Linewidth-narrowing of a continuous wave terahertz polariton laser using an intracavity etalon

An uncoated etalon was incorporated within an intracavity continuous wave terahertz polariton laser, leading to a tenfold reduction in linewidth, plus a factor of 2 increase in the THz output power. The increase in output power is explained in terms of phase matching considerations for the parametric downconversion process.