probing lattice dynamics pampa devi april 29,2009
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Probing Lattice Dynamics
Pampa Devi April 29,2009
Bragg Law
Pump Probe Set Up
Velocity Mismatch Problem
Way to overcome it
Go Through….
Bragg Law
W. L. Bragg presented a simple explanation of the diffracted beams from a crystal based on a reflection from planes of atoms.
d
{dsin
The difference in the pathstraversed by the two beams shown in the figure is:
2dsin = n
X-Ray diffraction
Electron Diffraction
Pump Probe
Photography
Au
Powder Diffraction
8Committee Meeting # 2Seeing is believing ..
Hard to see … Ruan et al.
Ultrafast Electron Diffraction Groups Around the World
Velocity Mismatch Picture
Pump (Laser):
c
Probe (Electron Beam):
0.34 c
Why not use laser as probe ???
Accessories :
Peter Baum and Ahmed H. Zewail
No excitation
Excitation
After Excitation
c
AB
v
AC
el
'
c
AB
v
ACt
el
))(
)((tan
2 1
11
CosCosvc
SinCosv
el
el
Passing through a grating does the job…
))((
)tan
(
1
1
rSind
Sini
dCosr
Implementation
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