We theoretically explore an all-optical method for generating tunable diffractive Fresnel lenses in coherent media based on electromagnetically induced transparency. In this method, intensity-modulated images in coupling light fields can pattern the coherent media to induce the desired modulo-2π quadratic phase profiles for the lenses to diffract probe light fields. We characterize the focusing and imaging properties of the induced lenses. In particular, we show that the images in coupling fields can flexibly control the images in probe fields by diffraction, where large focal length tunability from 1 m to infinity and high output (∼ 88% diffraction efficiency) can be achieved. Additionally, we also find that the induced Fresnel lenses can be rapidly modulated with megahertz refresh rates using image-bearing square pulse trains in coupling fields. Our proposed lenses may find a wide range of applications for multimode all-optical signal processing in both the classical and quantum regimes.
We theoretically explore an all-optical method for generating tunable diffractive Fresnel lenses in coherent media based on electromagnetically induced transparency. In this method, intensity-modulated images in coupling light fields can pattern the coherent media to induce the desired modulo-2π quadratic phase profiles for the lenses to diffract probe light fields. We characterize the focusing and imaging properties of the induced lenses. In particular, we show that the images in coupling fields can flexibly control the images in probe fields by diffraction, where large focal length tunability from 1 m to infinity and high output (∼ 88% diffraction efficiency) can be achieved. Additionally, we also find that the induced Fresnel lenses can be rapidly modulated with megahertz refresh rates using image-bearing square pulse trains in coupling fields. Our proposed lenses may find a wide range of applications for multimode all-optical signal processing in both the classical and quantum regimes.
Based on the theory of electromagnetically induced transparency, we study the formation of all-optical blazed transmission gratings in a coherently driven three-level atomic system using intensity-modulated images in coupling fields. Also, we analyze the feasibility of high-speed (megahertz) modulation for the induced gratings by means of image-bearing flat-top pulse trains. Consequently, continuous-wave probe fields can be efficiently and rapidly deflected in free space. When more sophisticated images are adopted, our scheme can provide further possibilities of all-optical beam splitting and fanning.
We show theoretical evidence that coherent systems based on electromagnetically induced transparency (EIT) can function as optically addressed spatial light modulators with megahertz modulation rates. The transverse spatial properties of cw probe fields can be modulated fast using two-dimensional optical patterns. To exemplify our proposal, we study real-time generation and manipulation of Laguerre-Gaussian beams by means of phase or amplitude modulation using flat-top image-bearing pulse trains as coupling fields in low-cost hot vapor EIT systems.
In modern physics, coherent manipulation of photons and electrons has been intensively studied, and may have important applications in classical and quantum information processing. In this dissertation, we consider some interesting schemes to realize photonic and electronic coherent manipulation. ^ In order to coherently manipulate photons, electromagnetically induced transparency (EIT) systems have been widely adopted because the optical response of EIT systems can be controlled by the laser-induced atomic coherence. ^ In the second chapter, we theoretically investigate image storage in hot-vapor EIT media. A so-called 4f system is adopted for imaging, and an atomic vapor cell is placed over the transform plane. The Fraunhofer diffraction pattern of an object in the object plane can thus be transformed into atomic Raman coherence according to the idea of "light storage". We investigate how the stored diffraction pattern evolves under diffusion and discuss the essence of the stability of its dark spots. Our result indicates under appropriate conditions that an image can be reconstructed with high fidelity. The main reason for this procedure is the fact that diffusion of opposite-phase components of the diffraction pattern interfere destructively. ^ In the third chapter, we show theoretical evidence that EIT systems can function as optically addressed spatial light modulators with megahertz modulation rates. The transverse spatial properties of continuous-wave probe fields can be modulated rapidly using two-dimensional optical patterns. To exemplify our proposal, we study real-time generation and manipulation of Laguerre-Gaussian beams by means of phase or amplitude modulation using flat-top image-bearing pulse trains as coupling fields in low-cost hot-vapor EIT systems. ^ In order to coherently manipulate electrons, we consider graphene systems, including single-layer graphene and bilayer graphene, which have recently attracted considerable attention. Due to the long coherence length and electrically tunable Fermi levels, electrons in graphene systems have some photon-like behaviors, and could be coherently manipulated. ^ Therefore, in the fourth chapter, we theorize that at a sharp electrostatic step potential in graphene massless Dirac fermions can obtain Goos-Hänchen-like shifts under total internal reflection. Also, we study coherent propagation of the quasiparticles along a sharp graphene p-n-p waveguide, and derive novel dispersion relations for the guided modes. Consequently, coherent graphene-based devices, e.g., movable mirrors, buffers and memories, induced only by the electric field effects may be proposed. ^ Finally, we theoretically investigate the coherent propagation of massive chiral fermions along a sharp bilayer graphene p-n-p waveguide, and indicate that the guided quasiparticles can be coherently slowed, stored and retrieved based on tunable electric field effects. Controlling group velocity in the bilayer graphene p-n-p waveguide is accomplished via interband tunneling through the p-n interfaces, and does not depend on the bandgap opening. ^
Coherent manipulation of stored images is performed at low light levels based on enhanced cross-Kerr nonlinearity in a four-level N-type electromagnetically induced transparency (EIT) system. Using intensity masks in the signal pulse, quadratic phase shifts with low nonlinear absorption can be efficiently imprinted on the Fraunhofer diffraction patterns already stored in the EIT system. Fast-Fourier-transform-based numerical simulations clearly demonstrate that the far-field images of the retrieved probe light can be flexibly modulated by applying different signal fields. Our studies could help advance the goals of nonlinear all-optical processing for spatial information coherently stored in EIT systems.
We explore optical manipulation of sculpted light based on phase-dependent electromagnetically induced transparency through both homogeneously and inhomogeneously broadened five-level atomic systems. A transverse magnetic field and a suitable spatially inhomogeneous control field can be used to create a spatial probe transparency modulation at a desired location. Such transparency modulation is the principle behind the shaping of the light. Further, the beam propagation equation shows that the control-field-induced selective phase information can be imprinted on the probe beam. Hence, this controlled light shaping paves a new way for high-contrast imaging, laser micromachining, and creation of optical lattices and optical tweezers. Our work may also have applications in optical communication and information processing.
We demonstrate coherence-controlled azimuthal modulation of electromagnetically induced transparency (EIT) and all-optical switching in a four-level atomic ensemble coupled to a Laguerre-Gaussian beam, a control field, and a microwave field. The spatial EIT patterns exhibit doublet, quartet, and sextuplet structures, evolving into more complex structures with increasing orbital angular momentum (OAM). These structures can be dynamically switched between EIT and absorption patterns, preserving mirror image symmetry (with even OAM) and rotation symmetry (with odd OAM) by adjusting the relative phase of the coupling fields. By creating two-dimensional electromagnetically induced gratings (EIGs), we find that the diffractive patterns are influenced by probe field detuning, OAM, and relative phase. Specifically, the diffraction patterns of a probe field exhibit complex behavior across first to fourth orders, with intensities influenced by topological charge and azimuthal angle. The diffraction patterns are further modulated by the relative phase, with patterns at 0 and π being mirror images of each other, while the pattern at π /2 exhibits distinct behavior. These findings highlight the potential for precise control over structural EIT, all optical switching and diffraction patterns in coherent atomic media.