Guiding effects in Nd : YVO4 microchip lasers operating well above threshold

Guiding of the transverse mode in Nd:YVO4 microchip lasers is examined both experimentally and theoretically at pump powers well above threshold. It i s found that thermal changes in the cavity geometry induced by intense diod e pumping can be well understood using a simple model. However, an understa nding of these effects is not sufficient to explain the nature of the trans verse mode. Gain-related guiding effects are found to play an important rol e even at pump powers well above threshold, For a 0.5-mm-thick microchip la ser, a difference of around 30% is observed between the minimum beam waist expected due to thermal guiding and the measured beam waist, The gain-relat ed effects are described theoretically and their importance is demonstrated experimentally.