spin polarization of atoms produced by laser excitation...

Workshop on Low-Energy Radioactive Isotope Beam (RIB) Production by In-Gas Laser Ionization for Decay Spectroscopy

at RIKEN, December 10-11, 2012

Spin polarization of atoms produced by

laser excitation and its applications to

atomic and nuclear physics

Yukari MATSUORIKEN Nishina Center

Laser ionization and spectroscopy are useful for the study of atoms and nuclei

atoms,

ions

photon

laser

By changing the polarization of lasers polarization of atoms/ions can be manipulated

I would like to introduce a few techniques to control spin polarizations, especially using pulsed lasers, and its applications to atomic and nuclear physics

WS on Low-Energy RIB Production by In-Gas Laser Ionization for Decay Spectroscopy @RIKEN 2012.12.11

Outline

(1) Background - Spin-polarized electrons and atoms / ions

- Optical pumping method

(2) Producing spin polarization using pulsed lasers- Cavity ring down method

- Multi-photon pulsed ionization method

- Optical pumping in superfluid helium

(3) Spin polarization of atoms in superfluid helium and its

applications to atomic and nuclear physics- Precision measurement of Zeeman and hyperfine structures of atoms in He II

- Novel nuclear laser spectroscopy of RI (radioisotope) atoms in He II :

OROCHI

(4) Summary

Developed in Japan

Results of our recent works


Spin-polarized electrons and atoms/ions

being used as important beam sources

in the fields of surface physics, atomic physics,

nuclear physics, and high energy physics, etc.

in particular, for spin related characteristics

spin-polarized electron

an electron whose spin state is

polarized either to or ↓

spin-polarized atom/ion

an atom/ion whose valence

electron is spin-polarized

Hyperfine interaction

nuclear spin-polarized atom

an atom whose nuclear spin

is polarized


How to produce spin-polarized

electrons and atoms / ions

disadvantages alternative

spin-polarized electron

irradiation of circularly

polarized light onto GaAs

crystal

possibility of

serious damage by

strong irradiation

gas phase

target

spin-polarized atom / ionoptical pumping of alkali like

atoms, spin exchange with

these atoms

need to use

narrow-band,

stabilized cw laser

conventional

pulsed laser


Optical pumping produces

electron spin polarization

2P3/2

2P1/2

2S1/2

23−=jm

21−=jm

21−=jm 2

1

21

21

23

21−

in the case of one-electron system（taking into account magnetic sub-level）

Irradiation of circularly

polarized light

if there are the other states to

which atoms are de-excited, the

system becomes out of the cycle

2P3/2

2P1/2

2S1/2

23−=jm

21−=jm

21−=jm 2

1

21

21

23

21−

Absorbing light and

emit light repeatedly

accumulation in the state of mj=½

corresponding to ms=½

＝０l

→ electron spin polarization

effective method for one-electron system

like alkali atoms, alkali-earth ions

atoms need to interact with lasers many times…

It will be good if we can use

conventional pulsed lasers for

spin polarized atomic / ion sources


Outline









OROCHI

(4) Summary

To make use of pulsed lasers,

when photons are trapped *


T. Majima, et.al.,

Phys. Rev. A 77,

033417 (2008)

"Cavity"Cavity"Cavity"Cavity----assisted optical pumping"assisted optical pumping"assisted optical pumping"assisted optical pumping"

Photon trap using cavity ring down method

Method by

A. Terasaki,

T. Majima

(Toyota

Technological

Institute)

Laser light goes

back and forth in

the cavity, which

elongates the

effective interaction

time with ions,

resulting in optical

pumping of ions.


Degree of polarization ＞ 49 ± 6 (%)

Spin polarized Mn+ ions

T. Majima, et.al., Phys. Rev. A 77, 033417 (2008)

Direct production of spin-polarized ions

in a short time using pulsed lasers


Simultaneous production of spin polarized

ions/electrons by multi-photon ionization

Nano second pulsed lasers

5s 5s 5s 5s 2222SSSS1/21/21/21/2

5p 5p 5p 5p 2222PPPP1/21/21/21/2

SrSrSrSr

MMMMJJJJ = = = = ----1111 0000 1111

excitationexcitationexcitationexcitation

ionizationionizationionizationionization

detectiondetectiondetectiondetection

5s5s5s5s2222 1111SSSS0000

MMMMJJJJ = = = = ----1/21/21/21/2 1/21/21/21/2SrSrSrSr++++

RHC

5s5p 5s5p 5s5p 5s5p 3333PPPP1111

LHC

689 nm689 nm689 nm689 nm

421 nm421 nm421 nm421 nm

248 248 248 248 ---- 308 nm308 nm308 nm308 nm

Method by T. Nakajima

(Kyoto Univ., IAE)

