Transcript Coulomb Explosion Imaging - International Symposium on

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High Harmonic Transient Grating
Spectroscopy
The key idea; F=ma
Mapped by
classical physics
to here
Attoseconds
arise first here
Classically an atom’s own electron,
driven by a strong electric field can
interact with its parent within a cycle.
The key idea
c=a(k)eikx-it
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Kinetic energy, amplitude and phase of the re-collision
electron is transferred to photons. Observing photons is
equivalent observing electrons. One is a replica of the
other
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High Harmonics/Attoseconds pulses
d(t) is essentially
the Fourier
transform of the
wave function
d(t)={|r|a(k)eikx d3r}e(IP+KE)t +

Reconstructed N2 g Orbital
• Reconstructed
from 19 angular
projections
• wave function,
not its square
We see electrons!
Amplitude and Phase!
Review: In the same experiment
•We have laser Electrical Forces that can
be as strong as (or stronger than) those
binding electrons to molecules.
•We can also apply internal and external
dipole forces that are significant with
respect to bond strengths
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electric field
•We can control these forces on the
natural time scale of molecules. And it
will improve covering all visible and ir
frequencies
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fem toseconds
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Review continue:
We can probe and excite molecules
with attosecond pulses --- exceeding
the electronic time scale.
And we have a re-collision electron
with wavelength of ~ 1 Angstrom,
giving us access to molecular scale
spatial resolution.
These are powerful and natural tools for
molecular science.
If we can “see” electrons,
We can “see” them move!
Attosecond Imaging
PRL 94, 083003 (2005)
The two wave packets collide
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Time maps into electron KE
1E-16
1E-18
Radiation intensity (a.u.)
1E-20
1E-22
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(b)330 as
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Laser Intensity (a.u.)
(a)290 as
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Time / fs
1×1014W/cm2
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1600 nm, ~6 fs
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(c)444 as
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Photon energy / eV
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Fixed carrier phase
If a pre-existing replica can be
used for imaging
So can a photoelectron replica
produced with the attosecond
pulse
PRL 94, 083003 (2005)
Photo-ionization in reverse.
The key idea
c=a(k)eikx-it
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Kinetic energy, amplitude and phase of the re-collision
electron is transferred to photons. Phase is determined by
the path length and the velocity --- each scales with E
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A diffraction grating
=
Since the control field is weak
we separate the generation from control.
Like 4-wave mixing
Generating
beam
Dressing beams
grating
Supersonic gas jet
MCP
Transient diffractive elements
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This is the
nth
order analogue to 4-wave
mixing
Since we control phase, we
can construct any phase
element
-Lenses
-prisms
-Digital optics
lasting less than one period if
needed.
Reaching below the electron
wavelength
•Optical interferometers measure subtle
changes in interference – Phase changes
much less 2 (10-6 x 2).
•In electron wavelengths, this is a very small
distance.
•Can small molecular features be resolved? dimension and local fields?
•These parameters --- shape and local fields
influence a molecule’s reactivity.
Transient grating spectroscopy
XUV Interferometry --- a two slit grating
Alignment Scan in N2
Visible phase shift, increasing with harmonic order
Accuracy about 1/100 of a fringe
Harmonic phase as a function of molecular
alignment
No Transient Grating
H17
H31
Dt < 0: No alignment
Transient Grating
Spectroscopy in HHG
2-D measurement of N2
(rotational temperature ~ 90°K.)
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t = 4.15 ps
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h
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t = 4.33 ps
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T im e (ps)
J=J(J+1) 1/2; 1=B/2; T1=2/1
Transient Grating Present
Dt=4.1 ps: Alignment
H17
H31
Direction of diffracted peaks for H17: +- 3.5 mrad.
13 microns
Corresponding interfringe in the near field: 13.5
microns
10 percent in each diffracted peak for harmonic 17
Very efficient diffraction
Zero order and diffracted signal
Diffracted
signal is
too great
to be only
an
amplitude
grating
Amplitude and phase information are
projected to direction with zero background
Resonance
Angle Dependent High Harmonic Spectrum
We are working hard to
obtain tomographic images
of CO2
What about collisions? Immediately the
atom sees a huge current surge.
15/09/2006 3:09 AM
Is there any hope for attosecond
science inside liquids and solids?
I think so. Sub-cycle science seems
perfectly compatible with transparent
solids and liquids
Highly multiphoton phenomena are not
limited to atomic and molecular gases
Quarter waveplate
Polarizer
•In solids, saturation is running
out of photons
40fs, 100KHz
800nm, 100nJ-1uJ
40x, NA=0.65
•Solids, acts back on the light -locally and globally
•In gases, we have a new
sample each shot
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•In gases, saturation is running
out of atoms
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n
ca
d
tio
c
ire
n
•In solids, the debris gives a
shot-to-shot memory (positive
feedback in SiO2)
Image of an Etched Structure (~1000 shots)
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A uniform focus
produces lines
spaced subwavelength
Image (laser polarization 900 to writing direction)
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Nanoplanes (< 5 nm wide) stretching
for 100’s of m
Image (laser polarization parallel to writing direction)
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Ionization produces dense plasmas, but
with p<  --- This is a unique nanoplasmonics.
Image (laser polarization 450 to writing direction)
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45o
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Nano-planes are spaced and aligned by
the laser field
PRL 96, 067404 (2006)
Attosecond and multiphoton
physics are entwined in dielectrics
•A 5-eV electron experiences a momentum
changing collision in ~ 100 attoseconds in SiO2
•Field assisted collisional ionization must be
ubiquitous
•(conventionally, avalanche ionization is
assumed to be absent for less than 100 fs)
•Enhanced ionization must also be ubiquitous
Understanding laser interaction with
dielectrics, cells, tissue, etc, will need
attosecond techniques
The absorption is greater for the major axis
than the minor axis.
02/02/2007 7:44 AM
Polarization
analyzer
spectator
/4
SiO2
More circular
The Atto sub-group (2007)
Scientists: Paul Corkum, David Villeneuve, Eli
Simova, Andrei Naumov and David Rayner
Technologists: Bert Avery, John Parsons
Postdoctoral Fellows: Nirit Dudovitch, Rajeev
Pattathil, Domagoj Pavicic and Yann Mairesse.
Visitors: Hiromichi Niikura (JST), Gennady Yudin and
Andre Staudte
Ph. D. Students: Kevin Lee (McMaster), Julien
Bertrand and Marina Gertsvolf (Ottawa).