Atomic Grating Research Articles

Optimization of Bragg scattering from atomic gratings for echo interferometry

Optimization of Bragg scattering from atomic gratings for echo interferometry

Long-range dipole-dipole exchange-induced atomic grating.

We propose a theoretical scheme for dipole exchange-induced grating (DEIG) based on a hybrid coherent atomic system. The system consists of an ultra-cold rubidium (87Rb) atomic ensemble and movable Rydberg spin atoms. The optical response of the grating appears as a superposition of three- and four-level configurations, which is similar to the cooperative optical nonlinearity caused by the dipole blockade effect. The far-field diffraction properties of the cooperative optical nonlinear grating are tuned by the probe field (intensity and photon statistics). However, our Rydberg atomic grating uniquely responds to the spatial positions of spin atoms, which offers a novel approach to dynamically control electromagnetically induced gratings (EIG).

Influence of phase diffusion on atomic grating in a three-level ladder-type system in lower-level microwave-driven scheme

In this paper, we consider a scheme for electromagnetically induced grating (EIG) in a three-level ladder-type system. A microwave field of finite bandwidth making a standing-wave pattern is applied on lower levels. In addition, we have also introduced an indirect pump in our system. A weak probe field is then applied to study the effects of phase diffusion associated with the microwave control field on EIG. It is found that phase diffusion associated with the strong microwave control field strongly affect the diffraction. We have incorporated the effect of different system parameters such as the strength of the microwave field, indirect pumping mechanism, interaction length, and detuning in the weak probe field. Interestingly, the stronger microwave control field retrieves the loss in diffraction intensity caused by the phase diffusion. Our results show that the introduction of detuning in the optical probe field results in the enhancement of the phase grating effect. Furthermore, our results show that an optimized indirect pump field can slightly improve the first-order diffraction intensities both in the absence and presence of phase diffusion.

Effect of composite vortex beam on a two-dimensional gain assisted atomic grating

We propose an atomic grating based on an electromagnetically induced transparency phenomenon that switches between zeroth-order diffraction to a distinct higher-order diffraction pattern by driving a planar gaseous medium of a four-level tripod () atoms with three laser beams: modulation of standing wave control beam propagating nearly perpendicular to the planar medium, while vortex and weak plane probe beams directed perpendicular to the medium. We numerically investigate the behavior of the amplitude, phase modulations, and probe field diffraction intensities of different orders by the variation of the field detunings and orbital angular momentum number of the composite vortex light beam. Specifically, in the off-resonant case, the interplay between a square lattice of the control and an additional spatial variation of the vortex beam allows the emergence of higher diffraction orders and variable gain due to double transparency windows in this complex optical system. We believe that our proposed scheme might be useful in optical memory devices via the storage of information to diffraction orders of the atomic grating.

Phase and amplitude control of atomic grating in a three level closed lambda System

We have theoretically studied the electromagnetically induced grating (EIG) in a three-level closed Λ-type atomic system. The upper level is coupled to the two lower levels via a strong control and a weak probe field. In addition to these two optical fields a weak microwave field is also applied to couple the lower two levels. Our results show that the relative phase of the three fields in the presence of microwave field enhances the dispersion in the medium and consequently provides control over magnitude of the diffraction intensities. We have optimized the system parameters such as strength of the fields and interaction length to attain increased first order diffraction. Furthermore, we have also studied the effects of probe detuning on diffraction intensities. Interestingly, the probe detuning results in suppression of the zeroth order intensity while increasing the higher order intensities.

Effects of finite bandwidth on atomic grating in a three level ladder type system

In this paper, we study the atomic grating produced by a three-level ladder type system which interacts with a strong standing microwave drive field of finite bandwidth. The upper levels of the atoms are coupled by the drive field while the probe field is applied on the lower two levels. We find that in the presence of phase fluctuations associated with the microwave drive field, the diffraction intensities are significantly affected. Our results show that if the probe and microwave drive are on resonance with their respective atomic transitions, then the diffraction intensities can be improved by properly adjusting the strength of the drive field. However, if the probe field is detuned from the resonance, then the diffraction intensities can be improved by appropriately selecting the strength of the drive field, probe detuning and interaction length of the medium. Interestingly, our results also show that the effects of phase grating can also be enhanced by a pertinent choice of various parameters even in the presence of phase diffusion. This results in the suppression of the zeroth order intensity while the first order intensity is increased.

