High-power density, single plasmon, terahertz quantum cascade lasers via transverse mode control

Terahertz (THz) quantum cascade lasers (QCLs) have been shown to emit peak powers greater than 1 W from a single facet in a single plasmon geometry. However, this is typically achieved by increasing the laser ridge width, resulting in higher-order transverse modes, limiting the achievable power density. Here, we control and fully suppress these modes through thin metallic side-absorbers, showing laser action solely on the fundamental transverse mode operation without sacrificing high THz peak powers. This leads to enhanced power densities and electric fields of up to 1.8 kW/cm² and 1.17 kV/cm, respectively, opening up the possibility of applying THz QCLs as pump sources for investigations of nonlinear THz physical phenomena.