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Effects of incomplete light extinction in frequency-agile, rapid scanning spectroscopy



David Long, S. Wojtewicz, Joseph T. Hodges


The effect of finite beam extinction ratio on the precision and accuracy of cavity ring-down decay time constant measurements was examined using the frequency-agile, rapid scanning, cavity ring-down spectroscopy (FARS-CRDS) technique. This new approach to CRDS uses a waveguide-based electro-optic phase modulator (EOM) to provide a laser beam extinction ratio as high as 80 dB: a value that is ≈30 dB greater than that typically achieved with acousto-optic-modulator-based beam switches. We find that the observed measurement precision scales inversely with extinction ratio, such that an EOM enables measurement of the cavity ring-down decay time with a relative precision of ≈8×10-5. We demonstrate that insufficient extinction can be the dominant cause of statistical uncertainty for extinction ratios below 60 dB. Furthermore, insufficient extinction can result in non-exponential decays, which cause systematic measurement biases in cavity losses and absorption.
SPIE Proceedings 2013 Defense Security and Sensing Conference


cavity ring-down spectroscopy, optical switch, electro-optic phase modulator


Long, D. , Wojtewicz, S. and Hodges, J. (2013), Effects of incomplete light extinction in frequency-agile, rapid scanning spectroscopy, SPIE Proceedings 2013 Defense Security and Sensing Conference, [online],, (Accessed June 25, 2024)


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Created July 31, 2013, Updated October 12, 2021