Double-pulse injection seeding of a terahertz quantum cascade laser

Double-pulse injection seeding is used to modify the spectral emission of a terahertz quantum cascade laser (THz QCL). Two broad-band THz pulses delayed in time imprint a modulation on the single THz pulse spectrum. The resulting seed enables modification of the QCL emission spectrum, even though, the spectral bandwidth of each THz pulse is much broader than the QCL gain bandwidth. For a proper time delay between the pulses, the seeded THz QCL emission can even be switched from a multimode to a single mode regime.