We report on the introduction of active optical elements into confocal and multiphoton microscopes in order to reduce the sample-induced aberration. Using a flexible membrane mirror as the active element, the beam entering the rear of the microscope objective is altered to produce the smallest point spread function once it is brought to a focus inside the sample. The conventional approach to adaptive optics, commonly used in astronomy, is to utilise a wavefront sensor to determine the required mirror shape. We have developed a technique that uses optimisation algorithms to improve the returned signal without the use of a wavefront sensor. We have investigated a number of possible optimisation methods, covering hill climbing, genetic algorithms, and more random search methods. The system has demonstrated a significant enhancement in the axial resolution of a confocal microscope when imaging at depth within a sample. We discuss the trade-offs of the various approaches adopted, comparing speed with resolution enhancement.

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The fabrication of gallium-nitride (GaN)-based light-emitting diode (LED) arrays by a direct writing technique, itself using micron-sized LEDs (micro-LEDs), is reported. CMOSdriven ultraviolet GaN-based micro-LED arrays are used to pattern photoresist layers with feature sizes as small as 500 nm. Checkerboard-type square LED array devices are then fabricated using such photoresist patterns based on either single pixel or multipixel direct writing, and implemented as part of a completely mask-less process flow. These exemplar arrays are composed of either 450-nm-emitting 199 × 199 µm 2 pixels on a 200-µm pitch or 520-nm-emitting 21 × 18 µm 2 pixels on a 23-µm pitch. Fill factors of 99% and 71.5% are achieved with optical output power densities per pixel of 5 and 20 W/cm 2 at 90-and 6-mA dc-injected currents, respectively.Index Terms-Gallium nitride, micro light-emitting diodes (micro-LEDs), nanolithography, semiconductor device manufacture.

Methods for developing more compact femtosecond Cr:LiSAF laser sources are examined. By careful modeling of the low threshold performance and intracavity dispersion characteristics of these cavities, a highly asymmetric z-cavity design with a single prism for dispersion compensation is developed. Transform-limited pulses as short as 113 fs and modelocked output powers up to 20 mW are demonstrated for less than 110 mW of laser-diode pump power. The complete laser system (including the laser diode pump system and drivers) has a footprint of 21.5 × 28 cm2, about the size of a sheet of US letter or A4 pape