Coherent transfer of optical vortices via three-wave mixing in an Er ³⁺ -doped YAG crystal

We investigate the effect of Er 3+ ion concentration on the transfer of orbital angular momentum (OAM) in an Er 3+ -doped yttrium aluminum garnet (YAG) crystal with a three-level ladder-type configuration, mediated by the optical nonlinear process of threewave mixing (TWM). The OAM information from the incident vortex probe field can be transferred to the generated mixing field through the optical nonlinear process. Due to the change of electric dipole moment and spontaneous emission decay induced by Er 3+ ion concentration, the OAM transfer depends sensitively on the ion concentration. Furthermore, under different Er 3+ ion concentrations, the intensity and detuning of the control field have different effects on the conversion efficiency of OAM. More importantly, the conversion efficiency of OAM can be significantly enhanced by choosing suitable values of the control intensity and detuning at 3% Er 3+ ion concentration. Finally, we explore the effect of Er 3+ ion concentration on the spatial distribution of the probe absorption. Moreover, the spatial absorption of the probe field is shown to evolve with propagation distance within the medium. It is obvious that the spatial pattern of the probe absorption can be effectively controlled via adjusting the detuning of the probe field. Therefore, our scheme enables efficient OAM transfer via second-order nonlinear three-wave mixing in an Er 3+ -doped YAG crystal by selecting suitable Er 3+ ion concentration, and may find potential applications in nonlinear quantum optics.