Field-resolved high-order sub- cycle nonlinearities in a terahertz semiconductor laser,
The exploitation of ultrafast electron dynamics in quantum cascade lasers (QCLs) holds enormous potential forintense, compact mode-locked terahertz (THz) sources, squeezed THz light, frequency mixers, and comb-basedmetrology systems. Yet the important sub-cycle dynamics have been notoriously difficult to access in operationalTHz QCLs. Here, we employ high-field THz pulses to perform the first ultr