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

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Kapitza-Dirac EffectElectron Diffraction from a
Standing Light Wave
Physics 138 SP05 (Prof. D. Budker)
Victor Acosta
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Contents

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

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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

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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
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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).
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Analogy Multiple-Slit Diffraction
Detector
?
d
d
Assume outgoing waves propagate at ? w.r.t
grating axis (zgtgtd).
Path Length Difference (PLD) dSin? Bragg
Condition satisfied iff PLD n? ? dSin? n?
z
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Figure from Bataleen group (U. Nebraska).
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Quantum Mechanical Theory

• Need full QM treatment to understand nature of
  diffraction peaks
• First find H using Classical EM
• Then solve Time-Dependent Schroedinger Equation

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Figure from Bataleen group (U. Nebraska).
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Legend Bragg Regime (Top) Raman-Nath
(Bottom) n0 (red) n1 (blue) n2 (green)
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Figure from Bataleen group (U. Nebraska).
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Figure from Bataleen group (U. Nebraska).
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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
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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
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Applications

• Coherent Electron Beam Splitter
• Electron Interferometry
• Greater Sensitivity than Atomic Version
• ?electron 10-11 gt .1?atom
• Low electron energies possible
• Microscopic Stern-Gerlach Magnet?
• Would separate Electrons by spin
• Need light grating that isnt standing wave