The effect of the discharge frequency on the performance of RF excited CO2 waveguide lasers

Research interest in the Ar-Xe laser has been strengthened considerably because this laser now produces output powers at the level of Watts and is becoming the most promising light source in the wavelength region of a few microns. The lasing occurs on the IR transitions (1.73-3.51 ¿m) between the 5d-6d manifolds of atomic xenon. Our breakthrough in this type of laser came when our results obtained with the electron beam sustained technology showed the beneficial effect of operating at high gas densities. From these observations and the accompanying modeling, the idea was supported to consider the dissociative recombination of ArXe+ or Xe2 + molecular ions with electrons as the primary channel for filling the upper laser level. Apart from this recombination process by three body collisions the increased density leads to homogeneous line broadening which has also a favourable effect on the power and efficiency. However, a homogeneous inversion density requires a homogeneous discharge in a high-density gas. This is from a technical point of view a great challenge. For continuous operation the waveguide structure with RF excitation has shown so far the best prospects for maintaining a homogeneous discharge at high densities, say above 100 Torr. The RF discharges are characterized by thin positively charged layers (sheaths) near the electrodes. They play an important role in the stabilisation of the discharge. At increasing current density the discharge switches from ¿- to ¿-mode