  We investigate deuteron-triton (DT) fusion in the presence of linearly
polarized strong electromagnetic fields in high-frequency limit, in which a
complex spherical square-well potential is exploited to describe the nuclear
potential. Within the framework of the Kramers-Henneberger (KH) transformation,
we have calculated the total and angular differential fusion cross sections by
investigating the asymptotical phase shifts of the Coulomb wavefunctions. With
introducing a dimensionless quantity of $n_d$ representing the ratio of the
particle quiver oscillation amplitude to the radius of nuclear potential, we
find that, even though the tunneling probability of passing through the Coulomb
repulsive potential keeps almost identical to that in the absence of
electromagnetic fields, the peak of total fusion sections shows an apparent
shift from the well known value of 110 keV to 78 keV for $n_d=0.01$. The
angular differential cross sections also show some resonance peaks that shift
from zero inclination angle to $\pi/2$ with increasing the parameter $n_d$. The
corresponding astrophysical $S$-factors are found to be enhanced by several
times in amplitudes. With the help of Wentzel-Kramers-Brillouin (WKB)
approximate wavefunctions, the shape-resonance tunneling mechanism of the above
findings are uncovered and some implications are discussed.
