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)