Generation and Stabilization of Continuous-Wave THz Emission From a Bi-Color VECSEL

We present a laser system for the generation and stabilization of continuous wave emission at 1.9 THz. The system is based on difference frequency generation (DFG) from a bi-color vertical external cavity surface emitting laser (VECSEL). The intracavity DFG process enables THz generation with milliwatt power level at room temperature with a clear quadratic dependence red on the intracavity power. The two colors are spectrally selected via an intracavity etalon while the laser cavity geometry is engineered to minimize mode competition between the two colors via spatial hole burning, improving the stability of the THz emission. The intensity noise of the THz output is further reduced by 16 dB/Hz with an active stabilization scheme. The origin of residual fluctuations is discussed and we found that the asymmetrical amplification of one color reduced the RIN even further, down to 21 dB/Hz, comparing to the free-running symmetrical lasing.