Arrayed Telecom-Wavelength Compatible THz n-i-pn-i-p Super lattice Photomixers for Spectroscopy Applications

We report on the progress of room-temperature operating, continuous-wave, tunable n-i-pn-i-p superlattice THz photomixers, compatible with 1.55 mu m telecom laser systems. An output power of 0.65 mu W at 1 THz has been achieved at a photocurrent of 9.5 mA, using a broadband antenna. The spectral power is at a level where high resolution spectroscopy becomes attractive. This is demonstrated by measuring the absorption spectrum of water vapor between 0.4 and 1.6 THz. We constructed an array of 4 mutually coherent photomixers for higher output power and spatial resolution. The interference of the four individual beams was measured in the target plane at a stand-off distance of 4.2 m. We report on both a small THz spot diameter along the array axis of < 1 cm for v > 0.3 THz and a high intensity of the central interference peak, in excellent agreement with numerical simulations. These features are very attractive for stand-off imaging and spectroscopy