Dicke narrowing in the dispersion mode of detection and in noise-immune cavity-enhanced optical heterodyne molecular spectroscopy - Theory and experimental verification

摘要

Dicke narrowing in both the absorption and dispersion modes of detection have been scrutinized by noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) using an isolated transition in the v _1 + ν_3 + ν_4~1 - ν_4~1 band of acetylene [P_e(33) at 6439:371 cm~(-1)] at room temperature. The results represent the first (to our knowledge) demonstration of Dicke narrowing detected in dispersion, as well as by NICE-OHMS, and the paper provides thereby the first comparison of the Dicke narrowing phenomenon for the two modes of detection. It is shown that Dicke narrowing in dispersion can be described by the dispersive counterparts to the conventional Galatry and Rautian absorption line-shape functions, which are explicitly given. Spectroscopic parameters for the targeted transition were extracted in both absorption and dispersion and found to be in agreement with those previously reported for other lines and bands. The shortcomings of the Galatry model to provide physically relevant parameters in this pressure range are discussed.