In-vacuum dry launching of silica microparticles using an array of custom MEMS devices.

To test the validity of the quantum superposition principle at unprecedented macroscopic scales, near-field matter-wave interferometry of free-falling massive 100nm silica nanospheres from an optically cooled laser trap has been proposed [Nat. Commun.5, 4788 (2014)10.

Application of GRIN-lens-based in-line digital holographic microscopy to automatic detection and localization of particles released from a MEMS device.

Recently, we developed a compact and easy-to-implement in-line digital holographic microscope (DHM) using a GRIN rod lens, which provides better resolution (1.3 µm) compared with commonly used pinhole-based DHM setups. Here, we employ this microscope to acquire 3D holographically reconstructed images of silica microparticles, within the 10-300 µm size range, launched/released from a microelectro-mechanical systems (MEMS) device.

GRIN-lens-based in-line digital holographic microscopy.

In-line digital holographic microscopy (DHM) provides three-dimensional images with large fields of view and depths of field and micrometer-scale resolution, using a compact, cost-effective, and stable setup. Here, we develop the theoretical background and experimentally demonstrate an in-line DHM based on a gradient-index (GRIN) rod lens. In addition, we develop a conventional pinhole-based in-line DHM with different configurations to compare the resolution and image quality of both GRIN-based and pinhole-based systems.

Locally adaptive super-resolution through spatially variant interpolation.

Systems that do not meet the requirements of the sampling theorem produce images corrupted by aliasing. Higher resolution images are attainable by unfolding aliased spatial frequencies. Multiple-image super-resolution has seen much attention in the literature though with no clear optimum algorithm for many real-world applications.

Development of a prototype active optics system for future space telescopes.

It is envisaged that future large space telescopes will be lightweight and employ active optics to maintain optical quality throughout the mission lifetime. We have proposed a 4 m, two-mirror space telescope with an active optics system based on reimaging the telescope primary mirror onto a small active mirror (110 mm optical pupil). Using Zemax, we demonstrate the feasibility of using this mirror to correct low-order Zernike aberrations and show that the aberration is well corrected across the 2.

Estimating axial resolution with diffraction theory.

Depth estimation is a classic machine vision and image processing problem aiming at mapping the distances of objects from the camera. The accuracy of this depth map depends on the axial resolution achieved by the system, which is usually estimated using geometrical optics theory. This paper proposes a novel formula using diffraction theory.

Registration for images in the presence of additive and multiplicative fixed-pattern noise.

Image registration under conditions of fixed-pattern noise is a difficult problem that has not been solved in the literature. While traditional registration methods are adequate for additive random noise, these are not suited to spatially invariant noise that is additive or multiplicative. We present a method for image registration using a difference operation in the frequency domain.

Phytochrome A and B Regulate Primary Metabolism in Leaves in Response to Light.

Primary metabolism is closely linked to plant productivity and quality. Thus, a better understanding of the regulation of primary metabolism by photoreceptors has profound implications for agricultural practices and management. This study aims at identifying the role of light signaling in the regulation of primary metabolism, with an emphasis on starch.

Analysis of Cone Mosaic Reflectance Properties in Healthy Eyes and in Eyes With Nonproliferative Diabetic Retinopathy Over Time.

Purpose: We investigate the reflectance properties of the cone mosaic in adaptive optics (AO) images of healthy subjects and subjects with nonproliferative diabetic retinopathy (NPDR) over time.

Methods: We acquired images of the parafoveal cone mosaic over 5 years in 12 healthy subjects and in six patients with mild NPDR. We analyzed the parameters of the cone intensity histogram distribution (mean, SD, and skewness), two metrics of the cone mosaic texture (sharpness and entropy), and two novel metrics (cone/intercone intensity and slope of the variogram).

Reliability and Agreement Between Metrics of Cone Spacing in Adaptive Optics Images of the Human Retinal Photoreceptor Mosaic.

Purpose: To assess reliability and agreement among three metrics used to evaluate the distribution of cell distances in adaptive optics (AO) images of the cone mosaic.

Methods: Using an AO flood illumination retinal camera, we acquired images of the cone mosaic in 20 healthy subjects and 12 patients with retinal diseases. The three spacing metrics studied were the center-to-center spacing (Scc), the local cone spacing (LCS), and the density recovery profile distance (DRPD).

Understanding the changes of cone reflectance in adaptive optics flood illumination retinal images over three years.

Although there is increasing interest in the investigation of cone reflectance variability, little is understood about its characteristics over long time scales. Cone detection and its automation is now becoming a fundamental step in the assessment and monitoring of the health of the retina and in the understanding of the photoreceptor physiology. In this work we provide an insight into the cone reflectance variability over time scales ranging from minutes to three years on the same eye, and for large areas of the retina (≥ 2.

Performance analysis of cone detection algorithms.

Many algorithms have been proposed to help clinicians evaluate cone density and spacing, as these may be related to the onset of retinal diseases. However, there has been no rigorous comparison of the performance of these algorithms. In addition, the performance of such algorithms is typically determined by comparison with human observers.

Registration of adaptive optics corrected retinal nerve fiber layer (RNFL) images.

Glaucoma is the leading cause of preventable blindness in the western world. Investigation of high-resolution retinal nerve fiber layer (RNFL) images in patients may lead to new indicators of its onset. Adaptive optics (AO) can provide diffraction-limited images of the retina, providing new opportunities for earlier detection of neuroretinal pathologies.

Pre-processing, registration and selection of adaptive optics corrected retinal images.

