Grant: Discovery Grants Program - Individual

Interaction between light and matter can be tuned, enhanced or inhibited by controlling the characteristic of a material on a small enough scale. When a material is periodically textured on a scale comparable to the wavelength of light, resonant scattering leads to strong dispersion and the appearance of photonic band gaps. When the scale of texturing is further reduced to the nanometer scale, quantum-size effects modify electronic states and the optical properties of the material itself, as can be seen in quantum wells, wires and dots. Considering the range of possibilities textured materials and nanomaterials offer (commercial, scientific or otherwise), it is understandable that this area of research is currently very active, and probably will be for the next decade. With this in mind, the research proposal will focus on two areas: 1) nanomaterials for optical applications and 2) novel optical methods and instruments to characterize materials. The first half of the program is to study laser-induced enhancement of some material properties embedded in periodic media. Photochromism is a property of some materials, such as MoO3 and WO3, that allows one to control their optical absorption by exposure to light. Thermochromism is the equivalent process where heat is the modifying agent (although heat can be created optically). The interaction between light and thermo- or photochromic materials is altered when they are embedded in a periodic structure. When light propagates through the periodic medium, its electric field may be enhanced, diminished or unaltered, depending on its frequency relative to the Bragg resonance. The goal is to study the interplay between the photochromic effect and the photonic band gap. We have done preliminary testing on SiO2/MoO3 multilayers and have found photochromism enhancement by a factor of >50 near the photonic band gap. We will extend our study to 3D structures as well as for thermochromic materials. Much remains to be done, since the theory for this combined effect doesn't exist and experiments are scarce. Photo- and thermochromism in periodic media is interesting for many reasons. While they are processes that are comparatively slow in relation to many nonlinear phenomena, they have the advantage of requiring extremely low light levels, which is desirable for some applications. The second half of the program deals with new optical techniques for measuring the thermal properties of materials on extremely low volumes. It involves thermal lensing, a self-induced effect that occurs when a laser beam travels through an absorbent medium. In 2003, the applicant and its research group revealed a new type of lensing that works in reflection, as opposed to transmission as it is in standard techniques. A laser beam focused on an absorbent surface can create a nanometer-scale thermal bump that causes the reflected beam to diffract slightly. The time-evolution of this thermal bump provides information about the thermal conductivity of the substrate underneath. A patent was filed in 2008 and the applicant teamed up with C-Therm Technologies Ltd, a Fredericton-based thermal instrument company, to further research and develop a new commercial product. The optical technique is appealing because it is applicable to both opaque and transparent materials. Because it uses a tightly focused laser beam, only a small region near the surface is probed, and the volume of material necessary is reduced by a factor of 10E6 compared to standard techniques. This is interesting for probing small samples, like droplets, colloids, thin films, emulsions and even powders, a form of material of utmost importance to the pharmaceutical and food industries. The next 5 years will see further research and development in partnership with industry to bring the instrument to completion.