Abstract
We describe sensitive opto-acoustic detection of chemical moieties with trace species selectivity far in excess of the selectivity available via the standard opto-acoustic approach. Rejection of typical interfering signals such as window and “dry-gas” absorptions, electronic pick-up, etc. is achieved by simultaneous modulation (chopping) of the excitation laser and frequency modulation (Zeeman or Stark) of the desired absorption line. The ability of this scheme to discriminate against overlapping absorptions in the NO/H 2O/buffer system is demonstrated. The measured discrimination ratio at ppmv levels of NO is 2×10 −4 NO/H 2O. Ultimate sensitivity for NO is expected to be ≈10 pptv.
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