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Kapitza-Dirac Effect: Electron Diffraction from a Standing Light Wave

Kapitza-Dirac Effect: Electron Diffraction from a Standing Light Wave. Physics 138 SP’05 (Prof. D. Budker). Victor Acosta. Contents. History Introduction Basic Setup/Results Theory Multi-Slit Analogy Particle Interaction Picture QM Treatment U. Nebraska 2001 Results Applications.

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Kapitza-Dirac Effect: Electron Diffraction from a Standing Light Wave

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  1. Kapitza-Dirac Effect:Electron Diffraction from a Standing Light Wave Physics 138 SP’05 (Prof. D. Budker) Victor Acosta

  2. Contents • History • Introduction • Basic Setup/Results • Theory • Multi-Slit Analogy • Particle Interaction Picture • QM Treatment • U. Nebraska 2001 Results • Applications

  3. History • 1804 • Young Proposes Double Slit Experiment • Wave nature of Light • 1905 • Einstein Photoelectric Effect • Particle nature of Light • 1927 • Davisson and Germer Electron Diffraction (crystalline metal) • Wave nature of matter • 1930 • Kapitza and Dirac propose KDE • Light Intensity of mercury lamp only allows 10-14 electrons to diffract • 1960 • Invention of Laser • First Real Attempts at KDE • All 4 were unsuccessful (poor beam quality? Undeveloped Theory?) • 2001 • KDE seen by U. Nebraska group

  4. Introduction to Kapitza-Dirac Effect (KDE) Figure 1. Adapted from Kapitza and Dirac's original paper. Electrons diffract from a standing wave of light (laser bouncing off mirror). Figure from Bataleen group (U. Nebraska). Analogy) KDE : Multi-Slit Diffraction Electron Beam : incident wave Light Source: grating

  5. Basic Setup/Results Data for atom diffraction from a grating of ’light’ taken at the University of Innsbruck. Diffraction peak separation = 2 photon recoil momenta. Figure from Bataleen group (U. Nebraska).

  6. Analogy: Multiple-Slit Diffraction Detector θ d d Assume outgoing waves propagate at θ w.r.t grating axis (z>>d). Path Length Difference (PLD) = dSin[θ] Bragg Condition satisfied iff PLD = nλ → dSin[θ] = nλ z

  7. Figure from Bataleen group (U. Nebraska).

  8. Quantum Mechanical Theory • Need full QM treatment to understand nature of diffraction peaks • First find H using Classical E+M • Then solve Time-Dependent Schroedinger Equation

  9. Figure from Bataleen group (U. Nebraska).

  10. Legend: Bragg Regime (Top) Raman-Nath (Bottom): n=0 (red) n=1 (blue) n=2 (green)

  11. Figure from Bataleen group (U. Nebraska).

  12. Figure from Bataleen group (U. Nebraska).

  13. U. Nebraska 2001 Results: Raman-Nath Regime Laser off (Top) and Laser on (bottom) Plaser= 10 W Ilaser= 271 GW/cm2 Vp= 7.18 meV. Eo = 5.31 µeV Ve=.0367c

  14. U. Nebraska 2001 Results: Bragg Regime Laser off (Top) and Laser on (bottom) Plaser= 1.4 W Ilaser= 0.29 GW/cm2 Vp= 7.66 µeV. Eo = 5.31 µeV Ve=.0367c

  15. Applications • Coherent Electron Beam Splitter • Electron Interferometry • Greater Sensitivity than Atomic Version • λelectron ~ 10-11 > .1λatom • Low electron energies possible • Microscopic Stern-Gerlach Magnet? • Would separate Electron’s by spin • Need light grating that isn’t standing wave

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