A Parametric Study on the Effects of the Electrode Size on the Performance of a Small-Size RF-Excited Fast-Axial-Flow CO2 Laser

We construct and characterize a small-size fast-axial-flow RF-excited CO₂ laser. The laser, including a pair of 10 cm long electrodes symmetrically positioned around a quartz tube, is driven by an RF generator with the 1 kW maximum power at a frequency of 13.56 MHz. The output power and efficiency of the laser are experimentally measured under different structural and operational conditions, such as the discharge tube diameter, width and length of electrodes, as well as the input RF power. The width of the electrodes is changed in such a way that the ratio of the total width of electrodes to the perimeter of the discharge tube (the so-called geometric ratio) varies in the 0.3 – 0.6 range. The diameter of the discharge tube is also changed in the 20 – 30 mm range. The results show that, for every given discharge tube diameter, optimum performance of the laser is obtained for 0.4 and 0.5 values of the geometric ratio. Although, a maximum output power of 63.5 W can be obtain applying the 1 kW input power, using the 2.6 cm discharge tube diameter, 0.6 geometric ratio, and CO₂ :N₂ :He=1 : 3 : 5 gas mixture at the 90 mbar total pressure. However, an optimum laser efficiency of 7.2% is reached under this condition for the 57.5 W output power. Further, the highest total output power and output power per unit length of the electrodes are obtained for the 20 and 10 cm electrode lengths, respectively.