In this work, we present another proof of the theoretical existence of super resolution, under certain conditions. The proof relies on an ideal model in which a prototypical discrete image is formed by summation of many discrete pulses placed anywhere on a regular grid. If the model is then band-limited in spatial frequency, the original, grid-resolution pulse image may be reconstructed from the band-limited information. The reconstruction uses “phase-gradient unravelling” — i.e., from a very limited number of terms of the discrete Fourier transform of an image, which defines a very limited spatial-frequency band, we extract or unravel the individual phase-gradients which, together, define the original image.

This paper presents the results of a preliminary investigation into the problems in through-the-atmosphere image restoration which are more suited to data from a small telescope, i.e., one having a diameter of about 0.5 m, using techniques of image geometric transformation (and eventually, parallel image processing) in their solution. We have imaged bright objects, over fields of view which subtend angles greater than those in most “large” telescope experiments, i.e., between 40 and 100 arc sec, for example, where the isoplanatic assumptions are less valid.

Diffraction in Michelson Stellar Interferometery, with particular reference to SUSI, is examined. A justification of the use of Fresnel diffraction is made, both theoretically and experimentally, and a calculation of fringe visibility loss for SUSI is given.

Within the recently completed Australia Telescope, optical fibres are used extensively to carry wideband IF data, LO reference signals, timing signals and computer communications. This paper discusses the various options considered in the design of the optical fibre system.

Four existing millimeter arrays have been very productive in the last few years and are currently being expanded in their capabilities. Recent technical developments in these arrays as well as the prospects for submillimeter interferometry and larger arrays are presented.

In 1984 Perley and Erickson proposed a 73.8 MHz [4 meter wavelength] observing system at the VLA site (NRAO Scientific Memo #146). They proposed a stand-alone antenna system that would feed its signals into an existing spare channel of the VLA waveguide and utilize a separate correlator. Over the 35 km VLA baselines this system would produce images with 20 arcsec resolution, unprecedented at this frequency. The major technical problems are ionospheric refraction and interference. Some doubt existed as to whether or not it would be possible to cope with the large, rapidly-changing ionospheric phase fluctuations to be expected over 35 km baselines. Thus it was proposed, as a first step in the development, that 73.8 MHz feeds be installed in the present VLA dishes and that trial observations be made to prove that techniques such as self-calibration can be successful. Eight dishes now have 73.8 MHz instrumentation and a number of radio source images have been made with this initial system.

In this paper I describe a new software package (“AIPS++”) being written by a consortium of seven astronomical institutions spread over four continents. I start by describing the background to the project, followed by a summary detailing what AIPS++ is and why it is being written in this way. Section 3 describes the challenge of running a globally distributed project spread over four continents. Finally I describe the current status and an estimated completion date.

Recent upgrades of the Infrared Spatial Interferometer are described. These provide improved sensitivity, precision and convenience of measurement. Analysis of phase fluctuations within the interferometer as well as in the atmosphere above indicates that popular simple atmospheric models need to be refined. Results of stellar observations are presented in another paper (cf. Danchi et al., in these Proceedings).

Integrated optical components (mostly single-mode fibers and couplers) can be used to achieve several functions that are needed in interferometry: coherent beam transportation and recombination, pathlength modulation and control for fringe tracking and double Fourier interferometry, spatial filtering of the wavefront and interferogram calibration. Their potential is assessed and the main problems encountered in their implementation are discussed: dispersion, polarization behavior, and especially starlight injection.

Adaptive optics systems are now being developed for astronomical applications. On large telescopes, a substantial image improvement can be obtained in the near infrared, using natural guide stars.

Feasibility demonstrations using one to two meter telescopes have confirmed the utility of laser beacons as wavefront references for adaptive optics systems. Laser beacon architectures suitable for the new generation of eight and ten meter telescopes are presently under study. This paper reviews the concept of laser guide star adaptive optics and the progress that has been made by groups around the world in implementing such systems. A description of the laser guide star program at LLNL and some experimental results is also presented.

The Starfire Optical Range 1.5 m telescope is equipped with a 241 actuator adpative optics system operating at visible wavelengths. The system can use either natural or laser guide star beacons for sensing wavefront distortions induced by atmospheric turbulence. This paper describes the main parameters of the system and presents a few examples of experimental results. The best results are Strehl ratios of 0.64 (star beacon) and 0.48 (laser beacon), both having full-width-half-maximum point spread functions of 0.13 arc second (0.88 μm).

