Interference in Atomic Fluorescence Excited by Photodissociation of Homonuclear Diatomic Molecules
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Photodissociation of a homonuclear diatomic molecule gives two identical atomic fragments, which, as a consequence of momentum conservation, are constrained to follow identical but oppositely directed trajectories with respect to their center of mass. For exciting radiation within a certain wavelength range only one of the atoms will be electronically excited. A photodetector viewing the subsequent atomic fluorescence sees a photon whose wavefunction is a superposition of two states corresponding to emission from either of the two oppositely directed atomic recoil trajectories. In a molecular beam experiment arranged to eliminate the Doppler effect, square law detection of the photon gives rise to beats in the detector signal at a frequency determined by the atomic velocity and the angle the recoil trajectory makes with the detection axis. Since photofragmentation takes place over a distribution of recoil directions the beats (which add incoherently) are found over a range of frequencies that mirrors the angular distribution of the atomic fragments. The power spectral density of the detector noise is found to depend upon the asymmetry parameter for the photofragment angular distribution, the atomic recoil velocity and the frequency of the fluorescence photon.
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