COLTRIMS Studies Of Correlation

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Correlation in the Sequential Release Of Two
Electrons from Atomic Targets by Short Laser
Pulses
Chakra Man Maharjan
Collaborators A. S. Alnaser, X. M. Tong, P.
Ranitiovic, I. Litvinuyk, and C.L. Cocke
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Basic Concept
e1-
Ar2
Ar
e2-
Fraction of an optical period
E
?t
Sub femto-second Electrons dynamics
Optical period2.6 fs
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OUTLINE

• The Goal to directly measure the time
  correlation between the two electrons and explore
  the clock that reads electronic dynamics of the
  system on sub-fs scale
• Tool Measure in COINCIDENCE the highly resolved
  momentum distributions of electrons and
  doubly-charged ions produced in the circularly
  polarized ultra short laser pulse.
• What is achieved the full vector momentum of
  the singly and doubly charged recoil ions (Ar and
  Ne) is measured. The ion momentum distributions
  can also be used to map the vector sum of the two
  emitted electrons momenta.

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Sequential ionization
Mechanism????
Tunneling Ionization
At high laser intensities
Over barrier ionization
EIp2/4Zeff
P E/?
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How electrons and ion gain momentum in laser
field?
Momentum conservation.
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How P1 and P2 related to E at time of release
EE0 e-t2/T2 (x Sinwt y Coswt)
Linearly polarized pulse
Circularly Polarized pulse
E
P2
P1
PE(t)/?
For Ar Electric field for over the barrier Ar
0.0841 a.u. (Io4.95x1014W/cm2) Ar0.1287 a.u.
(Io 1.16 x1015 W/cm2)
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The second hand clock!!
Angular correlation between two electrons
P1
F
E1
F cos-1(P1.P2/p1p2)
E2
P1E1/?
P2
P2E2/?
Time correlation
?t
t F/?
Phase stabilized laser.
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Experimental setup
(COLTRIMS)
Mirror
Y
Ion Detector
e detector
qn
Z
e-
Laser
X
Magnetic coil
Measure Time and position
JET
B
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Electron raw data( time of flight)
Counts
Tof (ns)
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Wiggles Spectrum
Calibration of parameters used in the experiment
r(0.5 mm)
Tc
TOF(ns)
Cyclotron Period
Pxm?c (X cot(?ctof/2)Y)/2
Pym?c (Y cot(?ctof/2)-X)/2
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Distribution of electrons in the plane
perpendicular to the direction of the laser
propagation
Y
Po
EoP?
Ioc?oEo2
X
Io4x1014 W/cm2
Z
PD 8 fs
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Ions Tofs and positions
Ar
Ar2
Time of Flight
O2
Background
Position Image
Target (jet)
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Single and Double Ionization of Ar Target (
Circular Polarization)
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Big Problem.
Random electron counts
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True coincidence
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Two ways to decrease random counts
1.Decrease counts rate 2.Decrease the size of
target beam
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Use piezoelectrical slits to minimize Volume
effects
jet
spherical mirror
laser
manipulator
laser focus
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Double Coincidence
Conservation of momentum !!!!
FWHM0.43a.u
Pze1Pzr
Io4x1014 W/cm2
PD 8 fs
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Triple coincidence
Pzr
Pze1Pze2Pzr
Pze1Pze2
Io1.8x1015 W/cm2
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How are these spectra related to the correlation
between two electrons ?
Model byX.M.Tong C.D.Lin
Ar2 momentum spectra
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Ion momentum distribution reflects the vector
sum of momenta of two electrons
Model byX.M.Tong C.D.Lin
Ne2 momentum spectrum
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The sum momentum spectrumNe as test case
Ne
Ne
Counts
pz
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Momentum of electrons at the over barrier.
Ar2
a.u.
P1 3.73 2.7
P2 2.257 5.0
P1-P2 0.7 2.3
P1P2 3.7 7.7
Ar2
Ne2
P1-P2
P1P2
Ne2
P1P2
P1-P2
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Momentum distribution of Ne2 and Ar2 in
the polarization plane
P1P2
P1-P2
Ne2
Ar2
(Io1x1016 W/cm2)
(Io4.5x1015 W/cm2)
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At the end
1.Random (false) counts is the main problem to
investigate the time correlation between two
electrons emitted sequentially with coincident
technique.
2.we are pretty much successful to get angular
correlation of two electrons using the doubly
charged ion momentum spectra