RF Injection Locking of THz Metasurface Quantum‐Cascade VECSEL

Abstract

AbstractRadiofrequency (RF) injection locking and spectral broadening of a terahertz (THz) quantum‐cascade vertical‐external‐cavity surface‐emitting laser (QC‐VECSEL) is demonstrated. An intracryostat VECSEL focusing cavity design is used to enable continuous‐wave lasing with a cavity length over 30 mm, which corresponds to a round‐trip frequency near 5 GHz. Strong RF current modulation is injected to the QC‐metasurface electrical bias to pull and lock the round‐trip frequency. The injection locking range at various RF injection powers is recorded and compared with the injection locking theory. Moreover, the lasing spectrum broadens from 14 GHz in free‐running mode to a maximum spectral width around 110 GHz with 20 dBm of injected RF power. This experimental setup is suitable for further exploration of active mode‐locking and picosecond pulse generation in THz QC‐VECSELs.