Stabilizing a terahertz quantum-cascade laser using near-infrared optical excitation

We demonstrate a technique to simultaneously stabilize the frequency and output power of a terahertz quantum-cascade laser. The technique exploits frequency and power variations upon near-infrared excitation and does not require an external terahertz optical modulator. By locking the frequency to a molecular absorption line, we obtain a linewidth of about 260 kHz and root-mean-square power fluctuations as low as 0.03%.