In other words, the orbital angular momentum

that the atomic system obtained from circularly

polarized light (689nm）breaks up into spin and

orbit components

emitted electrons are also spin-polarized

Degree of spin

polarization RHCLHC

RHCLHC

II

IIP

+−

=

If more ions are populated in the

MJ=1/2 state than -1/2, fluorescence

by LHC excitation is larger than RHC.

producing spin-polarized ions by

ionization through the triplet

states (no optical pumping)


Spin polarized Sr+ ions

Laser polarization dependence of 2P1/2-

2S1/2 LIF

Nakajima, et.al. APL 83, 2103 (2003)

64 ±±±± 9 %

Degree of spin

polarizationRHCLHC

RHCLHC

II

IIP

+−

=delay

Probe laser

Ionization

laser

Pump laser

trigger

trigger

Box-car

integratorComputer

Vacuum

chamber

Sr

disk

Ablation

laser532nm

(1x10-5Pa)

Monochro-

mator

PMT

689nm

421nm

285nm

Experimental setup at RIKENFurther developments (using auto-ionizing states,

isotope selective excitation) are in progress


Controlling the degree of spin polarization

using ultra-short pulsed lasers

Femto second laser

5s6d 5s6d 5s6d 5s6d 3333DDDD1,21,21,21,2

probe 794 nmprobe 794 nmprobe 794 nmprobe 794 nm5s 5s 5s 5s 2222SSSS1/21/21/21/2

5p 5p 5p 5p 2222PPPP1/21/21/21/2

MMMMJJJJ = = = = ----1111 0000 1111

excitationexcitationexcitationexcitation

detectiondetectiondetectiondetection

5s5s5s5s2222 1111SSSS0000

MMMMJJJJ = = = = ----1/21/21/21/2 1/21/21/21/2

RHC

5s5p 5s5p 5s5p 5s5p 3333PPPP1111

LHC

689 nm689 nm689 nm689 nm

421 nm421 nm421 nm421 nm

pumppumppumppump397 nm397 nm397 nm397 nm

∆τ∆τ∆τ∆τ

The orbital angular momentum obtained from

circularly polarized light is transferred to the spin

components ->Time dependent spin polarization

Delaygenerator

trig.

trig.

Digital

oscilloscope

Computer

Vacuum chamber

Sr disk

532 nm

PMT

689 nm

421 nm794 nm

Ion deflector

Femtosecond

Laser (Ti:S)

HV pulser

Ion detection laser

Ablation laser

(<1x10-4Pa)

Pol.397 nm

λλλλ/2BBO

delayline Monochro-

mator

Excitation laser

M

M

M

M

MM

M

M


Delay time dependence of

the degree of spin polarization

LHCRHC

Periodic variations (corresponding to the inverse of fine-structure splitting) of ILHC and P were observed.

LHC

RHC

Nakajima, et.al. PRA 77, 063404 (2008)

RHCLHC

RHCLHC

II

IIP

+−

=

When atoms are trapped in a matrix (He II),

pulsed lasers can be useful?


Multiple HFS levels can be Multiple HFS levels can be Multiple HFS levels can be Multiple HFS levels can be optical pumped simultaneouslyoptical pumped simultaneouslyoptical pumped simultaneouslyoptical pumped simultaneously

Optical pumping with circular polarized light

Laser σ+

M sub-levelspopulationaccumulated

emission

excitation

po

ten

tial

en

erg

y

rHe-M

broad,large blue-shift

sharp, small shift

S0,0

P1,0

• large shift, broad spectrum

could be an obstacle for spectroscopy

Behavior of atoms in superfluid He (He II)

If the relaxation between MIf the relaxation between MIf the relaxation between MIf the relaxation between M----sublevels is slowsublevels is slowsublevels is slowsublevels is slow

“spin polarization using optical pumping”

+ “double resonance spectroscopy”

=> precision spectroscopy

T. Furukawa, Doctoral thesis, Osaka Univ. (2007)

T. Furukawa, et. al., Hyp. Int., 196, 191 (2010).


Further development

optical pumping of atoms other than alkalis

In vacuum In He II

Needs many lasersA single laser can excite all the atomic levels

Absorption spectra are broadened

Atoms with complicated energy

levels may be optically pumped.