We made aperture masking optical interferometry experiments using up to 30 apertures and with a tip-tilt correction of wavefront error. We examined the performance of minimum redundant configurations of 11–30 sub-apertures on the pupil plane mask. These configurations have two advantages; the redundancy noise is as small as realized in non-redundant masking method, and the uv-coverage is as high as in speckle interferometry enabling to get reconstructed images without mask exchange. We also examined the effect of tip-tilt wavefront correction within a telescope pupil in front of the aperture masking optics. The light coherency between sub-apertures was shown to increase by the correction.

A variety of observations have been made of solar features (sunspots, faculae, the limb) using both array and single element scanning techniques. The telescope was the 1.6 m McMath-Pierce on Kitt Peak. Array data were acquired with a 58×62 pixel Si:Ga detector at 4.8, 7.8, 12.4, and 18 μm, while a CCD camera recorded the same image position at 0.5 μm. In a separate experiment, a nutating mirror device was used to generate a raster scan of solar disk areas, the output being fed to a Si PIN diode (0.5 μm filter) and a As:Si diode (12.4 μm filter). The scanner data yield simultaneous images at the two wavelengths and was essentially a repeat of the 1970 Turon-Léna experiment with updated equipment. Examples of images at the various wavelengths are given in the poster. Analysis of the data is incomplete at this time. We can report that the effects of seeing were encountered at all wavelengths, including 18μm, even though conditions were deemed good at times (for example, penumbral filaments were resolved in sunspots). We have thus been unable to verify, as yet, the conditions reported by Bester et al, in which exceptional seeing is realized in the infrared.

Some seeing statistics for the Narrabri site of SUSI are presented. These measurements are based on the motion of the wavefront tilt correcting mirrors used in the interferometer. The median seeing for the site to date is 1.3″.

This paper describes early results of a theoretical investigation of the performance of an adaptive optics system in which a limited number of Karhunen-Loeve modes of the wavefront distortion are corrected. We have determined the on-axis point spread function for an idealised adaptive optics system in Kolmogorov seeing, whose performance is defined in terms of radii of included energy and Strehl ratios for a range of examples. We discuss extensions of the analysis for the off-axis point spread function, and for non-Kolmogorov seeing.

Two high-fidelity computer simulations are used to study low-order adaptive optics systems operating in the near-infrared. We study obtainable system performance using very dim reference sources at three IR wavelengths.

At optical wavelengths there are a wide variety of techniques to detect interference fringes. Because detectors in the visible/IR are energy detectors, the fringe amplitude and phase must be encoded in some manner. Two fundamentally different methods are temporal and spatial encoding. This paper briefly describes the various techniques that have been used in operational interferometers along with their advantages and disadvantages. Several fringe detectors for next-generation interferometers will also be described. These fringe detectors often combine multiple functions, such as spectroscopy and multi-beam combination.

Unlike their radio counterparts, optical astronomers have paid relatively little attention to the role of the aperture function when designing their high resolution imaging experiments. This is despite the fact that it can be easily modified with the use of a suitable pupil plane mask. While the defining characteristics of the two most favoured pupil configurations have never been in doubt – negligible atmospheric noise in the case of a non-redundant configuration of small holes and high photon rates for a filled pupil – the relative merits of these two choices in terms of imaging performance in the presence of turbulence appear not to have been carefully investigated until very recently.

Most existing comparisons of fully-filled aperture (FFA) and non-redundant mask (NRM) based imaging strategies appear to have ignored a number of fundamental and practical difficulties that are often encountered in practice. In the intermediate regime, between very high and very low light levels, that characterizes most astrophysical applications hybrid imaging schemes seem most profitable. These utilize partially-redundant pupil geometries that combine the advantages of redundancy at low light levels without incurring the penalties associated with fully redundant beam recombination. Such pupil geometries are also useful in reducing the level of systematic effects that often plague speckle imaging experiments.

MAPPIT (Masked APerture-Plane Interference Telescope) is an optical interferometer mounted at the coudé focus of the 3.9 m Anglo-Australian Telescope. The instrument, shown schematically in Fig. 1, uses a pupil mask with five apertures of diameter ≲r 0. The apertures are arranged in a linear non-redundant array, with the spacings chosen to optimize the spatial frequency coverage (R. G. Marson, these Proceedings).