  A theory is developed and applied to the study of opportunities and specific
features of coherent control of four-wave mixing as well as of the accompanying
processes in the continuous-wave regime, which involve transitions between
bound and free quantum states. Such opportunities become feasible through
constructive and destructive interference of quantum pathways. Two coupling
schemes of practical importance are investigated. In the first, a ladder energy
level scheme, fully-resonant sum-frequency nonlinear-optical generation of
short-wavelength radiation driven by several strong fields is investigated. The
relaxation processes as well as absorption of the fundamental and generated
radiations, which play an important role, are taken into consideration. It is
shown that the generation output can be considerably increased through the
appropriate adjustment of several laser-induced continuum structures. In the
second, a folded scheme, a possible control of two-photon dissociation
(Lambda-scheme) using auxiliary laser radiation applied to the adjacent
bound-free transition (V-configuration) is investigated. Besides dissociation,
the proposed method enables one to control population transfer between two
upper discreet levels via the lower-energy dissociation continuum, while direct
transition between these states is not allowed. The opportunities of
manipulating these processes as well as of four-wave-mixing-based spectroscopy
are explored both analytically and through a numerical simulation for Na_2
dimers.
