Selective generation of Laguerre-Gaussian (LG0n) mode output in a diode-laser pumped Nd:YAG laser

Direct excitation of an arbitrary Laguerre-Gaussian (LG0n) doughnut mode in an end-pumped solid-state laser using a fiber-based pump beam conditioning scheme to produce a ring-shaped inversion distribution is reported. An analytical expression for the dependence of threshold pump power for a particular LG0n mode on the spatial overlap with the pump beam is derived and shows that the desired LG0n mode can be selectively excited through simple adjustment of the pump beam dimensions. This approach has been applied to a diode-laser pumped Nd:YAG laser to achieve selective lasing on the LG01, LG02 or LG03 mode. Predicted values for threshold pump power and beam propagation factor (M2) are in good agreement with measured values. The prospects for further improvement in laser performance will be discussed.