Room-temperature monolithic quantum-cascade laser sources operating from 1.1 to 1.5 THz

Abstract

Terahertz quantum cascade laser sources with intra-cavity difference frequency generation are currently the only electrically-pumped monolithic semiconductor light sources operating at room temperature in the 1-6 THz spectral range. These devices demonstrated drastic improvements in performance in the past several years and can produce broadband and narrow-linewidth single-mode terahertz emission with power output sufficient for spectroscopic applications. Recent efforts in the wavefunction engineering using an active region design based on a dual-upper-state concept led to a significant enhancement of the optical nonlinearity of the active region for efficient terahertz generation. Dual-upper-state terahertz quantum cascade laser sources exhibit the power of >0.3 mW. Here, we report low frequency generation from terahertz quantum cascade laser sources based on intra-cavity nonlinear frequency mixing. In order to achieve higher nonlinear susceptibility in low frequency region, we design a long wavelength dual-upper-state active region in which transition dipole moments are increased. A fabricated device with distributed feedback grating demonstrates a THz peak output power of 40 μW at room temperature, with multi-mode THz emission at a frequency of 1.4 THz. Besides, a device produces THz output power of >250 μW at 110 K, which is higher output power, compared to low- frequency THz-QCLs at liquid helium temperature.