OAM & Surface Plasmon Resonance - Revision history

Wikiuser at 17:12, 24 November 2014

2014-11-24T17:12:31Z

Wikiuser at 01:39, 13 June 2014

2014-06-13T01:39:05Z

Wikiuser at 01:38, 13 June 2014

2014-06-13T01:38:39Z

Wikiuser at 01:21, 13 June 2014

2014-06-13T01:21:17Z

Wikiuser at 01:11, 13 June 2014

2014-06-13T01:11:53Z

Bsboggs: Bsboggs moved page Surface Plasmon Resonance to OAM & Surface Plasmon Resonance

2013-12-14T16:18:01Z

Bsboggs moved page Surface Plasmon Resonance to OAM & Surface Plasmon Resonance

Wikiuser at 05:11, 8 December 2013

2013-12-08T05:11:32Z

Wikiuser at 05:10, 8 December 2013

2013-12-08T05:10:52Z

Wikiuser at 04:52, 8 December 2013

2013-12-08T04:52:52Z

Wikiuser at 04:37, 8 December 2013

2013-12-08T04:37:10Z

← Older revision		Revision as of 17:12, 24 November 2014
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		+	== SPR-OAM Project ==

−	== Background and Goal ==	+	[http://hank.uoregon.edu/experiments/SPR/spr.html SPR-OAM Web Page]
		+
		+	=== Background and Goal ===
	The ultimate goal of the Surface Plasmon Resonance (SPR) experiment is to understand angular momentum states of surface plasmons (SPs). This wiki article assumes that the reader has general knowledge of photonics and electrodynamics		The ultimate goal of the Surface Plasmon Resonance (SPR) experiment is to understand angular momentum states of surface plasmons (SPs). This wiki article assumes that the reader has general knowledge of photonics and electrodynamics

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 Detecting OAM in the form of an <math>LG_{0,m}</math> beam is fairly simple in principle and can be done easily one of two ways.
-Firstly, if m is a known or suspected quantity, a holographic grating of charge -m can be used to convert the beam to an <math>LG_}0,0}</math> beam. When focused through a pinhole, only LG modes with m=0 will be transmitted as LG beams with nonzero m present with a central vortex.
+Firstly, if m is a known or suspected quantity, a holographic grating of charge -m can be used to convert the beam to an <math>LG_{0,0}</math> beam. When focused through a pinhole, only LG modes with m=0 will be transmitted as LG beams with nonzero m present with a central vortex.
 Secondly, if m is unknown, a modified Mach-Zehnder interferometer can be used to infer m. A dove prism is used to flip the beam in one arm of the interferometer. Reinterference of the flipped beam with the original will result in an interference pattern with 2m spokes.

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 === Detection of Optical OAM ===
-Detecting OAM in the form
+Detecting OAM in the form of an <math>LG_{0,m}</math> beam is fairly simple in principle and can be done easily one of two ways.
 == Angular Momentum Conservation in the Generation of Surface Plasmons ==

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 === Generation of Optical OAM ===
-The most intuitive method for generating optical OAM is by use of a spiral phase plate. Such a phase plate retards the input wave by an amount depending on the azimuthal angle with respect to the optical axis (pictured below) giving rise to a helical wavefront characteristic of an LG<math>LG_0,m</math> beam, where m represents the topological charge. The shelf distance d of a phase plate made of a material with refractive index n must equal <math>d=m \lambda/n</math>.
+The most intuitive method for generating optical OAM is by use of a spiral phase plate. Such a phase plate retards the input wave by an amount depending on the azimuthal angle with respect to the optical axis (pictured below) giving rise to a helical wavefront characteristic of an <math>LG_{0,m}</math> beam, where m represents the topological charge. The shelf distance d of a phase plate made of a material with refractive index n must equal <math>d=m \lambda/n</math>. In practice, these are expensive optical elements that may produce questionable mode purity for m>3
 === Detection of Optical OAM ===

