Investigating the Applicability of Modern Widely Tunable Lasers to Laser Heterodyne Radiometry for Atmospheric Composition Monitoring

Greenhouse gas emissions are widely recognized by the scientific community as the main cause of climate change. This has led to an enormous increase in interest in techniques for studying atmospheric composition over the last few decades. Laser heterodyne radiometry (LHR) systems represent one of the most promising alternatives for such studies, given their inherent characteristics, which have led to enormous progress in the last decades. Although these systems offer a wide range of advantages, the optical span is limited by the tuning range of the local oscillator laser, usually using distributed feedback (DFB) lasers, which limits the span to a few absorption lines. This has a negative impact on the performance of atmospheric gas concentration retrieval compared to the multitude of absorption lines retrieved by traditional Fourier Transform spectroscopy systems. In this context, the use of widely tunable lasers represents an optimal approach to greatly expand the range of LHR systems straightforwardly. This article presents the first comprehensive study of the applicability of state-of-the-art widely tunable lasers to LHR systems in a direct comparison of their performance, in all aspects of interest, with DFBs. The conclusions of this work prove that, although there are still a number of challenges to be addressed before widespread use, these sources demonstrate enormous potential and remarkable advantages.