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

Abstract

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
Volume87
Issue number6
DOIs
StatePublished - Jun 1 2016

    Fingerprint

ASJC Scopus subject areas

  • Instrumentation

Cite this