We have developed a computer model calculating bare cavity transverse eigenmodes for super-gaussian unstable resonators, including aperture diffraction in the gain medium. This generalized simulation, based on the Fox and Li Power Method, reduces the input parameters to five: rod longitudinal position, cavity magnification, super-gaussian order of the output coupler reflectivity, and Fresnel numbers for the cavity and rod apertures. Using two-dimensional FFT's to discretize the Huygen-Fresnel numbers, the output fields at the plane of the rod aperture and exiting the output coupler were subjected to beam quality (M2) and extraction efficiency (Xeff) analysis. Beam quality was found to be the most sensitive to cavity magnification, with M2 values varying as much as 30% or more with 3% shifts in magnification, which can occur during rod lensing. Avoiding peaking M2 values is demonstrated with design curves for two different cavity Fresnel numbers, and super-gaussian orders. The cavity Fresnel number and the super-gaussian order are shown to only weakly affect beam quality, although extraction efficiency varies strongly with the latter. Finally, optimized rod longitudinal position was explored for promising combinations of the other four parameters, and it was found to be near the high reflector (HR) end of the cavity, in terms of M2 analysis.
We have modeled the passive Q-switch performance of divalent cobalt and its spectroscopic parameters in various host media for the Er:Yb:Glass laser that operates near 1.534 micrometers . Our method involves the use of rate equations that assume a three-level gain medium and a four-level absorber medium including excited-state absorption. Numerical integration techniques are used where analytical functions are unobtainable to describe the dynamics within the systems that we have examined. Input into the rate equations is obtained from experimental data that include Co2+ ion concentrations, cross-sections, and lifetimes obtained by time-resolved spectroscopy. The calculated laser output in terms of pulse energies and pulsewidths in ns is compared with experimental results based on different Co2+ absorber host matricies and different cavity designs.
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