Purpose: In this paper, the aim is to demonstrate enhanced processing of sequences of fundus images obtained using a commercial AO flood illumination system. The purpose of the work is to (1) correct for uneven illumination at the retina (2) automatically select the best quality images and (3) precisely register the best images.

Methods: Adaptive optics corrected retinal images are pre-processed to correct uneven illumination using different methods; subtracting or dividing by the average filtered image, homomorphic filtering and a wavelet based approach.

Adaptive optics technology for high-resolution retinal imaging.

Adaptive optics (AO) is a technology used to improve the performance of optical systems by reducing the effects of optical aberrations. The direct visualization of the photoreceptor cells, capillaries and nerve fiber bundles represents the major benefit of adding AO to retinal imaging. Adaptive optics is opening a new frontier for clinical research in ophthalmology, providing new information on the early pathological changes of the retinal microstructures in various retinal diseases.

On Advanced Estimation Techniques for Exoplanet Detection and Characterization Using Ground-based Coronagraphs.

The direct imaging of planets around nearby stars is exceedingly difficult. Only about 14 exoplanets have been imaged to date that have masses less than 13 times that of Jupiter. The next generation of planet-finding coronagraphs, including VLT-SPHERE, the Gemini Planet Imager, Palomar P1640, and Subaru HiCIAO have predicted contrast performance of roughly a thousand times less than would be needed to detect Earth-like planets.

Enhanced faint companion photometry and astrometry using wavelength diversity.

In this paper we examine approaches to faint companion detection and estimation in multi-spectral images. We will employ the Hotelling observer, which is the optimal linear algorithm for signal detection. We have shown how to use this observer to estimate faint object position and brightness in the presence of residual speckle, which usually limits astrometric and photometric techniques.

Experimental detection of optical vortices with a Shack-Hartmann wavefront sensor.

Laboratory experiments are carried out to detect optical vortices in conditions typical of those experienced when a laser beam is propagated through the atmosphere. A Spatial Light Modulator (SLM) is used to mimic atmospheric turbulence and a Shack-Hartmann wavefront sensor is utilised to measure the slopes of the wavefront surface. A matched filter algorithm determines the positions of the Shack-Hartmann spot centroids more robustly than a centroiding algorithm.

Correction of ocular and atmospheric wavefronts: a comparison of the performance of various deformable mirrors.

The main applications of adaptive optics are the correction of the effects of atmospheric turbulence on ground-based telescopes and the correction of ocular aberrations in retinal imaging and visual simulation. The requirements for the wavefront corrector, usually a deformable mirror, will depend on the statistics of the aberrations to be corrected; here we compare the spatial statistics of wavefront aberrations expected in these two applications. We also use measured influence functions and numerical simulations to compare the performance of eight commercially available deformable mirrors for these tasks.

Chromatic effects of the atmosphere on astronomical adaptive optics.

The atmosphere introduces chromatic errors that may limit the performance of adaptive optics (AO) systems on large telescopes. Various aspects of this problem have been considered in the literature over the past two decades. It is necessary to revisit this problem in order to examine the effect on currently planned systems, including very high-order AO on current 8-10 m class telescopes and on future 30-42 m extremely large telescopes.

Application of the Hotelling and ideal observers to detection and localization of exoplanets.

The ideal linear discriminant or Hotelling observer is widely used for detection tasks and image-quality assessment in medical imaging, but it has had little application in other imaging fields. We apply it to detection of planets outside of our solar system with long-exposure images obtained from ground-based or space-based telescopes. The statistical limitations in this problem include Poisson noise arising mainly from the host star, electronic noise in the image detector, randomness or uncertainty in the point-spread function (PSF) of the telescope, and possibly a random background.

Atmospheric dispersion compensation for extremely large telescopes.

Achieving diffraction limited imaging with future ground-based optical telescopes will require adaptive optics for correction of atmospheric turbulence and also efficient techniques for atmospheric dispersion compensation. We study the benefit of using a linear atmospheric dispersion corrector (ADC) coupled with a deformable mirror on a 42-m Extremely Large Telescope (ELT) operating in the VIRJ spectral bands. The ADC design consists of two identical thin wedges made of F5 glass.

Objective assessment of image quality. IV. Application to adaptive optics.

The methodology of objective assessment, which defines image quality in terms of the performance of specific observers on specific tasks of interest, is extended to temporal sequences of images with random point spread functions and applied to adaptive imaging in astronomy. The tasks considered include both detection and estimation, and the observers are the optimal linear discriminant (Hotelling observer) and the optimal linear estimator (Wiener). A general theory of first- and second-order spatiotemporal statistics in adaptive optics is developed.

Task Performance in Astronomical Adaptive Optics.

In objective or task-based assessment of image quality, figures of merit are defined by the performance of some specific observer on some task of scientific interest. This methodology is well established in medical imaging but is just beginning to be applied in astronomy. In this paper we survey the theory needed to understand the performance of ideal or ideal-linear (Hotelling) observers on detection tasks with adaptive-optical data.

Phasing segmented mirrors: a modification of the Keck narrow-band technique and its application to extremely large telescopes.

Future telescopes with diameters greater than 10 m, usually referred to as extremely large telescopes (ELTs), will employ segmented mirrors made up of hundreds or even thousands of segments, with tight constraints on the piston errors between individual segments. The 10-m Keck telescopes are routinely phased with the narrow-band phasing technique. This is a variation of the Shack-Hartmann wave-front sensor in which the signal is the correlation between individual subimages and simulated images.