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.
rPET detectors design and data processing
Small animal PET systems based on rotating planar detectors posses some interesting advantages for high sensitivity, high resolution imaging. We have designed the rPET detectors based on MLS crystals assembled on a 30times30 matrix optically coupled to a flat-panel PS-PMT. Weighted position readout circuits pre-process the 64 signals from the 8times8 anodes matrix, which are digitized using a charge-integrating converter. The amplification electronics, including the trigger output for coincidence detection, and the high voltage supply are integrated in a three PCBs stack that forms the base attached to the back of the PMT. The whole assembly is enclosed in a light tight, lead (Pb) shielded aluminum box. The detectors are mounted on a rotating gantry with more than 180 degrees rotation span. The digitized events are screened and histogramed, and a modified center of gravity algorithm removes from the position calculation those signals with poor signal to noise ratio. Apparent mean crystal size on the 511 keV field-flood images is 0.6 mm, mean peak-to-valley ratio is better than 8, and intrinsic resolution is 1.5 mm at the central row, with the energy window wide open. Sensitivity (CPS) for a pair of these detectors set in coincidence at 160 mm distance is 1%