  We discuss harmonic generation in the case of laser field-dressed
Hamiltonians that are invariant under so-called dynamical symmetry operations.
Examples for such systems are molecules which exhibit a discrete rotational
symmetry of order
  N (e.g. benzene with N=6) interacting with a circularly polarized laser field
and single atoms in a bichromatic field, with the two lasers having circular
polarizations. Within a general group theory approach we study the harmonics
one obtains from the interaction of a laser pulse and a circular molecule. When
the system is in a pure field-dressed state the known selection rule kN \pm 1,
k=1,2,3, ... results. However, other lines are observed when recombinations
with states of a symmetry different from the initial one become important. This
is the case for realistic laser pulses (i.e., with a finite duration). In
particular when the fundamental laser frequency (or one of its multiples) is
resonant with a transition between field-dressed states. Numerical ab initio
simulations, confirming our analytical calculations and illustrating the power
of the group theory approach, are presented.
