  Tunneling electron-positron pair production is studied in a new setup in
which a strong low-frequency and a weak high-frequency laser field propagate in
the same direction and collide head-on with a relativistic nucleus. The
electron-positron pair production rate is calculated analytically in the limit
in which in the nucleus rest frame the strong field is undercritical and the
frequency of the weak field is below and close to the pair production
threshold. By changing the frequency of the weak field one can reduce the
tunneling barrier substantially. As a result tunneling pair production is shown
to be observable with presently available technology.
