Probing Lattice Dynamics Pampa Devi April 29,2009.

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