Volume 2, Issue 1

The peculiar optical response of polydimethylsiloxane (PDMS) doped with metallic nanoparticles can be employed to develop optical sensing materials. These nanocomposites may work in an ample range of temperatures, showing good linearity and high sensitivity. Plasmon resonances of the metallic nanoparticles produce interesting effects on the optical response by affecting the effective refractive index of PDMS. The high resonant response leads to a number of different configurations of optical filters and phase devices whose resonant frequency depends on the chosen nanoparticle. Moreover, the wavelength can be tuned up by external manufacturing conditions such as nanoparticle size or fill factor, and by working parameters such as temperature. This work develops the theoretical background required for the design of these structures, and evaluates the adequate dimensional and doping ranges for device optimization.

A two-step method of writing high diffraction efficiency holographic gratings in photopolymer using just one writing beam during the second step is discussed. The technique is based on the use of weak gratings (<1%) recorded during a first step which during the second step are illuminated with a single beam to form strong highly efficient holographic gratings. The weak grating provides a second interfering beam by diffracting a small portion of the illuminating light. Although effects such as beam pumping and twowave mixing arewell known in dynamic re-writable recording media such as photorefractives, the ability to write with one beam, or ‘pump’ gratings is not usually observed in photopolymer materials. Other methods of recording with a single beam have been reported, especially for data storage, but they use compact optical systems, polarization effects or lenticular devices to produce the required second beam. In this method, the second beam is produced within the photopolymer medium. Earlierwork by the authors reported increases in efficiency of weak photopolymer gratings illuminated by a single exposure beam, and more recently evidence was presented that diffraction at the weak pre-recorded grating was responsible for this effect. Here we demonstrate a strong dependence of the diffraction efficiency on grating thickness and show that the method allows the writing of high diffraction efficiency gratings in adverse conditions using a single beam. The possibility of angular multiplexing is also demonstrated. The technique may find application in writing information using pre-recorded weak holographic gratings and, potentially, in other data storage applications. In this paper it is shown that multiple new gratings can be writtenwhich are angularly separated and distinct from the pre-written grating and it is also possible to choose one grating from among a number of pre-written gratings and selectively amplify it without amplifying the others.

Optical data storage is being investigated for use in enterprise archival data storage due to its stability, low energy consumption and low total cost of ownership. Here we present results on a method for manufacturing optical discs with dozens of writable layers using polymer coextrusion. This can greatly increase the capacity with low fabrication cost. Data are written by modulating the fluorescence of an organic dye, and exhibits a threshold dependence on the laser power, allowing the bits to be welllocalized in the intended layers. This is a result of the heat generated from the absorbed laser power, and is realizable with a continuouswave laser.We also discuss the lifetime and photostability of the dyes. These combined results promise a media that is lower in cost and higher in capacity than current commercial options.

We report on a novel procedure of fabrication to easily obtain highly reproducible nanocavities-shaped photonic crystals with strong plasmonic performances. Thus, we also report on the morphological and optical characterization of the obtained structures. They are classifiable as 2-layers (organic and inorganic) photonic crystals based on iso-Y-shaped nano-cavities. Such novel designed structures are compelling candidates for the development of highly sensitive biosensors due to their unique surface plasmon resonances (SPRs) and SPR enabled surface-enhanced Raman spectroscopy (SERS). The planar photonic crystal comprises a polymeric (ZEP520A) layer (thickness ~80 nm) sandwiched between a layer of gold (~50 nm thickness) and a glass substrate. For what concerns the cavities’ shape, iso-Y units are chosen on the basis of their third order nonlinearity and are coupled in hexagonal-based configuration to produce extended meta-structures. The substrates are functionalized with a probe made by a self-assembling monolayer (SAM) of 4-mercaptobenzoic acid (4-MBA). The average SERS Enhancement Factor >106 and SPR sensitivity of ~300 nm/RIU confirm that the proposed 2-layers iso-Y meta-structure is very suitable for high sensitive label-free plasmonic sensing.

Traditionally, models for neural dynamics in the brain have been formed through research conducted on slices, with electrodes, or by lesions to functional areas. Recent developments in functional dyes and optogenetics has made brain research more accessible through the use of light. However, this improved accessibility does not necessarily apply to deep regions of the brain which are surrounded by scattering tissue. In this article we give an overview of some of the latest methods in development for neural measurement and imaging.We specifically address methods designed to overcome the problem of imaging invivo for regions far beyond the mean free path of photons in brain tissue. These methodswould permit previously restricted neural research.