Broadly tunable mid-infrared noise-immune cavity-enhanced optical heterodyne molecular spectrometer

Abstract

The sensitive spectroscopic technique noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) has been successfully used in a variety of systems; however, no broadly tunable setup has been developed for the mid-infrared. To this end, we have integrated a difference frequency generation system into a NICE-OHMS setup. Initial optimization and characterization was completed with ro-vibrational spectroscopy of methane. Doppler-broadened frequency-modulated NICE-OHMS spectra were recorded at a sensitivity of $2\times {10}^{-7}{\mathrm{cm}}^{-1}{\mathrm{Hz}}^{-1/2}$. Sub-Doppler saturation signals (Lamb dips) were also observed using wavelength-modulated NICE-OHMS, achieving a sensitivity of $\sim 6\times {10}^{-9}{\mathrm{cm}}^{-1}{\mathrm{Hz}}^{-1/2}$.

© 2012 Optical Society of America

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