Photonic Diagnostics of Random MediaUCF College of Optics and Photonics

CREOL & FPCE

Spin Transfer and Power Flow at Subwavelength Scales

David Haefner

UNIVERSITY OF CENTRAL FLORIDACREOL, COLLEGE OF OPTICS AND PHOTONICS

Photonic Diagnostics of Random MediaUCF College of Optics and Photonics

CREOL & FPCE

Mechanical action of light

Comet tail points away from the Sun

Johannes Kepler: 1609

P. N. Lebedev “Experimental examination of

light pressure”, Ann. der Physik, 6, 433 1901Beth R. “Mechanical Detection and Measurement of the Angular Momentum of Light”, Physical. Rev. 50:

115-125 1936.

Quantitative experimental observations

Nature, 444, 823, 2006

James C. Maxwell: (1873)“In a medium in which waves are propagated there is a pressure in the direction normal to the wave…”

Linear momentum Force Push Angular momentum Torque Rotation

Joshua Tree National Park

Photonic Diagnostics of Random MediaUCF College of Optics and Photonics

CREOL & FPCE

Structuring energy flow with scattering?

Scattering redistributes the incident energy

Scattering depends on:

Wavelength

Polarization state

Incident angle

Photonic Diagnostics of Random MediaUCF College of Optics and Photonics

CREOL & FPCE

Scattering

ink

Photonic Diagnostics of Random MediaUCF College of Optics and Photonics

CREOL & FPCE

outk

ink

Scattering

Photonic Diagnostics of Random MediaUCF College of Optics and Photonics

CREOL & FPCE

outk

ink

Scattering

Photonic Diagnostics of Random MediaUCF College of Optics and Photonics

CREOL & FPCE

Conservation laws for electromagnetic waves

• Conservation of energy

• Conservation of linear momentum

• Conservation of angular momentum

* *0 0, ,2 2z z z

c cj x y z

i i

E r E E E

Orbital Spin

Angular momentum

C. Schwartz, A. Dogariu, Opt. Express 14, 8425-8433 (2006)

ink

Scattering

outk

ink

outk

Photonic Diagnostics of Random MediaUCF College of Optics and Photonics

CREOL & FPCE

2

LS

RS

Virtual location of a source

deg,

2sin211

sin

2 dipole

Distance along X axis [λ]

Dis

tanc

e al

ong

Y a

xis

[λ]

Right Circular

Left Circular

Linear

Photonic Diagnostics of Random MediaUCF College of Optics and Photonics

CREOL & FPCE

Energy flow

Complex behavior for larger spheres spans several λ

Photonic Diagnostics of Random MediaUCF College of Optics and Photonics

CREOL & FPCE

Direction sensitive observation

Dipole

x [μm]z [μm]

(IR

I L)

4.62μm polystyrene sphere in oil

x [μm]z [μm]

(IR

I L)

Single Mode Fiber

sE

Left RightLinear

*mod ˆ

2 s eC E E y d

Photonic Diagnostics of Random MediaUCF College of Optics and Photonics

CREOL & FPCE

Experimental setup

Laser

Polarizer

/2 /4

Coherent fiber bundle

CCD

Detector

Incoherent illumination

Typical incoherentimage on CCD

Micrometer size spheres

/4

Sumitomo IGN-08/30

Single mode fiberFiber scanned 5 microns from surface,NA of fiber = 0.3532nm light excitation4.62μm diameter polystyrene sphere in oil

Photonic Diagnostics of Random MediaUCF College of Optics and Photonics

CREOL & FPCE

Experimental results

D. Haefner, S. Sukhov, A. Dogariu, Phys. Rev. Lett. 102, 123903 (2009)

First demonstration of momentum conservation in scattering First demonstration of spin Hall effect in spherical geometry

-2 -1 0 1 2

-0.2

-0.1

0

0.1

0.2

Translation of optical fiber (μm)

(IR-I

L)/

max

(IR)

Analytical

-2 -1 0 1 2

-0.2

0

0.2

Translation of optical fiber (μm)

Experimental

(IR-I

L)/

max

(IR)

Photonic Diagnostics of Random MediaUCF College of Optics and Photonics

CREOL & FPCE

Torques on lossless spheres

Photonic Diagnostics of Random MediaUCF College of Optics and Photonics

CREOL & FPCE

Torques on lossless spheres

Spin Torque

Orbital Torque

T F F

T F F

IE

TF

TF

Spin Torque

Photonic Diagnostics of Random MediaUCF College of Optics and Photonics

CREOL & FPCE

210

1

210

410

610

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7Sphere radius a [λm]

0.8

Γo [

pN n

m]

Counter clockwise

2 2 4abs I absE a Q k 2 12B BF ak T

Brownian motion Intrinsic absorption

D. Haefner, S. Sukhov, A. Dogariu, Phys. Rev. Lett. 103, 173602 (2009)

1

210

410

610

810

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7Sphere radius a [λm]

0.8

Γs [

pN n

m]

Orbital Torque Spin Torque

Clockwise

Torques on lossless spheres

Photonic Diagnostics of Random MediaUCF College of Optics and Photonics

CREOL & FPCE

A new mechanism for momentum exchange

Optically induced torques

• Asymmetry

• Absorption

• Birefringence

• Near-field interaction

ink

outk

Angular momentum Torque

Linear momentum Force Push

Rotation

SymmetricLosslessHomogeneous

Photonic Diagnostics of Random MediaUCF College of Optics and Photonics

CREOL & FPCE

Summary

Right

Left

Linear

• Shift in perceived interaction volume

• Spin Hall effect of light

Angular momentum exchange in scattering

D. Haefner, S. Sukhov, A. Dogariu, “Spin Hall Effect of Light in Spherical Geometry”, Phys. Rev. Lett. 102, 123903 (2009)

Photonic Diagnostics of Random MediaUCF College of Optics and Photonics

CREOL & FPCE

Summary

Right

Left

Linear

• Shift in perceived interaction volume

• Spin Hall effect of light

Angular momentum exchange in scattering

Interaction provides a “new mechanism” for optical torques

D. Haefner, S. Sukhov, A. Dogariu, “Conservative and Nonconservative Torques in Optical Binding”, Phys. Rev. Lett. 103, 173602 (2009)

• Continuous spin and orbital torques

• Complex dependence on size for directionality of torques

D. Haefner, S. Sukhov, A. Dogariu, “Spin Hall Effect of Light in Spherical Geometry”, Phys. Rev. Lett. 102, 123903 (2009)