Nonlinear propagation effects on high-power optical-vortex pulses in anisotropic crystals

Having a helical wavefront, a Laguerre-Gaussian (LG) mode or optical vortex is one of the modes of paraxial solutions to wave equation. The optical vortex has unique properties. The beam has a phase singularity on its center, which shows a dark part on its center of intensity profile, and carries an orbital angular momentum of light well defined by the topological charge ℓ [1]. These characteristics recently attracted much attention. For more versatile applications, high power optical-vortex pulses are desired. Typically, optical vortices are generated by using a spiral plate [2], a spatial light modulator (SLM) [3], a photonic-crystal axially-symmetric polarizer/waveplate [4] or a uniaxial crystal [5]. Among them, the most flexible method is by SLM. However, this method using SLM is power-limited owing to its damage threshold. Hence, as an alternative to generate high power optical-vortex pulses, we choose the method using a uniaxial crystal, which is rather flexible. In this scheme, the nonlinear effects have not been clarified in detail. In the present paper, we investigate nonlinear effects on optical-vortex pulse generation through the spin-orbit interaction and its propagation in an anisotropic crystal.