Controling polarization of VUV radiation by dressing field |
|
| Elena Gryzlova | |
| Lomonosov Moscow State University | |
| Nonlinear optical activity in the VUV region containing autoionizing states (AIS) is considered. Nonlinear effects in the vicinity of an AIS originate from optical coupling of this state with a discrete state or another AIS by elliptically polarized laser radiation. The optical activity in the VUV manifests itself in photoionization processes when a beam of the probe VUV radiation passes through the gas medium with laser induced chirality. Two schemes are investigated: coupled doubly excited AISs in helium and Rydberg AIS in xenon coupled with discrete state. Two parameters characterize the probe field polarization: the direction of the polarization and the ellipticity. They are changing while the initially linearly polarized probe VUV radiation passes the medium. Thus rotation of the plane of polarization (?) and the acquired ellipticity (?) caused by the laser coupling are examined theoretically. We consider collinear laser and VUV beams. The Liouville equation is solved for the atomic density matrix within the rotating wave approximation and treating the probe field as a perturbation. The atomic continuum is eliminated in the adiabatic approximation. Interaction of the laser field with the atom is treated nonperturbatively, but neglecting multiphoton nonresonant processes. Our treatment is limited to moderately strong laser fields not exceeding a few units of 1012 W/cm2. Non-trivial behavior of the susceptibility is found in the region of AIS. The frequency dependence (dispersion curves) of the optical activity is sensitive to spectroscopic parameters of the AIS. The dependence of the nonlinear susceptibility on laser parameters (frequency, detuning, and intensity) is analyzed and conditions for maximum and minimum optical activity are determined. An efficient control of the rotatory power and acquired ellipticity by the parameters of the coupling field is predicted. |