Two-Stage Radio Frequency Power Generator-Amplifier Design for a TEM00 CO2 Slab Waveguide Laser
This letter presents the results of the research conducted on the design, construction and test of a two stage ra- dio frequency power generator-amplifier directed adapted to an in-house-built compact CO2 waveguide laser. The main characteristic of this power supply lies in the fact its design is based on MOSFET technology for both the oscillator and the amplifier stages. RF output power is centered at 81MHz frequency signal between 100W to 150W. The two-stage sys- tem device has a minimum electric conversion efficiency of 64%. Consequently, the laser head and RF excitation design must have an electrical termination of 50� impedance and the whole system may include a proper matching circuit. The overall test, for the entire system: RF excitation along with our CO2 laser head, is made with a typical gas mixture of CO2- N2-He with proportion of 1:1:3 correspondingly and at a final pressure of 40Torr. Under these specific conditions, a maximum optical output power of 10.7W was obtained for an input feed RF power of 147W. Regarding the optical qual- ity we measured the transverse mode of propagation TEM00 which indicate the entire system work very near the diffrac- tion limit specifications for similar laser systems.
Recent trends in oscillator design
Two decades ago, oscillators were typically designed by starting with a topology named for its discoverer, such as Colpitts or Pierce, and then analytically or empirically modifying element values to achieve a desired result. Later, the application of linear CAE tools provided more options and opportunity. The use of nonlinear analysis, along with other recent advancements, has contributed to the maturity of the knowledge. However, misunderstanding still abounds. This article briefly reviews classic linear analysis techniques, extends this analysis to closed-loop concepts, reviews a recent contribution by Randall and Hock, and adds nonlinear analysis to develop a thorough but intuitive feel for the oscillation phenomena. Finally, the nature of oscillator startup is illustrated using a new oscillator topology.
On the longitudinal voltage distribution in radio-frequency-discharged CO/sub 2/ lasers with large-area electrodes
The reduction of the voltage variations along the electrodes of RF transversely excited CO/sub 2/ lasers is of fundamental importance for the attainment of a uniform active medium pumping and for the consequent efficient laser power extraction. This problem has been studied by many authors in the case of narrow-channel waveguide lasers and methods have been found to reduce the relevant voltage variation due to the transmission line effect determined by the discharge channel structure. In this paper, we demonstrate the crucial role played by the electrode sheath's capacitance in determining the voltage distributions in the case of large area electrodes. A theoretical model for the "plasma loaded" strip-line is presented together with numerical simulations showing the voltage distributions expected in slab-type lasers of the 1-kW class. We also report experimental results confirming the predictions of the model and the fundamental role played by the sheath's capacitance. >