Construction of a scalable RF power supply for small CO2 waveguide lasers

Abstract

This paper presents the design, construction and test of a radio frequency self-oscillator-amplifier (SOA). The main goal is to develop a small reliable and non-expensive RF circuit generator capable to deliver up to 180W of RF power to sustain ionization in waveguide-like electrodes in CO2 laser amplifying media. The laser media amplifier (LMA) is a specific designed (or homemade) setup that can be coupled to our RF SOA circuit. The LMA was built as a simple inductive-capacitive (LC) component which has the capability to efficiently absorb above the 95% of the RF energy delivered by the SOA. RF energy between the SOA and the laser head is achieved by the use of a matching circuit (MC) in order to assess the LMA transient ionization stability. In this work we complete our study by adding a 5-pass (WI) optical resonator to have laser light output. The proposed circuit was designed to oscillate in a frequency within the range of 60MHz to 80MHz and a center frequency of 70MHz and its components were fine tuned to optimize its signal output power in the range from 120W to 180W (2–3 times the manufacturer output power specification at 70MHz). Before we interconnect the RF SOA into the laser head we test its performance by using a dummy load with 50W termination. The next step is to measure the complex impedance of our laser head. The LMA is a capacitive-like discharge that has several parallel-distributed inductors along the laser electrodes to create a steady and uniform plasma discharge. The complex impedance of our laser head is measured in two modes by using a Vector Impedance Analyzer (VIA) AEA-Via Echo 1000SF; in high vacuum and at the final gas mixture pressure. Once we know the complex impedance we input this value in the ADS software to find the best matching circuit (MC) between the SOA and the LMA. From this stage, we are able to perform an overall evaluation of the complete setup: SOA-MC-LMA. We proceed to test the ionization state of our laser performance using a typical gas mixture of CO2-N2-He with proportion of 1:1.2:3.7 correspondingly and at a final pressure of 70Torr a maximum optical output power better than 20W was obtained at a maximum RF feed power of 173W.