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Continuous-wave cavity-ringdown detection of stimulated Raman gain spectra
Authors:F. V. Englich  Y. He  B. J. Orr
Affiliation:(1) MQ Photonics Research Centre, Department of Physics, Macquarie University, Sydney, NSW, 2109, Australia;(2) Present address: Jet Propulsion Laboratory, California Institute of Technology, MS 300-123, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
Abstract:Cavity ringdown (CRD) spectroscopy, with its high sensitivity, provides a novel way to perform continuous-wave (cw) stimulated Raman gain (SRG) spectroscopy, rather than by conventional optically detected coherent Raman techniques. Tunable cw laser light at ∼1544 nm is used to probe ringdown decay from a rapidly-swept, high-finesse optical cavity containing a gas-phase sample of interest and itself located inside the cavity of a cw single-longitudinal-mode Nd:YAG ring laser operating at ∼1064.4 nm. This approach is used to measure cw SRG spectra of the ν 1 fundamental rovibrational Raman band of methane gas at ∼2916.5 cm−1. The resulting SRG-CRD resonances have ringdown times longer than in the off-resonance case, in contrast to the usual shorter ringdown times arising from absorption and other loss processes. Previously reported noise-equivalent sensitivities have been substantially improved, by using a second ringdown cavity to facilitate subtraction of infrared-absorption background signals. Moreover, by employing a ringdown cavity in the form of a ring, the SRG-pump and CRD-detected Stokes beams can co-propagate uni-directionally, which significantly reduces Doppler broadening.
Keywords:  KeywordHeading"  >PACS 42.62.Fi  42.65.Dr  82.53.Kp
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