An Orbital-Angular-Momentum- and Wavelength-Tunable 2 mu m Vortex Laser

In this paper, dual tuning of orbital angular momentum (OAM) and the wavelength of a Tm:YLF vortex laser was realized by off-axis pumping and F-P etalon. The tuning of Hermite-Gaussian (HG) modes by off-axis pumping was theoretically analyzed. In the experiment, the highest 17th order HG(17,0) mode was realized by off-axis pumping. The threshold power increased from 2 to 17.51 W with the increase in off-axis distance, and the curve of threshold power vs. off-axis distance was partially consistent with the theoretical simulation analysis. The Laguerre-Gaussian (LG) modes carrying OAM were produced by mode converter, and the beam quality of LG modes was good. The phase distribution of the LG modes was verified by interference. Subsequently, an F-P etalon was inserted into the resonant cavity to tune the wavelength. Finally, the OAM tuning of the vortex beam from LG(1,0)(OAM = -1(h)) to LG(16,0)(OAM = -16(h)) was realized, and the corresponding wavelength tuning range was from 1898-1943 nm to 1898-1937 nm.