Adaptive Wavefront Correction Research Articles

Adaptive wave-front correction by means of all-optical feedback interferometry

A novel adaptive wave-front correction system based on an all-optical feedback interferometer is described. In this system the two-dimensional output fringe intensity from a Mach-Zehnder interferometer with large radial shear is optically fed back to an optically addressed phase-only liquid-crystal spatial light modulator. Consequently, without a separate aberration-free reference wave, the modulator phase approximates the conjugate of the interferometer phase that is directly related to the phase of the input aberrated wave front, so this system is applicable in adaptive optics. We successfully achieved real-time correction of aberrated wave fronts: A diffraction pattern that was seriously distorted because of aberrations was transformed into a diffraction-limited spot immediately after the feedback loop was closed.

Stochastic parallel-gradient-descent technique for high-resolution wave-front phase-distortion correction

A new optimization technique, stochastic parallel-gradient descent, is applied for high-resolution adaptive wave-front correction. A performance criterion for parallel-perturbation-based algorithms is introduced and applied to optimize adaptive system architecture. We present numerical simulation results for an adaptive imaging system based on the stochastic parallel-perturbation technique, along with experimental results obtained for a white-light adaptive imaging system with 37 control channels. An adaptive system with a self-organized (adaptive) control channel hierarchy is introduced and analyzed.

Adaptive phase-distortion correction based on parallel gradient-descent optimization

We describe an adaptive wave-front control technique based on a parallel stochastic perturbation method that can be applied to a general class of adaptive-optical system. The efficiency of this approach is analyzed numerically and experimentally by use of a white-light adaptive-imaging system with an extended source. To create and compensate for static phase distortions, we use 127-element liquid-crystal phase modulators. Results demonstrate that adaptive wave-front correction by a parallel-perturbation technique can significantly improve image quality.

Binary adaptive optics: atmospheric wave-front correction with a half-wave phase shifter: addenda

We describe a binary approach to adaptive wave-front correction, especially suitable for narrow band applications, which would be simpler than conventional adaptive technology. Appropriate parts of the aberrant wave front are phase retarded by half a wavelength to ensure that none of the image-forming rays add together destructively. Simulations for monochromatic light show that the residual wave-front errors, in the absence of other errors, would result in Strehl ratios of ~40% with diffraction-limited widths at visible wavelengths. We simulate the imaging performance of such a system and describe a possible implementation that uses a ferroelectric liquid-crystal spatial light modulator.

Binary adaptive optics: atmospheric wave-front correction with a half-wave phase shifter

We describe a binary approach to adaptive wave-front correction, especially suitable for narrow band applications, which would be simpler than conventional adaptive technology. Appropriate parts of the aberrant wave front are phase retarded by half a wavelength to ensure that none of the image-forming rays add together destructively. Simulations for monochromatic light show that the residual wave-front errors, in the absence of other errors, would result in Strehl ratios of ~40% with diffraction-limited widths at visible wavelengths. We simulate the imaging performance of such a system and describe a possible implementation that uses a ferroelectric liquid-crystal spatial light modulator.

CLOSURE PHASE IMAGING WITH PARTIAL ADAPTIVE CORRECTION

ABSTRACT We explore the effects of localized adaptive wavefront correction on the performance of closure-phase (non-redundant mask, NRM) imaging. Specfically, we examine a system in which tip-tilt corrections are applied to individual beams transmitted by a mask in the telescope pupil plane. Piston errors between the beams are not corrected. Using numerical simulations we have investigated the optimization of the sub-aperture size and science detector integration time as a function of the seeing parameters for high and low light levels. Our calculations predict improvements in the signal-to-noise ratios of monochromatic power spectrum and bispectrum measurements by factors in the range 2-15 over their uncorrected values. For a given number of adaptive degrees of freedom, this type of sparse and localized adaptive correction is far more efficient in terms of improving the performance of NRM imaging than conventional low-order modal correction when applied to large optical telescopes. The simple AO system we examine represents a cost-effective method for extending the utility of closure phase imaging using a very small number of active optical components. Suitable astrophysical sources amenable to such an approach include evolved supergiant stars, long period variables and other bright compact objects.