Miami University, Molecular Microspectroscopy Laboratory, Department of Chemistry and Biochemistry, Oxford, Ohio 45056 USA.
Appl Spectrosc. 2013 Nov;67(11):1252-63. doi: 10.1366/12-06935.
Advances in fiber optic materials have allowed for the construction of fibers and waveguides capable of transmitting infrared radiation. An investigation of the transmission characteristics associated with two commonly used types of infrared-transmitting fibers/waveguides for prospective use in a fiber/waveguide-coupled attenuated total internal reflection (ATR) probe was performed. Characterization of silver halide polycrystalline fiber optics and hollow silica waveguides was done on the basis of the transmission of infrared light using a conventional fiber optic coupling accessory and an infrared microscope. Using the fiber optic coupling accessory, the average percent transmission for three silver halide fibers was 18.1 ± 6.1% relative to a benchtop reflection accessory. The average transmission for two hollow waveguides (HWGs) using the coupling accessory was 8.0 ± 0.3%. (Uncertainties in the relative percent transmission represent the standard deviations.) Reduced transmission observed for the HWGs was attributed to the high numerical aperture of the coupling accessory. Characterization of the fibers/waveguides using a zinc selenide lens objective on an infrared microscope indicated 24.1 ± 7.2% of the initial light input into the silver halide fibers was transmitted. Percent transmission obtained for the HWGs was 98.7 ± 0.1%. Increased transmission using the HWGs resulted from the absence or minimization of insertion and scattering losses due to the hollow air core and a better-matched numerical aperture. The effect of bending on the transmission characteristics of the fibers/waveguides was also investigated. Significant deviations in the transmission of infrared light by the solid-core silver halide fibers were observed for various bending angles. Percent transmission greater than 98% was consistently observed for the HWGs at the bending angles. The combined benefits of high percent transmission, reproducible instrument responses, and increased bending tolerance indicated HWGs should be preferred in the construction of a fiber/waveguide-coupled ATR probe.
光纤材料的进步使得能够构建能够传输红外辐射的光纤和波导。为了在光纤/波导耦合衰减全内反射 (ATR) 探头中潜在地使用，对两种常用类型的红外传输光纤/波导的传输特性进行了研究。基于使用常规光纤耦合附件和红外显微镜传输红外光，对卤化银多晶光纤光学和空心硅波导进行了特性描述。使用光纤耦合附件，与台式反射附件相比，三根卤化银光纤的平均透射率为 18.1 ± 6.1%。使用耦合附件的两个空心波导 (HWG) 的平均透射率为 8.0 ± 0.3%。（相对透射率的不确定度表示标准偏差。）观察到 HWG 的透射率降低归因于耦合附件的高数值孔径。在红外显微镜上使用硒化锌透镜物镜对纤维/波导进行的特性描述表明，初始输入到卤化银纤维的光中有 24.1 ± 7.2%被传输。HWG 的透射率为 98.7 ± 0.1%。HWG 的透射率增加是由于空心空气芯的存在或最小化了插入和散射损耗，以及更好地匹配的数值孔径。还研究了纤维/波导的弯曲对传输特性的影响。对于各种弯曲角度，实心卤化银光纤的红外光传输存在明显的偏差。HWG 在弯曲角度下始终观察到大于 98%的透射率。高透射率、可重复的仪器响应和增加的弯曲公差的综合优势表明，在构建光纤/波导耦合 ATR 探头时，HWG 应该是首选。
