Research On Electromagnetic Induction Grating In The Coupling System Of Coherent Light And Multi-level Atom

In the process of atomic-light interaction,people found a kind of atomic coherent(quantum interference)effect.At the same time,it is also found that the effect can generate many novel physical phenomena.Therefore,it has attracted great attention from researchers and become one of the most popular research topic in the field of quantum optics in recent years.The absorption coefficient and the refractive index of the media can be changed by interacted with a strong field,and then the phenomenon of electromagnetically induced transparency can be produced.Based on the theory,the absorption and dispersion of media for probe light will change periodically when the atomic media is driven by a standing-wave field.Thus,there is a grating structure forming in the media,which makes the transmitted probe light being diffracted.It is the phenomenon of electromagnetically induced grating.In this paper,the EIG and its induced modulation in a five-level and double ?-type mixed atomic system is investigated emphatically based on the EIT.The main contents are as follows:1.We theoretically propose a scheme for two-dimensional electromagnetically induced grating in a five-level atomic system interacting with two orthogonal standing-wave fields.In such atomic system,nonlinear absorption or refractivity can be significantly enhanced with nearly vanishing linear absorption under different resonant conditions.When applying two coupling fields with standing-wave pattern,absorption grating or phase grating,which efficiently diffracts a probe beam into high-order directions,can be formed in the media.The diffraction efficiencies of the gratings depend strongly on the interaction length,the intensities and detunings of the coupling fields.By investigating the third-order nonlinearity of the system,it is found that the amplitude and phase variations arise from the nonlinear modulation.2.we demonstrate the modulation for a coherently induced grating in a scheme based on a mixture of two three-level atomic species.In this system interacting with two standing-wave fields,as a result of interference between the absorptive and amplified Raman resonances,the refractive index of the media can be enhanced and modulated periodically.And then a sinusoidal grating,which can diffract the probe field into high-order directions,is coherently formed in the media.The proposal is simulated in a mixture of atomic isotopes of rubidium.It is shown that the diffraction efficiency depends strongly on the two two-photon detunings of the two Raman transitions and the intensities of the two driving standing-wave fields.3.The saw-toothed coupling fields,obtained by applying an amplitude mask,interact with the mixture of two A-type atomic species to achieve electromagnetically induced blazed grating.An incident weak probe beam can be diffracted through the media and most of the energy is deflected into the first-order direction due to the modulo-2? phase modulation by modulating Rabi frequency of two coupling fields.It can be achieved that the diffraction efficiency of induced blazed grating is much higher than 100%by modulating two-photon detunings.When an amplitude mask with symmetric form is introduced,a probe light can be split in two beams with equal intensity.Hence,the proposed system may be more suitable to be developed as all-optical beam splitting and fanning if more sophisticated masks are applied.4.Electromagnetically induced grating of different types are realized in atomic medium by adding the spatially varying coupling fields.At the same time,the diffraction efficiency of the grating can be improved via modulating the relevant parameters.The research has potential development prospects in all-optical network and communications.