Even when corrected with the best spectacles or contact lenses, normal human eyes still suffer from monochromatic aberrations that blur vision when the pupil is large. We have successfully corrected these aberrations using adaptive optics, providing normal eyes with supernormal optical quality. Contrast sensitivity to fine spatial patterns was increased when observers viewed stimuli through adaptive optics. The eye's aberrations also limit the resolution of images of the retina, a limit that has existed since the invention of the ophthalmoscope. We have constructed a fundus camera equipped with adaptive optics that provides unprecedented resolution, allowing the imaging of microscopic structures the size of single cells in the living human retina.

/pdf/supernormal-vision-and-high-resolution-retinal-imaging-54uzhrh9sx.pdf

Supernormal vision and high-resolution retinal imaging through adaptive optics

A solution to the inversion problem of scattering would offer aberration-free diffraction-limited three-dimensional images without the resolution and depth-of-field limitations of lens-based tomographic systems. Powerful algorithms are increasingly being used to act as lenses to form such images. Current image reconstruction methods, however, require the knowledge of the shape of the object and the low spatial frequencies unavoidably lost in experiments. Diffractive imaging has thus previously been used to increase the resolution of images obtained by other means. Here we experimentally demonstrate an inversion method, which reconstructs the image of the object without the need for any such prior knowledge.

/pdf/x-ray-image-reconstruction-from-a-diffraction-pattern-alone-3ecjgo7w8y.pdf

X-ray image reconstruction from a diffraction pattern alone

Wave front shaping, the ability to manipulate light fields both spatially and temporally, in complex media is an emerging field with many applications. This review summarizes how insights from mesoscopic scattering theory have direct relevance for optical wave control experiments and vice versa. The results are expected to have an impact on a number of fields ranging from biomedical imaging to nanophotonics, quantum information, and communication technology.

Light fields in complex media: Mesoscopic scattering meets wave control

In the field of biomedical optics, optical scattering has traditionally limited the range of imaging within tissue to a depth of one millimetre. A recently developed class of wavefront-shaping techniques now aims to overcome this limit and achieve diffraction-limited control of light beyond one centimetre. By manipulating the spatial profile of an optical field before it enters a scattering medium, it is possible to create a micrometre-scale focal spot deep within tissue. To successfully operate in vivo, these wavefront-shaping techniques typically require feedback from within the biological sample. This Review summarizes recently developed 'guidestar' mechanisms that provide feedback for intra-tissue focusing. Potential applications of guidestar-assisted focusing include optogenetic control over neurons, targeted photodynamic therapy and deep tissue imaging.

/pdf/guidestar-assisted-wavefront-shaping-methods-for-focusing-3pl7c6sufk.pdf

Guidestar-assisted wavefront-shaping methods for focusing light into biological tissue

An extension of Joint Phase Diverse Speckle image restoration is presented. Multiple realizations of multiple objects having known wavefront relations with each other can now be restored jointly. As the alignment of the imaging setup does not change, near-perfect alignment can be achieved between different objects, thus greatly reducing false signals in the determination of derived quantities, such as magnetograms, Dopplergrams, etc. The method was implemented in C++ as an image restoration server, to which worker clients can connect and disconnect randomly, so that a large number of CPUs can be used to speed up the restorations. We present a number of examples of applications of the restoration method to observations obtained with the Swedish 1-m Solar Telescope on La Palma.

Solar Image Restoration By Use Of Multi-frame Blind De-convolution With Multiple Objects And Phase Diversity

SASI is a cost-effective approach to image silhouettes of geosynchronous satellites at fine resolution. We report on a laboratory demonstration of SASI that is a scaled version of the geosynchronous-imaging geometry.

Synthetic-Aperture Silhouette Imaging (SASI) Laboratory Demonstration

Space-variant blur occurs when imaging through volume turbulence over sufficiently large fields of view, and it is particularly severe in horizontal-path imaging and slant-path (air- to-ground or ground-to-air) geometries. We report on pre and post-detection correction methods based on the method of Phase-Diverse-Speckle (PDS), and demonstrate its potential for dramatic improvement via simulation results.

Imaging through volume turbulence by using phase-diverse speckle

Nearly all imaging systems exhibit aberrations with some degree of field dependence. We examine sensing and managing space-variant wavefront error when imaging (1) with multiple-telescope arrays, (2) through extended-path turbulence, and (3) through turbid media.

Sensing and Managing Field-Dependent Wavefront Error

The relevant issues in the design of laboratory experiments to demonstrate phase retrieval from Fourier intensity (far-field speckle pattern) data from a laser-illuminated diffuse object are considered. Based on the results of these considerations, a demonstration phase retrieval experiment was conducted. A diffuse object was coherently illuminated, Fourier intensity data was collected and an image was reconstructed by the iterative Fourier transform algorithm using the Fourier intensity data and an a priori known triangular image support constraint. The intensity of the complex-valued reconstructed image compares favorably to a conventional image with the same spatial frequency bandwidth, thus providing an experimental demonstration of the phase retrieval method.

Design And Execution Of A Phase Retrieval Demonstration Experiment

: This report summarizes a research program in which we evaluated the use of a Long-Range Laser Imaging (LRLI) system to perform the imaging tasks associated with laser target designation. The motivation for LRLI is to improve crew and aircraft survivability by increasing the standoff range, and reducing the required time interval, for air-based laser target designation. In this program we analyzed the capabilities of LRLI systems. We considered the signal level and its impact on sensor field-of-view. This analysis includes laser selection, atmospheric transmission, target reflectivity and optical system characteristics. It is shown that the laser signal level ultimately limits the number of target pixels. It is also shown that a pulsed system is required for background rejection. The impact of optical turbulence on system performance is also discussed. We evaluated the achievable resolution and considered the use of adaptive optics. It is shown, however, that severe anisoplanatism limits the utility of adaptive optics. We conclude that the most promising sensor design is based on conventional imaging and recommendations for proof-of-concept experiments are given. Active Imaging, Atmosphere, Absorption, Turbulence

Long-Range Laser Imaging

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