Guiding effects in Nd:YVO/sub 4/ microchip lasers operating well above threshold

Guiding of the transverse mode in Nd:YVO/sub 4/ microchip lasers is examined both experimentally and theoretically at pump powers well above threshold. It is found that thermal changes in the cavity geometry induced by intense diode pumping can be well understood using a simple model. However, an understanding of these effects is not sufficient to explain the nature of the transverse mode. Gain-related guiding effects are found to play an important role even at pump powers well above threshold. For a 0.5-mm-thick microchip laser, a difference of around 30% is observed between the minimum beam waist expected due to thermal guiding and the measured beam waist. The gain-related effects are described theoretically and their importance is demonstrated experimentally.