A highly efficient source of collimated terahertz radiation has been made by coupling two microdisk lasers via a suspended metal wire. Alessandro Pitanti of the CNR - Istituto Nanoscienze in Pisa, Italy, and co-workers made the miniature device, which acts as a linear dipole antenna, emitting continuous-wave radiation at 3.5 terahertz in a vertical beam that has a low divergence. Significantly, the design is highly efficient, has a low threshold current and operates with a high slope efficiency. An output power of up to 250 microwatts was obtained. Each microdisk contains an 11-micrometer-thick active core of a GaAs/AlGaAs quantum cascade laser heterostructure covered by a 200-nanometer-thick metal layer. The small size and low divergence of the emitted beam make the terahertz source attractive for portable imaging and sensing applications.
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