“…Active methods involve directly generating the LG modes inside the laser cavity by controlling the gain and loss of different modes to suppress the oscillation of the TEM 00 mode, so as to obtain the target LG 0m mode. Several active methods have been reported, including the use of annular pump light [13][14][15][16][17], spot-defect mirror [18,19], off-axis pumping [20,21], the introduction of naturally or thermally induced birefringence [22,23] and mode-selecting devices into the cavity [24,25]. Among these methods, annular pumping has been proven to be an effective way to generate LG 0m vortex beams since the annular pump beam has the optimal spatial overlap with LG 0m modes.…”