
Physics 2005
Exact Solution for a TwoLevel Atom in Radiation Fields and the Freeman ResonancesDOI: 10.1103/PhysRevA.73.023419 Abstract: Using techniques of complex analysis in an algebraic approach, we solve the wave equation for a twolevel atom interacting with a monochromatic light field exactly. A closedform expression for the quasienergies is obtained, which shows that the BlochSiegert shift is always finite, regardless of whether the original or the shifted level spacing is an integral multiple of the driving frequency, $\omega$. We also find that the wave functions, though finite when the original level spacing is an integral multiple of $\omega$, become divergent when the intensitydependent shifted energy spacing is an integral multiple of the photon energy. This result provides, for the first time in the literature, an abinitio theoretical explanation for the occurrence of the Freeman resonances observed in abovethreshold ionization experiments.
