  We present both chip-scale and free space coherent arrays of continuous-wave
THz photomixers. By altering the relative phases of the exciting laser signals,
the relative THz phase between the array elements can be tuned, allowing for
beam steering. The constructive interference of the emission of N elements
leads to an increase of the focal intensity by a factor of NxN while reducing
the beam width by ~1/N, below the diffraction limit of a single source. Such
array architectures strongly improve the THz power distribution for stand-off
spectroscopy and imaging systems while providing a huge bandwidth at the same
time. We demonstrate this by beam profiles generated by a free space 2x2 and a
4x1 array for a transmission distance of 4.2 meters. Spectra between 70 GHz and
1.1 THz have been recorded with these arrays.

Optics