Linear And Nonlinear Optical Manipulation Of A Laguerre-gaussian Beam In A Metasurface

"The surface wave" was originally proposed by A.Sommerfeld and others in 1899.When the light impringes a metal surface,the collective oscillation of the free electrons form a surface wave,which will propagates at the interface of metal and the air.Such surface wave is also called as surface plasmon polariton(SPP).With furtherstudies of the SPP's physical mechanism,people starts to apply it to other physical process,such as the extraordinary optical transmission(EOT)phenomenon.At the same time,due to the enhancement of local field,nonlinear optics in metal metasurface is becoming a research hotspot.The Laguerre-gaussian(LG)mode is one of the high-order modes of light.Such LG beams have strong applications in many fields,such as optical manipulation,optical trapping,and quantum information processing.In addition,light with high-order LG mode can increase the sensitivity of precision measurement because of its spatial intensity distributions.In this thesis,we use the metal metasurface to produce the high-order LG modes.Our results open a door to utilize the metallic nanostructure for the generation of spatial light beam in integrated optical devices.The detail results are listed as follows:1.We have determined the second-order susceptibility tensor of a metallic nanohole array by a forward second-harmonic scattering method.Because of the enhanced local field is vital to the nonlinear optical process,we design a sample with finite-different time-domain(FDTD)method to ensure plasmon-resonance(shape-resonance)happens at fundamental wave.Via theoretical simulation and experimental analysis,we get the accurate values for the second-order susceptibility components:?_xxx and ?_yyy.The study is very essential for engineering high-efficiency nonlinear nanophotonic devices based on metal metasurface.2.We study on the EOT process of an orbital angular momentum(OAM)state of light in the paraxial approximation.Firstly,we design a sample with FDTD method to ensure that EOT phenomenon happens at the specific wavelength.The mode of the transmission light is analyzed by using a Mach-Zehnder interferometer.We get the conclusion that the transmitted light well conserves the OAM information while the EOT happens.Further study shows that the OAM mode has no significant influence on the transmission spectrum of the EOT paraxial process under our experimental configuration.3.We have studied the plasmon-assisted second-harmonic generation of an OAM beam.We also utilize the shape resonance,The plasmons in a periodic array of rectangular metal holes can greatly enhance the nonlinear optical conversion of an OAM state.The OAM conservation(i.e.,2l1=l2 with l1 and l2 being the OAM numbers of the fundamental and second-harmonic waves,respectively)holds well in the metal metasurface with periodic structure.Our results provide a potential way to realize nonlinear optical manipulation of an OAM mode in a nano-photonic device.4.We experimentally demonstrate the generation of high-order LG modes with non-zero radial indices using a metal meta-surface.In the experiment,the metal metasurface is composed of a series of rectangular nanoholes with different orientation angles.We can know that the phase shift ? after transmission through the metasurface is determined by the orientation angle ? of the nanohole,i.e.?=±2?.We design and fabricate a high-order LG mode generator,which works over a broad wavelength band ranging from 700 nm to 1000 nm.Moreover,we achieve a LG mode with a radial mode index of 10.Our results provide an integrated method to obtain high-order LG modes,which can be used to enhance the capacity in optical communication.