Presence Of Local Field Research Articles

Effects of a chiral atomic medium on the manipulation of light birefringence and lateral Goos–Hänchen shifts via Kerr nonlinearity and local field effects

We present a new scheme to report on the effects of a five-level chiral atomic medium on the lateral Goos–Hänchen (GH) shift in Gaussian probe beams via Kerr nonlinearity (KNL) and local field effects. The physical realization of birefringence in absorption, dispersion, reflection and transmission beams is investigated, with special emphasis on the manipulation of absolute and fractional change in lateral GH shifts in birefringence transmission and reflection beams, via local fields and Kerr nonlinearity. We have employed a semiclassical atomic density-matrix formalism so as to obtain the expression for electric and magnetic susceptibilities of the chiral medium and the corresponding chirality coefficients in conjunction with Kerr and local fields, both separately and in combination. Stationary-phase theory is used to compute GH shift from the calculated birefringent reflection and transmission coefficients of probe beams. A negative and positive GH shift is observed in reflection and transmission beams, respectively, subjected to local field and Kerr effect. In contrast, a positive GH shift is observed in both reflection and transmission beams in the presence of both local field and Kerr effects. The local and Kerr fields also alter the divergence angle between left and right circularly polarized birefringence beams. GH shift depends on incident angle and probe detuning. The anisotropy of medium is lessened by switching ON the Kerr field in the medium. We observed a positive fractional change of ±30% in the GH shift in the birefringence reflection beam in the presence of a local field without KNL, while a 20% fractional GH shift was observed in the presence of both local field and KNL effects. Our results suggest promising applications in nonlinear optical, plasmonic and biophotonic devices for the manipulation of light propagation and optical signal processing.

Effect of material properties on the accuracy of antiresonant approximation: Linear and second-order optical responses

Many ab initio calculations, in particular in solid state physics, rely on the antiresonant approximation. In this paper we discuss the derivation, the validity, and the accuracy of this approximation, analyzing how the optical properties of several bulk semiconducting materials and surfaces can be affected. We present accurate results for different spectroscopic quantities in the linear and nonlinear responses and we analyze the discrepancies between approximated and exact formulas. An investigation is made of the effect of the approximation on absorption spectra for different materials, showing the reliability of the approximation even in the presence of local field and excitonic effects. The energy loss is shown to be drastically affected. The effect of the band gap of materials on the quality of the approximation is also discussed. Finally, we report on the influence of the antiresonant approximation on second harmonic generation spectra.

Linear Birefringence in GaAs/AlAs Multiple Quantum Wells

Transmission spectroscopy has been used to investigate the in-plane linear birefringence of GaAs/AlAs multiple quantum wells (MQWs) with symmetric wells/barriers from 20/20 to 70/70 A. Varying optical thicknesses of the samples have been used to measure a reference value of the birefringence. While the resonant part in the dispersion of the birefringence has been attributed to the contribution from the confined electronic gaps, a nonresonant background birefringence has been analyzed as a function of the MQW period and explained by the presence of local fields.