1. Integrated optical tornadoes for efficient light harvesting Svetlana V. Boriskina, Selcuk Yerci & Gang Chen NanoEngineering group Department of Mechanical Engineering Massachusetts Institute of Technology

2. 2 Cat. F5 tornado (Manitoba, Canada, June 2007) Image credit: Juri Hahhal

3. 3 Ray picture dominates conventional thinking about light propagation Image credit: Teresa Matfield A. Mavrokefalos et al, Nano Lett. 12, 2792-2796, 2012

4. 4 Light trapping schemes typically rely on constructive interference of light rays scattering J. VanCleave, Colors & Thin-Film Interference, John Wiley & Sons, Inc. Atwater & Polman, Nature Mater. 2010 field enhancement waveguiding

5. 5 There is another way: making use of destructive interference ‘Black holes are where God divided by zero’ Steven Alexander Wright phase vortex = indefinite phase zero intensity

6. 6 There is another way: making use of destructive interference ‘Black holes are where God divided by zero’ Steven Alexander Wright = indefinite phase zero intensity Credit: iStockphoto.com/David Ciemny

7. 7 There is another way: making use of destructive interference ‘Black holes are where God divided by zero’ flow vortex Steven Alexander Wright phase vortex Optical energy flows in the direction of the phase change

8. 8 Hydrodynamic analogy of light trapping S.V. Boriskina, “Plasmonics with a twist,” in Plasmonics in metal nanostructures: Theory & applications ( Shahbazyan & Stockman eds.) Springer, 2013 Image credit: Teresa Matfield Image credit: http://www.forestwander.com

9. 9 Hydrodynamic analogy of light flow Maxwell’s equations: S.V. Boriskina & B.M. Reinhard, Nanoscale, 4, 76-90, 2012 ‘mass’ conservation: momentum conservation: Navier-Stokes-like equations: (Madelung, 1926)

10. 10 Hydrodynamic analogy of light flow Maxwell’s equations: S.V. Boriskina & B.M. Reinhard, Nanoscale, 4, 76-90, 2012 convective term ‘mass’ conservation: momentum conservation: potential created by the light trapping structure material loss or gain Navier-Stokes-like equations: ‘Photon fluid’ density: ‘Photon fluid’ velocity: (Madelung, 1926)

11. 11 How are optical tornadoes generated?

12. 12 By colliding several light beams with appropriate phases …

13. 13 … or by strategically positioning obstacles in the light flow path S.V. Boriskina & B.M. Reinhard, Nanoscale, 4, 76-90, 2012 Zero intensity

14. 14 S.V. Boriskina & B.M. Reinhard, Nanoscale, 4, 76-90 (2012) W. Ahn, S.V. Boriskina, et al, Nano Lett. 12, 219-227 (2012) Example of a vortex-pinning nanostructure 50-nm radius Au nanoparticles

15. 15 S.V. Boriskina & B.M. Reinhard, Nanoscale, 4, 76-90 (2012) W. Ahn, S.V. Boriskina, et al, Nano Lett. 12, 219-227 (2012) Example of a vortex-pinning nanostructure 50-nm radius Au nanoparticles

16. 16 S.V. Boriskina & B.M. Reinhard, Nanoscale, 4, 76-90 (2012) W. Ahn, S.V. Boriskina, et al, Nano Lett. 12, 219-227 (2012) Optical energy is circulating outside the metal volume!

17. 17 What is the origin of the strong field enhancement?

18. 18 Optical vortices generate local velocity fields Tangential velocity ~1/r r compressible fluid potential steady- state flow local convective acceleration possible

19. 19 ‘Photon fluid’ is convectively accelerated in the vortex velocity field… compressible fluid potential steady- state flow local convective acceleration possible

20. 20 … and when threaded through nanoscale gaps, generates ‘hydraulic jumps’ - areas of high field intensity

21. 21 … and when threaded through nanoscale gaps, generates ‘hydraulic jumps’ - areas of high field intensity

22. 22 Vortex-pinning nanostructures are photonic analogs of turbopumps

23. 23 Optical vortices can be moved and ‘stretched’ by repositioning the obstacles

24. 24 Tunable or broadband light trapping possible

25. 25 Beyond light trapping …

26. 26 Nanoscale light switching S.V. Boriskina & B.M. Reinhard, Opt. Express, vol. 19, no. 22, pp. 22305, 2011

27. 27 Nanoscale light switching S.V. Boriskina & B.M. Reinhard, Opt. Express, vol. 19, no. 22, pp. 22305, 2011

28. 28 Nanoscale light switching S.V. Boriskina & B.M. Reinhard, Opt. Express, vol. 19, no. 22, pp. 22305, 2011

29. 29 Nanoscale light switching S.V. Boriskina & B.M. Reinhard, Opt. Express, vol. 19, no. 22, pp. 22305, 2011

30. 30 Nanoscale light switching S.V. Boriskina & B.M. Reinhard, Opt. Express, vol. 19, no. 22, pp. 22305, 2011

31. HT2013-17406 ‘Surface Plasmon Enhanced Radiative Nanoscale Heat Transfer’ Thu, July 18, 3:58pm, Salon G 31

32. Conclusions and outlook New way of trapping light by molding it into nanoscale vortices Higher field concentration than traditional schemes based on constructive interference Strong energy flow outside of the metal volume of nanoparticles – PV applications New way of designing light absorbers via the hydrodynamic analogy

33. Many thanks to Prof. Gang Chen & MIT NanoEngineering group 33 SOLID STATE SOLAR THERMAL ENERGY CONVERSION (S 3 TEC) CENTER The audience