Nonlinear Fast-Beam Laser Interactions

High-resolution spectroscopy performed on fast-moving absorbers has several desirable features. First, in a collinear geometry, the residual Doppler width of the fast atoms is low due to the velocity bunching taking place during acceleration. Second, the velocity of these cooled atoms can easily be changed very precisely. Third, this makes possible Doppler tuning of a laser into resonance with a particular atomic transition. Doppler shifts tip to ¿80 Ã… are present, dependent on the beam energy and the atom used. This, in turn, makes it possible to ´create´ completely harmonic three-level atoms, using the relativistic transformation between laboratory and atom rest frame and to perform optical pumping in well defined spatial regions. Applications to velocity control, resonant three-level nonlinear field-atom interactions, high-resolution laser-r.f. double-resonance spectroscopy, and lifetime determinations are discussed.