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Coherent Phase Control of Electronic Transitions in Gallium Arsenide

This study explores passive and active control methods for manipulating electronic transitions in Gallium Arsenide, utilizing ultrafast laser pulses. The results reveal insights into the underlying mechanisms and propose new pathways for achieving control.

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Coherent Phase Control of Electronic Transitions in Gallium Arsenide

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  1. Coherent Phase Control of Electronic Transitions in Gallium Arsenide Robert J. Gordon, SimaSingha, and Zhan Hu Department of Chemistry University of Illinois at Chicago FRISNO 11 Aussois, France March 31, 2011

  2. Passive Control F. Crim

  3. Active Control

  4. JPC

  5. Outline • Motivation and methods • Results from open loop experiments • Results from closed loop experiments • Proposed mechanism • Conclusions

  6. Cut in Decemet’s Membrane 6 ns, 1064 nm 30 ps, 1064 nm Vogel, et al., Invest. Ophthalmol. Vis. Sci. 35, 3033 (1997)

  7. Surface Modification with Ultrafast Pulses Stoian, et al., Appl.Phys. Lett. 80, 353 (2002)

  8. SEM images of the ablation craters on GaAs 1, 5 and 5+1 pulse trains

  9. Outline • Motivation and methods • Results from open loop experiments • Results from closed loop experiments • Proposed mechanism • Conclusions

  10. LIBS/Photoluminescence Spectrum Phys. Rev. B 82, 115205 (2010)

  11. Effect of Laser Polarization

  12. PL Signal at 450.8 nm

  13. Control Landscape

  14. Effects of Polarization and Incidence Angle

  15. Effect of Laser Fluence

  16. Effect of Laser Phase

  17. Outline • Motivation and methods • Results from open loop experiments • Results from closed loop experiments • Proposed mechanism • Conclusions

  18. Closed Loop Control Sine phase optimized for 390-450 nm sine phase optimized for 420-440 nm random phase optimized for 390-450 nm J. Phy. Chem. A (in press)

  19. Optimum Pulse Shapes for Open and Closed Loops PRB paper graph 20100528-115537

  20. Effect of Laser Fluence

  21. Effect of Laser Polarization on Optimized PL Spectrum

  22. Effect of Laser Phase on Open-Loop Spectrum

  23. Effect of Laser Phase on Closed-Loop Spectrum

  24. Outline • Motivation and methods • Results from open loop experiments • Results from closed loop experiments • Proposed mechanism • Conclusions

  25. Mechanistic Questions • Where does the new band come from? • How is it possible to excite optical phonons at fluences above the threshold for melting? • How does light couple to the plasma? • How does energy couple to the phonons? • Where does the coherence come from?

  26. Ratio of double pulse to single pulse fluorescence as a function of delay time and total energy Si<111> App. Phys. Lett. 90, 131910 (2007), J. Appl. Phys. 104, 113520 (2008)

  27. Light Propagation in a Plasma • Dispersion relation for a light wave in a plasma: • Critical density: • Index of refraction: • Total reflection:

  28. Brunel or vacuum heating

  29. Comparison of Closed and Open-Loop Pulses

  30. Conclusions • Coherent control of carrier recombination was achieved at fluences well above the damage threshold. • The primary mechanism for open loop control appears to be phonon-hole scattering, with trapping of carriers in the L-valley. • Brunel (ponderomotive) heating launches ballistic electrons that excite the phonons. • Effect of laser phase suggests a competition between photoemission and phonon excitation. • Random phase optimization appears to converge to a different control pathway.

  31. Yaoming Lu, Youbo Zhao, Slobodan MilasinovicJohn Penczak, SimaSingha, Zhan Hu Supported by NSF, USAF Surgeon General, UIC

  32. Time Delay Scans

  33. Properties of the Optimum Pulse vs. Fluence

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