Download Coulomb Explosion Imaging - ultrafast dynamic imaging 2009

A Laser STM for Molecules
Tunneling has transformed surface science.
Tunneling is one of
the simplest
quantum
mechanical
process
An STM
Measures I(r)
Scanning the field around
the molecule is like
scanning the tip across a
surface -- a molecular STM
H2 ionization in circularly polarized light
e
p
•The electron direction determines the field direction
at the moment of ionization
•The bond softened ion determines the molecule’s
direction at the moment of ionization
COLTRIMS – measuring the 3d-momenta of
correlated particles
The angle-dependent ionization probability
PRL 102, 033004 (2009)
Implications of high tunneling rates:
 E 5 / 2
 i 
(t )  4  
0 E 
 h

3
/
2



E
 Ei 
2

a exp  
 3E 
E(t )
 h 



E 
a

E(t ) 


“DC” tunneling – The exponent is ~ 30-40. A
small change in Ei is highly leveraged by the
large Ea/E(t).
Laser tunneling: -- The exponent is ~ 8. The
leverage is weakened. Lower orbitals will
contribute.
Measuring excited states
PRL 94, 033003 (2005)
The laser STM senses the structure of
orbitals:
SU1 – direct tunneling
SU2 – excitation by
bound state interaction
with the departing
electron
IP~4 eV
Applying the “laser STM” to HCl
Deeper orbitals tunnel ionize (directly)
Two or more orbitals can ionize
HCl
Transient alignment of molecules
time
Phys. Rev. A. 68, 023406 (2003)
A molecular STM has much more information
 p2 IP 
c ( )  p  exp 

 E 2 
Normalized Differences
Notice:
1 Low lateral
momentum
structures –
tunneling
and
2 High lateral
momentum
structures –
elastic
scattering
Science 3201478 (2008)
The Model:
1.
Assume
2.
Propagate
swarm of
electron
trajectories
classically
3.
Including
electron-ion
interaction
4.
Include
alignment
distribution
 p2 IP 
c ( )  p  exp 

 E 2 
laser

pmolecule
pnormal
Low Lateral momentum electrons
Science 3201478 (2008)
The angle dependent probability
N2
PRL 98, 243001 (2007)
O2
CO2
Transparent Solids: E = O(10eV)
crystal structure
a-SiO2
c
b
a
Al2O3
LiF
Extending to Solids? The Lawn Mower Model
Time
Radius
Normalized Transmission
1.2
1.1
• Self-controlled energy
deposition.
1
0.9
0.8
• electron and energy density is
predicted.
0.7
0.6
0.5
0.4
0
50
100
150
200
250
300
Input Pulse Energy (nJ)
Opt. Express 13, 3208 (2005).
Transmission as a function of angle
O
Si
G
K
M
Angle dependent changes in the reduced-mass
change the ionization rate.
~ m3 resolution
(l/2)
5
Quartz
2.5
0
1
Sapphire
0.5
5
0
LiF
2.5
0
1
Fused Silica
0.5
0.5
1
1.5
2
2.5
3
3.5
azymuthal symmetry in transmission [ x - fold ]
4
0
4.5
Only the focal region is measured
fused
crystalline
amorphous
0
crystal
Phys. Rev. Lett. 101, 243001 (2008)
The laser STM
Atoms: The filter function
•
using circular polarization.
Molecules: The orbital
•
Filtered image of the orbital
•
Quantify the contribution of lower
orbitals.
Solids: The reduced tunneling mass
•
Measuring crystal symmerty
Link to HHG – correlated measurements
• A mixture of
optical and
collision science
•Coherence can be
transferred several
times between
electrons and
photons
•The mixture offers
new opportunities
for each
To optics -Angstrom spatial
imaging.
To collision
physics -- Time
resolution.
Bertrand P1, Wörner P3, Meckel
Three new forms of nonlinear spectroscopy
1 Tunneling (to characterize orbitals)
2 Elastic scattering or Laser Induced
Electron Diffraction (to determine
nuclear positions) – see Meckel et al.
3 Interferometry (to image orbitals -photoelectron spectroscopy in
reverse) – see poster by Bertrand P1
and Wörner P3
The tunneling electron wave packet of O2
normalized difference
0.05
Experiment 90°
Experiment 45°
Experiment 0°
Simulation 90°
Simulation 45°
Simulatio 0°
0.00
-0.05
-0.10
-0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5
px (atomic units)