Precision cavity enhanced velocity modulation spectroscopy

The new technique of cavity enhanced velocity modulation spectroscopy has been further developed, incorporating a tighter cavity to laser lock and an optical frequency comb for absolute frequency calibration. Several N 2 + transitions have been observed with much higher precision than previously possible, and transitions that were blended in earlier Doppler-limited experiments are now resolved. The full-width at half-maximum of the observed Lamb dips is ∼ 40 MHz , and appears to be dominated by a broadening due to the velocity modulation. Future extension of this technique into the mid-infrared should enable significant improvements in the sensitivity and resolution of vibrational spectroscopy of molecular ions.