Sub-Doppler mid-infrared spectroscopy of molecular ions

• Published in: Chemical physics letters Vol. 551; pp. 1 - 6
• Main Authors: Crabtree, Kyle N., Hodges, James N., Siller, Brian M., Perry, Adam J., Kelly, Joseph E., Jenkins, Paul A., McCall, Benjamin J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-11-2012
• ISSN: 0009-2614; 1873-4448
• DOI: 10.1016/j.cplett.2012.09.015

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► An instrument for sub-Doppler mid-IR spectroscopy of molecular ions is described. ► NICE-OHMS is performed with an optical parametric oscillator (OPO). ► Fitting to Lamb dips provides ∼70kHz precision in line center determination. ► Velocity modulation with phase sensitive detection gives ion-neutral discrimination. ► A sensitivity of 8.5×10-10cm-1Hz-1/2 is achieved.
The technique of velocity modulation spectroscopy has recently been combined with cavity enhancement and frequency modulation methods into a technique called noise-immune cavity-enhanced optical heterodyne velocity modulation spectroscopy (NICE-OHVMS). We have implemented NICE-OHVMS with a cw-optical parametric oscillator (OPO) tunable from 3.2 to 3.9μm, and used it to record spectra of the R(1,0) and R(1,1)u transitions of the ν2 fundamental band of H3+. The high optical power and cavity enhancement enable saturation of rovibrational transitions, which allows for line center frequencies to be measured with a precision of 70kHz.