a compact , solid - state thz source based on the driven josephson vortex lattice in a highly anisotropic superconductor such as bi 2 sr 2 cacu 2 o 8 that allows cw emission at tunable frequency . a second order metallic bragg grating is used to achieve impedance matching and to induce surface emission of thz - radiation from a bi 2 sr 2 cacu 2 o 8 sample . steering of the emitted thz beam is accomplished by tuning the josephson vortex spacing around the grating period using a superimposed magnetic control field .