Raman Performance Characteristics of Teflon®-AF 2400 Liquid-Core Optical-Fiber Sample Cells

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Abstract
Several properties of Teflon®-AF liquid-core optical-fiber (LCOF) sample cells relevant to their utility in analytical Raman spectroscopy have been investigated. These include the nature and extent of cladding-related background and its effect on signal-to-noise ratio, and the dependence of intensity enhancement on LCOF length, core diameter, excitation wavelength, and scattering wavelength. Significant improvements in signal-to-noise ratio relative to conventional sampling techniques were demonstrated in LCOFs filled with dilute (6 × 10−2 M and 6 × 10−4 M) aqueous solutions of phenylalanine. A maximum intensity enhancement factor of approximately 120 was measured by using 50 μm i.d. LCOFs filled with methanol and 532 nm excitation. Enhancement in 785 nm-excited spectra was found to vary with Raman shift in a manner consistent with self-absorption by high-overtone vibrational bands in the core liquid.