Atomic, Molecular and Optical Physics Laboratory______________________________ Collisional Depolarization of Zeeman Coherences in the 133 Cs 6p 2 P 3/2

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


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


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


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


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


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


)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).


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


HV

Polarizer

Dye Laser 1

Dye Laser 2

Nd:YAG Pulse Laser 532 nm

Filter

BoxcarBoxcar


PMT

Experimental ApparatusExperimental Apparatus

LC Retarder

AmplifierAmplifier

frequency controller

ComputerComputer

852.1 nm 603.4 nm


Typical ScansTypical Scans

Linear polarization spectra at 70oC.

6s2S1/2-6p2P3/2-9d2D5/2 7.11 cm-1

6s2S1/2-6p2P3/2- 10s2S1/2


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)


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.


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


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) %


Nonlinear least-square fit of the polarization spectrum


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


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


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


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.

Documents

Atomic, Molecular and Optical Physics Laboratory______________________________ Collisional Depolarization of Zeeman Coherences in the 133 Cs 6p 2 P 3/2