Orbital angular momentum exchange in a picosecond optical parametric oscillator.

We report on the orbital angular momentum (OAM) exchange among the interacting beams in an ultrafast optical parametric oscillator (OPO). The singly-resonant OPO is synchronously pumped by a picosecond vortex beam from a frequency-doubled Yb-fiber laser at 532 nm in the green. We demonstrate successful transfer of the pump OAM mode to the non-resonant idler beam tunable across 1109-1209 nm, with OAM as high as l _p =3. Controlling the cavity loss and spatial overlap between the resonant signal and the pump beam in the nonlinear crystal, we have generated signal and idler OAM mode combinations, (l _s ,l _i ) of (0,2) and (1,1), and (0,3) and (1,2) for pump OAM mode l _p =2 and 3, respectively. Using a pump power of 1 W, we have generated idler OAM mode of orders, l _i =1, 2, and 3, with maximum output powers of 202, 113, and 57 mW, respectively. To the best of our knowledge, this is the first report on controlled generation of OAM modes from an ultrafast OPO.