Generation of Laguerre-Gaussian modes in Nd:YAG laser using diffractive optical pumping

A beam of pulsed laser radiation at the wavelength lambda = 0.532 mu m was diffracted at a circular diaphragm to produce a hollow-shape intensity distribution in the near field. This light distribution was used to pump an Nd:YAG laser, resulting in the formation of an inversion profile with a minimum at the laser resonator axis and enabling the suppression of the fundamental mode. Under this condition, the oscillation at lambda = 1.064 mu m of Laguerre-Gaussian modes LG(0m)) with low and high values of the azimuthal index m was produced in the gain-switching regime. By changing the geometry of the resonator, the size of its waist parameter was changed, enabling the selection of the mode with an index m that best overlaps with the inversion profile. Oscillation of LG(0m) modes with indices ranging from m = 1 to more than m = 200 was obtained. LG(0m) modes with m <= 50 were produced using the dependence of the waist parameter on the length of the resonator near the boundary of its stability region. A LG(0m) mode of the highest order, m approximate to 240 was obtained by building a miniature laser resonator and using a pair of diaphragms in order to form a sharper ring-shape pumping distribution. Applications of diffractive optical pumping and "hollow" LG(0m) laser beams are discussed.