RF Injection Locking of THz Metasurface Quantum-Cascade VECSEL

Radiofrequency (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.

Automated summary

This paper demonstrates the use of radiofrequency injection locking and spectral broadening in a terahertz quantum-cascade vertical-external-cavity surface-emitting laser. By injecting RF current modulation, the round-trip frequency can be pulled and locked. The lasing spectrum can be broadened from 14 GHz to a maximum of 110 GHz with injected RF power, opening up possibilities for active mode-locking and picosecond pulse generation in THz lasers.