William J. Hossack

High-speed holographic optical tweezers using a ferroelectric liquid crystal microdisplay

We demonstrate the advantages of a ferroelectric liquid crystal spatial light modulator for optical tweezer array applications. The fast switching speeds of the ferroelectric device (compared to conventional nematic systems) is shown to enable very rapid reconfiguration of trap geometries, controlled, high speed particle movement, and tweezer array multiplexing.

Time-Multiplexed Laguerre-Gaussian holographic optical tweezers for biological applications

A ferroelectric liquid crystal spatial light modulator is used to generate up to 24 independently controllable traps in a holographic optical tweezers system using time-multiplexed Fresnel zone plates. For use in biological applications, helical zone plates are used to generate Laguerre-Gaussian laser modes. The high speed switching of the ferroelectric device together with recent advances in computer technology enable fast, smooth movement of traps that can be independently controlled in real time. This is demonstrated by the trapping and manipulation of yeast cells and fungal spores.

A switchable liquid crystal binary Gabor lens

Abstract Nematic liquid crystal is used in a transparent patterned electrode cell to implement an electrically switchable Gabor lens. The binary Gabor zone plate used produces only a single pair of conjugate foci, unlike the multiple foci associated with Fresnel zone plates. Fabrication of a device is detailed and its focusing ability demonstrated.

Intracellular imaging of host-pathogen interactions using combined CARS and two-photon fluorescence microscopies.

Intracellular imaging is a key tool in the investigation of host-pathogen interactions. Advances in this area are particularly sought to understand the effect of viral infection processes on the host cell and its metabolic functions including those cases where host cell lipid metabolism is modulated as a result of infection. We demonstrate the use of combined coherent anti-Stokes Raman scattering (CARS) and two-photon fluorescence microscopies to image fibroblast cells infected by cytomegalovirus. CARS is used to image the host cell membrane, lipid droplets and morphology of the nucleus. Cell nuclei are found to expand during infection, approximately doubling in area. Some cells also show accumulations of lipid droplets at the nuclear periphery. Using a genetically modified virus strain expressing the green fluorescent protein also enables two-photon imaging of the same cells to reveal the location, nature and extent of viral protein expression.

Changes to lipid droplet configuration in mCMV-infected fibroblasts: live cell imaging with simultaneous CARS and two-photon fluorescence microscopy

We have performed multimodal imaging of live fibroblast cells infected by murine cytomegalovirus (mCMV). The infection process was monitored by imaging the two-photon fluorescence signal from a GFP-expressing strain of mCMV, whilst changes to lipid droplet configuration were observed by CARS imaging. This allowed us to identify three visually distinct stages of infection. Quantitative analysis of lipid droplet number and size distributions were obtained from live cells, which showed significant perturbations across the different stages of infection. The CARS and two-photon images were acquired simultaneously and the experimental design allowed incorporation of an environmental control chamber to maintain cell viability. Photodamage to the live cell population was also assessed.

A high resolution, full colour, head mounted ferroelectric liquid crystal-over-silicon display

Abstract The development of a compact, head mounted display based on ferroelectric liquid crystal-over-submicron CMOS technology is described. The reflective display has an array of 1024 × 768 DRAM pixels with aperture ratios of ∼55% (being upgraded to 75%) and covers an area of 12·3mm × 9·2mm providing a resolution of >2000 lines per inch. Colour images are created using time sequential illumination of binary images displayed on the array of DRAM pixels with light from red (660nm), green (525nm) and blue (470nm) pulsed LEDs. The images are projected into the eye over a field of view of 40° diagonal with less than 4% geometrial distortion. Pictures are presented of XGA images with three red, three green, and two blue bit-frames at a frame rate of 1·2KHz (upgrade 2·5KHz) giving 256 colour hues with full 1024 × 768 pixel resolution in each colour (upgrade 216 hues).

PIV analysis using an optically-addressed spatial light modulator

Abstract An optical processor for generating a two-dimensional squared auto-correlation function is proposed in this paper. The incoherent-to-coherent conversion is performed by an optically-addressed spatial light modulator. The processor is meant to be used as integrated part of a system for post processing Particle Image Velocimetry (PIV) photographs of fluid flows. The optical processor to be able to present a fast and comparable alternative to the numerical processors, which typically are used for this purpose. This work demonstrates that the priciple is very promising.

Microfabrication and packaging of deformable mirror devices

We describe the fabrication and testing of deformable membrane mirrors over silicon backplanes using our in-house CMOS processing facilities. The fabrication of dense arrays of electrostatic actuators on the backplane potentially allows fine control of the membrane surface shape than can be produced when using a printed circuit board as the backplane. We presents a range of techniques for fabrication the membrane mirrors in various materials and mating the structure to a silicon backplane. We characterise membrane deflection with electric field for silicon nitride and polymer membranes over a passive silicon backplane consisting of 37 directly-addressed electrode pads configured in a hexagonal array.

Very-large-scale-integration fabrication technique for binary-phase gratings on sapphire

An efficient, high-yield process for the production of binary-phase holograms is presented by controlled deposition of silicon nitride over a sapphire substrate with the binary structure formed by plasma etch of the silicon nitride. Optical results are presented for a 16 × 16 transmission fanout element that shows near-optimal performance.

Condensation of hydrodynamically stretched DNA using single-molecule fluorescence imaging and optical tweezers

We have observed a latency time of the order 10 s in the spermidine-induced condensation of YOYO-1-labelled DNA in flow. Higher flow speeds, longer DNA and higher salt all led to an increase in the latency time. We propose that two effects may be relevant to these observations (1) the competition between spermidine and YOYO-1 for DNA binding sites, and (2) the bending of DNA upon spermidine binding, so that flow-induced straightening of the DNA weakens spermidines affinity for DNA. Moreover, literature data on the mechanical properties of condensed DNA chains suggest that the hydrodynamic drag forces in our experiments should indeed significantly perturb condensation kinetics.