Use of polycrystalline Nd:YAG rods to achieve pure radially or azimuthally polarized beams from high-average-power lasers

We report maintenance of perfect radial-polarization purity in high-power, cw pump chambers using strengthened, polycrystalline Nd;YAG laser rods. Although the cubic symmetry of single-crystal rods caused threefold symmetric birefringence due to shear stresses at the ends of the pumped zone, polycrystalline rods macroscopically behaved as isotropic material and enabled polarization preservation. Elimination of this source of depolarization prevents the major source of bifocusing aberrations in a chain of amplifiers.