Tunable double electromagnetically induced grating with an incoherent pump field

We introduce here double electromagnetically induced grating (DEIG) using a tripod atomic structure, wherein two probe and signal fields with different frequencies simultaneously experience an atomic grating. Properties of presented DEIG can be substantially modified by the detuning of the applied fields. It has also been found that applying an incoherent pump field has a remarkable influence on the high-order diffraction efficiencies. Amplification of travelling weak lights via the incoherent pump field results in large diffraction efficiencies in the first-order and second-order directions. Such a novel scheme might open up the possibility for designing a two-qubit switch that would be advantageous to quantum information processing and quantum networking.

Perfectly asymmetric Raman-Nath diffraction in disordered atomic gratings.

We investigate the effects of geometrical and structural disorders on perfectly asymmetric diffraction (PAD) in Raman-Nath regime. The two types of disorders are realized by introducing random fluctuations in the position and width of one-dimensional (1D) driven atomic lattices. Raman-Nath diffraction is modified differently with respect to the geometrical and structural disorders. It is shown that the PAD is observed with a certain strength range of geometrical disorder, exceeding which it can be destroyed, while the PAD is rather robust against structural disorder. The different behaviors originate from the disorder-induced random variations of the spatial phase shifts of the standing-wave (SW) coupling field and atomic lattices with Gaussian profile. Furthermore, we find that, in the presence of geometrical disorder, the PAD is more susceptible to correlated disorder than to uncorrelated disorder. Our scheme may be useful for understanding the effects of disorder on the diffraction of light and matter waves in disordered potentials..

A Phase Switch for Electromagnetically Induced Gratings in a Medium with Λ Atoms

We have theoretically studied the possibility of using the phenomenon of phase switching of coherent population trapping for creating a switch of light propagation direction in electromagnetically induced gratings in a medium with Λ-atoms. The permissible region of this effect application is determined and the parameters are found which ensure the obtaining of a high-efficiency scheme of the spatial redistribution of probing field intensity on atomic density gratings.

Lop-sided Raman-Nath diffraction in PT-antisymmetric atomic lattices.

Two-dimensional (2D) optical lattices of driven cold atoms can provide a useful platform to construct 2D electromagnetically induced grating (EIG) with parity-time (PT) antisymmetry. This atomic grating is achieved by the spatial modulations of the atomic density and frequency detunings in the four-level double-Λ atomic system. Gain-assisted PT antisymmetry allows us to realize lop-sided Raman-Nath diffraction with high diffraction efficiency at the exception point. It is shown that the nontrivial phenomenon originates from non-Hermitian degeneracy of PT antisymmetry. Our scheme may provide the possibility for active all-optical control and conversion of the spatial beam in optics.

One- and two-dimensional Raman-induced diffraction gratings in atomic media

We propose and analyze an efficient scheme for the one- and two-dimensional atomic gratings based on periodic spatial modulation of the Raman gain and dispersion, which we name the Raman-induced diffraction gratings (RIDGs). There are fundamentally different from those based on electromagnetically induced transparency. As the probe field propagates along the direction normal to the standing pump wave, it can be effectively diffracted into high-order directions. The grating is a hybrid grating, i.e. it represents a mixture of amplitude and phase gratings. We identify the conditions when all high-order diffractions are amplified. In addition, we also show that diffraction of a probe field could be dynamically controlled using an additional laser field. With its help, it is possible to suppress or amplify diffraction beams. The RIDGs can be considered as all-optical multibeam splitters with amplification.

Asymmetric diffraction by atomic gratings with optical PT symmetry in the Raman-Nath regime