Pumping rate Γ

Spin relaxation rate γ ・・・・wavelength do not need to be exactly tuned

・・・・spin polarization is generated if pumping

rate is larger than the relaxation rate

・・・・pulsed laser can be used as well as cw lasers

Taking advantage of characteristic

feature of He II

freedom to choose lasers

Group 11 elements (Ag, Au) are spin polarized using UV pulsed lasers


Y. Matsuura, Master thesis, Meiji univ. (2011).


Outline









OROCHI

(4) Summary


Nuclear structure and laser spectroscopy

nuclear spins

electromagnetic moments

Spins nucleon orbital state

Magnetic dipole momentswave function of nucleus

Electric quadrupole momentsdeformation of nucleus

precision

measurement

nuclear structure

hyperfine interactionsInteraction between Interaction between Interaction between Interaction between

nucleus and electronsnucleus and electronsnucleus and electronsnucleus and electrons

charge radii

e

IJ

Fexternal

magnetic

field B

interaction between

nuclear moments

and electrons

interaction between

atomic spin mF and

external magnetic field

hyperfine structures

Zeeman splittings

atomic sublevel structure

IJ

laser spectroscopy

isotope shift

There are many works on

Laser Ionization and Spectroscopy in Gas

Why not in Liquid?

But, precision measurement cannot be expected

Stopping efficiency is much better for liquid

Precision laser spectroscopy of atoms

spin polarized in superfluid helium

=> Off-line experiment:


LIF

decreases

Double resonance spectroscopy

MW

RF

mF= -1F=1

0 +1

0F=0

2S1/2

2P1/2

mF= -1F=1

0 +1

0F=0

X

LIF intensity

MW or RF frequency

expected spectrum

LIF increases

Optical pumping

mF= -1F=1

0 +1

0F=0

2S1/2

2P1/2

mF= -1F=1

0 +1

0F=0

X

mF= -1F=1

0 +1

0F=0

2S1/2

2P1/2

mF= -1F=1

0 +1

0F=0

Xcircularly

polarized

laser light

Zeemansplittings

hyperfinesplitting

ground state

excited state

Mearsurement of atomic sublevel structures

electronic transition is

perturbed by surrounding He

atomic sublevel structures

not much affected

Double resonance spectroscopy


Experimental setup

Femto sec pulsed Ti:SH

e

ⅡHeⅡSuperfluid

fountain

LIF

Monochro-matorP.M.T

Pumping laser

EOMAOD

samplePulsed Nd:YAG atom

cluster Helmholtz coil

Ablation laser

Dissociation laserHeⅡ

λ/4 Dipole antennaλ/4 Dipole antennaλ/4 Dipole antennaλ/4 Dipole antenna

Off-line

our method introducing atoms/ions into He II

above surface laser ablation method


Time (arb. unit)

LIF

Co

un

t (c

ou

nts

/ b

in)

0

100

200

300

400

500

600

700

800

5 ms

直線偏光

円偏光

Time (ms)

ph

oto

n c

ou

nts

5 ms

偏光切替Change the laser polarization

linearly

polarized

lightcircularly

polarized

light.

・ Polarization：：：：~90 %(Cs), ~50 %(Rb)

・Long spin relaxation time:

2.24(19) sec (Cs)

T. Furukawa et al., Phys. Rev. Lett. 96, 095301 (2006)

long spin relaxation time

Precision laser spectroscopy in He II

・Zeeman splittings

（Rb isotope, 4 Gauss）I85Rb = 2.6(1) → 5/2

I87Rb = 1.55(5) → 3/2

∆EZmn= gF µB B

Zeeman splittings(alkali atoms, s-state)

2.8(MHz)×B(Gauss)=

(2I+1)

h

・Hyperfine structure splittings

（Cs, Rb isotopes）

・determine nuclear moments

・as accurate as in vacuum

T. Furukawa, Doctoral thesis, Osaka Univ. (2007)


magnetic moment

This work (from AHeII)

evaluated (from Avacuum)

literature value

µI85Rb (µN)

1.357 83 (7) µN

1.358 071(1) µN1.353 351 5 µN

Rb

IRbRb

RbRbRb

IIA

IA 87

8787

858585 µµ ×=

hyperfine resonance: width-50kHzPrecision measurement of hyperfine structure


PMT

Monochromator

LIF

Pumping Laser

Helmholz Coil

λ/4

αBBO

σ＋＋＋＋

Au sampleAblation Laser

Dissociation Laser

263.5nm, 1-10kHz

Spin polarization achieved ~ 72%

BBBB⊥⊥⊥⊥

BBBB∦∦∦∦

Bresidual

Bmax

B0Coil

current

LIF

t

t

Spin polarization of Au atoms

using a pulsed laser


Pumping

Laser

λ/4 LIF

RF coil

RF resonance

νMHz = 1.4 gF Bgauss

νMHz = 0.71 (Bcoil-Bresidaul)

Ⅰ=1.49 (→ 3/2)

slope 0.710 (5)

