We derive a new integral equation for the nonperturbative evaluation o
f transition matrix elements of multiphoton processes at high laser fi
eld intensities. Our approach to the problem is partly based on the us
e of die Kramers-Henneberger transformation. As a specific example, we
apply our method to the generation of harmonics by an electron in a s
hort range potential, supporting a single bound state. We evaluate the
rates R2m+1 for the odd harmonics created in this process for a set o
f specifically chosen parameters and we compare our results with prese
ntly available experimental data.