The recent availability of large format near-infrared detectors with sub-election readout noise is revolutionizing our approach to wavefront sensing for adaptive optics. However, as with all near-infrared detector technologies, challenges exist in moving from the comfort of the laboratory test-bench into the harsh reality of the observatory environment. As part of the broader adaptive optics program for the GMT, we are developing a near-infrared Lucky Imaging camera for operational deployment at the ANU 2.3 m telescope at Siding Spring Observatory. The system provides an ideal test-bed for the rapidly evolving Selex/SAPHIRA eAPD technology while providing scientific imaging at angular resolution rivalling the Hubble Space Telescope at wavelengths lambda = 1.3-2.5 mu m.

The Giant Magellan Telescope (GMT) Integral-Field Spectrograph (GMTIFS)c is one of six potential first-light instruments for the 25m-diameter Giant Magellan Telescope. The Australian National University has completed a Conceptual Design Study for GMTIFS. The science cases for GMTIFS are summarized, and the instrument capabilities and design challenges are described. GMTIFS will be the work-horse adaptive-optics instrument for GMT. It contains an integral-field spectrograph (IFS) and Imager accessing the science field, and an On-Instrument Wave-Front Sensor (OIWFS) that patrols the 90 arcsec radius guide field. GMTIFS will address a wide range of science from epoch of reionization studies to forming galaxies at high redshifts and star and planet formation in our Galaxy. It will fully exploit the Laser Tomography Adaptive Optics (LTAO) system on the telescope. The tight image quality and positioning stability requirements that this imposes drive the design complexity. Some cryogenic mechanisms in the IFS must set to ~ 1 μm precision. The Beam-Steering mechanism in the OIWFS must set to milli-arcsecond precision over the guide field, corresponding to ~ 1 μm precision in the f/8 focal plane. Differential atmospheric dispersion must also be corrected to milli-arcsecond precision. Conceptual design solutions addressing these and other issues are presented and discussed.

A two-dimensional photon counting array in operation at Mount Stromlo is described and its performance discussed. The detector consists of a highly intensified Fairchild SL 62925 charge coupled device (CCD) where the spectral response of the system can be varied by the use of intensifiers which have different cathode types (S-20, S-25) as the first electron-emitting surface. The format of the external memory is 760 x 488 event-centered pixels. Prior frame subtraction is used to achieve counting rates of 5 Hz pixel with 3% coincidence correction. The advantages of photon-counting array systems over analog CCD detectors are discussed.

Publisher Summary This chapter discusses the photon counting with intensified solid state arrays. The photon counting array (PCA) system has certain objectives: count every photoelectron; count these only once; centre the photon event pulse to obtain maximum resolution; and eliminate all non-photon noise. The spectrum is imaged onto a tandem stack of six electrostatically focused, fiber optically coupled 40 mm diameter image tubes. The image tubes provide sufficient gain so that the video pulses from the diode array are much larger than the preamplifier noise. A feature of the MOS arrays is that the video signal is superimposed on a coherent clock noise level. The experience with linear arrays encourages one to believe that a similar approach to the use of two-dimensional CCD arrays will prove fruitful. For spectroscopic use, it is believed that a system such as the PCA where detective quantum efficiency is nearly equal to the theoretical quantum efficiency has advantages over the use of the unintensified CCD with its high theoretical QE and attendant problems of charge leakage, diode non-uniformity, high dark current, and low noise preamplifier requirements.