  Using analytical techniques and Langevin dynamics simulations, we investigate
the dynamics of polymer translocation through a nanochannel embedded in two
dimensions under an applied external field. We examine the translocation time
for various ratio of the channel length $L$ to the polymer length $N$. For
short channels $L\ll N$, the translocation time $\tau \sim N^{1+\nu}$ under
weak driving force $F$, while $\tau\sim F^{-1}L$ for long channels $L\gg N$,
independent of the chain length $N$. Moreover, we observe a minimum of
translocation time as a function of $L/N$ for different driving forces and
channel widths. These results are interpreted by the waiting time of a single
segment.
