Photodetachment microscopy

Article By:

Blondel, Christophe Laboratoire Aime-Cotton, Centre National de la Recherche, Université Paris, Paris, France.

Last reviewed:January 2020

DOI:https://doi.org/10.1036/1097-8542.801860

Detachment is the removal of an electron from a negative ion, which produces a neutral atom or molecule and a free electron. Photodetachment is detachment in which the necessary energy is provided by light, more precisely by a photon. Photodetachment microscopy consists in observing accurately the motion of the free electron produced when this process takes place in the presence of an external electric field. In such a field, the electron undergoes constant acceleration, as in free fall, and its possible trajectories are parabolas. With the magnitude of the initial electron velocity set by the photon energy, every point within reach on the detection plane can be reached by two, and only two, such parabolas. The ability of a single electron to follow several trajectories simultaneously is an essential feature of quantum mechanics, which is revealed visually in this case by the observation of an electron interference pattern. The sensitivity of the pattern to variations of the electron's ejection energy makes it possible to measure that energy with an accuracy 1000 times better than by classical techniques. Photodetachment microscopy is used to measure the electron affinities of atoms and molecules with unprecedented accuracy. See also: Electron; Electron affinity; Interference of waves; Negative ion; Photon; Quantum mechanics; Superposition principle

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