Terahertz semiconductor laser chaos.

In the terahertz (THz) range, due to the lack of effective THz light sources, chaos generation in THz semiconductor lasers, e.g., quantum cascade lasers (QCLs), is particularly challenging. Here, we experimentally demonstrate a THz chaos source based on a sole multimode THz QCL without any external perturbations. Such a dynamical regime is characterized by the largest Lyapunov exponent of the measured radio frequency signal of the laser. The experimental results are confirmed by our simulations based on effective semiconductor Maxwell-Bloch Equations. Furthermore, a reduced model based on two coupled complex Ginzburg-Landau equations is derived to systematically investigate the effects of the linewidth enhancement factor and group velocity dispersion on the chaotic regime. It is found that the chaos generation in the THz QCL is ascribed to the defect-mediated turbulence. Our findings pave the way for the generation of controllable and integrated THz chaos sources, as well as potential applications.