Transcript Slide 1

Wavelength-dependence of Momentum-Space Images
of Low-Energy Electrons Generated by
Short, Intense Laser Pulses
at High Intensities
Chakra Man Maharjan
A S Alnaser, P Ranitiovic , I Litvinuyk and C L Cocke
Department of Physics, Kansas State University
2006
MOTIVATION :
To understand and resolve the energy
and angular structure of the laser generated
electrons in the low energy region
Experimental Setup
Parabolic mirror
Supersonic jet
Electron detector
Y
Z
X
Short pulse laser
COLTRIMS
Ionization In Laser field
Keldysh Parameter
γ=
Ip = Ionization potential
Up = Pondermotiv energy
γ >1
Multi photon process
γ <1
Tunneling process
Ip
2U p
, Up ~ I λ2
Freeman Resonance and Above
Threshold Ionization (ATI)
n=∞
n=5
n=4
n=0
Freeman Resonance
ATI
Intensity
Up=I/4ω2
E  nhv  ( Ip  Up)
Freeman Resonance : sub-structures in ATI peaks
800nm_30V_1A_10mW_argon
250
Counts (arb.u)
200
4p 4d4f 5g 6g
150
4p 4d4f 5g 6g
4p 4d4f 5g 6g
100
50
0
0
1
2
3
E(eV)
4
5
6
Density plot of the electron monenta along
and perpendicular to the laser polarization
for different wavelengths
Diffraction effect (GRT)
Laser driven e
ρ
Kepler Hyperbola
0
Z
The same set of data in two different scale for 640nm.The
upper panel is optimized to reveal weak features for large
640nm
momenta, while the
lower panel is optimized to show stronger
30vlow energy features
18mw
640 nm
intensity features
main low
features
only
γ=0.54
Pt
14 W/cm2
7.08X10
14
2
7.08X10
W/cm
640nm
30v
18mw
640 nm
main features only
γ=0.54
7.08X1014 W/cm2
Pz
21mw
γ=0.5 640 nm 8.2X1014 W/cm2
Comparison of the
energy and angular
structure with three
different intensities
for 640 nm
640nm
30v
18mw
γ=0.54 640 nm 7.08X1014 W/cm2
Pt
640nm
30v
10mw
γ=0.72
640 nm 3.94X1014 W/cm2
Pz
Plots of the energy spectra, integrated over
all angles, in the region of the first ATI group
4f
5g 6h 7i
Intensity (arbitrary units)
2000
1000
800 nm
680 nm
640 nm
615 nm
590 nm
400 nm
0
-2.0
-1.0
Binding energy (eV)
0.0
Energy Vs Angle
0
10
20
30
40
50
60
70
80
90
Θ (deg)
0
10
20
30
40
50
60
70
80
90
0
10
20
30
40
50
60
70
80
90
640nm
400nm
590nm
680nm
800nm
615nm
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
E (eV)
Projections of the data from energy spectrum onto
the angle axis for a wavelength of 640 nm for
selected energy slices
4f resonance
5g resonance
The square of the Legendre
polynomial P6(cosθ),
multiplied by sinθ
Energy and angular
structure of electrons in
momentum image
generated by a laser field
from align N2 and 02
molecules
PUMP – PROBE SETUP
Delay Stage
KLS, VP
Probe
Detector
chamber
Pump
Source
chamber
N2
λ/4
Test of alignment of molecules (N2)
Probe Pulse
only
With both
Pump and Probe
pulses
N2+/N2+
Coulomb explosion
Rotational revival ( N2)
B
0.75
1
Ipump = 1.1 x1014 W/cm2
Iprobe=5.5X1014 W/cm2
0.65
0.60
1
N2
2
2
<cos theta>
0.70
0.55
0.50
0.45
2
0.40
3600
3800
4000
4200
4400
Delay(fs)
4600
4800
5000
Rotational revival
B
0.75
1
0.65
0.60
N2
2
<cos theta>
0.70
0.55
0.50
0.45
2
0.40
3600
3800
4000
4200
4400
4600
4800
Delay(fs)
1
5000
ATI STRUCTURES
2
Rotational revival
B
0.75
1
0.65
0.60
N2
2
<cos theta>
0.70
0.55
0.50
0.45
2
Photoelectron angular
distribution
0.40
3600
3800
4000
4200
4400
4600
Delay(fs)
4800
5000
90
90
120
120
60
30
150
180
60
30
150
0
180
0
1
330
210
240
2
210
330
300
270
E (4-5 eV) 4050 fs
240
300
270
E (4-5 eV) 4300 fs
0.80
0.75
O2
Ipump=4.0 x1013 W/cm2
0.65
Iprobe=1.0X1014 W/cm2
2
<cos >
0.70
0.60
0.55
0.50
0.45
0.40
2400
2600
2800
3000
3200
3400
Delay(fs)
2920 fs
3100 fs
Probe only
0.80
O2
0.75
0.65
2
<cos >
0.70
0.60
0.55
0.50
0.45
0.40
2400
2600
2800
3000
3200
3400
ATI STRUCTURES
Delay(fs)
2920 fs
3100 fs
Probe only
Photoelectron
angular distribution
(5-6 eV)
0.80
O2
0.75
0.65
2
<cos >
0.70
0.60
0.55
0.50
0.45
0.40
2400
2600
2800
3000
3200
3400
Delay(fs)
2920 fs
3100 fs
Probe only
Thanks for your attention !!