Coherent superposition of terahertz beams from a phased linear photomixer array

We report on a 4 element linear array of free standing, tunable THz n-i-pn-i-p superlattice photomixers. The individual THz beams are coherently combined at a target plane distance of 4.2 m. The measurements of the interference pattern confirm the theoretically expected quadratic intensity increase of the center beam with the number of sources. At the same time, the beam waist is reduced in one dimension by a factor of 6 compared to a single beam. This technique allows for high resolution, THz stand off imaging.