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

作者：Talicska Courtney N^*; Porambo Michael W; Perry Adam J; McCall Benjamin J

来源：Review of Scientific Instruments, 2016, 87(6): 063111.

DOI：10.1063/1.4953652

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 mu m and demonstrates a noise equivalent absorption of similar to 1 x 10(-9) cm(-1). The effectiveness of concentration-modulated NICE-OHMS is tested through the acquisition of transitions in the nu(1) fundamental band of HN2+ centered near 3234 cm(-1), with a signal-to-noise of similar to 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 similar to 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. Published by AIP Publishing.

• 出版日期2016-6