Investigation of laser radar systems based on mid-infrared semiconductor lasers

This dissertation deals with the possibility of utilizing mid-infrared semiconductor lasers in systems of optical remote sensing with range resolution, called laser radar or lidar.; The main subject investigated in this dissertation is two-fold: firstly, an analysis of the signal-to-noise ratio (SNR) and related maximum sensing range calculations in this type of lidar based on available system components, and—secondly—improvements in the Random-Modulation Continuous-Wave (RM-CW) lidar technique to better utilize available mid-infrared semiconductor lasers.; As far as the SNR analysis is concerned, an appropriate framework has been constructed to analyze post-demodulation noise in mid-infrared direct-detection RM-CW lidar. It is based on a generalization of the Wiener-Khintchine theorem; noise is assumed to be additive, stationary, and have an arbitrary power spectrum. This is in contrast to the SNR analysis in the literature on this subject, which is inadequate for mid-infrared RM-CW lidar as it only considers Poissonian fluctuations of the number of detected photons. In addition to regular SNR analysis, the framework derived in this dissertation allows treatment of singularities such as demodulation with an unbalanced sequence in 1/f noise.; To calculate maximum lidar sensing range, the following detection limits have been considered: signal shot noise, background blackbody radiation shot noise based on the Background-Limited Photodetection (BLIP) detectivity limit, and minimum-size detector noise given by diffraction-limited focusing. The latter is found to be of greatest practical interest. Furthermore, a lidar figure of merit has been introduced, and all quantities related to lidar performance and its detection limits have been presented graphically.; Since pseudo-random sequences discussed in the literature have been found highly non-optimal for most applications of RM-CW lidar, a framework for the construction of new pseudo-random sequences of desired correlation properties has been introduced. As an example, a new pseudo-random sequence has been devised, and shown to have significantly improved and nearly-ideal signal and noise properties. Also, a novel scheme of continuous-wave Differential Absorption Lidar (DIAL) using only one transmitter and one receiver has been proposed, which combined with its minimal baseband signal modulation requirements should lead to greatly simplified and improved practical chemical-sensing lidar.; The results of this dissertation prove the feasibility of mid-infrared semiconductor laser based lidar in many important applications, and provide an analytical framework to advance their practical realization. The most immediate applications of this work are expected in remote detection of noxious airborne biological and chemical substances, and in automobile collision avoidance systems.