Sharly Fleischer, Yan Zhou, Robert W. Field, Keith A. Nelson FRISNO 11 Orientation and Alignment of...
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Transcript of Sharly Fleischer, Yan Zhou, Robert W. Field, Keith A. Nelson FRISNO 11 Orientation and Alignment of...
Sharly Fleischer, Yan Zhou, Robert W. Field, Keith A. Nelson
FRISNO 11
Orientation and Alignment of Gas Phase Molecules by Single Cycle THz Pulses
Multiphoton Ionization Self focusing & Filamentation
0 2n n n I
High Harmonic GenerationUltrafast x-ray diffraction
Up – Down SymmetryConserved
Sakai and colleagues:
DC electric field + laser pulse with adiabatic turn-on and nonadiabatic turn-off.
Approaches for field – free orientation
A. Goban, S. Minemoto, and H. Sakai, “Laser-Field-Free Molecular Orientation,“ Phys. Rev. Lett. 101, 013001 (2008).
Vrakking and colleagues:
Hexapole state selector (Producing molecules in a single quantum state) + a combination of a DC and intense fs laser field.
Approaches for field – free orientation
O. Ghafur, A. Rouzée, A. Gijsbertsen, W. K. Siu, S. Stolte and M. J. J. Vrakking, “Impulsive orientation and alignment of quantum-state-selected NO molecules,” Nature Phys. 5, 289-293 (2009).
Approaches for field – free orientation
L. Holmegaard, J. L. Hansen, L. Kalhøj, S. L. Kragh, H. Stapelfeldt, F. Filsinger, J. Küpper, G. Meijer, D. Dimitrovski, M. Abu-samha, C. P. J. Martiny and L. B. Madsen, “Photoelectron angular distributions from strong-field ionization of oriented molecules,” Nature Phys. 6, 428-432 (2010).
Holmegaard and colleagues:
Electrostatic quantum state selector + deflector combination of a DC and femstosecond laser field.
Kling and colleagues:
Approaches for field – free orientation
two-color excitation scheme in which the fundamental laser frequency (800 nm) is mixed with its second harmonic with a specified relative phase.
S. De, I. Znakovskaya, D. Ray, F. Anis, Nora G. Johnson, I. A. Bocharova, M. Magrakvelidze, B. D. Esry, C. L. Cocke, I.V. Litvinyuk, and M. F. Kling “Field-Free Orientation of CO Molecules by Femtosecond Two-Color Laser Fields,” Phys. Rev. Lett. 103, 153002 (2009).
Optical Pulse vs. Half Cycle Pulse
),(2
ˆˆ
2
tVI
LH 2( (, c) os )V t
( )
( ) sin(2 )
dV
d
c( (, s) o )V t
( )
( ) sin( )
dV
d
1.3 fs
11
22
33
44
55
13
24
3531
42
53
11T
22T
33T
44T
55T
Population Transfer
2J J Coherences
2cosV
Alignment 2 2 2cos cos cospopulation coherence
Density matrix – non resonant
11
22
33
44
55
13
24
3531
42
53
11
22
33
44
55
Population Transfer
2J J Coherences
2cosV
Alignment 2 2 2cos cos cospopulation coherence
15
51
xx
xx
xx
xx
x
xx
x
Density matrix – non resonant
11T
22T
33T
44T
55T
11
22
33
44
55
Population Transfer
1J J Coherences
cosV
12
23
34
45
21
32
43
54
Orientation cos
Density matrix - resonant
11
22
33
44
55
Population Transfer
1J J Coherences
cosV
12
23
34
45
21
32
43
54
Orientation and Alignment
13
24
3531
42
53
14
25
41
52
15
51
Density matrix - resonant
ResonantNon resonant
| , | 2,J m J m | , | 1,J m J m
May induce all therotational cohernces
May induce only evenrotational coherences
No orientationOnly alignment
Both orientationand alignment
Short summary
Intense single cycle THz pulse
K. L. Yeh, M. C. Hoffmann, J. Hebling and K. A. Nelson, “Generation of 10 μJ ultrashort THz pulses by optical rectification”, Appl. Phys. Lett. 90, 171121 (2007);
LiNb
Time (ps)
Am
pli
tud
e (a
.u)
Frequency (THz)
Spec
tral
Am
plit
ude
(n
oram
lize
d)
Resonant Non - Resonant
Time(ps) Time(ps)J states (m=0) J states (m=0)
Am
plit
ud
e (a
.u)
Am
plit
ud
e (a
.u)
Population TransferJ,J+1 coherencesJ,J+2 coherences
O=C=S
BS
G
LiNb
LaserDelay
P PD
Pellicle BS
BS
P 450 to THz polarization
Pellicle BS
ZnTe W/ 4
PD
PD
Delay
Detection of Molecular Alignment
Time (ps)
Inte
nsi
ty (
a.u
.)
12 revT
1 revT3
2 revT
Population Transferred To higher J’s
Alignment of OCS, 350torr, 300K
Each molecule is forced to rotate in a plane2cos 1/2
Non thermal rotational distributionTime independent alignment
Max
Ori
enta
tion
@ 1
Tre
v (x
102 )
Max
Alig
nm
ent
@ 1
/2T
rev(
x104 )
Peak field amplitude (a.u.)
Max Alignment=1.207x10-4 x Peak2
Max Orientatio
n=1.441x10-2 x Peak
Time (ps)
Am
pli
tud
e (a
.u)
1% orientation5% orientation8% orientation
Summary
Table top single cycle THz pulses can inducesignificant field-free orientation under ambient conditions
Relatively high orientation is not necessarily associatedRequires with high degree of alignment.
With jet cold molecular samples, higher degree of orientationis expected.
Combining optical and THz pulses may enable two independent handles for manipulating molecular angular distributions in 3D.