We propose and analyze an efficient scheme for the lopsided Raman-Nath diffraction of one-dimensional ($1\mathrm{D}$) and two-dimensional ($2\mathrm{D}$) atomic gratings with periodic parity-time ($\mathcal{PT}$)-symmetric refractive index. The atomic grating is constructed by the cold-atomic vapor with two isotopes of rubidium, which is driven by weak probe field and space-dependent control field. Using experimentally achievable parameters, we identify the conditions under which $\mathcal{PT}$-symmetric refractive index allows us to observe the lopsided Raman-Nath diffraction phenomenon and improve the diffraction efficiencies beyond what is achievable in a conventional atomic grating. The nontrivial atomic grating is a superposition of an amplitude grating and a phase grating. It is found that the lopsided Raman-Nath diffraction at the exceptional point (EP) of $\mathcal{PT}$-symmetric grating originates from constructive and destructive interferences between the amplitude and phase gratings. Furthermore, we show that the $\mathcal{PT}$-phase transition from unbroken to broken $\mathcal{PT}$-symmetric regimes can modify the asymmetric distribution of the diffraction spectrum and that the diffraction efficiencies in the non-negative diffraction orders can be significantly enhanced when the atomic grating is pushed into a broken $\mathcal{PT}$-symmetric phase. In addition, we also analyze the influence of the grating thickness on the diffraction spectrum. Our scheme may provide the possibility to design a gain-beam splitter with tunable splitting ratio and other optical components in integrated optics.

Active control of bright electron beams with RF optics for femtosecond microscopy.

A frontier challenge in implementing femtosecond electron microscopy is to gain precise optical control of intense beams to mitigate collective space charge effects for significantly improving the throughput. Here, we explore the flexible uses of an RF cavity as a longitudinal lens in a high-intensity beam column for condensing the electron beams both temporally and spectrally, relevant to the design of ultrafast electron microscopy. Through the introduction of a novel atomic grating approach for characterization of electron bunch phase space and control optics, we elucidate the principles for predicting and controlling the phase space dynamics to reach optimal compressions at various electron densities and generating conditions. We provide strategies to identify high-brightness modes, achieving ∼100 fs and ∼1 eV resolutions with 106 electrons per bunch, and establish the scaling of performance for different bunch charges. These results benchmark the sensitivity and resolution from the fundamental beam brightness perspective and also validate the adaptive optics concept to enable delicate control of the density-dependent phase space structures to optimize the performance, including delivering ultrashort, monochromatic, high-dose, or coherent electron bunches.

Effect of partial coherence on diffraction intensity of a Gaussian Schell-model beam using two-level atomic grating

The role of spatial coherence on diffraction intensity is investigated for a partially coherent incident Gaussian Schell-model beam which is diffracted from a two-level atomic grating. It is shown that the performance of the atomic grating is greatly influenced by the spectral coherence width of the partially coherent fields. It is observed that relatively large intensity of the diffracted light can be obtained via spatial coherence, beam width, interaction length, and mode index of partially coherent incident light. The scheme provides possibilities for the potential applications of atomic grating in lensless imaging using the partially coherent light field.

Theoretical study of atom collision by two-nondegenerate four-wave mixing

In recent years, the collisional redistribution of radiation and collision-induced broadening of Rydberg atomic spectral lines by buffer gas perturbation have aroused the renewed interest. Rydberg atoms having a large dipole moment and long lifetime can interact with each other coherently for relatively long time, which makes them a potential candidate for quantum information processing. Besides, collisional redistribution has an important potential application in laser cooling and trapping. Based on previous experimental data, in this paper, two-nondegenerate four-wave mixing (NFWM) for studying atom collision, composed of two-photon resonant NFWM and collisional redistribution NFWM, is reported. The spectrum variation of the two-NFWM affected by the pressure, temperature, detuning and collision-broadening rate coefficient is analyzed. The principle of two-NFWM involving three incident beams is explained as follows. Consider two-NFWM in a |0-|1-|2 cascade three-level system, where states between |0 and |1 and between |1 and |2 ightangle are coupled by resonant frequencies 1 and 2 , respectively. Beam 1 with frequency 1 propagates along the direction opposite to the direction of beam 2, beams 2 and 2' have the same frequency 2, and between their directions there exists a small angle. Assuming that 1 1 and 2 2 so that 1 drives the transition from |0 to |1 while 2 drives the transition from |1 to |2, the simultaneous interactions of atoms with beams 1 and 2 will induce atomic coherence between |0 and |2 through two-photon excitation. This coherence is probed by beam 2', and as a result a two-photon resonant NFWM signal of frequency 1 is generated in the direction almost opposite to the direction of beam 2'. To avoid strong absorption at the resonant frequency of transition from |0 to |1, here the wavelength of beam1 is detuned from the exact resonance. An atom population of level |1 caused by collisional redistribution can be induced when a certain buffer gas pressure is imposed. The collisional redistribution NFWM process also exists in this case. Beam 2 drives the transition from |1 to |2 to induce an atomic coherence which is probed by beam 2' for giving rise to an atomic population grating. A collisional redistribution NFWM signal propagating along the same direction as the two-photon resonant NFWM signal is generated when beam 1 is scattered by the grating. Much information about atomic collisions can be obtained by analyzing the two NFWM signals. In a cascade three-level system composed of ground state, intermediate state and Rydberg state, and the two-NFWM can be used to investigate not only the broadening and shifting of the Rydberg level but also the collisional redistribution of the intermediate state. Unlike other experiments studying the pressure dependence of the longitudinal relaxation rate of atom states, this technique is a purely optical coherent means, and can measure the transverse relaxation rate 20 between Rydberg state and ground state as well as the pressure dependence of the transverse relaxation rate 21 between Rydberg state and intermediate state.

