Parametric generation within a strontium plasma created by two-photon ionization

An experiment has been performed to demonstrate a third-order nonlinear optical effect involving the ground state of the strontium ion. Evidence of strong and slightly tunable parametric generation from a doubly resonant four-wave mixing process is provided when a single-wavelength laser is used to two-photon ionize strontium vapor and simultaneously pump close to the
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two-photon resonance of the ion. This result appears to conform with a semiclassical wave equation description, although there is evidence that a population rate equation analysis will also be necessary if the process is to be modeled more accurately.