Threshold and slope efficiency of Nd 0.5La 0.5Al 3(BO 3) 4 ceramic random laser: effect of the pumped spot size

We have experimentally found that in a random laser based on Nd _0.5La _0.5Al ₃(BO ₃) ₄ scattering ceramic, the threshold pumping density decreases and the output slope efficiency increases with the increase of the diameter of the pumped spot. The experimental behavior is explained in terms of random photon's walk in an amplifying medium.