Ultrafast Saturation of Electronic-Resonance-Enhanced Coherent Anti-Stokes Raman Scattering and Comparison for Pulse Durations in the Nanosecond to Femtosecond Regime
Journal Article - Open Access
AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH WRIGHT-PATTERSON AFB United States
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Saturation threshold of a probe pulse in an ultrafast electronic-resonance-enhanced CARS ERECARS configuration is calculated. We demonstrate that while underdamping condition is a sufficient condition for saturation of ERE-CARS with the long-pulse excitations, a transient-gain must be achieved to saturate ERE-CARS signal for ultrafast probe regime. We have identified that the area under the probe pulse can be used as a definitive parameter to determine the criterion for saturation threshold for ultrafast ERE-CARS. From a simplified analytical solution and a detailed numerical calculation based on density-matrix equations, the saturation threshold of ERE-CARS is compared for a wide range of probe-pulse durations from 10-ns to 10-fs regime. The theory explains both qualitatively and quantitatively the saturation thresholds of resonant transitions, and also gives a predictive capability for other pulse duration regimes. The presented criterion for saturation threshold will be useful in establishing the design parameters for ultrafast ERE-CARS.