FIR lasers typically consist of a long (1–3 meters) waveguide filled with gaseous organic molecules, optically pumped or via HV discharge.
[1] It operates in crossed electric and magnetic fields at liquid helium temperatures.
Wavelength selection can be achieved by changing the applied electric/magnetic fields or through the introduction of intracavity elements.
It is a solid-state semiconductor laser that can operate continuously with output power of over 100 mW and wavelength of 9.5 μm.
[3] A molecular FIR laser optically pumped by a QCL has been demonstrated in 2016.