Dipole saturated absorption modeling in frequency modulation spectroscopy: Dealing with a Gaussian beam, resonance narrowing

Abstract

Quantitative, nonlinear sub-Doppler sensitive spectroscopy requires reliable formalism for optimizing the detection of weak molecular absorption patterns. Phase modulation spectroscopy (FMS) is a common technique usedto challenge the ultimate photon-shot-noise limit. In addition, nonlinear spectroscopy can exhibit surprising effects like resonance narrowing, i.e., resonance width below the transit-time rate, like it has been pointed out in the seventies. Here, by extending our previous work, we propose an analytical development associated with numerical integration to simulate the equivalent Lamb-dip under Gaussian beam conditions. Simulations of nonlinear profiles of two transitions belonging to the polyad ∆P 11 of acetylene are discussed, and analyzed by fitting with standard functions. The respective roles of the transit-time, of the collision rate, and of the Rabi frequency (including the power broadening) are carefully discussed and reviewed. It shows "super-narrowing" effects under specific low pressure and low power conditions. A reviewing introduction states previous experimental reports as well about previous modeling.

Hyperfine transitions in the first overtone mode of hydrogen deuteride

“…A now available and their analysis requires full attention, particularly, by extensively investigating the pressure and power dependencies. At low pressures, the molecular interaction transit time, resulting from the finite size of the excitation beam is undoubtedly a source of additional complexity since resonance super-narrowing effects may be anticipated as it has been discussed on several molecular systems [40][41][42][43][44]. Actually, collisional speed-dependence frequency shift [45] may contribute to the asymmetric resonance profiles observed on HD.…”