Study On Two-dimensional Electromagnetically Induced Grating In Multi-level Atomic Medium

In recent years,some physical phenomena of the interaction between light field and atomic system,such as coherent population trapping,electromagnetically induced transparency,spontaneous emission coherence,have attracted extensive attention.Among them,the phenomenon of electromagnetically induced grating(EIG)based on electromagnetically induced transparency has become a research hotspot in recent years.When the propagation wave field in the electromagnetically induced transparency effect is replaced by a standing wave field with spatial modulation,the high transmission area and the absorption area can appear alternately,and the incident detection light will be diffracted and generate EIG after passing through the standing wave modulation area.EIG can regulate the grating constant,diffraction energy,and diffraction order of electromagnetic induction gratings,thereby achieving real-time modulation of probe light diffraction,overcoming many limitations of traditional gratings.Due to its many advantages,EIG has been applied in fields such as optical communication,quantum computing,optoelectronics,and optical information storage.In addition,the unique characteristics of the spiral wavefront structure and the determined orbital angular momentum of the vortex beam can also be cross combined with the electromagnetic induction grating to improve the diffraction efficiency of the probe light and explore new research schemes.The use of vortex beam controlled EIG can be helpful for research in fields such as optical micromanipulation,quantum secure communication,and remote sensing.The main work of this thesis is focused on the study of two-dimensional EIG effect in multi-level atomic media,and the specific contents are as follows:1.Three basic pictures used to describe the motion of quantum system with time are introduced.Under the semiclassical theory of the interaction between light and atom,the system interaction Hamiltonian,three basic approximations and slow-varying amplitude equations used for theoretical calculation,the probability amplitude method and the density matrix method used to describe the interaction between atom and light field are briefly described.The principle of electromagnetic induction grating is explained,and its essence is similar to Fraunhofer diffraction principle.The basic principle of vortex beam is explained,and some basic characteristics of Laguerre-Gaussian beam are described mathematically.This beam is a typical vortex beam often used in simulation and experiment.2.A theoretical research scheme for realizing two-dimensional electromagnetically induced grating in a four-level atomic system using microwave field is proposed.The metastable state of two dipole forbidden atoms in this atomic system is coupled by microwave field.The influence of microwave field on Fraunhofer diffraction pattern of weak detection field is analyzed.The effects of detuning of detection field,intensity of control field and interaction length on the diffraction efficiency of two-dimensional electromagnetic induction grating in the presence of microwave field are discussed.The results show that the two-dimensional electromagnetic induction grating with high diffraction efficiency can be realized in the studied system by properly adjusting the system parameters.3.A new theoretical scheme for two-dimensional(2D)electromagnetically induced grating(EIG)is proposed in a three-level (?)-type atomic system.The system is driven by a weak probe field and two position-dependent coupling fields-a 2D standing-wave field and a vortex field.Due to lopsided spatial modulation of the vortex Laguerre-Gaussian field,the weak probe light could be diffracted into different domains and asymmetric 2D EIG is formed.The result shows that the diffraction patterns and efficiency could be effectively modulated by the azimuthal parameter of the vortex field.Also,the system parameters such as the probe field detuning,the intensity of the vortex field,and the interaction length could be used to regulate the diffraction properties of the 2D EIG effectively.