  It is proved that when the retarded effect (or multiple moment effect) of
radiation fields is taken into account, the high order stimulated radiation and
stimulated absorption probabilities of light are not the same so that time
reversal symmetry would be violated, though the total Hamiltonian of
electromagnetic interaction is still unchanged under time reversal. The reason
to cause time reversal symmetry violation is that certain filial or partial
transitive processes of bounding state atoms are forbidden or can not be
achieved actually due to the law of energy conservation, the asymmetric actions
of effective transition operators before and after time reversal, as well as
the special states of atoms themselves. These restrictions would cause the
symmetry violation of time reversal of other filial or partial transition
processes which can be actualized really. The symmetry violation is also
relative to the initial state asymmetries of bounding atoms before and after
time reversal. For the electromagnetic interaction between non-bounding state
atoms and radiation field, there is no this kind of symmetry violation of time
reversal. In this way, the current formula of light stimulated radiation and
absorption parameters with time reversal symmetry should be revised. The
influence of time reversal symmetry violation on the foundational theory of
laser is also discussed and the phenomena of non-population inversion and
non-radiation transition can also be explained well. In this way, a more
reliable foundation can be established for the theories of laser and nonlinear
optics in which non-equilibrium processes are involved.
