Development of a model of the interaction of light with nano-holes in thin metal films

Allan, R

Development of a model of the interaction of light with nano-holes in thin metal films

Allan, R

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Publication Type:: Thesis
Issue Date:: 2008

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Field	Value	Language
dc.contributor.author	Allan, R
dc.date.accessioned	2015-11-09T03:08:08Z
dc.date.available	2015-11-09T03:08:08Z
dc.date.issued	2008
dc.identifier.uri	http://hdl.handle.net/10453/37719
dc.description	University of Technology, Sydney. Faculty of Science.	en_AU
dc.description.abstract	We develop an analytical electromagnetic model of a conducting film perforated by slits with subwavelength slit width and periodicity. We use a plane wave expansion methodology to calculate the reflected and transmitted fields diffracted by the conducting grating, with the exception that the sub-wavelength periodicity means that the diffracted field is composed of non-propogating surface waves rather than plane waves. We label the non-propogating surface waves evanescent diffracted waves EDWs. We show how the collection of all EDWs present can be treated as an effective medium described by an impedance and that the reflectance and transmittance of a plane wave incident on the grating can be calculated as if the plane wave where interacting with an effective medium. We find that depending on slit depth this effective medium allows for transmittances of 100% even when slit width is so narrow that it is negligable compared to slit periodicity. Thus our analytical model reproduces the extraordinary optical transmission reported in the literature. We show that the EDWs on either side of the grating also act like mirrors coupling to a standing wave in the grating with the result that slit depth determines whether transmission is high or low. We find that when the effective permittivity of the effective medium created by the EDWs is equal to the permittivity of the metal film then the EDWs collectively become a surface plasmon. We also find that except for films with no absorption the state in which EDWs are also a surface plasmon corresponds to low transmittance not high transmittance and thus surface plasmons appear to hinder rather than help transmittance for a grating composed of slits. We also develop an FDTD model of Maxwell's equations which reproduces the predictions of our analytical model. We further develop our analytical electromagnetic model of conducting gratings to also include the situation in which a planar conducting lens is placed under the grating. We demonstrate that such a lens can create a near-field focusing effect that enables sub-wavelength imaging so that incident light can produce a periodic intensity pattern in a substrate with periodic feature less than the wavelength of the incident light. We show that this sub-wavelength imaging is possible with or without surface plasmons being present.	en_AU
dc.format	Thesis (PhD)
dc.language.iso	en	en_AU
dc.relation	https://opus.lib.uts.edu.au/bitstream/10453/37719/9/02Whole.pdf
dc.rights	The author owns the copyright in this thesis including all reproduction and reuse rights for the work. The work may not be altered without the permission of the copyright owner. Attribution is essential when quoting or paraphrasing from this thesis.
dc.rights	info:eu-repo/semantics/openAccess
dc.rights	au.edu.uts.lib/ppc
dc.subject	Analytical electromagnetic model.	en
dc.subject	Thin metal films.	en
dc.subject	Plane wave expansion methodology.	en
dc.subject	Evanescent diffracted waves (EDWs).	en
dc.subject	Effective permittivity.	en
dc.subject	Sub-wavelength imaging.	en
dc.subject	Near-field focusing effect.	en
dc.title	Development of a model of the interaction of light with nano-holes in thin metal films	en_AU
dc.type	Thesis	en_AU
utslib.copyright.status	open_access	en_AU

Abstract:

We develop an analytical electromagnetic model of a conducting film perforated by slits with subwavelength slit width and periodicity. We use a plane wave expansion methodology to calculate the reflected and transmitted fields diffracted by the conducting grating, with the exception that the sub-wavelength periodicity means that the diffracted field is composed of non-propogating surface waves rather than plane waves. We label the non-propogating surface waves evanescent diffracted waves EDWs. We show how the collection of all EDWs present can be treated as an effective medium described by an impedance and that the reflectance and transmittance of a plane wave incident on the grating can be calculated as if the plane wave where interacting with an effective medium. We find that depending on slit depth this effective medium allows for transmittances of 100% even when slit width is so narrow that it is negligable compared to slit periodicity. Thus our analytical model reproduces the extraordinary optical transmission reported in the literature. We show that the EDWs on either side of the grating also act like mirrors coupling to a standing wave in the grating with the result that slit depth determines whether transmission is high or low. We find that when the effective permittivity of the effective medium created by the EDWs is equal to the permittivity of the metal film then the EDWs collectively become a surface plasmon. We also find that except for films with no absorption the state in which EDWs are also a surface plasmon corresponds to low transmittance not high transmittance and thus surface plasmons appear to hinder rather than help transmittance for a grating composed of slits. We also develop an FDTD model of Maxwell's equations which reproduces the predictions of our analytical model. We further develop our analytical electromagnetic model of conducting gratings to also include the situation in which a planar conducting lens is placed under the grating. We demonstrate that such a lens can create a near-field focusing effect that enables sub-wavelength imaging so that incident light can produce a periodic intensity pattern in a substrate with periodic feature less than the wavelength of the incident light. We show that this sub-wavelength imaging is possible with or without surface plasmons being present.

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