Supersonic molecular beam experiments are ideal for creating and studying transient chemical species of astrophysical importance. While direct absorption of sub-THz radiation in such beams has proven to be an important and relatively simple technique for probing the rotational states of these molecules, low number densities and short pathlengths call for signal enhancement techniques; two recent publications outline multi-pass and cavity based strategies (Widicus Weaver group and Blake group, respectively).1,2 To our knowledge, conventional confocal Fabry-Perot resonators have not been used at sub-THz wavelengths owing to the difficulty of creating dielectric coatings suitable for sub-THz partially reflective mirrors.2 We have recently overcome this obstacle by fabricating the our own mirrors using concave wire-grid polarizers with which we have achieved a cavity Q on the order of ~75,000. The simple geometry allows us to robustly couple the sub-THz beam waist into the cavity, saturating the transitions and leading to a 75-fold increases in the integrated line intensities as well as causing novel dispersion effects, even from non-polar molecules. We have simulated these line shapes and will present the results of recent studies exploring the dynamics of the O(1D) reactions with chlorinated compounds such as carbon tetrachloride to form vibrationally excited ClO.

Sub-THz cavity enhanced absorption with a conventional confocal Fabry-Perot resonator

256th National Meeting (2018)

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