REMOTE SPECTROSCOPIC DETECTION AND 3D LOCALIZATION OF TRACE-GASES

Remote sensing systems represent an important class of photonics solutions used in a variety of applications, including autonomous navigation, topographic mapping, atmospheric research, and agriculture. Laser-based spectroscopic sensors are a subgroup of remote sensing systems, and they have distinct advantages enabled by wavelength-specific, narrow-linewidth, and single-frequency laser sources. This subgroup includes open-path spectroscopic sensors, which have high sensitivity, high selectivity, high temporal resolution, and robust operation. Despite their great practical importance, open-path spectroscopic sensors have been limited in their ability to localize, map, and quantify emissions sources such as hazardous gas emissions and fugitive leaks. This dissertation is centered on the development of techniques and sensor architectures to alleviate the existing drawbacks associated with open-path spectroscopic sensors. The solutions outlined were applied to fugitive methane emissions localization and detection and have broader applications in photonics to fields such as free-space optical communications, light detection and ranging (LiDAR), and directed energy systems. This work is divided into three main sections. The first section is devoted to the implementation of innovative receiver solutions that allow for better photon collection efficiencies with reduced complexity. The second section focuses on the development of higher-power laser transmitters, which employ amplification and coherent beam combination while preserving the spectral properties of the narrow-linewidth seed lasers. Finally, the third section is devoted to a performance assessment developed of open-path spectroscopic sensing systems that combine the proposed transceiver technologies with the novel architecture of drone-assisted 3D atmospheric scanning methodologies. Throughout this work, multiple systems were developed, and their performances have been evaluated in the field for both stationary and drone-mounted retro-reflector sensing configurations. The results of this thesis define a path toward advanced laser-based remote sensing spectroscopic systems with enhanced reach, sensitivity, and spatial resolution

Urban open-air chemical sensing using a mobile quantum cascade laser dual-comb spectrometer

Detection of airborne chemical releases in densely populated urban environments requires precise sensors with high temporal and spatial resolution capable of covering large areas. For this purpose, we present a mobile mid-infrared quantum cascade laser dual-comb spectrometer for identification and quantification of chemical plumes. Field tests with the remote sensor were conducted during daytime in the downtown Boston area over a five day period during which chemical releases were simulated by intermittently emitting non-toxic substances. Open-air sensing was performed with retroreflectors positioned at up to 230 m distance and with sensitivities in the ppm m range for one second of averaging time. The field campaign demonstrates a step toward a semiconductor dual-comb spectroscopic sensor in the mid-infrared fingerprint region, suitable for long-term deployments. These types of sensors will be valuable complements to existing optical sensors for urban hazardous gas leak monitoring, air quality assessments, and localization of clandestine chemical production