  Order $\alpha_s$-corrections to the diffractive structure functions $F_L^D$
and $F_2^D$ at large $Q^2$ and small $x$ are evaluated in the semiclassical
approach, where the initial proton is treated as a classical colour field. The
diffractive final state contains a fast gluon in addition to a quark-antiquark
pair. Two of these partons may have large transverse momentum. Our calculations
lead to an intuitive picture of deep-inelastic diffractive processes which is
very similar to Bjorken's aligned-jet model. Both diffractive structure
functions contain leading twist contributions from high-$p_{\perp}$ jets.
