In
this research we examine atomic and molecular systems, which are subjected to
high intensity radiation in the high frequency regime. We study the mechanism
for generation of high harmonics in the high frequency regime and examine the
transition from high frequency mechanism to low frequency mechanism. This
transition involves a transition from dominant contribution of bound-bound interactions
in the high frequency regime to predominant bound-continuum interaction in the
low-frequency regime. In order to obtain a better view on high frequency behavior
of driven systems we develop here a new transformation of the time dependent Schrodinger
equation. This transformation leads to an effective potential, which is time
independent and depends on the laser frequency as 1/ω making it applicable
in the high frequency regime. The advantage of this transformation over the well-known
Kramers-Henneberger transformation is the dependence of the effective potential
on the field parameters. As stated the effective potential resulting from our
transformation depends only on the laser frequency, ω, while the effective
potential of the Kramers-Henneberger representation depends also on the maximum
field amplitude. The effective potential obtained by the use of our representation
resembles the effective potential for a classical particle subjected to rapidly
oscillating time dependent field, proposed by Kapitza. We show that a free
quantum particle subjected to high frequency radiation can be trapped even when
the mean of the oscillations is equal to zero. Such temporary trapping can
occur when the particle is in a metastable state of the effective Hamiltonian.
We show that at least one resonance state exists when the potential decays
sufficiently fast.
