InGaN/GaN Laser Diodes and their Applications


Gallium nitride (GaN) laser diodes are becoming popular sources not only for lighting but for applications ranging from communications to quantum. This paper presents the use of a commercial, off-the-shelf laser diode, with an emission wavelength of 450 nm, for visible light communication, both in free space and for underwater scenarios. Data rates up to 15 Gbit/s have been achieved by making use of orthogonal frequency division multiplexing (OFDM). In addition, distributed feedback (DFB) lasers have been realised emitting at a single wavelength which lend themselves towards applications where high spectral purity is crucial such as atomic clocks or filtered free space transmission systems. These devices have the grating structure etched into the sidewall of the ridge and work is ongoing to measure the linewidth of these lasers with the intended application of cooling Sr+ ions.

Scott Watson, Steffan Gwyn, Shaun Viola, Giovanni Giuliano, Thomas J. Slight, Szymon Stanczyk, Szymon Grzanka, Amit Yadav, Duncan Rowe, Leslie Laycock, Kevin E. Docherty, Edik Rafailov, Piotr Perlin, Steve Najda, Mike Leszczynski, and Anthony E. Kelly.

Published in: 2018 20th International Conference on Transparent Optical Networks (ICTON). DOI: 10.1109/ICTON.2018.8473864

Image analysis framework with focus evaluation for in situ characterisation of particle size and shape attributes


Particle processing industries, such as pharmaceutical, food processing and consumer goods sectors, increasingly require strategies to control and engineer particle attributes. In both traditional batch and continuous processes, particle size and shape need to be effectively monitored through in-line measurements from Process Analytical Technologies. However, obtaining quantitative information from these measurements has proven to be challenging and in-line imaging techniques are primarily used for qualitative purposes. Two key challenges are: (1) the presence of out-of-focus objects and (2) images only represent 2D projections of three-dimensional objects. In this work, a novel framework to process frames from in-line imaging probes incorporates a focus evaluation step in order to extract meaningful quantitative shape and size information through rejection of out-of-focus particles. Furthermore, a model is proposed that simulates the 2D projection of three-dimensional particles onto the focal plane and computes the corresponding size and shape distributions. The framework is quantified and evaluated against standard particles of well-defined size and shape such as polystyrene microspheres and needle-like cuboid silicon particles.

Javier Cardona; Carla Ferreir; John McGinty; Andrew Hamilton; Okpeafoh S.Agimelen; Alison Cleary; Robert Atkinson; Craig Michie; Stephen Marshall; Yi-Chieh Chen; Jan Sefcik; Ivan Andonovic; Christos Tachtatzis. Chemical Engineering Science Volume 191, 14 December 2018, Pages 208-231

InGaN distributed feedback laser with sidewall gratings emitting at 42X nm


We demonstrate a single wavelength operation from an InGaN/GaN distributed feedback (DFB) blue laser at 42X nm. The 39 th order grating is etched in the sidewall to achieve single wavelength. The laser has a FWHM of ~ 25 pm at 500mA pulsed current with 15 mW output power.

A. Yadav, T. J. Slight, S. Watson, S. Grzanka, S. Stanczyk, N. B. Chichkov, K. E. Docherty, P. Perlin, S. Najda, M. Leszczyński, A. E. Kelly, E. Rafailov.

Published in: 2018 International Conference Laser Optics (ICLO). DOI: 10.1109/LO.2018.8435673

Distributed feedback InGaN/GaN laser diodes


We have realised InGaN/GaN distributed feedback laser diodes emitting at a single wavelength in the 42X nm wavelength range. Laser diodes based on Gallium Nitride (GaN) are useful devices in a wide range of applications including atomic spectroscopy, data storage and optical communications. To fully exploit some of these application areas there is a need for a GaN laser diode with high spectral purity, e.g. in atomic clocks, where a narrow line width blue laser source can be used to target the atomic cooling transition. Previously, GaN DFB lasers have been realised using buried or surface gratings. Buried gratings require complex overgrowth steps which can introduce epi-defects. Surface gratings designs, can compromise the quality of the p-type contact due to dry etch damage and are prone to increased optical losses in the grating regions. In our approach the grating is etched into the sidewall of the ridge. Advantages include a simpler fabrication route and design freedom over the grating coupling strength. Our intended application for these devices is cooling of the Sr+ ion and for this objective the laser characteristics of SMSR, linewidth, and power are critical. We investigate how these characteristics are affected by adjusting laser design parameters such as grating coupling coefficient and cavity length.

Thomas J. Slight, Scott Watson, Amit Yadav, Szymon Grzanka, Szymon Stanczyk, Kevin E. Docherty, Edik Rafailov, Piotr Perlin, Steve Najda, Mike Leszczyński, Anthony E. Kelly. Proceedings Volume 10532, Gallium Nitride Materials and Devices XIII; 1053219 (2018)

InGaN/GaN Laser Diodes With High Order Notched Gratings


We report on InGaN/GaN distributed feedback laser diodes with high order gratings emitting at a single wavelength around 428 nm. The 39th order notched gratings have the advantage of a simplified fabrication route with no need for overgrowth. The laser ridge and grating were formed by electron beam lithography followed by ICP etching. The as-cleaved lasers emitted in the pulsed regime with a peak single-mode output power of 15 mW. Optimization of the grating design should lead to higher power single wavelength operation.

Thomas J. Slight; Amit Yadav; Opeoluwa Odedina; Wyn Meredith; Kevin E. Docherty; Edik Rafailov and Anthony E. Kelly. InGaN/GaN Laser Diodes With High Order Notched Gratings. IEEE Photonics Technology Letters 29(23), 2020-2022.

