Nicholas Devaney

We investigate the performance of TDWFS for turbulent wavefronts described by modified von Kármán statistics. A previously developed gradient- and Hessian-based framework is extended to derive analytical expressions for the mean wavefront gradient and deformation energies, providing characteristic propagation distances associated with speckle decorrelation and reconstruction degradation. The influence of Fried’s parameter, turbulence inner scale, and finite spatial sampling is examined theoretically and through numerical phase-screen simulations. Reconstruction performance is compared using the Demon, Lucas–Kanade, and Farnebäck displacement-estimation algorithms. Our previously published direct modal wavefront estimation method is also briefly demonstrated for turbulent wavefront reconstruction. The results show that TDWFS performance is strongly governed by the spatial structure of the turbulent wavefront, with decreasing Fried parameter and inner scale reducing the usable diffuser–detector propagation distance. Finite-difference models closely reproduce the behaviour of numerically sampled phase screens and account for discrepancies from the continuous analytical predictions at small inner scales. These results provide a framework for evaluating TDWFS performance under turbulent wavefront.

MORFEO (Multi-conjugate adaptive Optics Relay For ELT Observations) is the post-focal adaptive optics module for the ESO Extremely Large Telescope (ELT). The instrument provides MCAO correction for two instruments: MICADO and HARMONI. The TAC (Test and Alignment Camera) is a piece of equipment that will be installed inside the MES (MICADO Emulating Structure), under the LOR (Low Order and Reference Wavefront Sensor): its main function is to simulate and verify all the requirements regarding the interface between MORFEO and MICADO in the Bologna Integration Hall, before the whole system is sent to the ELT in Chile. The TAC is subdivided into a Stage system, equipped with three linear stages – one for each axis – to precisely control the position of the assembly in space, and a Camera system, an Aluminium plate housing sensors and the necessary opto-mechanics. This paper focuses on the optomechanical design of the TAC, presenting how challenges were overcome and the choice of equipment.

Context. The origin(s) of fast radio bursts (FRBs), mysterious radio bursts coming from extragalactic distances, remains unknown. Multiwavelength observations are arguably the only way to answer this question unambiguously. Aims. We attempt to detect hard X-ray/soft γ -ray counterparts to one of the most active FRB sources, FRB 20121102A, as well as improve our understanding of burst properties in radio through a long-term monitoring campaign using the Nançay Radio Telescope (NRT). Methods. Multiwavelength campaigns involving the International Gamma-ray Astrophysics Laboratory (INTEGRAL) satellite, the Nançay Radio Observatory, the optical telescopes at the Observatoire de Haute-Provence, as well as Arecibo were conducted between 2017 and 2019. In 2017, the telescopes were scheduled to observe simultaneously between September 24–29. We specifically used the Fast Response Enhanced CCDs for the optical observations to ensure a high time resolution. In 2019, we changed the strategy to instead conduct ToO observations on INTEGRAL and other available facilities upon positive detection triggers from the NRT. Results. In the 2017 campaign, FRB 20121102A was not in its burst active phase periodic window. We obtain a 5 σ optical flux limit of 12 mJy ms using the GASP and a 3 σ limit from OHP T120cm R -band image of R = 22.2 mag of any potential persistent emission not associated with radio bursts. In the 2019 campaign, we have simultaneous INTEGRAL data with at least 11 radio bursts from the NRT and Arecibo. We obtain a 5 σ upper limit of 2.7 × 10 ⁻⁷ erg cm ⁻² in the 25–400 keV energy range for contemporary radio and high energy bursts, and a 5 σ upper limit of 3.8 × 10 ⁻¹¹ erg cm ⁻² for permanent emission in the 25–100 keV energy range. In addition, we report on the regular observations from NRT between 2016–2020, which account for 120 additional radio bursts from FRB 20121102A. We observe temporal dispersion measure (DM) variations at a level of ΔDM ∼ +2.04(4) pc cm ⁻³ /yr, in broad agreement with the literature. We also present an updated fit of the periodic active window, the emission bandwidth and the burst width distribution.

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. We show that in a high-magnification regime, where the sample is positioned near a source that produces spherical waves, our optimized GRIN-based setup provides better resolution ( ∼1.38µm ). Furthermore, we employed this microscope to holographically image dilute polystyrene micro-particles with diameters of 3.0 and 2.0 µm. We investigated the effect of light source–detector and sample–detector distances on the resolution, by both theory and experiment. Our theoretical and experimental results are in good agreement.

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. We propose a method of multiframe super-resolution using a set of convolutional sinc kernels, tailored to the specific shifts between images, capable of resolving up to the diffraction limit. We demonstrate our method for the case of global shifts before we treat a pixel-level super-resolution.

Active optics has been proposed for application to space telescopes since the mid 1960s since it can help to relax manufacturing tolerances while guaranteeing diffraction-limited image quality, correct for thermal gradients and any errors due to launch loads. The James Webb Space Telescope, which will be segments, will incorporate active optics to ensure alignment of the segments as well as controlling segment shape. Monolithic mirror space telescopes have been proposed incorporating active control, either acting on the primary mirror or at a relayed pupil. This paper provides a historical review of Active Optics, with emphasis on the application to Space Telescopes concluding with some results of a laboratory prototype system developed for the European Space Agency.

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. A comparison with the geometrical approach for estimating the axial resolution is provided, and results for several simulations are discussed.

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 2.5 arcmin field of the telescope, operating at 0.55 μm. We describe the modeling carried out to develop the active mirror design. Using end-to-end modeling, a 25-actuator mirror with polar actuator geometry, and a ratio of mechanical to optical pupil diameter of 2 has been chosen. A single-actuator prototype has been manufactured and used to test stroke, linearity, and hysteresis. Finally, we describe the design of a laboratory breadboard that will image phase screens onto an exact replica of the space active mirror and show the results of measuring the phase screen accuracy.

The detection of exoplanets in coronographic images is severely limited by residual starlight speckles. Dedicated post-processing can drastically reduce this ‘stellar leakage’ and thereby increase the faintness of detectable exoplanets. Based on a multispectral series expansion of the diffraction pattern, we derive a multimode model of the residuals which can be exploited to estimate and thus remove the residual speckles in multispectral coronographic images. Compared to other multispectral processing methods, our model is physically grounded and is suitable for use in an (optimal) inverse approach. We demonstrate the ability of our model to correctly estimate the speckles in simulated data and demonstrate that very high contrasts can be achieved. We further apply our method to removing speckle from a real data cube obtained with the SPHERE integral field spectrograph instrument.

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). Each metric was calculated on the same four retinal locations (200 × 200 μm areas, 2° from the fovea along the four meridians) over time for each subject. Results: The histogram distributions of cone intensities were similar between the two study groups. However, the cone/intercone intensity, slope of the variograms and entropy showed a significant difference between healthy and NPDR subjects (P = 0.036, P = 0.002, P = 0.014, respectively). All parameters, except for mean cone intensity, did not change with time in this study. Conclusions: We observed significant differences in cone mosaic reflectance properties between healthy eyes and eyes with NPDR, in its spatial organization and in its intensity, especially between directional and nondirectional backscattering. We introduced a novel method for the study of the spatial distribution of cone reflectance, the variogram, which was able to quantify differences of the spatial dependence of cone intensities over a short range between NPDR and healthy eyes.