Ultra-broadband quantum cascade laser operating from 1.88 to 3.82 THz
  We report on a heterogeneous active region design for terahertz quantum cascade laser based frequency combs. Dynamic range, spectral bandwidth as well as output power have been significantly improved with respect to previous designs. When operating individually the lasers act as a frequency comb up to a spectral bandwidth of 1.1 THz, while in a dispersed regime a bandwidth up to 1.94 THz at a center frequency of 3 THz can be reached. A self-detected dual-comb setup has been used to verify the frequency comb nature of the lasers. 
Markus R\"osch, Mattias Beck, Martin J. S\"uess, Dominic Bachmann,   Karl Unterrainer, J\'er\^ome Faist, and Giacomo Scalari
physics.optics