Advanced signal processing for dual comb interferometry

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Dual comb spectroscopy is a paradigm that has greatly matured in recent years. It basically went from a lab curiosity championed by a few groups and exhibiting potential to actually finding "real-world" applications such a leak detection in oil and gas fields. The technique uses two high precision lasers each emitting well controlled discrete frequencies. The radiation of the laser combs is controlled (or known) one respect to the other to astounding accuracy, over 15 decimal places! Those combs are used to probe matter retrieving, from a distance, unique signatures for several chemical compounds. In optical spectroscopy, frequency combs provide better resolution and sensitivity than classical approaches. Comb spectroscopy shines particularly when trying to detect trace constituents in complex mixes. The high resolution over a broad spectral range enables distinguishing between unique signatures, quite literally reading "between the lines" of abundant components while the simultaneous high sensitivity permitting parts per million or per billion detection of contaminants. A first important application is greenhouse gases monitoring. Several gases when present even in trace amounts are significant contributors to our carbon budget. This is the case for methane and ethane whose monitoring is essential not only to make sure that industries meet regulations, that countries respect international agreements but also to reduce waste of resources since around 2% of natural gas is lost through leaks. A second application is diagnosis through breath detection. Much like a breath analyser can quantify your blood alcohol level, a similar device could detect different volatile organic compounds whose concentration in breath is indicative of several diseases. For instance, traces of ammonia indicate renal issues while butane marks lung cancer. Comb spectroscopy has a very good merit factor in terms of achievable sensitivity for a given resolution and measurement time. It is however severely limited in the possibility of increasing measured laser power. Non-linearity in the detection chain and systematic errors quickly arise. These are known since a decade but were not the worst offenders in the adoption of the technique, so they were not properly addressed from a correction perspective. Now that they limit several measurements, this program proposes addressing these issues. This will allow better use of available laser power, better detection sensitivity and faster measurements, contributing in unlocking practical applications. Canada has a strong industrial base in optical spectroscopy, with companies in several provinces selling instruments worldwide to different market segments: from quality control in food and pharmaceutical production lines to remote sensing for security and environmental monitoring. Canadian industrial receptors are already in place.