Coherent effects in He I under laser interaction

Summary form only given. The resonance laser interaction with an atomic system with degenerate levels creates coherent properties in the medium. Depending on the laser polarization and the experimental geometry it could be alignment, orientation or optical pumping. This coherence could be destroyed by application of a magnetic field, which removes the level degeneracy. This process has an effect on the optical characteristics of the medium, such as absorption and fluorescence from the levels involved. They show the resonance dependence on the applied magnetic field with widths, depending on γ_a, γ _b, and γ_ab, where γ_I is the width of the upper or lower state of the transition, resonant to the laser beam, γ_ab is the width of the optical transition a→b. Using different experimental geometry, γ_a, γ_b, and γ_ab could be measured, as well as some rate constants of these levels. We investigated the coherent properties of the 2³ P→3³ D transition of He I under resonant laser radiation. Due to the peculiarities of the coherent signals, registered in the lateral and forward direction the cross-section for velocity selective collisions for the 3³ D He I level were obtained. The influence of the strong laser field on the widths and shapes of the signals was determined. The cross-section, for depolarizing collisions of the 3³ D level was measured, too