Curvature Wavefront Sensor For Solar Adaptive Optics

Active or adaptive optics often require the ability to characterize wavefront aberrations using natural extended sources. The task becomes especially challenging when dealing with widely extended sources such as the solar granulation. We propose a new approach based on the processing of oppositely defocused images. This method, which is a generalization of a technique known as curvature sensing, derives the wavefront curvature from the difference between two oppositely defocused images and determines the second momenta of the point spread function. The proposed method measures the wavefront aberration from the images themselves, requires little computational resources, is fast enough to be used in a real-time adaptive optics system and is particularly adapted to random patterns such as solar granulation or spot penumbras whose morphology evolves during the observation. We envision the application of the method to real-time seeing compensation in solar astronomical telescopes, and to the correction of optical system aberrations in remote sensing instrumentation. This effort is directed towards building a curvature sensor for the real-time applications.     

A fourier spectrum analysis of long samples of solar line oscillations

Sequences of the oscillations of solar lines up to 2 hours 20 min long have been recorded at the same point on the sun. The power spectra show several peaks separated by 0.85 × 10^–3 cps on average from each other. A sharp main peak at 3.3 × 10^–3 cps (300 sec period) is almost always present.These results suggest that the lifetime of the phase of the oscillation is much longer than that of the amplitude and is likely to exceed one hour. We actually observe the modulation of a wave in smaller wave trains about 11 min long and 20 min apart (average values).Observations with low spatial resolution also suggest that the area of coherence is much greater for the phase than for the amplitude.Kitt Peak National Observatory Contribution No. 425.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

A sodium experiment for photospheric velocity field observations

A method for studying small scale photospheric velocity fields with a balloon experiment is proposed. A sodium resonance cell is used with a diffraction limited telescope. Good pointing accuracy is not necessary. Preliminary results of ground-based observations are given.