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. (c) 2006 Optical Society of America.

Development of smart variable stiffness actuators using polymer hydrogels

In this work, compliant actuators are developed by coupling braided structures and polymer gels, able to produce work by controlled gel swelling in the presence of water. A number of aspects related to the engineering of gel actuators were studied, including gel selection, modelling and experimentation of constant force and constant displacement behaviour, and response time. The actuator was intended for use as vibration neutralizer: with this aim, generation of a force of 10 N in a time not exceeding a second was needed. Results were promising in terms of force generation, although response time was still longer than required. In addition, the easiest way to obtain the reversibility of the effect is still under discussion: possible routes for improvement are suggested and will be the object of future work.

An optical study of multiple NEIAL events driven by low energy electron precipitation

Optical data are compared with EISCAT radar observations of multiple Naturally Enhanced Ion-Acoustic Line (NEIAL) events in the dayside cusp. This study uses narrow field of view cameras to observe small-scale, short-lived auroral features. Using multiple-wavelength optical observations, a direct link between NEIAL occurrences and low energy (about 100 eV) optical emissions is shown. This is consistent with the Langmuir wave decay interpretation of NEIALs being driven by streams of low-energy electrons. Modelling work connected with this study shows that, for the measured ionospheric conditions and precipitation characteristics, growth of unstable Langmuir (electron plasma) waves can occur, which decay into ion-acoustic wave modes. The link with low energy optical emissions shown here, will enable future studies of the shape, extent, lifetime, grouping and motions of NEIALs.

Proposed design for an ultrasonic optical force-feedback microphone

We discuss a novel approach that would lead to the development of an ultrasonic optical force-feedback measurement microphone.

Determination of the optical properties of plastic films used as cladding materials in novel energy efficient greenhouses

Greenhouse cladding materials are a major component in the design of energy efficient greenhouses. The optical properties of cladding materials determine a major part of the overall performance of a greenhouse both in terms of the energy balance of the greenhouse and on crop behavior. Various film plastic greenhouse-cladding materials were measured under laboratory conditions using a spectroradiometer equipped with an integrating sphere. Films were measured over a range of angles of incidence and the effect of increasing distance between double films was also measured. PAR transmission remained nearly constant for angles of incidence increased up to 30 degrees but fell rapidly thereafter as the angles of incidence increased up to 90 degrees. Increasing distance between double films did not significantly affect PAR transmission in all films examined. These results are discussed in relation to the design criteria for an energy efficient greenhouse.