Very-low-noise H2O laser with rf pumping

An rf (27.5 MHz) discharge was used for the first time to pump a cw H₂O laser emitting at λ = 118.6 μm. This made it possible to reduce the noise by more than two orders of magnitude compared with dc lasers. Optimisation of the active medium, by adding various gases (H₂, He, Xe), and of the type and geometry of the laser cavity, was carried out. The unsaturated gain, the saturation intensity of the active medium, and the internal cavity losses were measured. The maximum output power of a laser was 48 mW when the cavity was 2.5 m long. The noise\/signal ratio was less than 10^-4 in the frequency range 0.01– 40 kHz.