Generation of very-high order Laguerre-Gaussian modes in Yb:YAG ceramic laser

The use of a simple short-focus plano-convex glass lens with strong spherical aberration for Laguerre-Gaussian mode selection in a continuous wave (CW) LD-end-pumped Yb:YAG ceramic laser is demonstrated. Mode selection was obtained in a nearly meter long plane-parallel cavity by shifting an intra-cavity lens of 2.5 cm focal length along the resonator axis. Sequence of Laguerre-Gaussian (LGp,l) modes with different combinations of radial (p) and azimuthal (l) indices from low to high orders (p = 0 – 12, l = 0 – 28) with output beam diameters 2 – 13 mm and power up to 30 mW was produced. Along with many low order modes, the whole lineage of very high order pure ``hollow'' LGp,l modes (p = 5 – 10, l = 7 – 28) was produced by this method for the first time. The region of stability of the resonator with an intra-cavity aberrating lens was found to be enclosed between ``focusing'' and ``imaging'' configurations in the cavity, which the aberrating lens could provide simultaneously. The mechanism of LGp,l mode selection in such a cavity and possible applications of the proposed laser scheme are considered.