Chasing systematic errors in dual comb spectroscopy
Prof. Jerome Genest, PhD
Université Laval, Quebec, Canada
16:15 - 17:15 Tuesday 12 December 2023 TUG
The dual comb interferometer emerges as a tool of choice to improve spectroscopic models and databases as well as to monitor green house gases at a regional level.
To reach the required quantification of carbon dioxide or methane in the atmosphere, a sub percent accuracy is needed on the retrieved concentrations. With current sources of systematic errors, accuracy hovers around 1%. In this talk, we will present three different interpretations for dual comb interferometry: the two wave interferometer, the multi-heterodyne beat note and the optical sampling oscilloscope. Known sources of systematic errors as well as ways to mitigate them will be described. These include detection chain and acquisition card non linearities as well as self and cross phase modulation in fibres carrying the optical signals. A visualisation of two pulse interference at the field level, including optical non linearities, will provide a new perspective on the dual comb interference. With systematic errors reduced, fundamental random noise sources, such as shot noise, limit the measurement sensitivity. It will be shown that contrary to what was assumed by the community since at least decade, dual comb spectrometers have a much better shot noise limit than classical Fourier transform spectrometers. Carbon dioxide measurements will be presented to demonstrate that absolute spectroscopy with sub percent concentration accuracy is within reach.
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