Tunable high-order photonic band gaps of ultraviolet light in cold atoms

We study a five-level $\text{quasi}\ensuremath{-}\ensuremath{\Lambda}$ system of cold atoms for achieving high-order photonic band gaps (PBGs) probed by an ultraviolet field in two cases where either an infrared or a visible control field works in the standing-wave configuration to induce one atomic grating. Transfer-matrix calculations for appropriate rubidium levels demonstrate that three fifth-order band gaps or two second-order band gaps can be generated near the probe resonance when the standing-wave control field is modulated to satisfy relevant Bragg conditions in the regime of electromagnetically induced transparency. These high-order PBGs, as characterized by homogeneous high reflectivities, can be dynamically tuned in positions and widths on demand and may be extended to develop efficient devices (like diodes and reflectors) for manipulating weak high-frequency light with strong low-frequency light.

Chromium Atomic Deposits under the Disturbance of Straight Edge Diffraction

The ideal Gaussian standing wave field model and the Gaussian standing wave field model under the condition of straight edge diffraction disturbance were established, and computer simulation and numerical analysis were done to the two kinds of models. It is concluded that the center position of Chromium atomic sedimentary grating in the straight edge diffraction disturbance standing wave will be away from the diffraction edge; near the given ideal deposit position, the PTVH(Peak to Valley Height) of Chromium atomic sedimentary grating in the ideal standing wave is higher than that in the straight edge diffraction disturbance standing wave, and the FWHM(Full Width at Half Maximum) is also narrower than in the ideal standing wave; for the exist of straight edge diffraction the size of the acceptable sedimentary pattern will be smaller, which has theoretical guidance on the practical operation.

Electromagnetically induced grating with maximal atomic coherence

We describe theoretically an atomic diffraction grating that combines an electromagnetically induced grating with a coherence grating in a double-$\ensuremath{\Lambda}$ atomic system. With the atom in a condition of maximal coherence between its lower levels, the combined gratings simultaneously diffract both the incident probe beam as well as the signal beam generated through four-wave mixing. A special feature of the atomic grating is that it will diffract any beam resonantly tuned to any excited state of the atom accessible by a dipole transition from its ground state.

Gain-phase grating based on spatial modulation of active Raman gain in cold atoms

In order to obtain an atomic grating which can diffract light into the high-order directions more efficiently, a gain-phase grating (GPG) based on the spatial modulation of active Raman gain is theoretically presented. This grating is induced by a pump field and a standing wave in ultracold atoms, and it not only diffracts a weak probe field propagating along a direction normal to the standing wave into the high-order directions, but also amplifies the amplitude of the zero-order diffraction. In contrast with electromagnetically induced grating or electromagnetically induced phase grating, the GPG has larger diffraction efficiencies in the high-order directions. Hence it is more suitable to be utilized as an all-optical router in optical networking and communication.

Four-Wave Mixing Dipole Soliton in Laser-Induced Atomic Gratings

We demonstrate a novel type of stable multicomponent vector solitons consisting of two perpendicular four-wave mixing (FWM) dipole components induced by electromagnetically induced gratings. We analyze the formation and steering of the steady dipole solitons and their dynamical (energy transfer) effects. The dipole-mode solitons of two FWM processes have horizontal and vertical orientations, respectively. Omnidirectional Bragg reflections are also investigated.