PRESSURE-INDUCED EXTRA RESONANCES IN NONLINEAR SPECTROSCOPY

We present three examples of pressure-induced extra resonances that can be observed in nonlinear spectroscopy: fluorescence of a three-level atom driven by two laser fields, two-photon ionization of a three-level atom (plus continuum) driven by two laser fields, and excitation of a four-level atom driven by four laser fields. We show that all these extra resonances can be interpreted in terms of quantum pathways, each pathway involving a collisionally aided excitation. We also demonstrate that the two first extra resonances can be obtained with incoherent fields, while relatively coherent fields are required in the last example. © 1990 The American Physical Society.