Mid-infrared concentration-modulated noise-immune cavity-enhanced optical heterodyne molecular spectroscopy of a continuous supersonic expansion discharge source

Courtney N. Talicska, Michael W. Porambo, Adam J. Perry, Benjamin J. McCall

Research output: Contribution to journalReview article


Concentration-modulated noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) is implemented for the first time on a continuous gas-flow pinhole supersonic expansion discharge source for the study of cooled molecular ions. The instrument utilizes a continuous-wave optical parametric oscillator easily tunable from 2.5 to 3.9 μm and demonstrates a noise equivalent absorption of ∼1 × 10-9 cm-1. The effectiveness of concentration-modulated NICE-OHMS is tested through the acquisition of transitions in the ν1 fundamental band of HN2+ centered near 3234 cm-1, with a signal-to-noise of ∼40 obtained for the strongest transitions. The technique is used to characterize the cooling abilities of the supersonic expansion discharge source itself, and a Boltzmann analysis determines a rotational temperature of ∼29 K for low rotational states of HN2+. Further improvements are discussed that will enable concentration-modulated NICE-OHMS to reach its full potential for the detection of molecular ions formed in supersonic expansion discharges.

Original languageEnglish (US)
Article number063111
JournalReview of Scientific Instruments
Issue number6
StatePublished - Jun 1 2016


ASJC Scopus subject areas

  • Instrumentation

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