High-Order Vortex Generation From CW and Passively Q-Switched Pr:YLF Visible Lasers

We report on the high-order transverse-mode generation in a diode-pumped Pr:YLF visible laser operating at 639 nm. Using a two-mirror linear cavity and operating the laser in continuous-wave regime, tunable Hermite-Gaussian modes HG0,m have been directly generated with m varying from 0 up to 120 by off-axis pumping and misaligning the laser resonator. In the same way, but using a V-shaped cavity and adding a Co:ASL saturable absorber, high-order HG0,m modes were also generated in Q-switched regime with m varying up to 12. The achieved passively Q-switched laser has a pulse width of about 149 ns at a repetition rate of 91 kHz, which leads to a pulse energy of about 2.5 μJ and a pulse peak power of 16.9 W. In both cases, intracavity HG0,m modes were converted into the corresponding Laguerre-Gaussian modes LG0,m via a pair of cylindrical lenses placed outside the cavity and the helical nature of the wavefronts were checked by using a specially designed Fizeau interferometer. Such tunable and directly generated high-order laser transverse modes obtained in continuous-wave as well as in Q-switched regimes are well suited for various modern applications, such as optical manipulation and 3D material processing.