Model of a Fiber-Optic Evanescent-Wave Fluorescence Sensor
D L. Woerdeman, Richard~undefined~undefined~undefined~undefined~undefined Parnas
A fiber-optic cure sensor based on evanescent wave fluorescence spectroscopy has been designed to probe the interphase region of glass-reinforced composites. The size of the interphase can vary significantly, d epending on the exact nature of the fiber surface treatment and its interaction with the surrounding resin matrix. In this study, a model based on mode coupling theory is developed to determine if the fiber provides information about the bulk resin or theinterphase. Model predictions include the fraction of fluorescence signal collected as a function of radial distance from the optical fiber surface. The refractive index of the fiber was set to 1.617 to match the value of the fiber used in experments, and the resin index was varied from 1.56 to 1.615 to represent the changes that occur in curing epoxy resin. The dependence of the fluorescence signal on modal coupling selection is demonstrated. Finally we examine the role of coupling optics by analyzing the relationship between penetration depth and beam angle relative to the fiber axis.