There is a great technological need for the development of devices capable of producing wide-angle and efficient, transmissive optical beam steering. In this article, variable pitch phase diffraction gratings using electroconvection in liquid crystals are considered for applications in electrically controllable beam-steerers. The devices contain thin layers of nematic liquid crystal mixtures of negative dielectric anisotropy, which are doped with different concentrations of an ionic species to determine the effect of conductivity on the beam-steering characteristics. The devices are seen to act as continuously variable diffraction gratings, where the pitch increases with the frequency of the applied electric field. The second order diffraction peak is found to be the most efficient, with absolute efficiency ranging from 5% to 15%, and continuous steering from 4° to 8° within 20 μm spaced devices. Devices with thinner layers of liquid crystal were also examined; these demonstrated wider angle steering but had substantial losses of efficiency due to lowering of optical contrast. Suggestions for possible methodologies for optimizing such devices are discussed.

Liquid crystals are valuable materials for applications in beam steering devices. In this paper, an overview of the use of liquid crystals in the field of adaptive optics specifically for beam steering and lensing devices is presented. The paper introduces the properties of liquid crystals that have made them useful in this field followed by a more detailed discussion of specific liquid crystal devices that act as switchable optical components of refractive and diffractive types. The relative advantages and disadvantages of the different devices and techniques are summarised.

Electrohydrodynamic Instabilities in nematic liquid crystals cause uniform and continuously variable pitch diffraction gratings. Liquid crystal dimers allow greater range of elastic constants, allowing wider angle diffraction to be achieved.

Inducing hydrodynamic flow in nematic liquid crystals (NLCs) reorients the symmetry axis of the material- the director, causing changes in the optical properties. The resulting optical gratings have potential use as switchable diffractive optical elements (DOEs). In this study, surface acoustic waves (SAWs) are applied to an NLC device to induce periodic vortices through hydrodynamic instabilities. We show a linear relationship between the wavelength of the applied SAW and induced grating period, where the coefficient is determined by the ratio of the speed of sound in the substrate to that in the nematic liquid crystal. This relationship is further used to design a novel device, where the period of the hydrodynamic grating can be continuously varied from 90 μm to 260 μm by utilising a broadband (chirped) SAW transducer. These devices present great potential for creating a new class of continuously variable DOEs, overcoming current technological limitations.

In Quebec City, facing north, from the Pierre-Dugua-De-Mons Terrace (a small hill close to the city centre), there is a particularly spectacular view overlooking the city (see Figure 1). The view here encompasses many of Quebec's famous sites: On the left, there is the eminent Chateau Frontenac, a luxury hotel built to attract visitors from around the world; in the centre, there is the historic Quebec old town, a UNESCO world heritage site; and on the right is the St Lawrence river, dominating the landscape and dotted with the occasional cruise ship to bring people from far-flung lands into the city. All of these sights show Quebec to be a city that celebrates the coming together of international travellers: even the name 'Quebec' is taken from the Algonquin word 'kébec' meaning 'where the river banks come together'. As the sun sets, the view from the Pierre-Dugua-De-Mons Terrace is bathed with a pinky-orange light, emphasising the view's beauty. Together these two key elements, the coming together of people and the presence of beautiful light, seemed to make Quebec a fitting place for an international optics conference.The 18th Optics of Liquid Crystals (OLC) conference took place in Quebec City from the 8th until the 13th of September 2019 and was hosted by the Laval University, with Professor Tigran Galstian heading the organising committee, together with Dr David Hélie and Diane Déziel of the Centre for Optics, Photonics and Lasers and Cora Roy of Conferium. As the first OLC to be hosted in Canada, and given Quebec's international appeal, it was appropriate to find that the conference was a truly international event, attracting representatives from 20 countries, with delegates from as far as Portugal,