Transportable dual-modulation Faraday rotation spectrometer for time-multiplexed nitric oxide isotope ratiometry

We present a transportable dual-modulation Faraday rotation spectrometer with minor isotope (
¹⁵
NO) detection sensitivity of 0.35 ppbv·Hz
^-12
, corresponding to 1.4x the shot-noise limit. NO isotope line-switching is implemented for quasi-simultaneous time-multiplexed isotope measurements.