Research On Vortical Chiroptical Response Of Chiral Structures By Femtosecond Laser Direct Writing And Their Applications

Chiroptical response refers to the unique optical phenomena caused by the interaction between chiral light and chiral medium.Common chiral waves can be divided into two categories:circularly polarized light,which carries spin angular momentum,and vortex beams,which carry orbital angular momentum.In the dimension of photonic spin angular momentum,significant circular dichroism response can be generated by the interaction of circular polarized light with artificial chiral structures,which is of great value in integrated optical device design and enantiomer sensing.In recent years,with the discovery of photonic orbital angular momentum,the unique chiroptical response caused by the interaction between vortex beams and artificial chiral structures has attracted extensive attention.However,the relevant researche is still in the initial stage,and how to induce,enhance and flexibly modulate the vortical chiroptical response using artificial chiral structures has become a key issue.In addition,practical optical applications based on the interaction between vortex beams and artificial chiral structures also remains to be explored.This dissertation mainly combines spatial light field modulation technology and femtosecond laser direct writing technology to study the helical dichroism chiroptical response in the dimension of photonic orbital angular momentum.The detailed content of the work is as follows:1.Research on the helical dichroism response induced by planar chiral structure.Based on femtosecond laser direct writing technique,planar chiral Archimedean helical structures are designed and fabricated.It has been proved theoretically and experimentally that significant helical dichroism signals(-20%)can be induced on a single planar chiral structure by the orbital angular momentum of vortex beam,and the chirality of the planar structure can be clearly distinguished by helical dichroism signals.The effects of planar chiral structures’ thickness,rotation symmetry and material properties on helical dichroism signals are quantitatively analyzed,which confirm the universality of orbital angular momentum for chiral optical sensing.2.Research on the helical dichroism response enhanced by three-dimensional copper microhelix structure.Based on the combination of femtosecond laser direct writing and electrochemical deposition,three-dimensional copper microhelices structures with high geometric accuracy and high purity are fabricated.It has been proved theoretically and experimentally that three-dimensional copper microhelices can enhance the helical dichroism signal(～50%),and the origin of helical dichroism is revealed by surface photocurrent model.In addition,the influence of parameters and temperature of helical dichroism spectra on copper microhelices structures is studied,which proves that copper microhelical structures can be used as chiral photonic devices with excellent thermal stability.3.Reaearch on the modulable helical dichroism response on rotating stacked structure.A strategy for flexibly modulating the helical dichroism response using the rotating stack structure is proposed,and the origin of helical dichroism on the structure is theoretically revealed through differential votical electric field transmission and discrete orbital angular momentum spectra.Based on femtosecond laser direct writing technology,it has been experimentally confirmed that rotating stacked structures with different configurations can show-97%～+98%of modulable helical dichroism signals.In addition,all the characteristics of helical dichroism spectrum(symbol,peak and peak position)can be modulated by engineering the geometric parameters and rotation symmetry of the rotating stacked structure.4.Optical encryption of orbital angular momentum based on chiral metahelices.Based on femtosecond laser direct writing technique,a stepped chiral metahelix structure is designed and fabricated.It has been proved theoretically and experimentally that the chiral metahelix can selectively transmit or block incident vortex beams with different orbital angular momentum modes,and its polarization and broadband performance are verified.Based on single-mode vortex array and single-chiral metahelical array,selective optical display and hiding in the orbital angular momentum dimensions are realized.Furthermore,the applications of optical encrypted communication in the orbital angular momentum dimension are demonstrated successfully based on encoded chiral metahelix array and encrypted vortex arrays.