Non-Gaussian optical vortex in a degenerate resonator with an intra-cavity spiral phase plate

We propose a simple concept to generate non-Gaussian optical vortex beams using a near semi-spherical optical cavity with an intra-cavity spiral phase plate (SPP). Although the azimuthal symmetry breaking induced by SPP prevent Laguerre Gaussian mode to oscillate in the resonator, the beamlet retracing skewed V-shaped paths by the aid of beamlet coupling effect in the resonator are coherently phase-locked to form coherent optical vortex beam with wavefront dislocation mirroring the topological charge of the SPP. The circulating skewed V-shaped beamlet paths can be modeled by coupled mode equations taking into account linear coupling, laser gain and resonator loss. Experimental demonstrations using diode-pumped Nd:YAG solid state system emitted randomly polarized non-gaussian optical vortices of a positive unit topological charge at a central wavelength of 1064 nm when the pump power went above 1.52 W. Moreover This system also serves an useful platform to shape laser beams structurally, to study the laser dynamics and to combine radiations coherently.