Chirped Laser Dispersion Spectroscopy: Fundamentals and Applications

Abstract

The subject of this thesis is the fundamentals, implementation, and applications of Chirped Laser Dispersion Spectroscopy (CLaDS), an alternative dispersion spectroscopy technique that aims to overcome some limitations of absorption-based sensing. CLaDS preserves many of the benefits of dispersion sensing, namely baseline-free operation, immunity to received intensity, and linearity with sample concentration, and is fairly easy to implement without the need for stabilized interferometers, mode-locked lasers, and complex optical configurations required by many other dispersion-based sensors.

First an introduction to CLaDS and a derivation of the spectroscopic signals are provided, highlighting fundamental similarities and differences to absorption-based sensing. Next the fundamental limit of CLaDS is investigated through analysis of the shot-noise limited performance under ideal operating conditions. This in turn allows for a theoretical and direct comparison to the shot-noise-limited performance of direct laser absorption spectroscopy (DLAS). This investigation shows that when full spectral scan fitting of realistic unknown parameters for each technique is used, both techniques demonstrate the same efficiency of parameter extraction. Following this theoretical investigation of ideal CLaDS performance, the technical details, methods of implementation, and component-introduced limitations of real-world CLaDS systems are discussed. Also included is a discussion of the first demonstration of an optical heterodyne enhanced CLaDS technique (HE-CLaDS). To overcome some of the technical limitations imposed by system instability, a modulation based technique (CM-CLaDS) was developed; the theory, optimization and noise characteristics of which are detailed. Finally, several applications of CLaDS are provided. These include atmospheric sensing, distributed sensor networks, and fiber dispersion characterization, all of which aim at demonstrating the technical advantages of the CLaDS technique.