Remote-detection of UV absorbing ATMospheric trace gases using broadband and resolved Coherent femtosecond Spectroscopy. – UV-ATMOCOS

The development of increasingly sensitive and robust instruments and new methodologies are essential to improve our understanding of the Earth’s climate and air pollution. In this context, Dual-Comb spectroscopy (DCS) methodology has been successfully demonstrated as a remote laser-based instrument to probe infrared absorbing species such as greenhouse gases. We here present a new project aiming to develop UV-Dual-Comb spectroscopy to remotely monitor atmospheric gases that absorb in the ultraviolet range, where the most reactive molecules of the atmosphere (OH, BrO, NO2, IO, ClO...) have their highest absorption cross-sections. Understanding the complex chemistry of such molecules are crucial to improve atmospheric models and air quality forecast. More sensitive instruments are necessary to discover new physical and chemical pathways related to those molecules, all the more so as significant discrepancies have been highlighted in several studies between measured and modeled concentrations. Extending, for the first time, DCS into the UV range raises several challenges. For atmospheric applications, the necessary radiation power of the UV laser sources must reach a critical value for a light path a few km long, taking into account the diffusion and absorption of the atmosphere in the UV. In addition, the relative phase noise of the laser sources required for DCS must be addressed with precision and innovative averaging strategies must be applied. An original laser source and acquisition protocols will be developed to meet the objective of UV-DCS. As a high-resolved and broadband type experiment, the instrument here developed and based on UV-DCS, will provide in situ, multi-components detection of the very reactive UV absorbing trace-gases of the atmosphere.