Directional terahertz emission from diffusion-engineered InAs structures
  We have designed and fabricated a new type of terahertz (THz) emitter that radiates THz waves along the surface-normal direction because of the lateral distributions of the transient electric dipoles. The excitation and measurements were performed using a conventional THz time-domain spectroscopy scheme with femtosecond optical pulses. The corrugated mirror patterns on the InAs layers made the radiation directional along the surface-normal direction, and the emission efficiency was controlled by adjustment of the pattern width. 
Jong-Hyuk Yim, Hoonil Jeong, Jin-Dong Song, and Young-Dahl Jho
physics.optics