A Circular Nanoslit as a Spin-to-Orbital Angular Momentum Converter

A Circular Nanoslit as a Spin-to-Orbital Angular Momentum Converter

Philip ChimentoGert ‘t HooftEric Eliel

Suspicious behavior insubwavelength slits

Chimento, Kuzmin, Bosman, et al. (2011). Opt. Expr. 19 (24), 24219.

Slit in a metal film

Chimento, Kuzmin, Bosman, et al. (2011). Opt. Expr. 19 (24), 24219.

Slit in a metal film

Subwavelength in one direction

“Infinite” in the other

Chimento, Kuzmin, Bosman, et al. (2011). Opt. Expr. 19 (24), 24219.

Almost ideal metal

TM

TE

Slit width in λ

Chimento, Kuzmin, Bosman, et al. (2011). Opt. Expr. 19 (24), 24219.

Real metal

TM

TE

Slit width in λ

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

Photo credit: Dandelion And Burdock, Flickr

We roll the slit up into a circle

Space-variant λ/4 plate

Space-variant λ/4 plate

TM

TM

TE

TE

Space-variant λ/4 plate

Input: circular polarizationσ+ state

Space-variant λ/4 plate

Output: ?

Transmitted polarization stateSchematic

Transmitted intensity

Experiment

Transmitted polarization state

Left-handed ellipticalRight-handed ellipticalEllipticity <10%

Experiment

Photo credit: Cayusa, Flickr

Where did the spin angular momentum

disappear to?

Cylindrical symmetry means no angular momentum is transferred to the plate

Photo credit: pixaio, sxc.hu

Fascinating!What does the far field

look like?

Far field

Angle

Angl

e

Inte

nsity

(arb

. uni

ts)

Far field

Angle

Angl

e

Inte

nsity

(arb

. uni

ts)No hole in

the middle!

Far field

Component with the same handedness as the input (σ+)

Component with opposite handedness to the input (σ−)

Phase of central spot

Component with the same handedness as the input (σ+)

Component with opposite handedness to the input (σ−)

A proper calculation

modecon-

verter

� +, � = � � +, � = �

� − , � = �

A proper calculation

modecon-

verter

� � = −�� � = �

� � = +�� � =

� +, � = � � +, � = �

� − , � = �

A proper calculation

modecon-

verter

� � = −�� � = �

� � = +�� � =

Total angular momentum remains the same!

� +, � = � � +, � = �

� − , � = �

We found, constructed, and understood a novel spin-to-orbit angular momentum coupling device.

Orbital angular momentum

⟨Jspin⟩ = 0⟨Jorbit⟩ = h̵