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 == Background and Goal ==
-The ultimate goal of the Surface Plasmon Resonance (SPR) experiment is to understand angular momentum states of surface plasmons (SPs). This wiki article assumes that the reader has general knowledge of optics and light fields.
+The ultimate goal of the Surface Plasmon Resonance (SPR) experiment is to understand angular momentum states of surface plasmons (SPs). This wiki article assumes that the reader has general knowledge of photonics and electrodynamics
 === Surface Plasmon Resonance ===
-A surface plasmon is very similar, conceptually, to a photon confined to a 2-dimensional surface. The coupling of light to a conductor generates charge density waves that propagate based on the dielectric constant and thickness of the conductor. These two conditions generally dictate the momentum of a surface plasmon (and therefore the associated wave number, k).
+A surface plasmon is very similar conceptually to a photon confined to a 2-dimensional conductor. The coupling of light to a conductor generates charge density waves that propagate based on the (complex) dielectric constant and thickness of the conductor. These two conditions generally dictate the momentum of a surface plasmon (and therefore the associated wave number, k).
 When coherent light undergoes total internal reflection in at an interface in a dialectric, an [http://en.wikipedia.org/wiki/Evanescent_wave evanescent field] propagating parallel to the component of the incident light in the plane of the dielectric interface is generated. When a conducting film as described above, whose associated plasmon wave number matches the wave number of the evanescent field, a surface plasmon resonance is is generated. In order to tune the resonance, the incident angle of the light can be adjusted, thereby adjusting the wave number of the evanescent field. The wave number of the evanescent field can also be changed by using light of a different wavelength.
-In practice, an approximately 43nm thick gold film applied to the back of a glass prism makes for an excellent plasmon setup. Gold is an excellent conductor. Better conduction increases the wave number associated with surface plasmons in a material, allowing for the plasmon resonant angle to be above the critical angle. While silver is an even better conductor, its corrosion in atmosphere makes it less practical.
+In practice, an approximately 43nm thick gold film or 40nm thick silver film applied to the back of a glass prism of index n=1.5 makes for an excellent plasmon setup. While silver is more conductive than gold, thereby allowing for a deeper resonance, its corrosion in atmosphere makes it less practical.
 When a surface plasmon encounters a defect such as a bump or a hole in the conducting surface along which it is propagating, the defect acts as a scatterer for the SP (as it is locally off-resonance for that wavelength of SP) and the SP either deflects off the defect or is re-radiated from the surface, converting back to a photon. In order to conserve linear momentum, a re-radiated SP leaves the dielectric film at the angle of incidence matching its momentum in the plane of propagation. In other words, if a plasmon generated by light of a given wavelength whose resonant angle is θ is ejected from the conductive surface, it will be ejected at the same wavelength as the generated light at the angle θ.
-Since any azimuthal angle in the plane of the conductor can satisfy the above constrain on the angle of exit of a re-radiated plasmon, a hollow cone of radiation is observed when a surface plasmon resonance is generated in a film with defects sufficiently large to scatter and eject SPs.
+Since any azimuthal angle in the plane of the conductor can satisfy the above constraint on the exit of a re-radiated plasmon, a hollow cone of radiation is observed when a surface plasmon resonance is generated in a film with defects sufficiently large to scatter and eject SPs.
-The observation of this radiation cone is perhaps the easiest way to observe the effects of SPR, and because it is a cone whose vertex is at the dielectric/conductor interface, it is convenient to use a prism with cylindrical or spherical symmetry in the axis normal to the dielectric/conductor interface.
+A great deal of information can be inferred by measurements of this radiation cone. Because it is a cone whose vertex is at the dielectric/conductor interface, it is convenient to use a prism with cylindrical or spherical symmetry in the axis normal to the dielectric/conductor interface.
 === Angular Momentum ===
-[[File:Helix oam.png|250|thumb|right|Diagram of wavefront helicity and associated topological charge]]Light can carry both orbital and spin angular momentum. Orbital angular momentum (OAM) of light is a consequence of its spacial distribution, such as helicity, while spin angular momentum (SAM) corresponds to circular polarization states. OAM states are quantized by topological charge M which carriers any integer value, while SAM states are quantized by 1, 0, or -1 as photons are bosons.
+[[File:Helix oam.png|250|thumb|right|Diagram of wavefront helicity and associated topological charge]]Light can carry both orbital and spin angular momentum. Orbital angular momentum (OAM) of light is a consequence of its spacial distribution, such as helicity, while spin angular momentum (SAM) corresponds to circular polarization states. OAM states are quantized by topological charge m which carriers any integer value, while SAM states are quantized by 1, 0, or -1 as photons are bosons.

← Older revision	Revision as of 16:18, 14 December 2013
(No difference)

← Older revision		Revision as of 05:11, 8 December 2013
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	#Assume that colinear and spatially identical OAM/non-OAM light can be generated. Then observation of angular momentum in radiation from an SPR generated by OAM light, and subsequent observation of no angular momentum in radiation from an SPR generated by non-OAM light is a likely indicator that angular momentum is conserved in the electromagnetic fields through the plasmon conversion processes. This may not be conclusive, but may be rigorous.		#Assume that colinear and spatially identical OAM/non-OAM light can be generated. Then observation of angular momentum in radiation from an SPR generated by OAM light, and subsequent observation of no angular momentum in radiation from an SPR generated by non-OAM light is a likely indicator that angular momentum is conserved in the electromagnetic fields through the plasmon conversion processes. This may not be conclusive, but may be rigorous.
−
	#It is plausible that milling defects into the conductive film that break circular symmetry, such as skewed "escape arms," could provide insight into the local optical field.		#It is plausible that milling defects into the conductive film that break circular symmetry, such as skewed "escape arms," could provide insight into the local optical field.

← Older revision		Revision as of 04:37, 8 December 2013
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	== Angular Momentum ==		== Angular Momentum ==

−	Light can carry both orbital and spin angular momentum. Orbital angular momentum (OAM) of light is a consequence of its spacial distribution, such as helicity, while spin angular momentum (SAM) corresponds to circular polarization states. [[File:oam ~~diagram~~]]	+	Light can carry both orbital and spin angular momentum. Orbital angular momentum (OAM) of light is a consequence of its spacial distribution, such as helicity, while spin angular momentum (SAM) corresponds to circular polarization states. [[File:Helix oam.png\|450px\|thumb\|right\|Diagram of wavefront helicity and associated topological charge]]