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