On-chip, self-detected THz dual-comb spectrometer
  We present a directly generated on-chip dual-comb source at THz frequencies. The multi-heterodyne beating signal of two free-running THz quantum cascade laser frequency combs is measured electrically using one of the combs as a detector, fully exploiting the unique characteristics of quantum cascade active regions. Up to 30 modes can be detected corresponding to a spectral bandwidth of 630 GHz, being the available bandwidth of the dual comb configuration. The multi-heterodyne signal is used to investigate the equidistance of the comb modes showing an accuracy of $10^{-12}$ at the carrier frequency of 2.5 THz. 
Markus R\"osch, Giacomo Scalari, Gustavo Villares, Lorenzo Bosco,   Mattias Beck and J\'er\^ome Faist
physics.optics