Microchip lasers

Microchip lasers are made of a simple slice of solid-state laser material, coated on both sides, and pumped with a diode laser. This geometry forms a particularly simple laser cavity. The cavity, which is otherwise on the edge of stability, is made stable by thermal and gain-related effects, producing a high quality TEM₀₀ laser beam. The simplicity leads to ease of mass-manufacture and low cost. The short length encourages single-frequency operation, and the short cavity decay time can allow the generation of short pulses. The extension of these ideas to involve additional intracavity components has allowed the demonstration of “simple” lasers that operate in an actively or passively Q-switched mode, lasers that are frequency agile, and CW and pulsed lasers that are frequency shifted into the visible and other spectral ranges. One part of our work has been in investigating the cavity stability mechanisms of these lasers. These can be thermally-related involving a distributed thermal lens through dn/dT effects or involving thermal expansion of the pumped face, or they can be gain-related involving elements of gain guiding or changes in refractive index associated with the spatially dependent gain. Such effects are strongly dependent on the gain material used. Under certain conditions we have observed a form of self-Q-switching in Nd:YVO₄ microchip lasers, which our experiments and modelling suggest is associated with spatial variation of the gain and how this impacts on the guiding of different longitudinal modes