Diffraction grating equation a level10/5/2023 In recent years it has been demonstrated, that in the PT-symmetric media it is possible to observe an asymmetric diffraction pattern since light undergoes spatially modulated refractive index 13. It is well known, that in ordinary media the formed gratings typically diffract light symmetrically. While phase modulation is similar to the process of frequency modulation, in phase modulation the frequency of the carrier signal is not increased. Phase modulation is used to transfer data/information for example in mobile systems. On the other hand, during phase modulation the phase of the carrier wave changes accordingly to the amplitude of the modulating signal, keeping the carrier amplitude and frequency constant. The carrier wave amplitude is modified in order to send data or information, usually over long distance. In the process of amplitude modulation the amplitude of the carrier wave is changed accordingly to the amplitude of the modulating signal, while the carrier phase and frequency remain constant. EIG has also been extended to two-dimensions in multi-level atomic systems 10, involving non-linear modulation 11, as well as Raman processes 12.ĮIGs may provide flexible amplitude and phase modulation of the weak probe beam, as well as manipulation of the intensity distribution of different orders of the grating. 3, observed by Mitsunaga and Imoto in sodium atoms 4, and later widely investigated in different systems 5– 7, including Rydberg atoms 8, 9. In this case the traveling-wave (TW) probe field can be diffracted into higher order directions, due to the spatial periodic modulation for the absorption and dispersion of the medium, implemented by the SW field. When a strong coupling field in an Electromagnetically Induced Transparency (EIT) 1, 2 scheme is replaced by a standing-wave (SW), the so called Electromagnetically Induced Grating (EIG) is observed. A detailed analysis of the probe field energy transfer to different orders of diffraction in the case of off-resonant standing wave coupling field proves the possibility of direct control over the performance of the grating. The asymmetry is due to the constructive and destructive interference between the amplitude and phase modulations of the grating system, resulting in complete blocking of the diffracted photons at negative or positive angles, due to the coupling of the vortex beam. Unlike in previously reported asymmetric diffraction gratings for PT symmetric structures, the parity time symmetric structure is not necessary for the asymmetric diffraction grating presented here. The asymmetry is especially seen in the case of combining a resonant probe with an off-resonant standing wave coupling and optical vortex fields. We show that due to the azimuthal modulation of the Laguerre–Gaussian field, a two-dimensional asymmetric grating is observed, giving an increase of the zeroth and high orders of diffraction, thus transferring the probe energy to the high orders of direction. Upon derivation of the Maxwell wave equation, describing the dynamic response of the probe light in the atomic medium, we perform numerical calculations of the amplitude, phase modulations and Fraunhofer diffraction pattern of the probe field under different system parameters. We propose a theoretical scheme for creating a two-dimensional Electromagnetically Induced Grating in a three-level Λ-type atomic system interacting with a weak probe field and two simultaneous position-dependent coupling fields-a two dimensional standing wave and an optical vortex beam.
0 Comments
Leave a Reply.AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |