A Circular Nanoslit as a Spin-to-Orbital Angular Momentum Converter
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A Circular Nanoslit as a Spin-to-Orbital Angular Momentum Converter
Philip ChimentoGert ‘t HooftEric Eliel
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Suspicious behavior insubwavelength slits
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Chimento, Kuzmin, Bosman, et al. (2011). Opt. Expr. 19 (24), 24219.
Slit in a metal film
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Chimento, Kuzmin, Bosman, et al. (2011). Opt. Expr. 19 (24), 24219.
Slit in a metal film
Subwavelength in one direction
“Infinite” in the other
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Chimento, Kuzmin, Bosman, et al. (2011). Opt. Expr. 19 (24), 24219.
Almost ideal metal
TM
TE
Slit width in λ
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Chimento, Kuzmin, Bosman, et al. (2011). Opt. Expr. 19 (24), 24219.
Real metal
TM
TE
Slit width in λ
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Chimento, Kuzmin, Bosman, et al. (2011). Opt. Expr. 19 (24), 24219.
Real metal
If designed carefully, there is a point where the slit is a quarter-wave plate
Analyzer rotationInput stateMeasured output
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Photo credit: Dandelion And Burdock, Flickr
We roll the slit up into a circle
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Space-variant λ/4 plate
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Space-variant λ/4 plate
TM
TM
TE
TE
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Space-variant λ/4 plate
Input: circular polarizationσ+ state
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Space-variant λ/4 plate
Output: ?
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Transmitted polarization stateSchematic
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Transmitted intensity
Experiment
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Transmitted polarization state
Left-handed ellipticalRight-handed ellipticalEllipticity <10%
Experiment
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Photo credit: Cayusa, Flickr
Where did the spin angular momentum
disappear to?
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Cylindrical symmetry means no angular momentum is transferred to the plate
Photo credit: pixaio, sxc.hu
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Fascinating!What does the far field
look like?
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Far field
Angle
Angl
e
Inte
nsity
(arb
. uni
ts)
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Far field
Angle
Angl
e
Inte
nsity
(arb
. uni
ts)No hole in
the middle!
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Far field
Component with the same handedness as the input (σ+)
Component with opposite handedness to the input (σ−)
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Phase of central spot
Component with the same handedness as the input (σ+)
Component with opposite handedness to the input (σ−)
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A proper calculation
modecon-
verter
� +, � = � � +, � = �
� − , � = �
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A proper calculation
modecon-
verter
� � = −�� � = �
� � = +�� � =
� +, � = � � +, � = �
� − , � = �
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A proper calculation
modecon-
verter
� � = −�� � = �
� � = +�� � =
Total angular momentum remains the same!
� +, � = � � +, � = �
� − , � = �
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We found, constructed, and understood a novel spin-to-orbit angular momentum coupling device.
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Orbital angular momentum
⟨Jspin⟩ = 0⟨Jorbit⟩ = h̵