Electromagnetic radiation from vortex flow in type-II superconductors

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.