Electronic Population Inversions by Fluid-Mechanical Techniques

The promotion of population inversions between electronic excited states by fluid-mechanical techniques is suggested. Three methods are proposed as illustrations, and the possible degree of inversion in each is estimated. The first makes use in part of the known inversion obtained in excited Ne levels by energy transfer from He metastables. A flow system separates the region of excitation of the He from the region of the resonant excitation of the Ne by the He metastable, and the undesirable electron excitation of the lower Ne state is avoided. The second proposal involves the supersonic expansion of a dissociated mixture of O and H atoms obtained by combustion. An inversion is anticipated between the v′ = 2 and v′ = 1 vibrational levels of the OH(2Σ+) state through the process of inverse predissociation occurring during the expansion. The third illustration involves the rapid expansion of a highly excited gas where radiative depopulation of the lower state promotes an inversion. Results of exploratory experiments involving this particular scheme are discussed. However, it was not possible to observe a population inversion within the noise level of the experiment which involved the sudden expansion of Xe heated by a shock tube.