Q-switched, YAG laser
This is an example of a Q-switched YAG laser. The configuration is indicated below.

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This YAG laser has two roof prisms as end mirrors, an electro-optic Q-switch, and outcoupling into converging lens and circular aperture where energy-in-the bucket will serve as a simple measure of beam quality. (expand)

YAG configuration
Energy level diagram Modeling of the transient response of the Q-switched laser is based on the four-level modeL; ground state, lower level N1, upper level N2, and pump level. (expand)
Output power as a function of the number of round-trips of the optical pulse. Views of the instantaneous output will be shown at 5 and 15 round trips.(expand) Power vs. pass number
Instantaneous output after 5 round trips Instantaneous output of the Q-switch pulse early in pulse (after 5 round-trips) showing the speckeled nature of the beam.
Instantaneous output after 15 round trips, showing larger speckles indicating improved beam quality. Instantaneous output after 15 round trips
Beam quality vs. number of round trips The beam quality vs. number of passes through the resonator, as measured by the energy through the pinhole in the outcoupled beam. (expand)