ABSTRACT
A possible solution for the global warming problem consists of scattering the solar radiation by a cloud of screens, placed near the inner Lagrange point (L1), between the sun and the earth. The thin film material for such a screen should have a high longevity in space environment, low areal density, high on-axis scattering, very low integral reflectivity over the whole solar spectrum, and good handling properties such as foldability and robustness. We report on experimental fabrication of free-standing robust nitride films satisfying to most optical and mechanical requirements for such a screen.
ABSTRACT
An adaptive optical system with a subjective feedback loop is used to improve the visual acuity and to determine the aberrations of the human eye. Corrections of as many as 12 low-order aberration modes were made, based on the perceived sharpness of the test object observed through the adaptive optical system. The acuity of vision was improved by adjustment of the weights of the orthogonal modes produced by a deformable mirror. Objective measurements of the correcting aspherical figures, obtained in independent subjective correction cycles for one person, demonstrated good repeatability. Participants in the study with strong ocular aberrations reported moderate to significant improvement of their visual acuity, estimated with the U.S. Air Force 1951 acuity chart.
Subject(s)
Image Enhancement/methods , Image Interpretation, Computer-Assisted/methods , Refractive Errors/diagnosis , Refractive Errors/rehabilitation , Therapy, Computer-Assisted/methods , User-Computer Interface , Vision Tests/methods , Adaptation, Physiological , Adolescent , Adult , Aged , Data Display , Feedback , Humans , Image Enhancement/instrumentation , Image Interpretation, Computer-Assisted/instrumentation , Interferometry/instrumentation , Interferometry/methods , Middle Aged , Reproducibility of Results , Sensitivity and Specificity , Treatment Outcome , Visual AcuityABSTRACT
Results are presented of the properties of a liquid crystal wavefront corrector for adaptive optics. The device is controlled using modal addressing in which case the device behaves more like a continuous facesheet deformable mirror than a segmented one. Furthermore, the width and shape of the influence functions are electrically controllable. We describe the construction of the device, the optical properties, and we show experimental results of low order aberration generation.
ABSTRACT
Liquid crystal modal lenses are switchable lenses with a continuous phase variation across the lens. A critical issue for such lenses is the minimization of phase aberrations. In this paper we present results of a simulation of control signals that have a range of harmonics. Experimental results using optimal sinusoidal and rectangular voltages are presented. A lack of uniqueness in the specification of the control voltage parameters is explained. The influence of a variable duty cycle of the control voltage on an adaptive lens is investigated. Finally we present experimental results showing a liquid crystal lens varying its focal length.
ABSTRACT
We report on a novel approach to the realization of nematic liquid-crystal (LC) phase correctors to form spherical and cylindrical wave fronts. A LC cell with a distributed reactive electrical impedance was driven by an ac voltage applied to the cell boundary to yield the desired spatial distribution of the refractive index. The two-dimensional function of the phase delay introduced into the light beam depends on the frequency of the ac control voltage, the geometry of the boundary electrode surrounding the LC cell, and the electrical parameters of the cell. We realized a cylindrical adaptive lens with a clear aperture of 15 mm x 4mm and a spherical adaptive lens with circular aperture of 6.5 mm. Both devices are capable of focusing collimated light in the range infinity...0.5 m.