Silicon microfabricated linear segmented ion traps for quantum technologies


This paper describes a microfabricated linear segmented RF Paul trap for atomic quantum technologies. The microtrap geometry, initially demonstrated in [1], has been augmented and includes a linear array of trapping segments. Trapping of individual and strings of 88Sr+ ions is demonstrated. The fabrication process has been optimized such that for 80 % of the fabricated devices, the achieved geometry is within ± 5 μm (or ± 3 %) of a prescribed design. This is critical for scalable quantum information processing, where arrays of traps with consistent parameters are required.

Kaushal Choonee ; Guido Wilpers ; Alastair G. Sinclair. 2017 19th International Conference on Solid-State Sensors, Actuators and Microsystems (TRANSDUCERS)

Influence of probe-sample temperature difference on thermal mapping contrast in scanning thermal microscopy imaging


The purpose of this work is to investigate the influence of a temperature difference through a probe-sample contact on thermal contrast in Scanning Thermal Microscopy imaging. A variety of combinations of temperature differences in the probe-sample system were first analyzed based on an electro-thermal finite element model. The numerical analysis included cooling the sample, as well as heating the sample and the probe. Due to the simplicity in the implementation, experimental verification involved modifying the standard imaging technique by heating the sample. Experiments were carried out in the temperature range between 298 K and 328 K. Contrast in thermal mapping was improved for a low probe current with a heated sample.

Kaźmierczak-Bałata, A., Juszczyk, J., Trefon-Radziejewska, D., & Bodzenta, J. (2017). Influence of probe-sample temperature difference on thermal mapping contrast in scanning thermal microscopy imaging. Journal of Applied Physics, 121(11), 114502.

Generation and precise control of dynamic biochemical gradients for cellular assays


Spatial gradients of diffusible signalling molecules play crucial roles in controlling diverse cellular behaviour such as cell differentiation, tissue patterning and chemotaxis. In this paper, we report the design and testing of a microfluidic device for diffusion-based gradient generation for cellular assays. A unique channel design of the device eliminates cross-flow between the source and sink channels, thereby stabilizing gradients by passive diffusion. The platform also enables quick and flexible control of chemical concentration that makes highly dynamic gradients in diffusion chambers. A model with the first approximation of diffusion and surface adsorption of molecules recapitulates the experimentally observed gradients. Budding yeast cells cultured in a gradient of a chemical inducer expressed a reporter fluorescence protein in a concentration-dependent manner. This microfluidic platform serves as a versatile prototype applicable to a broad range of biomedical investigations.

Saka, Y., MacPherson, M., & Giuraniuc, C. V. (2017). Generation and precise control of dynamic biochemical gradients for cellular assays. Physica A: Statistical Mechanics and its Applications, 470, 132-145.

Thermal properties measurements of a silica/pyrocarbon composite at the microscale


Laminar pyrocarbons are used as interphases or matrices of carbon/carbon and ceramic-matrix composites in several high-temperature aerospace applications. Depending on their organization at the microscale, they can have a variety of mechanical and thermal properties. Hence, it is important to know, before thermal processing, the properties of these matrices at the micrometer scale in order to improve and control the composite behavior in a macroscopic scale. We use the scanning thermal microscopy on a silica fiber/regenerative laminar pyrocarbon matrix composite to provide an insight into the effective thermal conductivity of pyrocarbon as well as the thermal contact resistance at the interface between fiber and matrix. The conductivity of pyrocarbon is discussed as a function of its nanostructural organization.

De, I., Battaglia, J. L., & Vignoles, G. L. (2016). Thermal properties measurements of a silica/pyrocarbon composite at the microscale. Journal of Applied Physics, 120(24), 245101.

Probing Nanoscale Heat Transport in Liquid Environments—Contact and Non-Contact Immersion Scanning Thermal Microscopy (iSThM)


Operation of Scanning Thermal Microscopy (SThM) [1] in liquid environment probing thermal phenomena with nanoscale resolution could open unique opportunities for studies of biological materials, processes in the rechargeable energy storage and catalysis. Until recently such SThM operation would be deemed fully impossible, due to dominating heat dissipation from the heated probe into the surrounding liquid that thought to drastically deteriorate both the sensitivity of the probe and its spatial resolution. Nevertheless, Tovee and Kolosov [2] showed that such immersions SThM, or iSThM, is not only possible for the certain widely used type of the probe (Kelvin Nanotechnology, Scotland), but also opens the possibility to make nanoscale mapping of the heat transport with the near-field operation of SThM. Here we show that the presence of liquid provides highly stable thermal contact between the probe tip and the sample eliminating one of the major drawbacks of the ambient or vacuum SThM’s – variability of such contact. iSThM can effectively observe the semiconductor devices and 2D materials with the resolution of few tens of nanometres, providing new tool for exploring thermal effects of chemical reactions and biological processes with nanoscale resolution. Using finite element modeling analysis we show that selecting suitable thermal conductivity of the liquid allows to to significantly enhance contrast of iSThM for the particular material. We also experimentally demonstrate that by applying of the ultrasonic vibration to the probe and by detecting a shear response of the probe it is possible to achieve near – non-contact iSThM paving the way for efficient zero-damage nanoscale thermal probing.

Kolosov, O. V., Spiece, J., & Robinson, B. J. (2017). Probing Nanoscale Heat Transport in Liquid Environments—Contact and Non-Contact Immersion Scanning Thermal Microscopy (iSThM).