We report the control of an emission direction in two-dimensional (2D) angular space for the terahertz master-oscillator power-amplifier quantum cascade lasers. The device exploits a rhombohedral array of subwavelength air slits as the wave coupler. The available range of the emission direction and the polarization state are determined by the unit slit, while the emission direction and the beam divergence are determined by the array configuration. An analytic relationship between the beam direction and the array parameters was established and experimentally confirmed. The lasers exhibit single mode emission around 3.4 THz, with a low divergence of 14 degrees x 14 degrees. The resultant emission direction varies controllably in a range that the polar angle belongs to 0 degrees to 70 degrees and the azimuth angle belongs to 0 degrees to 90 degrees, which can be further extended. Published under an exclusive license by AIP Publishing.
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