Modeling free-electron laser (FEL) oscillators requires calculation of both the light-beam interaction within the undulator and the light propagation outside the undulator. We have developed a paraxial optical propagation code that can be combined with various existing models of gain media, for example, Genesis 1.3 for FELs, to model oscillators with full paraxial wave propagation within the resonator. A flexible scripting interface is used both to describe the optical resonator and to control the codes for propagation and amplification. To illustrate its capabilities, we numerically investigate two significantly different FEL oscillators: the free-electron laser for infrared experiments (FELIX) system and the vacuum-ultraviolet (VUV)-FEL oscillator of the proposed high-gain fourth generation light source. For the FELIX system, we find that diffraction losses are a considerable part of the single-pass cavity loss (at a wavelength of 40 μm). We also demonstrate that a resonator with hole coupling may be a viable alternative to a standard resonator with transmissive optics for the high gain VUV-FEL oscillator.
An inverse class-F cross-coupled push-pull PA in a 0.5um SiGe technology is presented. It is shown that inverse class-F in combination with C BC compensation is preferred over class-F operation in terms of gain roll-off and efficiency as function of collector supply voltage. The active mixed-mode load-pull system is used to set up the proper output differential and common-mode impedances at the fundamental (870MHz) and harmonics to experimentally verify inverse class F operation with a measured PAE of 67% at 20dBm output power.Index Terms -active harmonic load pull, class F, inverse class-F, Mextram, power-added efficiency, push-pull power amplifier.
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