In this paper we have investigated three external fields interacting with the four-level Y-type atomic system described by the density-matrix approach. The results show that left-handedness with zero absorption is achieved. The zero absorption property displays the possibility of manipulation by varying the phase and the intensity of the coupling field. Also, the zero absorption property may be used to amplify the evanescent waves that have been lost in imaging by traditional lenses. We propose an approach to obtain a negative refractive medium with zero absorption and the possibility of enhaneeingthe imaging resolution in realizing ＇superlenses＇.
In the present paper, we investigate the behavior of two-dimensional atom localization in a five-level M-scheme atomic system driven by two orthogonal standing-wave fields. We find that the precision and resolution of the atom localization depends on the probe field detuning significantly. And because of the effect of the microwave field, an atom can be located at a particular position via adjusting the system parameters.
This paper intends to realize negative refraction with absorption suppressed by the electromagnetically induced transparency (EIT) in a dense four-level atomic system.Without the two equal transition frequencies responding to the probe field,the atomic system displays a negative refraction with the simultaneously negative permittivity and negative permeability (left-handedness).The response of the probe field is amplified and propagates transparency in some frequency extents.Therefore,our aim for searching the low-loss negative refraction can be achieved in the scheme,given the main applied limitation of the negative refractive materials is the large amount of dissipation and absorption.However,an excessive signal field intensity would increase the absorption near the resonance in our scheme.
This paper suggests a scheme of electromagnetic chirality-induced negative refraction utilizing magneto-lectric cross coupling in a four-level atomic system. The negative refraction can be achieved with the two chirality coefficients having the same amplitude but the opposite phase, without requiring the simultaneous presence of an electric-dipole and a magnetic-dipole transition near the same transition frequency.
A closed four-level system in atomic vapour is proposed, which is made to possess left handedness by using the technique of quantum coherence. The density matrix method is utilized in view of the rotating-wave approximation and the effect of a local field in dense gas. The numerical simulation result shows that the negative permittivity and the negative permeability of the medium can be achieved simultaneously （i.e. the left handedness） in a wider frequency band under appropriate parameter conditions. Furthermore, when analysing the dispersion property of the left-handed material, we can find that the probe beam propagation can be controlled from superluminal to subluminal, or vice versa via changing the detuning of the probe field.
A new scheme for fabricating a kind of flexible semiconductor micro-laser is put forward.And the optical properties of this kind of flexible semiconductor laser are investigated by the finite difference time domain(FDTD) method.The results show that the light should be localized by photonic crystals(PCs),and the interaction between light and gain medium should be enhanced,while the mode of laser should be modulated.These results indicate that the PCs could control the spontaneous emission,and lead the radiation emission to the needed frequency.
