Adiabatic excitation and adiabatic inversion of multilevel systems

Adiabatic excitation is accomplished by irradiating an atom or molecule with one or more time-varying fields whose frequencies and field strengths vary sufficiently slowly for the system to adjust continuously and reversibly to the changing conditions. The atomic and molecular states produced by adiabatic excitation have a number of unique properties. One of the most interesting of these properties is adiabatic inversion. Laser pulses with fields that vary slowly enough can often transfer an atom or molecule from its ground state to one or more excited states with nearly 100% efficiency, producing an inversion with respect to the ground state. This work is concerned with the physical principles of adiabatic excitation of atoms and molecules, and the behavior of these systems during the excitation. Particular attention is focused upon adiabatic inversion. Adiabatic inversion is found to be a common phenomenon in a large number of multilevel models, and can often be induced solely by variations in the laser field strength. Adiabatic inversion can often be produced in the multilevel models considered in this work by laser pulses with rise times as short as one of ten nanoseconds. However, the presence of damping from sources such as spontaneous emission or atomic and molecular collisions is found to destroy adiabatic inversion. Consequently, it is necessary to use laser pulses that are short in comparison with the mean damping time in order to produce adiabatic inversion