ABSTRACT
A passively Q-switched microchip laser consists of a gain medium and a saturable absorber in a short, plane-parallel Fabry–Perot cavity. As the gain medium is pumped it accumulates stored energy and emits photons. The high peak powers of passively Q-switched microchip lasers make it easy to perform nonlinear frequency generation, with or without amplification. Energy levels in ionic gain media are grouped into manifolds. Most diode-pumped systems that are referred to as “three-level” lasers have a lower laser level that is slightly above the ground level, typically within the same ground-state manifold. The rate-equation model can be derived as an approximation to the fundamental equations relating the electromagnetic field, the material polarization, and the quantum-state populations. The electrical field within the optical beam of a high-power laser can be large enough to damage optical components. This is particularly important in high-peak-intensity pulsed lasers such as passively Q-switched microchip lasers.
