Diffusion-cooled radio-frequency-excited CO2 lasers

The use of capacitive Radio-Frequency discharges for the excitation of thin diffusion cooled regions of gas has caused a remarkable breakthrough in the establishment of new CO2 laser sources. Indeed this technique allows specific power loadings more than one order of magnitude higher than those of conventional slow-flow lasers. At the same time it enables efficient laser operation in sealed or quasi-sealed conditions determining an enormous advantage of these sources over fast-flow ones.Advantages are also determined by the potentiality of pulsing this kind of discharge at high repetition rates, in the range 1-10 kHz. Triggered by these considerations a lot of R and D efforts have been made in this field during the laser decade, giving rise to rugged and extremely compact CO2 laser sources in the 100-2000 W power segment, useful in medical as well as in low-power industrial applications. To obtain this result several problems had to be faced such as the attainment of a uniform plasma excitation in large area discharges or the extraction of a good quality beam form non-conventional gain region formats. The solutions adopted so far are reviewed, hints on further developments are given.