Spin Transfer and Power Flow at Subwavelength Scales

1. Spin Transfer and Power Flow at Subwavelength Scales David Haefner UNIVERSITY OF CENTRAL FLORIDA CREOL, COLLEGE OF OPTICS AND PHOTONICS

2. Angular momentum Torque Rotation Linear momentum Force Push Mechanical action of light Johannes Kepler:1609 James C. Maxwell: (1873) “In a medium in which waves are propagated there is a pressure in the direction normal to the wave…” Comet tail points away from the Sun Joshua Tree National Park Nature, 444, 823, 2006 Quantitative experimental observations Beth R. “Mechanical Detection and Measurement of the Angular Momentum of Light”, Physical. Rev. 50: 115-125 1936. P. N. Lebedev “Experimental examination of light pressure”, Ann. der Physik, 6, 433 1901

3. Structuring energy flow with scattering? Scattering redistributes the incident energy Scattering depends on: Wavelength Polarization state Incident angle

4. Scattering

5. Scattering

6. Scattering

7. Scattering Conservation laws for electromagnetic waves • Conservation of energy • Conservation of linear momentum • Conservation of angular momentum Angular momentum Spin Orbital C. Schwartz, A. Dogariu, Opt. Express 14, 8425-8433 (2006)

8. Virtual location of a source Right Circular Linear Distance along Y axis [λ] Left Circular Distance along X axis [λ]

9. Energy flow Complex behavior for larger spheres spans several λ

10. 4.62μm polystyrene sphere in oil Dipole (IR IL) (IR IL) z [μm] z [μm] x [μm] x [μm] Direction sensitive observation Single Mode Fiber Linear Left Right

11. Experimental setup Micrometer size spheres Coherent fiber bundle Sumitomo IGN-08/30 CCD /4 Detector Typical incoherent image on CCD Polarizer Laser /4 /2 Incoherent illumination Fiber scanned 5 microns from surface, NA of fiber = 0.3 532nm light excitation 4.62μm diameter polystyrene sphere in oil Single mode fiber

12. Analytical Experimental 0.2 0.2 0.1 0 0 (IR-IL)/max(IR) (IR-IL)/max(IR) -0.1 -0.2 -0.2 -2 -1 0 1 2 -2 -1 0 1 2 Translation of optical fiber (μm) Translation of optical fiber (μm) Experimental results • First demonstration of momentum conservation in scattering • First demonstration of spin Hall effect in spherical geometry D. Haefner, S. Sukhov, A. Dogariu, Phys. Rev. Lett. 102, 123903 (2009)

13. Torques on lossless spheres

14. Torques on lossless spheres Spin Torque Spin Torque Orbital Torque

15. Γo [pN nm] 0 0 0.1 0.1 0.2 0.2 0.3 0.3 0.4 0.4 0.5 0.5 0.6 0.6 0.7 0.7 0.8 0.8 Sphere radius a [λm] Sphere radius a [λm] Γs [pN nm] Torques on lossless spheres Orbital Torque Spin Torque Brownian motion Intrinsic absorption Nano-mixer Clockwise Counter clockwise D. Haefner, S. Sukhov, A. Dogariu, Phys. Rev. Lett. 103, 173602 (2009)

16. A new mechanism for momentum exchange Linear momentum Force Push Angular momentum Torque Rotation • Optically induced torques • Asymmetry • Absorption • Birefringence • Near-field interaction Symmetric Lossless Homogeneous

17. Summary Angular momentum exchange in scattering Right • Shift in perceived interaction volume • Spin Hall effect of light Linear D. Haefner, S. Sukhov, A. Dogariu, “Spin Hall Effect of Light in Spherical Geometry”, Phys. Rev. Lett. 102, 123903 (2009) Left

18. Summary Angular momentum exchange in scattering Right • Shift in perceived interaction volume • Spin Hall effect of light Linear D. Haefner, S. Sukhov, A. Dogariu, “Spin Hall Effect of Light in Spherical Geometry”, Phys. Rev. Lett. 102, 123903 (2009) Left Interaction provides a “new mechanism” for optical torques • Continuous spin and orbital torques • Complex dependence on size for directionality of torques D. Haefner, S. Sukhov, A. Dogariu, “Conservative and Nonconservative Torques in Optical Binding”, Phys. Rev. Lett. 103, 173602 (2009)