Parametric Amplification Of Orbital Angular Momentum Beams Based On Light-acoustic Interaction

Orbital angular momentum(OAM)of light can be regarded as a degree of freedom of photons,which has attracted people's attentions and become an international hotspot in the fields of classical and quantum optics,because of it has the special mechanical effects and can be built a complete infinite Hilbert dimension.In recent years,significant achievements have achieved in the applications based on the OAM of light,especially in the fields such as particle manipulation,space optical communication,microscopic imaging and quantum information.However,energy gap in the level of generation and transmission have mainly restrained the application of OAM beams.Therefore,we utilize the technique of light-acoustic parametric amplification(LAPA)based on stimulated Brillourin scattering to amplify the OAM signals,and have analyzed the amplification mechanisms of OAM beams in theory and experiment.Firstly,starting from the concept of OAM,we analyzed the method of generating OAM beam,and derived the principle of OAM generation by spiral phase plate.The parametric amplification of OAM based light-acoustic interaction was also deduced.Secondly,the acoustic fields generated by pump and signals with different Laguerre-Gaussian modes based on the theory model of LAPA have been simulated using MATLAB,and the OAM conservation relations among the pump field,signal field and acoustic field was verified.In order to obtain detailed information including the intensity and phase distributions about the output signals,the finite element method is applied in simulation of signals.The simulation results show that the modes of output signal is independence of pump modes.Finally,the experimental setup of collinear and noncollinear LAPA frames are built,which have verified the OAM conservation relations among the pump field,signal field and acoustic field before and after amplification,respectively.Moreover,the intensity,phase structure of amplified signals and energy conversion efficiency of photon-phonon coupling are investigated.In the collinear frame,the conversion efficiency will exceed 40% when the energy of pump field is Ep>4m J and the topological charge is 1,which demonstrate that lower noise and higher amplification of OAM beam will be realized by LAPA technique,and the phase and structure distribution of output signals have few relations with pump field.In addition,considering the effect of noise on amplification of weak signal in the collinear frame,employing the noncolliner frame will realize amplification of weak OAM signals with lower noise.The incident angle has few influences on the amplified OAM when the noncolliner angle q is less than 10 mrad.The signal amplification factor(SAF)is about 109 for weak OAM modes in the noncolliner frame for the angle q of 10 mrad.Therefore,the noncolliner frame is more advantageous to amplify and extract the weak OAM signals.