  We show that a moving vortex lattice, as it comes to a crystal edge, radiates
into a free space the harmonics of the washboard frequency, $\omega_0=2\pi
v/a$, up to a superconducting gap, $\Delta/\hbar$. Here $v$ is the velocity of
the vortex lattice and $a$ is the intervortex spacing. We compute radiation
power and show that this effect can be used for generation of terahertz
radiation and for characterization of moving vortex lattices.
