atomic, molecular and optical physics laboratory______________________________ collisional...
TRANSCRIPT
Atomic , Molecular and Optical Physics Laboratory______________________________Collisional Depolarization of Zeeman Collisional Depolarization of Zeeman Coherences in the Coherences in the 133133Cs 6pCs 6p22PP3/23/2 level level
Collisional Depolarization of Zeeman Collisional Depolarization of Zeeman Coherences in the Coherences in the 133133Cs 6pCs 6p22PP3/23/2 level level
Burçin BayramBurçin Bayram
Physics DepartmentMiami University
Oxford, OH
Atomic , Molecular and Optical Physics Laboratory______________________________
Two-photon Polarization SpectroscopyTwo-photon Polarization SpectroscopyTwo-photon Polarization SpectroscopyTwo-photon Polarization Spectroscopy
Group Members:
Undergraduate Students: Morgan Welsh, Jacob Hinkle
Graduate Students: Seda Kin, Ramesh Marhatta
Advisor: Dr. BurDr. Burççin Bayramin Bayram
Collaborations:
-Mark Havey, Old Dominion University, Physics Dept., VA-Andrei Sieradzan, Central Michigan University, Physics Dept., MI -Marianna Safronova, University of Delaware, Phys. Dept., DE
Funding:
-Research Corporation
-Miami University, Oxford, Ohio
Atomic , Molecular and Optical Physics Laboratory______________________________
focuses on the fundamental properties of atomic/molecular systems using a novel nanoseconds pulse laser spectroscopic technique
investigates the evaluation of rotational angular momentum and collisional dynamics between atoms/molecules in the gas phase.
Information about the alignment-dependent collisional depolarization cross section – property of great potential for combustion diagnostics, gas phase chemistry, etc.
Significance of Polarization SpectroscopySignificance of Polarization Spectroscopy
Atomic , Molecular and Optical Physics Laboratory______________________________
Polarization Spectroscopy (nonlinear coherent technique) can be applied to:
- Detection of trace constituents, flame and plasma analysis, concentration measurements and in various atmospheric and combustion processes.
What does polarization spectra reflects?
It reflects the distribution of the molecular/atomic population on the electronic level of transition. Because of the polarization state of light, excited state become very sensitive to any alignment and/or orientation of the product angular momenta. Rotational Polarization: in molecular product: angular momentum is rotational-Angular dependence of potential surfacesElectronic Polarization in atomic product: angular momentum is electronic; polarization reveals information about electron density distribution function (EDF).-Atmospherically important process
Information: temperature, collisional depolarization
Atomic , Molecular and Optical Physics Laboratory______________________________
Why collisional depolarization?Why collisional depolarization?
-Measure degree of polarization
-Evaluation of the angular momenta (radicals, atoms, molecules)
- Collisional evaluation of the alignment tensor moments
-Relevant to the detection of radicals in flames: measurement of absolute concentrations of radicals require knowledge of collisional depolarization.
Two techniques can be applied to study the collisional depolarization and alignment in atomic collisions;
Optical excitation of atoms in a beam Optical excitation during the collision itself
Atomic , Molecular and Optical Physics Laboratory______________________________
Partial Energy level diagram and Partial Energy level diagram and illustration of the experimental schemeillustration of the experimental scheme
9d2D5/29d2D3/2
9p2P3/2
6p2P3/2
6s2S1/20.0
1.0
1.5
2.0
2.1
2.5
3.0
En
ergy
(10
4 cm
-1)
852.1 nm
347.8 nm
Ionization Energy: 3.89 eV
10s2P1/2
~584.5 nm
Atomic , Molecular and Optical Physics Laboratory______________________________
Kastler Diagram for the Cs 6sKastler Diagram for the Cs 6s22SS1/21/2- 6p- 6p22PP3/23/2 – 9d – 9d22DD5/25/2
+1/2
+1/2+3/2
+3/2
-1/2
-1/2
-1/2
-3/2
-3/2 -5/25/2
6s2S1/2
9d2D5/2
6p2P3/2
Δm= 0
Δm= ±1
Δm= 0
+1/2
'
2222
0 )1'('
)]1'(''3[)'(
)1'('
''3
m
z
JJ
JJmma
JJ
JJA
Axially symmetric electronic-alignment component (information of the spatial distribution of angular momentum vector J) is produced by excitation of the 6s2P1/2 - 6p2P3/2 state:
pump laser
probe laser
Atomic , Molecular and Optical Physics Laboratory______________________________Atomic , Molecular and Optical Physics Laboratory______________________________
z
yk k
1
12
Laser 2
Laser 1
EE
x
2E1 E2 , = 90 o
E1 // E2 , = 0 o
interaction region
Experimental Geometry & General ConceptExperimental Geometry & General Concept
]}2/)2cos(sin3)(cos[),(2
11{
3
1 22
)2( PAJJhII ofio),,(
detector
II
II
//
//LP
Atomic , Molecular and Optical Physics Laboratory______________________________
)cos()2;'()12(
)1'2)(12()( '
2
'
2 tIJFJFWI
FFtg FF
FF
)()',(4
)()',(3
02
02
tAJJh
tAJJhPL
)()0()( 200 tgAtA
Basic Formulas for Data AnalysisBasic Formulas for Data Analysis
Compare with Experimental Data
Electronic alignment at t = 0
Time evolution of I and J
h2(J,J’):ratio of Racah coefficients that is derived from the reduced matrix elements of the density matrices and depend on the angular momenta of the initial J and final J’ levels.Reference: C.H. Greene and R.N. Zare, Ann. Rev. Phys. Chem., vol.33, 119 (1982).
