Micron-sized particles can be trapped by means of a highly focused beam; light is concentrated in a tiny spot
using a high numerical aperture objective. In this communication we describe a numerical tool we have developed
for obtaining the force exerted by a beam on a spherical dielectric particle in realistic conditions. The system
(a water immersion microscope objective) is simulated using an optical system design software that provides
the required information to feed the application. The calculation of the force is carried out using the ray-optics (Mie) approach.
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 <i>C<sub>n</sub><sup>2</sup></i>(<i>h</i>), 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.