  Cavity attenuated phase shift Faraday rotation spectroscopy has been
developed and demonstrated by oxygen detection near 762 nm. The system
incorporates a high-finesse cavity together with phase-sensitive balanced
polarimetric detection for sensitivity enhancement and achieves a minimum
detectable polarization rotation angle (1{\sigma}) of $5.6\times 10^{-9}$
rad/$\surd$Hz, which corresponds to an absorption sensitivity of $4.5\times
10^{-10}$ cm$^{-1}/{\surd}$Hz without the need for high sampling rate data
acquisition.
