Intensity Considerations in Liquid Core Optical Fiber Raman Spectroscopy

Abstract

This paper develops expressions for the Raman power emitted by liquid core optical fiber (LCOF) sample cells in six simple excitation/collection geometries and the fraction of that power that can be utilized in a conventional Raman spectrometer. From these expressions a “figure of merit” is developed that can be used to predict the relative intensity enhancement provided by LCOFs having different inside diameters and loss characteristics. For the apparatus used here, we show theoretically and experimentally that the figure of merit takes the simple form (α d)−1 where α and d are, respectively, the loss coefficient and inside diameter of the LCOF. Given the varying optical quality of Teflon®-AF LCOFs currently in use, the analysis presented here should be useful in optimizing the performance of LCOF accessories in Raman and related spectroscopic applications.