In this talk, we report the use of frequency-modulation (FM) spectroscopy to determine, from the phase of the FM signal, the sign of the population difference in a two-level system (i.e. whether the two-level system is inverted). We demonstrate that FM signals from an inverted I2 B-X system, prepared by a pulsed laser, have opposite phase with respect to signals from the Rb D1-line absorption transition (i.e. a non-inverted system). We believe that this modified application of FM spectroscopy can be readily applied to determine the quantum-state branching ratios of chemical species formed in astro-chemical processes, i.e. photo-dissocation by the sun. We apply the technique to probe the A-X transitions of the C2 fragments, generated from one-color (~220 nm) resonance-enhanced (S1-S0), multi-photon dissociation of acetylene, with the goal of determining the relative abundance of the nascent C2 A and X-state products.

Determination of the sign of the population difference in a two-level system by frequency-modulation spectroscopy

256th National Meeting (2018)

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