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We report a set of practical multi-circle spot patterns produced by two-spherical-mirror multi-pass cells (MPCs). Such a set of intricate spot patterns takes full account of the evolution and deformation of spot shapes caused by aberrations on two spherical mirror surfaces by means of a multi-ray calculation model, thus avoiding spot overlaps and reducing an etalon effect. An eight- and nine-multi-circle spot pattern was demonstrated experimentally in order to verify the validity of the calculated results. Furthermore, a 2f spectrum measurement of ambient methane was performed using the eight-multi-circle spot pattern MPC to verify the practicability. An approach to search for multi-circle spot patterns in a two-spherical-mirror MPC is discussed in detail. A set of dense spot patterns results in sensitive, low-cost, compact trace gas sensors based on MPCs, which can be used to implement a large-scale deployment of distributed sensor networks for monitoring pollutants or to realize handheld mobile sensor devices for safety inspection, leakage detection, and medical diagnostics.
Cui et al. (Mon,) studied this question.
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