The Distribution and Evolution of Refractive Index in a Polystyrene Whispering Gallery Microcavity during Glass Transition

摘要

There is limited knowledge on the evolution of physical and chemicalparameters near the surface of polymer materials at the microscopic levelduring glass transition, owing to the complexity of this process. For example,the distribution and evolution of the refractive index near the surface ofpolymer materials during glass transition are thus far unknown; however,this information is necessary for the design of optical micro-elements basedon polymer materials. Herein, a strategy is proposed to achieve the expressionof the refractive index as a function of depth and temperature inside apolystyrene microsphere. The difference in the wavelength shifts between twowhispering gallery modes with different radial orders is employed to detectthe evolution of the refractive index during the glass transition. A model isestablished based on experimental observations and further confirmed bynumerical simulations. It is believed that the results obtained can assist withthe design of polymer optical micro-elements and systems as well as sensingapplications of whispering gallery microcavities.