Abstract
We demonstrated that orbital angular momentum (OAM) of light can be conserved in optical parametric amplification process. By means of a simple experiment setup, it is revealed that the OAM of the pump vortex beam transfers spontaneously and uncontrollably to the signal beam in optical parametric generator. In comparison, injection with a seed vortex beam with fixed topological charge (l(seed) = +/- 1 or +/- 2), the signal beam exhibiting the same vortex profile is obtained efficiently. In this way, the optical parametric amplification can be seen as a simple OAM possessor which allows us to produce high power vortex beam with determined topological charge. This work may open the way for generation of vortex beam with controllable OAM, which can be a powerful tool for material processing and super-resolution microscopy.