The Optical Response of Rectangular Metallic Gratings and Metal/Dielectric Multilayers

The ability of periodic surface variations to influence and control the electromagnetic response of interfaces and structures has been recognised for many years. Concurrently with these investigations, it has been found that individual particles and wires support interesting electromagnetic resonances. It has also long been established that multi-layer structures of planar interfaces may also result in interesting electromagnetic responses. Multi-layer structures of alternating dielectrics have been shown to produce periodic transmission resonances, however, if one of the dielectrics is replaced with a thin metallic film, it has recently been demonstrated that wide band-pass regions are formed in the electromagnetic response of the structure. The work presented in this thesis can be considered to be separated into two distinct, but related, areas. One of the areas involves the analysis of wire grid arrays. It is demonstrated that, like the case of deep surface relief perturbations, the waveguide modes in the slits can be considered as the evolution of surface modes on shallow surface relief perturbations. The perturbation effects of the slits on the surface modes and the effect of their excitation on optically thick and thin wires are also investigated. Finally, a new electromagnetic resonance is presented on both 1-dimensional and 2-dimensional wire grid arrays. It is shown that this is closely related to the localised surface modes that have been shown to occur on individual particles and wires. However, the resonance presented is shown to be subtly different from these modes, which typically result in a transmission and reflection extinction, because the planar geometry of the wires and the periodicity result in a reflection enhancement, even when the wires are optically thin. The second area of this work may be separated into two distinct sub-sections. The first section examines the electromagnetic response of dielectric/metal multi-layer stacks. These are confirmed to exhibit a periodic series of broad band-pass regions, with the spectral location of these regions being dependent only on the unit cell, not the full extent of the structures. The location of each band-edge of these regions are then demonstrated to be a result of the matching of boundary conditions between standing waves in the cavities having either a cos or a sin standing wave function, and the evanescent fields inside the metal layers having either a sinh or a cosh field distribution. The second section examines the electromagnetic response of continuous surface relief gratings, with a rectangular cross-section, whose ridges are very thin. It is shown that vertical standing waves form, similar to the cavity waveguide modes, except with the fields coupled through the wires not across the grooves. These are then shown to reach a finite limit frequency as the grating height tends to infinity. Thus, the resonances have evolved into a different mode beyond a certain grating amplitude. This mode is shown to to be equivalent to the band-pass region described in multi-layer metal/dielectric stacks. However, scattering and periodicity considerations require that only the low frequency band-edge can be coupled to at normal incidence, while only the high frequency band-edge may be coupled to at grazing incidence.EPSRC Industrial CASE award with Sharp Laboratories of Europ

Surface plasmon polaritons on deep, narrow-ridged rectangular gratings

Copyright © 2009 Optical Society of America. This paper was published in Journal of the Optical Society of America B and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/josab/abstract.cfm?URI=josab-26-6-1228 Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.The dispersion diagrams of surface plasmon polaritons have been calculated for rectangular gratings, with very narrow wires, of varying depths. For gratings with a moderate height a family of vertical-standing-wave resonances may be excited, which consist of surface plasmons, oscillating on either vertical surface, coupling together through the metal wires. These modes evolve similarly to the manner in which shallow-grating surface-plasmon dispersion curves evolve into cavity modes in the grooves of the structure. However, on further increase in grating height these vertical standing waves evolve into a second resonant feature, which is independent of yet further increases in height. This new mode is shown to be equivalent to the resonances found on infinite multilayer metal/dielectric structures illuminated at normal incidence

Electromagnetic resonances of a multilayer metal-dielectric stack

Copyright © 2009 Optical Society of America. This paper was published in Journal of the Optical Society of America B and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/abstract.cfm?URI=josab-26-4-734 . Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.The electromagnetic resonances of multilayer metal–dielectric stacks are investigated. These structures support periodic bandpass regions, whose band edges may be predicted by considering the character of the fields inside the different layers. It is shown that the response of the structure is largely independent of its overall length, and that only the geometry of the unit cell is important. In the metal layers, the fields may have either a cosh or a sinh distribution function and match to standing waves inside the adjacent dielectric cavities at the metal–dielectric interface. It is shown that the different boundary conditions, imposed by the evanescent fields, result in the dielectric layers having a different effective length for the two modes. The sinh fields result in an effective length being very close to that of the physical length, and adjacent cavities oscillating out of phase, while the cosh fields may result in a significantly larger effective dielectric length and adjacent cavities oscillating in phase. A bandpass region is opened, with its high frequency edge always being near the dielectric Fabry–Perot limit, while the low frequency band edge is significantly redshifted

Heat transfer to binary liquid mixtures in natural circulation evaporators

Experiments were made to investigate the effects of submergence, temperature difference and composition on the heat transfer rates to boiling water, isopropyl alcohol and their mixtures. The apparatus used was a natural circulation vertical tube evaporator, the test section being a copper tube 0.485" i.d., wall thickness 0.085" and heated length 47.75". The heating medium was steam contained in an annulus surrounding the test section. To ensure that the whole test section was used for boiling, the liquid was introduced to the evaporator at its local boiling temperature. Analysis of the results so obtained has indicated that within experimental limits nucleate boiling became less predominant with increasing temperature difference and decreasing submergence, being displaced by a convective-type heat transfer mechanism. [Continues.

Optical resonances on sub-wavelength silver lamellar gratings

Copyright © 2008 Optical Society of America. This paper was published in Optics Express and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/abstract.cfm?URI=oe-16-26-22003 Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.The optical response of sub-wavelength silver lamellar gratings has been theoretically investigated. Two distinct types of resonance have been predicted for incident radiation with E-field perpendicular to the long axis of the wires. The first resonance has been identified as a cavity mode resonance that is associated with transmission enhancement. The second resonance has been identified as an entirely new horizontal plasmon resonance on the incident (and transmission) surfaces of the wires of the grating. Normal surface plasmon modes are investigated on discontinuous gratings, and their relation to those found on continuous gratings is highlighted by focusing on the perturbation effect of the discontinuities. It is shown that the new horizontal plasmon mode is in no way related to the well known diffractively coupled surface plasmon, and is shown to have a particle plasmon-like nature. It is therefore termed a horizontal particle plasmon, and may be either an uncoupled horizontal particle plasmon resonance (a 1-dimensional particle plasmon) or a coupled horizontal particle plasmon resonance (a 2-dimensional particle plasmon) depending on the height of the grating. It is shown that this resonance may result in a reflection efficiency that is very high, even when the grating would be optically thin if it were a homogeneous film, therefore, it behaves as an inverse wire grid polariser as it reflects more TM than TE incident radiation

Heather Jewell bookplate

Medium: etchingsigned and dated."Heather Jewell bookplate" [1996.2139.000.000], Gadsdon, JohnArtist and Role: Gadsdon, John,Extent: imageExtent: shee

A histological and immunocytochemical analysis of stented vein grafts

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