Fiber-optic evanescent-wave spectroscopy (FEWS) is a novel method for measuring the absorption spectra of samples in contact with a segment of an optical fiber that serves as a sensing element. We used a cylindrical IR-transmitting AgClBr fiber whose central section, of length , was flattened to a thickness . This section was used as the FEWS sensing element. Our theoretical work predicted that the signals obtained in FEWS measurements should be linearly dependent on and inversely proportional to . Decreasing the thickness can significantly increase its sensitivity of the sensor. These theoretical results were verified experimentally by measurements of methanol and water.
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