Terahertz Sources Based on Metrological?Grade Frequency Combs

Broadband metrological-grade frequency comb (FC) synthesizers with a rich number of phase locked modes are the ideal sources for quantum sensing and metrology. At terahertz (THz) frequencies, electrically pumped cascade lasers (QCLs) have shown quantum-limited noise operation, phase/frequency absolute referencing self-starting FC albeit over rather restricted dynamic range, governed by nature gain media that entangles group velocity dispersion at different bias points. Here, technological approach is conceived to achieve operation entire available bandwidth THz frequencies. The intracavity light intensity multistack QCL, inherently showing giant Kerr nonlinearity, altered increasing mirror losses its Fabry-Perot cavity through coating back facet an epitaxially-grown multilayer graphene film. This enables modulated proliferation emitted across more than 60% operational ?0.18 mW per mode optical power. QCL then experimentally characterized assess coherence, reconstructing emission profile, instantaneous frequency, electric field, thus proving metrological nature.