Optical Imaging in Microstructures

This research was focused on developing morphology-dependent stimulated raman scattering (MDSRS) spectroscopy as an analytic optical imaging technique. MDSRS uses the cavity modes (called morphology dependent resonances, MDRs) associated with axisymmetric dielectric microstructures to generate nonlinear optical signals. Since different cavity modes span different regions inside the microstructure, it becomes possible to generate location-specific spectra. The information gotten from MDSRS imaging experiments is analogous with that generated from magnetic resonance imaging (MRI) studies in that spatial variations in chemical composition and molecular configuration within a structure can be mapped out. The authors demonstrated that MDSRS imaging is feasible and is free from nonlinear artifact. They did this by measuring the molecular structure variations that are present in the interfaces of 180 {micro}m dia. charged water droplets. The 4 publications that resulted from these studies are attached. From a chemical perspective a water droplet is, however, a simple thing. Will it be possible to use MDSRS imaging to study more complex systems such as combusting fuel droplets, layered polymer or glass fibers, or biological cells? The long-term goal of the research was to answer this question. The answer they have come up with is yes and no. The results on nitrate aerosols show that it is possible to do imaging studies on optically non-absorbing, ion containing systems, but that the ultimate sensitivity is dictated by ion concentration. hence systems containing large quantities of mobile ions will be difficult to look at, so this essentially eliminates being able to look at biological samples in situ. But on the positive side, organic systems, such as layered polymer and glass fibers, and combusting organic fuel droplets can be looked at with MDSRS imaging