Excitation of surface plasmons at a SiO2/Ag interface by silicon quantum dots: Experiment and theory

The excitation of surface plasmons (SPs) by optically excited silicon quantum dots (QDs) located near a Ag interface is studied both experimentally and theoretically for different QD-interface separations. The Si QDs are formed in the near-surface region of an SiO2 substrate by Si ion implantation and thermal annealing. Photoluminescence decay-rate distributions, as derived from an inverse Laplace transform of the measured decay trace, are determined for samples with and without a Ag cover layer. For the smallest, investigated Si-QDs-to-interface distance of 44 nm the average decay rate at lambda=750 nm is enhanced by 80% due to the proximity of the Ag-glass interface, with respect to an air-glass interface. Calculations based on a classical dipole oscillator model show that the observed decay rate enhancement is mainly due to the excitation of surface plasmons that are on the SiO2/Ag interface. By comparing the model calculations to the experimental data, it is determined that Si QDs have a very high internal emission quantum efficiency of (77±17)%. At this distance they can excite surface plasmons at a rate of (1.1±0.2)×104 s¿1. From the model it is also predicted that by using thin metal films the excitation of surface plasmons by Si QDs can be further enhanced. Si QDs are found to preferentially excite symmetric thin-film surface plasmons

Time resolved motion of pulses in photonic crystal waveguides : a real space investigation

This thesis describes the result of a research project on time-resolved Near-field Scanning Optical Microscopy (NSOM) experiments aimed at visualizing the amplitude and phase of ultrashort optical pulses en route while they propagate inside photonic crystal structures

Phase mapping of ultrashort pulses in bimodal photonic structures: A window on local group velocity dispersion

The amplitude and phase evolution of ultrashort pulses in a bimodal waveguide structure has been studied with a time-resolved photon scanning tunneling microscope (PSTM). When waveguide modes overlap in time intriguing phase patterns are observed. Phase singularities, arising from interference between different modes, are normally expected at equidistant intervals determined by the difference in effective index for the two modes. However, in the pulsed experiments the distance between individual singularities is found to change not only within one measurement frame, but even depends strongly on the reference time. To understand this observation it is necessary to take into account that the actual pulses generating the interference signal change shape upon propagation through a dispersive medium. This implies that the spatial distribution of phase singularities contains direct information on local dispersion characteristics. At the same time also the mode profiles, wave vectors, pulse lengths, and group velocities of all excited modes in the waveguide are directly measured. The combination of these parameters with an analytical model for the time-resolved PSTM measurements shows that the unique spatial phase information indeed gives a direct measure for the group velocity dispersion of individual modes. As a result interesting and useful effects, such as pulse compression, pulse spreading, and pulse reshaping become accessible in a local measuremen

Thin Rationality Review

Under the Administrative Procedure Act, courts review and set aside agency action that is “arbitrary [and] capricious.” In a common formulation of rationality review, courts must either take a “hard look” at the rationality of agency decisionmaking, or at least ensure that agencies themselves have taken a hard look. We will propose a much less demanding and intrusive interpretation of rationality review—a thin version. Under a robust range of conditions, rational agencies have good reason to decide in a manner that is inaccurate, nonrational, or arbitrary. Although this claim is seemingly paradoxical or internally inconsistent, it simply rests on an appreciation of the limits of reason, especially in administrative policymaking. Agency decisionmaking is nonideal decisionmaking; what would be rational under ideal conditions is rarely a relevant question for agencies. Rather, agencies make decisions under constraints of scarce time, information, and resources. Those constraints imply that agencies will frequently have excellent reasons to depart from idealized first-order conceptions of administrative rationalit

Water Solubility in CO2 Mixtures: Experimental and Modelling Investigation

AbstractThe capture of CO2 from power plants and other large industrial sources is offering a main solution to reduce CO2 emissions. The captured mixture will contain impurities like nitrogen, argon, oxygen, water and some toxic elements like sulfur and nitrogen oxides, the types and quantities of which depend on the type of fuel and the capture process. The presence of free water formation in the transportation pipeline causes severe corrosion problems, flow assurance failure and might damage valves and instrumentations. In the presence of free water, CO2 dissolves in the aqueous phase and will partly ionize to form a weak acid. Thus, free water formation should be avoided.This work aims to investigate the solubility of water in CO2 mixtures under pipeline operation conditions in the temperature range of (5–35°C) and the pressure range of (90–150bar). A test set up was constructed, which consists of a high pressure reactor in which a CO2 mixture containing water at initial soluble conditions was prepared. The purpose of this study is to identify the maximum water content level which could be allowed in CO2 transportation pipelines. The experimental data generated were then compared to the calculations of two mixture models: the GERG-2008 model and the EOS-CG model