Experimental Detection Of Complex-vortex's Second Harmonic Generation

Optical Vortex,as a particular field phenomenon,has been widely used in various fields of imaging systems,optical information processing,communications,biological microscope operation and so on.A light beam carrying orbital angular momentum is a typical vortex-carried beam.They have attracted much attention because of their outstanding applications in quantum entanglement and optical tweezers.Optical vortex has taught us to think differently about light.Orbital angular momentum as important degree freedom of photon can be infinite in theory,so it can be used to create high-dimensional Hilbert space for transmit more information.Vortex beams play an important role in second order nonlinear frequency conversion,give rise to numerous fascinating phenomenon,and has became the highlights of research in recent years.In this work,we have studied the second harmonic generation of vortex beams,including a single LG beams and composite vortex beam in nonlinear optical crystal KTP and PPLN roundly.First,we have demonstrated topological charge conservation via theoretically studying the second harmonic generation of vortex beams and theoretical simulation results are obtained.The approach to the generation of a helically phased beam is to pass a plane wave beam through a spiral phase plate.Then the vortex beams are focused into the nonlinear optical crystal KTP to generate second harmonic light.A?/2 mode converter is used to transform between HG and LG modes,thereby,the topological charge conservation are demonstrated experimentally.In addition,the composite beams using two beams with different topological charge by Mach-Zehnder interferometer as fundamental pump light have been studied in the second harmonic generation process experimentally.We obtain the second harmonic light's vortex distribution,and demonstrate topological charge conservation via studying the second harmonic generation of composite vortex.In conclusion,we have proved the topological charge conservation of optical vortex in the second harmonic generation process theoretically and experimentally.It certainly does help in microscopic particle operation,the detection of near-infrared vortex and so on.