Digitally enhanced molecular dispersion spectroscopy

A frequency and intensity noise immune fiber dispersion spectrometer with a digitally enhanced homodyne P hase extraction system is presented. A hydrogen cyanide ((HCN)-C-13) vapor cell is placed in a digitally enhanced Sagnac interferometer, and the anomalous dispersion at the 1550.515 nm P11 transition is interrogated with a tunable laser. An analytical model of the dispersion induced phase readout shows close agreement with the experimentally obtained phase signal. Immunity to frequency and intensity noise confers sub-microradian phase sensitivity, corresponding to a spectroscopic detection limit of 77ppb x m/root Hz. (C) 2020 Optical Society of America