Atomic , Molecular and Optical Physics Laboratory______________________________
Signal DetectionSignal Detection
6s2S1/2
6p2P3/2
I1z
I2z , I2x
9p2P3/2
S// (j'), S(j')
S// (j') = I//(j') I(10p 6s) where I//(j') = I1z I2z
S (j') = I(j') I(10p 6s) where I(j') = I1z I2x
10s2S1/2
Atomic , Molecular and Optical Physics Laboratory______________________________
HV
Polarizer
Dye Laser 1
Dye Laser 2
Nd:YAG Pulse Laser 532 nm
Filter
BoxcarBoxcar
Atomic , Molecular and Optical Physics Laboratory______________________________
PMT
Experimental ApparatusExperimental Apparatus
LC Retarder
AmplifierAmplifier
frequency controller
ComputerComputer
852.1 nm 603.4 nm
Atomic , Molecular and Optical Physics Laboratory______________________________
Typical ScansTypical Scans
Linear polarization spectra at 70oC.
6s2S1/2-6p2P3/2-9d2D5/2 7.11 cm-1
6s2S1/2-6p2P3/2- 10s2S1/2
Atomic , Molecular and Optical Physics Laboratory______________________________
decoupling radius Rc
zc
perturber path
degree of depolarization depends on the durationof the collision
degree of depolarization depends on the durationof the collision
Reorientation of the atomic dipole results in a reduced observed polarization when measured with respect to the original excitation z-axis.
coupling radius
Modification of atomic collisional Modification of atomic collisional dynamics dynamics
Ar
polarized Cs (p-Orbital)
Atomic , Molecular and Optical Physics Laboratory______________________________
Rate equation analysis of Zeeman Rate equation analysis of Zeeman coherences and depolarization cross sectioncoherences and depolarization cross sectionThe variety of possible distributions of atoms in the Zeeman sublevels depends on the given experimental conditions such as optical pumping with a circularly or linearly polarizedlight source.
Population mixing among the Zeeman coherences.
Atomic , Molecular and Optical Physics Laboratory______________________________
Polarization spectroscopy as a function of pump-probe delay timePolarization degree for I=7/2 , J=3/2, h (2) <Ao> = 0.2
TheoreticalExpected
)()',(4
)()',(3
02
02
tAJJh
tAJJhPL
)()0()( 200 tgAtA
Atomic , Molecular and Optical Physics Laboratory______________________________
Linear Polarization DegreeLinear Polarization Degree
<A0> = -0.8
**Havey et. Al, J. Chem. Phys., 86, 1648 (1987)
* Greene et al, Ann. Rev. Phys. Chem., 33, 119 (1982)
PPLLg(2) =1
(w/o hpf)
g(2) =0.219
Theory**
h(2)(Ji, Jf) MeasuredMeasured
9d2D5/2 14.60 % 3.25 % -1/4 3.3(1) %
10s2S3/2 60.00 % 15.57 % -4/5 15.6(3) %
Atomic , Molecular and Optical Physics Laboratory______________________________
Nonlinear least-square fit of the polarization spectrum
Atomic , Molecular and Optical Physics Laboratory______________________________
Pressure dependence of the signalPressure dependence of the signal
Z
Z
II
II
4
3
//
//LP
)]1(1
1[
)]1(1
1[)2(
T
T
a
a eT
eTg
a
Z
a
dArCsdAr kkT
Pv
where
and
kd :disalignment rate coefficientP: buffer gas pressurekT: thermal energy constantσd : alignment dependent cross section
Atomic , Molecular and Optical Physics Laboratory______________________________
References:
[4] J. Guiry and L. Krause, Phys. Rev. A 14, 2034 1976.
[5] A.I. Okunevich and V.I. Perel, Soviet Physics JETP 31, 356 (1970).
[16] Havey et. Al, J. Chem. Phys., 86, 1648 (1987)
Bayram et al, Phys. Rev A 73, 042713 (2006)
σd (Å2) g (2) References
186(58) 0.219(44) This work (6S-10S)
0.222(20) This work (6S-9D)
0.219(10) Ref. 16
238 Ref. 5
288(72) Ref. 4
The depolarization cross section of the excited electronic state of cesium atom
Atomic , Molecular and Optical Physics Laboratory______________________________
Calculated and measured the alignment tensor moments in the excited state of cesium atoms •Calculated and measured the effects of nuclear hyperfine depolarization•Measured the linear polarization spectrum during the collisions between cesium and argon atoms•Collisional dependence of the linear polarization spectra is found to decrease significantly with a decreasing Ar pressure•Extracted the alignment-dependent collisional depolarization cross section from the spectra
•Main future goal: apply polarization spectroscopy using two-photon pump-probe technique to a system of colliding radicals with various pressures of He,Ne,Kr,Xe: great potential for combustion diagnostics.
Conclusions and Future DirectionsConclusions and Future Directions
Atomic , Molecular and Optical Physics Laboratory______________________________
A view from our laboratory at Miami University, Physics Department
Thank you for your attentionThank you for your attentionRelationship with Ohio Third Frontier Project: Relationship with Ohio Third Frontier Project:
The overall goal of our research is to promote fundamental research leading to a better
understanding of the atomic/molecular dynamics (evaluation of rotational angular
momentum and atomic/molecular collisions) in the gas phase. This research has direct
application in the areas of gas phase chemistry such as combustion, plasma, and
Atmospheric chemistry. Collaborations with other institutions/laboratories in Ohio state
can contribute boosting the economy of the State of Ohio.