This document describes research into using a circular nanoslit to convert spin angular momentum to orbital angular momentum. Experiments showed that a circularly polarized input beam was converted to an elliptically polarized output with opposite handedness and a phase difference between components. This demonstrated that the nanoslit acts as a space-variant quarter-wave plate, effectively coupling spin and orbital angular momentum while conserving total angular momentum. The researchers constructed and analyzed a novel spin-to-orbit angular momentum coupling device.

1. A Circular Nanoslit as a
Spin-to-Orbital Angular
Momentum Converter
Philip Chimento
Gert ‘t Hooft
Eric Eliel

2. Suspicious
behavior in
subwavelength
slits

3. Slit in a metal film
Chimento, Kuzmin, Bosman, et al. (2011). Opt. Expr. 19 (24), 24219.

4. Slit in a metal film
Subwavelength “Infinite” in the other
in one direction
Chimento, Kuzmin, Bosman, et al. (2011). Opt. Expr. 19 (24), 24219.

5. Almost ideal metal
TM
TE
Slit width in λ
Chimento, Kuzmin, Bosman, et al. (2011). Opt. Expr. 19 (24), 24219.

6. Real metal
TM
TE
Slit width in λ
Chimento, Kuzmin, Bosman, et al. (2011). Opt. Expr. 19 (24), 24219.

7. Real metal
Input state Analyzer rotation
Measured output
If designed carefully,
there is a point where the
slit is a quarter-wave plate
Chimento, Kuzmin, Bosman, et al. (2011). Opt. Expr. 19 (24), 24219.

8. We roll the slit up
into a circle
Photo credit: Dandelion And Burdock, Flickr

9. Space-variant λ/4 plate

10. Space-variant λ/4 plate
TE
TM
TM
TE

11. Space-variant λ/4 plate
Input: circular p
olarization
σ+ state

12. Space-variant λ/4 plate
Output: ?

13. Transmitted polarization state
Schematic

14. Transmitted intensity
Experiment

15. Transmitted polarization state
Experiment
Left-handed elliptical
Right-handed elliptical
Ellipticity <10%

16. Where did the spin
angular momentum
disappear to?
Photo credit: Cayusa, Flickr

17. Cylindrical symmetry means
no angular momentum is
transferred to the plate
Photo credit: pixaio, sxc.hu

18. Fascinating!
What does the far field
look like?

19. Angle
Angle
Far field
Intensity (arb. units)

20. Far field
No hole in
Intensity (arb. units)
the middle!
Angle
Angle

21. Far field
Component with the same Component with opposite
handedness as the input (σ+) handedness to the input (σ−)

22. Phase of central spot
Component with the same Component with opposite
handedness as the input (σ+) handedness to the input (σ−)

23. A proper calculation
+, =
+, = mode
con-
−,
verter
=

24. A proper calculation
+, =
+, = mode
= +
con-
verter
−,
=
=
= −
=

25. A proper calculation
+, =
+, = mode
= +
con-
verter
−,
=
=
= −
Total angular momentum
remains the same!
=

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

29. Orbital angular momentum
⟨Jspin ⟩ = 0
̵
⟨Jorbit ⟩ = h