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16 February 2012 Broadband ATR-sensor with variable path lengths
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A spectral Attenuated Total Reflection (ATR-) sensor with variable path lengths is proposed. Based on a new polymer cladding material, the numerical aperture and the related maximum propagation angle in Polymer Clad Silica Fiber (PCSF) have been increased significantly. The penetration depth of the evanescent field into the cladding of step-index fibers depends strongly on the propagation angle. We found that when removing its cladding, the effective path length in the interaction section can be adjusted, using meridional rays/modes of different propagation angles. Because the fiber length is short, the mode conversion in the light-transporting section of the PCSF is negligible. After measuring the optical properties of the PCSF, the ATR with selected liquids surrounding the light-guiding core is determined in dependence of wavelength and excitation-angle. Especially, the possibilities to change from low to high propagation angles including the excitation and detection system will be discussed.
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Karl-Friedrich Klein, Subash Pandey, Pasma Dahal, Moritz Klein, Mathias Belz, and Georg Hillrichs "Broadband ATR-sensor with variable path lengths", Proc. SPIE 8218, Optical Fibers and Sensors for Medical Diagnostics and Treatment Applications XII, 82180T (16 February 2012);

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