In this paper we present a preliminary analysis of variation in the isoplanatic patch size over short timescales and
wide angular separations. We tested a visible band photon counting camera running with four 1<i>K</i><sup>2 </sup>detectors
to provide a contiguous field of view of 1000 × 4000 pixels. Resolution was 35-100 mas per pixel at frame rates
from 20-111hz, providing data on atmospheric turbulence at angular separations of up to 400 arcseconds. We
discuss the potential of such cameras to perform high resolution optical surveys using developments of standard
lucky imaging techniques, and the implications of our results for adaptive optics systems design.
Lucky imaging is a proven technique for near diffraction limited imaging in the visible; however, data reduction
and analysis techniques are relatively unexplored in the literature. In this paper we use both simulated and real
data to test and calibrate improved guide star registration methods and noise reduction techniques. In doing
so we have produced a set of "best practice" recommendations. We show a predicted relative increase in Strehl
ratio of ~ 50% compared to previous methods when using faint guide stars of ~17th magnitude in I band, and
demonstrate an increase of 33% in a real data test case. We also demonstrate excellent signal to noise in real
data at flux rates less than 0.01 photons per pixel per frame above the background flux level.
Near-diffraction limited imaging and spectroscopy in the visible on large (8-10 meter) class telescopes has proved to be
beyond the capabilities of current adaptive optics technologies, even when using laser guide stars. The need for high
resolution visible imaging in any part of the sky suggests that a rather different approach is needed. This paper describes
the results of simulations, experiments and astronomical observations that show that a combination of low order adaptive
optic correction using a 4-field curvature sensor and fast Lucky Imaging strategies with a photon counting CCD camera
systems should deliver 20-25 milliarcsecond resolution in the visible with reference stars as faint as 18.5 magnitude in I
band on large telescopes. Such an instrument may be used to feed an integral field spectrograph efficiently using
configurations that will also be described.
The design of electron multiplying CCD cameras require a very different approach from that appropriate for slow scan
CCD operation. This paper describes the main problems in using electron multiplying CCDs for high-speed, photon
counting applications in astronomy and how these may be substantially overcome. With careful design it is possible to
operate the E2V Technologies L3CCDs at rates well in excess of that claimed by the manufacturer, and that levels of
clock induced charge dramatically lower than those experienced with commercial cameras that need to operate at unity
gain. Measurements of the performance of the E2V Technologies CCD201 operating at 26 MHz will be presented
together with a guide to the effective reduction of clock induced charge levels. Examples of astronomical results
obtained with our cameras are presented.
Faint object diffraction limited imaging in the visible from the ground has recently been demonstrated on a 5 m
telescope with more than twice the resolution of Hubble for the first time. It has shown the way towards diffraction
limited imaging in the visible with the next generation of large telescopes. This paper describes the results of
experiments to show how this is achieved and what is needed to work well with faint natural guide stars. The
importance of a large isoplanatic patch size is also emphasised. In particular, we will describe a new approach to the
design of high efficiency, low order adaptive curvature sensors which use photon counting CCD detectors. Such
systems used on larger telescopes together with image segmentation and resynthesis techniques using closure phase
techniques are shown to have an important place in achieving these goals. The optimum combination of these different
techniques will be explained for a variety of different applications.