CW theory of quasi-three level end-pumped laser oscillators

Equations describing the pump excitation and power extraction of end-pumped quasi-three level CW laser oscillators are derived which are useful in the optimization of such systems. The theory takes into account arbitrarily large ground state depletion due to intense pumping as well as gain saturation due to the extracting laser beam. The presented theory is more general than previously published works on the subject as it allows for the possibility of double passing the pump through the gain medium which in some instances can be an important technique for increasing system efficiency. To illustrate the utility of the derived equations, a diode end-pumped kilowatt class CW laser oscillator using Yb:YAG as the gain element is optimized and studied.