The interface of deep learning and imaging has seen extraordinary progress in the past few years as computational power now enables image processing that can exceed human capability. Much of the recent work at this interface involves the application of variants of convolutional neural networks, for a wide variety of techniques including image enhancement, style transfer and labelling. However, whilst deep learning can unlock extremely powerful capabilities, the collection and processing of appropriate training data remains a significant challenge. In this talk, a brief tutorial on the practical application of neural networks for image processing will be presented, followed by experimental results associated with optical and scanning electron microscopy. The focus of this talk will be on the demonstration of image enhancement of optical microscopy from 20x resolution to 1500x, whilst simultaneously identifying the objects present and hence enabling automated labelling, colour-enhancing and removal of specific objects in the magnified image.
We demonstrate the application of deep learning for the identification of particles, directly from their backscattered light. The particles were illuminated using a single-mode fibre-coupled laser light source and the scattered light was collected by a 30-core optical fibre. The technique enabled identification of the specific species of pollen grains with an accuracy of ~97%, even in the presence of high levels of background light equivalent to daytime sunlight. In addition, the technique determined the distance between the fibre tip and the particles with an accuracy of ± 6 µm.
2D materials such as graphene have great potential as the basis for novel optoelectronic devices. Typically, 2D materials are produced via chemical vapor deposition and therefore form continuous layers. Here Laser Induced Backwards Transfer (LIBT) is used to deposit pixels of 2D materials with precisely controlled size, shape and position. In LIBT, part of the laser energy that is absorbed in the donor substrate becomes kinetic energy imparted to the 2D material, causing localised transfer of 2D material onto the receiver. The capability to deposit high-quality intact 2D materials, in well-defined microscale pixels will eliminate costly and time-consuming lithographic processing.
B. Mills, E. T. F. Rogers, J. Grant-Jacob, S. L. Stebbings, M. Praeger, A. M. de Paula, C. A. Froud, R. T. Chapman, T. J. Butcher, W. S. Brocklesby, J. G. Frey
High Harmonic Generation is a well established technique for generating Extreme Ultraviolet radiation. It is a promising
technique for both structure and spectroscopic imaging due to both the high flux and coherence of the source, and the
existence of multiple absorption edges at the generated wavelengths. To increase the flux, a focussing device can be
used. Here we present focussing results for a Mo/Si spherical mirror that has been used in an off-axis arrangement, and
give extensive analysis of the resulting astigmatic focus and its consequence on diffractive imaging. The astigmatic beam
exists as a vertical and horizontal focus, separated by a circle of least confusion. With the help of a theoretical model we
show that the most intense part of the beam is always the second line foci and that the phase at the focus is strongly
saddle-shaped. However, this phase distortion cannot explain the significant interference peak splitting that is
experimentally observed in our diffraction patterns. Instead we propose that the beam quality is degraded upon reflection
from the multilayer mirror and it is this asymmetric phase distortion that causes the diffraction peak splitting.
Ultra-high bandwidth continua generated by ultrashort fs pulses have
been attracting enormous interest for applications such as general
spectroscopy, Optical Coherence Tomography and metrology. Dispersion
engineering is one of the key aspects of optimised continuum generation in optical waveguides. However in addition, the dispersion
of the pump pulse can be continuously adapted to control bandwidth and spectral characteristics of the generated continua. In this work we report on a systematic investigation of how 2nd, and 3rd order dispersion affects the continuum generated in strongly nonlinear planar waveguides. A ~30 fs Ti:Sapphire tuned to 800 nm was used as a pump source delivering ~3 nJ pulses. The chirp of the pulses was controlled completely-arbitrarily by an acousto-optic programmable dispersive filter (Dazzler). The power launched into the structures was kept constant to compare the generated continua as the pulse dispersion is varied. High refractive index tantalum pentoxide (Ta2O5) waveguides grown by standard silicon processing techniques were used. The devices investigated were specially designed tapered ridges with ~5 mm2 input modal volume and zero group velocity dispersion
at ~l - 3.7 mm. Self-phase modulation, which is responsible for
the spectral broadening of the continua, is tracked by finely tuning the both 2nd and 3rd order dispersions. The nonlinear propagation is dramatically influenced by the simultaneous presence of these dispersive effects resulting in a change of bandwidth and spectral shape. Pulse widths of up to Dl > 100 nm for launched powers as low as 300 pJ. Spectral peak intensity can also be systematically modulated by simply scanning the 2nd and 3rd order dispersion around their relative zeros. Specific combinations of high order dispersion contribution are currently targeted as a route to control and optimise the continua bandwidths and to control dispersion lengths in specifically engineered waveguides.
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