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory

The Photodetector Array Camera and Spectrometer (PACS) is one of the three science instruments on ESA's far infrared and submillimetre observatory. It employs two Ge:Ga photoconductor arrays (stressed and unstressed) with 16x25 pixels, each, and two filled silicon bolometer arrays with 16x32 and 32x64 pixels, respectively, to perform integral-field spectroscopy and imaging photometry in the 60-210\mu\ m wavelength regime. In photometry mode, it simultaneously images two bands, 60-85\mu\ m or 85-125\mu\m and 125-210\mu\ m, over a field of view of ~1.75'x3.5', with close to Nyquist beam sampling in each band. In spectroscopy mode, it images a field of 47"x47", resolved into 5x5 pixels, with an instantaneous spectral coverage of ~1500km/s and a spectral resolution of ~175km/s. We summarise the design of the instrument, describe observing modes, calibration, and data analysis methods, and present our current assessment of the in-orbit performance of the instrument based on the Performance Verification tests. PACS is fully operational, and the achieved performance is close to or better than the pre-launch predictions

ARGOS: the laser guide star system for the LBT

ARGOS is the Laser Guide Star adaptive optics system for the Large Binocular Telescope. Aiming for a wide field adaptive optics correction, ARGOS will equip both sides of LBT with a multi laser beacon system and corresponding wavefront sensors, driving LBT's adaptive secondary mirrors. Utilizing high power pulsed green lasers the artificial beacons are generated via Rayleigh scattering in earth's atmosphere. ARGOS will project a set of three guide stars above each of LBT's mirrors in a wide constellation. The returning scattered light, sensitive particular to the turbulence close to ground, is detected in a gated wavefront sensor system. Measuring and correcting the ground layers of the optical distortions enables ARGOS to achieve a correction over a very wide field of view. Taking advantage of this wide field correction, the science that can be done with the multi object spectrographs LUCIFER will be boosted by higher spatial resolution and strongly enhanced flux for spectroscopy. Apart from the wide field correction ARGOS delivers in its ground layer mode, we foresee a diffraction limited operation with a hybrid Sodium laser Rayleigh beacon combination.12 page(s

Science and Adaptive Optics Requirements of MICADO, the E-ELT adaptive optics imaging camera

MICADO is the adaptive optics imaging camera being studied for the E-ELT. Its design has been optimised for use with MCAO, but will have its own SCAO module for the initial operational phase; and in principle could also be used with GLAO or LTAO. In this contribution, we outline a few of the science drivers for MICADO and show how these have shaped its design. The science drivers have led to a number of requirements on the AO system related to astrometry, photometry, and PSF uniformity. We discuss why these requirements have arisen and what might be done about them.Comment: 6 pages, to appear in the proceedings of the AO4ELT conference, held in Paris, 22-26 June 200

Development of a large scale stressed Ge:Ga detector array for SAFARI

We report on the development of a large format stressed gallium doped germanium (Ge:Ge) array for the SAFARI instrument. Building on flight proven PACS heritage, the goal of our development is a 32 pixel stressed Ge:Ga module enabling a 32 × 32 pixel photoconductor array for the wavelength range between 110 and 210 μm. The unprecedented size of this array would allow the use of almost all of the 3.8 × 3.8 arcmin field of view provided for SAFARI in the SPICA focal plane. We are currently in the process of manufacturing the individual components of the 32 pixel demonstration module. This prototype module will feature three selectable read out architectures enabling the evaluation and optimisation of the detector performance as well as a two stage multiplexer to distribute the dissipative heat load on the temperature levels provided by the satellite. Thermal modeling has shown that the heat loads are in compliance with the thermal budgets of the SPICA cryogenic system. The ultimate development goal with optimised read out circuits is an NEP of 1 × 10-18 W/Hz1/2, which would present a factor of 8 improvement in the noise performance compared to the PACS stressed Ge:Ga array

Wide-field AO correction: the large wavefront sensor detector of ARGOS

Wide field correction allowing large field to benefit from adaptive optics (AO) is challenging in more than one aspect. We address here the wavefront sensor (WFS) detector side where, in addition to high sensitivity and low noise, the simultaneous detection of multiple laser beacons and the large number of sub-apertures in a Shack-Hartmann WFS require a detector to have a large imaging area while preserving a very high readout frame rate. The detector considered has a frame area of 264×264 pixels with a pixel size of 48 microns. By splitting the image into two framestore areas during readout, repetition rates of more than 1000 frames per second can be achieved. The electronic noise contribution is approximately 3 electrons at the operating temperature. We therefore analyze its performances, showing it fulfills the requirements, in a wavefront sensing application: the measurement of centroids in the case of a Shack-Hartmann WFS for the Argos AO project