We present a theoretical analysis of surface-plasmon-mediated mode-coupling in a planar thin film metal/insulator stack. The spatial overlap of a surface plasmon polariton (SPP) and a waveguide mode results in a Fano interference analog. Tuning of the material parameters effects the modes and output fields of the system. Lastly, the intensity and phase sensitivity of the system are compared to a standard surface plasmon resonance (SPR). We begin with background information on Fano interference, an interference effect between two indistinguishable pathways. Originally described for autoionization, we discuss the analogs in other systems. We discuss the features of Fano interference in the mode diagrams, and the Fano resonance observed in the output field. The idea of a geometric Fano resonance (GFR) occurring in the angular domain is presented. Background information on surface plasmon polaritons is covered next. The dielectric properties of metals and how they relate to surface plasmons is first reviewed. The theoretical background of SPPs on an infinite planar surface is covered. The modes of a two planar interface metal/insulator stack are reviewed and the leaky properties of the waveguide are shown in the reflectance. We solve for modes of a three interface metal/insulator stack and shows an avoided crossing in the modes indicative of Fano interference. We observe the asymmetric Fano resonance in the angular domain in the reflectance. The tunability of the material parameters tunes the GFR of the system. The GFR tuning is explored and different Fano lineshapes are observed. We also observe a reversal of the asymmetry Fano lineshape, attributed to the relate phase interactions of the non-interacting modes. The phase of the GFR is calculated and discussed for the variations of the parameters. The reflected field is explored as the insulator permittivities are varied. As the waveguide permittivity is varied, we show there is little response from the system. As the exterior permittivity is varied, the reflectance exhibits the geometric Fano resonance and the tunability of the lineshape is explored. Finally, we calculate the sensitivities of our metal/insulator stack to changes in the permittivity and compare them to the sensitivities of SPRs.

We demonstrate the existence of tunable bound-states in continuum (BIC) in a 1-dimensional quantum wire with two impurities by an intense monochromatic radiation field. We found that there is a new type of BIC due to the Fano interference between two optical transition channels, in addition to the ordinary BIC due to a geometrical interference between electron wave functions emitted by impurities. In both cases the BIC can be achieved by tuning the frequency of the radiation field. / text

Quantum coherence and interference(QCI) effects have been studied for decades and are widely exploited in many areas. For media with QCI effect, the optical properties can change drastically, which leads to many interesting effects, such as coherent population trapping, electromagnetically induced transparency(EIT), lasing without population inversion(LWI) and so on. We have theoretically studied the pulsed regime of EIT. In particular, simulations of propagation of gaussian and 0 - pi co-propagating laser pulses in a medium consisting of 3-level Lambda-atoms have been performed. It has been found that, even at the two-photon resonance, the length of propagation for the 0 - pi pulses is much smaller than that for the Gaussian probe pulses. We explained such a behavior using the dark and bright basis and the dressed state basis. Some possible applications are discussed. We also investigated the collision-induced coherence of two decay channels along two optical transitions. Quantum interference will suppress the spontaneous emission. The degree of this suppression is measured by the branch ratio of these two transitions. Our preliminary calculations show that a significant decrease of the branching ratio with increase of electron densities is reproduced in the theory. We have developed a new variant of Raman spectroscopy with shaped femtosecond pulses. It has several advantages to be applied in multiscatterd media. It is based on change of the spectra of femtopulses due to Raman scattering (stimulated or coherent). The technique can be used for a broad range of applications from atomic and molecular optical and IR spectroscopy to spore detection and tissue microscopy. Finally, we have shown that Fano interference in the decay channels of three levels system can lead to considerably different absorption and emission profiles. We found that a coherence can be built up in the ground state doublet whose strength depends on a coupling parameter that arises from Fano interference. This can in principle lead to breaking of the detail balance between the absorption and emission processes in atomic systems.