Y coupled terahertz quantum cascade lasers
  Here we demonstrate a Y coupled terahertz (THz) quantum cascade laser (QCL) system. The two THz QCLs working around 2.85 THz are driven by independent electrical pulsers. Total peak THz output power of the Y system, with both arms being driven synchronously, is found to be more than the linear sum of the peak powers from the individual arms; 10.4 mW compared with 9.6 mW (4.7 mW + 4.9 mW). Furthermore, we demonstrate that the emission spectra of this coupled system are significantly different to that of either arm alone, or to the linear combination of their individual spectra. 
Owen P. Marshall, Subhasish Chakraborty, Md. Khairuzzaman, Harvey E.   Beere and David A. Ritchie
physics.optics cond-mat.other