Time-sequential Pipelined Imaging with Wavefront Coding and Super Resolution

Wavefront coding has long offered the prospect of mitigating optical aberrations and extended depth of field, but image quality and noise performance are inevitably reduced. We report on progress in the use of agile encoding and pipelined fusion of image sequences to recover image quality

Optimal design of hybrid optical digital imaging systems

Several types of pupil modulation have been reported to decrease the aberration variance of the modulation-transfer-function (MTF) in aberration-tolerant hybrid optical-digital imaging systems. It is common to enforce restorability constraints on the MTF, requiring trade of aberration-tolerance and noise-gain. In this thesis, instead of optimising specific MTF characteristics, the expected imaging-error of the joint design is minimised directly. This method is used to compare commonly used phase-modulation functions. The analysis shows how optimal imaging performance is obtained using moderate phasemodulation, and more importantly, it shows the relative merits of different functions. It is shown that the technique is readily integrable with off-the-shelf optical design software, which is demonstrated with the optimisation of a wide-angle reflective system with significant off-axis aberrations. The imaging error can also be minimised for amplitudeonly masks. It is shown that phase aberrations in an imaging system can be mitigated using binary amplitude masks. This offers a low-cost, transmission-mode alternative to phase correction as used in active and adaptive optics. More efficient masks can be obtained by the optimisation of the imaging fidelity

Parent participation at school: a research study on the perspectives of children

The present article discusses the attitude of children towards parent participation at school. To this end, a quantitative study was conducted among 250 10-year-old children in Flanders. The analysis shows that children tend to rather like parent participation, and that this attitude is related to the extent to which parents participate. Children from 'deprived' schools tend to like parent participation better. This article argues that children should be approached as fully-fledged, active participants in their parents' participation process and that it is necessary to take account of the specific perspectives of children on this topic

A universal matrix-free split preconditioner for the fixed-point iterative solution of non-symmetric linear systems

We present an efficient preconditioner for linear problems $A x=y$. It guarantees monotonic convergence of the memory-efficient fixed-point iteration for all accretive systems of the form $A = L + V$, where $L$ is an approximation of $A$, and the system is scaled so that the discrepancy is bounded with $\lVert V \rVert<1$. In contrast to common splitting preconditioners, our approach is not restricted to any particular splitting. Therefore, the approximate problem can be chosen so that an analytic solution is available to efficiently evaluate the preconditioner. We prove that the only preconditioner with this property has the form $(L+I)(I - V)^{-1}$. This unique form moreover permits the elimination of the forward problem from the preconditioned system, often halving the time required per iteration. We demonstrate and evaluate our approach for wave problems, diffusion problems, and pantograph delay differential equations. With the latter we show how the method extends to general, not necessarily accretive, linear systems.Comment: Rewritten version, includes efficiency comparison with shift preconditioner by Bai et al, which is shown to be a special cas

Computing coherent light scattering on the millimetre scale using a recurrent neural network without training

Heterogeneous materials such as biological tissue scatter light in random, yet deterministic, ways. Wavefront shaping can reverse the effects of scattering to enable deep-tissue microscopy. Such methods require either invasive access to the internal field or the computational solving of an inverse problem. However, calculating the coherent field on a scale relevant to microscopy remains excessively demanding for consumer hardware. Here we show how a recurrent neural network can mirror Maxwell's equations without training. By harnessing public machine learning infrastructure, the light-field throughout a $6 \, \textrm{mm}^2$ area or $110^3 \, \mu\textrm{m}^3$ volume can be calculated in 16 minutes. The elimination of the training phase cuts the calculation time and, importantly, it ensures a fully deterministic solution, free of training bias. We integrated our method with an open-source electromagnetic solver. This enables any researcher with an internet connection to calculate complex light-scattering in volumes that are larger by two orders of magnitude.Comment: 7 pages, 3 figure

Wavefront shaping of a Bessel light field enhances light sheet microscopy with scattered light

The project was supported by the UK Engineering and Physical Sciences Research Council, RS MacDonald Charitable Trust, SULSA, and the St. Andrews 600th anniversary BRAINS appeal. K. D. is a Royal Society Wolfson Merit Award holder.Light sheet microscopy has seen a resurgence as it facilitates rapid, high contrast, volumetric imaging with minimal sample exposure. Initially developed for imaging scattered light, this application of light sheet microscopy has largely been overlooked but provides an endogenous contrast mechanism which can complement fluorescence imaging and requires very little or no modification to an existing light sheet fluorescence microscope. Fluorescence imaging and scattered light imaging differ in terms of image formation. In the former the detected light is incoherent and weak whereas in the latter the coherence properties of the illumination source, typically a laser, dictate the coherence of detected light, but both are dependent on the quality of the illuminating light sheet. Image formation in both schemes can be understood as the convolution of the light sheet with the specimen distribution. In this paper we explore wavefront shaping for the enhancement of light sheet microscopy with scattered light. We show experimental verification of this result, demonstrating the use of the propagation invariant Bessel beam to extend the field of view of a high resolution scattered light, light sheet microscope and its application to imaging of biological super-cellular structures with sub-cellular resolution. Additionally, complementary scattering and fluorescence imaging is used to characterize the enhancement, and to develop a deeper understanding of the differences of image formation between contrast mechanisms in light sheet microscopy.Publisher PD