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

Scientific talk I gave at Physics@FOM Veldhoven 2012.

Transcript

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

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2. Suspicious
   behavior in
   subwavelength
   slits
   

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

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

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

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7. 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 rotation
   Input state
   Measured output
   

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

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9. Space-variant λ/4 plate
   

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

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

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12. Space-variant λ/4 plate
    Output: ?
    

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13. Transmitted polarization state
    Schematic
    

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14. Transmitted intensity
    Experiment
    

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

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

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

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

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

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

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

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

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24. A proper calculation
    mode
    con-
    verter
    +TQJO = −
    I
    +PSCJU =
    I
    +TQJO = +
    I
    +PSCJU =
    ѫ
    +, = ѫ+
    , =
    ѫ
    −, =
    

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

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

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

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