NOISE-FREE INCORPORATION OF MULTIMODE FIBERS INTO ABSORPTION SPECTROSCOPY EXPERIMENTS

Abstract

This project develops and evaluates alternative methods to the traditional way of detecting light transmitted through optical fibers in spectroscopy experiments. The main motivation behind this work is to develop an alternative that allows for (1) use in harsh environments (e.g. combustion engines) where glass optical fiber is among the few materials that can survive, (2) use in multi-beam experiments where space is extremely limited, and (3) large throughput with minimal noise yielding high signal-to-noise ratios. Several alternatives are identified and tested with varying results. A fiber bundle based image guide was found to produce undesirable noise but had physical characteristics that, if properly defined, could be changed to produce more desirable results. To demonstrate the potential for fiber bundle approaches, a linear array of single mode fibers was tested and shown to produce good results. The most significant finding in this work is that very careful installations of standard multimode fiber were found to reduce mode noise to near other limits (e.g. shot noise). This result provides a solution that meets all the needs outlined above with a low-cost solution.