The efficiency of the CHARA Array has proven satisfactory for a wide variety of scientific programs enabled by the
first-generation beam combination and detector systems. With multi-beam combination and more ambitious scientific
goals, improvements in throughput and efficiency will be highly leveraged. Engineering data from several years of
nightly operations are used to infer atmospheric characteristics and raw instrumental visibility in both classic optical and
single-mode fiber beam combiners. This information is the basis for estimates of potential gains that could be afforded
by the implementation of adaptive optics. In addition to the very important partial compensation for higher order
atmosphere-induced wavefront errors, the benefits include reduction of static and quasi-static aberrations, reduction of
residual tilt error, compensation for differential atmospheric refraction, and reduction of diffractive beam propagation
losses, each leading to improved flux throughput and instrumental visibility, and to associated gains in operability and
The Applied Optics group at the National University of Ireland, Galway, is engaged in research into various aspects of
the application of adaptive optics to both ocular and atmospheric wavefront correction. A large number of commercially available deformable mirrors have been selected by the group for AO experiments, and these mirrors have been carefully characterised to determine their suitability for these tasks. In this paper we describe the approach we have used in characterising deformable mirrors and present results for several MEMs mirrors, including membrane mirrors from AgilOptics and Flexible Optical BV, a segmented micromirror from IrisAO and a 140-actuator mirror from Boston micromachines.
This paper details a generalised SCIDAR system developed for characterising atmospheric parameters using single star targets. The instrument, which is based on a commercially available 250 mm diameter telescope, offers the potential for characterising atmospheric parameters for wide areas of the sky. Here, we describe the system and results of a proof of principle study performed at an observing site in Galway, Ireland with the instrument. The paper also outlines the approach adopted in the data reduction and in solving the altitude dependence of refractive index structure constant given the raw data from the instrument.
Astronomical images obtained on large ground based telescopes are blurred due to the effect of the atmospheric turbulence but this can be compensated by means of adaptive optics. A knowledge of the vertical profile of the turbulence might help to optimize the adaptive optics control system, especially when an attempt is made to correct over a wide field of view (MCAO). We present the development of a remote sensing technique called Single-Star SCIDAR (SSS) system for characterizing atmospheric parameters, such as the refractive-index structure function constant Cn2(h), using single star targets. The technique is based on the analysis of stellar scintillation produced by the passage of the light through the atmospheric turbulence. The instrument is intended to be used in generalized mode, i.e. with several measurement planes. The autocorrelation of scintillation images, taken at several measurement planes with a short exposure time using a 25cm diameter telescope, allows us to characterize atmospheric parameters for wide-ranging area in the sky. Computational simulations of a wave propagating through atmospheric turbulence are made using a Kolmogorov model. Retrieving the refractive-index fluctuation profile of the turbulence at different heights from single stars is challenging, contrary to the triangulation inherent to the binary star SCIDAR technique. The problem is an ill-posed one, made easier to solve by the use of multiple conjugated altitudes. A least square method solution with a Tikhonov regularization is used for the resolution. Methods to enforce non-negativity, reflecting the physical property of the quantity, are investigated.