Supercontinuum Lidar for Spectroscopic Sensing Applications

Light detection and ranging (lidar) is a well established optical remote sensing technique with varying applications including atmospheric, environmental, automotive and other industrial applications. Lidar generally employs a monochromatic light source, which typically restricts its measurement capability to one observable at a time. The advent of a broadband light source termed supercontinuum (SC), also known as "white laser", offers novel possibilities for simultaneous multispectral analysis owing to its broad spectral bandwidth and laser like properties such as spatial coherence.

This thesis presents a new lidar system employing spectrally tailored SC light sources. The system exploits differential absorption between specific wavelength bands of the SC spectrum, enabling the first experimental demonstration of real-time simultaneous monitoring of flue gas parameters (including aerosol particle distribution, water vapor temperature and concentration) in an industrial biomass boiler. In the context of combustion diagnostics, this is particularly of great interest as real-time analysis of flue gas parameters is central to the optimization of the process efficiency and reduction of pollutants emission.

The technique is extended towards a more generic hyperspectral remote sensing in the mid-infrared wavelength range, where molecules possess characteristic absorption features known as the molecular fingerprints. Robust hypersepctral identification of black plastic waste is demonstrated with the aid of a micro-electro-mechanical system (MEMS) tunbale Fabry-Pérot interferometer filter. This is significant for recycling processes, as detection of black plastics with conventional near infrared sensors is tedious due to their strong absorption.

The results reported herein demonstrate excellent versatility and unique capability of supercontinuum lidar for robust diagnosis in combustion units and other industrial environments. Opening up novel perspective for real-time 3D analysis of industrial processes and other hyperspectral sensing applications.