Electrically pumped photonic-crystal terahertz lasers controlled by boundary conditions

Terahertz semiconductor lasers Terahertz radiation finds promising applications in very different areas of science and technology such as astronomy, environmental monitoring and biological imaging. However, its spectral location, between optical and microwave frequencies, has hindered the development of compact semiconductor terahertz sources. An attractive approach is to make use of photonic-crystal structures, which allows surface emission of radiation, so that the spectral and spatial modes can be simultaneously engineered. To fabricate electrically driven devices, it is necessary to define boundary structures around the active, pumped area and Chassagneux et al. now demonstrate a general technique to implement such boundaries. They fabricate photonic-crystal terahertz semiconductor lasers, where the photonic-crystal pattern is defined in the device top metallization. Single-mode laser action is obtained in the (2.55–2.88) THz range, and the far-field emission exhibits a small angular divergence, thus providing a solution for the quasi-total lack of directionality typical of THz semiconductor lasers.