Highly collimated and directional continous-wave Terahertz emission by photomixing in semiconductor device arrays - art. no. 61940F

CW-photomixing semiconductor devices have hardly exceeded an output power of 10 mu W around 1 THz. Availability of a few mNV, however, would stimulate the demand for THz-imaging, -scanning, and spectroscopy. Increasing the poor power conversion efficiency from the optical pump to THz-output is most desirable. On the other hand, the thermal threshold "per pixel" is limited to about 100 mW of pump laser power. So both limits have to be pushed towards higher performance. In this paper we report on arrays of photomixing devices to overcome the thermal threshold limit. If each individual photomixer in the array can be driven to the same thermal threshold power, the overall THz output can be larger by a factor N x AY for an array. The power of directed emission, however, can be increased even by a factor (N x M)' compared to the individual device. In addition, by adjusting the two laser beams slightly noncollinear, a directional control of the emitted THz-beam is achieved. The angular difference of the incident beams is enhanced by the ratio of the THz-wavelength (approximate to 300 mu m) and the optical wavelength (approximate to 0.85 mu m) with regard to direction of the emitted THz-beam. Thus, a full steering of the THz beam can be achieved by tuning this angle by less than 1 degree (17.5 mrad)