We investigated the propagation of an electromagnetic pulse through a one-dimensional photonic crystal doped with quantum-dot (QD) molecules in a defect layer. The QD molecules behave as a three-level quantum system and are driven by a coherent probe laser field and an incoherent pump field. No coherent coupling laser fields were introduced, and the coherence was created by the interdot tunnel effect. Further studied was the effect of tunneling and incoherent pumping on the group velocity of the transmitted and reflected probe pulse.
We study the absorption properties of a weak probe field in a four-level atomic system. By employing a strong driving
field, we investigate the Electromagnetically Induced Transparency (EIT) in this system. We show that, in certain
condition, the absorption peak vanishes and the medium become transparent to the weak probe field.
We show that, by simple modifications of the usual three-level Λ-type scheme used for obtaining electromagnetically induced transparency (EIT), phase dependence in the response of the atomic medium to a weak probe field can be introduced. This gives rise to phase dependent susceptibility. By properly controlling phase and amplitudes of the drive fields we obtain variety of interesting effects. On one hand we obtain phase control of the group velocity of a probe field passing through medium to the extent that continuous tuning of the group velocity from subluminal to superluminal and back is possible. While on the other hand, by choosing one of the drive fields to be a standing wave field inside a cavity, we obtain sub-wavelength localization of moving atoms passing through the cavity field.
Spontaneous emission in atomic system arises due to the interaction of atoms with environmental modes. Atomic coherence and quantum interference are the most important mechanisms for controlling the spontaneous emission. We show that under certain conditions complete quenching of spontaneous emission is possible. By using V type three level system driven by two fields, the phase dependence of quantum interference is investigated. The Fano type and P type interference mechanism in atomic coherence system driven by microwaves are investigated. In particular we find that both phase dependence interference mechanism may be destructive simultaneously and thus lead to spontaneous emission cancellation in different parts of the spectrum. One of the most important applications of this system is the refractive index enhancement.
We investigate the propagation of a partially coherent beam produce by a plane source. By utilizing Helmholtz equation, the intensity of the source in plane z = 0, and plane z are obtained. Then by considering new theoretical prediction on cross-spectral density function of the field in the plane z = 0, the root-means square (rms) beam radius, as a function of distance z are calculated. The effects of the size and coherence of the source on beam directionality will be then discussed. In the special case when the beam is the Gaussian Schell-Model type, our results reduces to well known expression.
By using new theoretical point of view on cross-spectral density function of the field, the propagation of partially coherent beam produce by a plane source is investigated. Then we show, experimentally, the coherence length in the source plane can be measured directly from the far zone intensity distribution. The effects of the size and coherence of the source on beam directionality will be discussed. Our experimental results will be compared with the special case when the beam is the Gaussian Schell-Model type and it is shown that our prediction has a good agreement.