Bcoil [Gauss]R

F f

req

ue

ncy

[MHz]

assume nuclear spin is unknown

Y. Matsuura, Master thesis, Meiji univ. (2011).

Laser-RF double resonance spectroscopy

of Au atoms

⇒On-line experiment:

A new nuclear laser spectroscopy

OROCHI


Optical RI-atom Observation in Condensed Helium as Ion-catcher

He stopper of RI beam

Laser spectroscopy

+

For the systematic determination of nuclear spins and moments

by measuring atomic Zeeman and hyperfine splittings

RI beam

Laser

Ion beam

(radioisotope atoms)

separator

Accelerator

RI atoms

target

LIF

He II

Advantageous for the

study of low yield and

short-lived unstable

nuclei

Application to the Radioactive Isotope Beam :

“OROCHI”




Laser spectroscopy

+



RI beam

Laser

Ion beam


separator

Accelerator

RI atoms

target

LIF

He II




nuclei


“OROCHI”

Photo @ Matsue 2012.12.06


Rb beam

laser

cryostat

Photo-detection system

All the devices were mounted

on RIKEN RIPS beam line

All the devices were mounted

on RIKEN RIPS beam line

Rb beam66 MeV/nucleon104-5 pps = 0.01pnA

Cryostat

Photo-detection system

Experimental setup




Laser spectroscopy

+



RI beam

Laser

Ion beam


separator

Accelerator

RI atoms

target

LIF

He II




nuclei


“OROCHI”

84,85Rb RI beam

Sep. 2012

87Rb primary beam

Sep. 2010

Laser induced fluorescence Laser induced fluorescence Laser induced fluorescence Laser induced fluorescence (LIF) from ion beam injected (LIF) from ion beam injected (LIF) from ion beam injected (LIF) from ion beam injected at accelerator facility is at accelerator facility is at accelerator facility is at accelerator facility is observed for the first time !observed for the first time !observed for the first time !observed for the first time !


BroomB

Bcoil

Bcoil: Max = Large polarization

Bcoil: 0 = Small polarization

Bcoil: hννννrf/gFµµµµB = Resonance

B Sweeping magnetic field strength*

With applying rf field *

Small resonance peak :due to the incomplete injectionof rf power.

85Rb: 8.6 x 104 pps, 15 min. measurement

Preliminarily

Bcoil=0

Ma

gn

etic f

ield

str

en

gth

Clearly see the resonance !

85Rb, I=5/2-

84Rb: 5.7 x 104 pps, 30 min. measurement

Bcoil=0

Preliminarily

Ma

gn

etic f

ield

str

en

gth

84Rb, I=2-

Highlight data of on-line experiment


OROCHI targetsProton number

Neutron number

Z=50 magic number

N=50 magicnumber

Z=82 magic number

extending neutron number increased variety of atomic species

Nuclear chart

In

Under

development

of optical

pumping

Au

Rb

Ag

promising

candidates

for OROCHI

Cs


Summary

・ Controlling the polarization of lasers can manipulate spin polarization of atoms, ions, and electrons.

・ Spin polarization of atoms can be efficiently achieved using superfluid helium as a trapping matrix.

・ New methods to produce spin polarization of atoms and ions are being developed using pulsed lasers.

・ Laser spectroscopy of atoms in superfluid helium will be a powerful technique to study nuclear structure of short-lived radioisotopes (RIs) generated at accelerator facilities; OROCHI (Optical RI-atom Observation in Condensed Helium as Ion-catcher) project.

OROCHI collaborators

RIKENRIKENRIKENRIKEN：：：：X.Yang,X.Yang,X.Yang,X.Yang, H. Ueno, H. Ueno, H. Ueno, H. Ueno, Y. IshibashiY. IshibashiY. IshibashiY. Ishibashi, M. Wada, T. Sonoda, , M. Wada, T. Sonoda, , M. Wada, T. Sonoda, , M. Wada, T. Sonoda, Y. Itou Y. Itou Y. Itou Y. Itou , , , , T. Kobayashi, S. Nishimura, M, Nishimura, K. YonedaT. Kobayashi, S. Nishimura, M, Nishimura, K. YonedaT. Kobayashi, S. Nishimura, M, Nishimura, K. YonedaT. Kobayashi, S. Nishimura, M, Nishimura, K. Yoneda

Osaka Univ.:Osaka Univ.:Osaka Univ.:Osaka Univ.:T. FujitaT. FujitaT. FujitaT. Fujita, T. Shimoda, T. Shimoda, T. Shimoda, T. Shimoda

CYRIC, Tohoku Univ.:CYRIC, Tohoku Univ.:CYRIC, Tohoku Univ.:CYRIC, Tohoku Univ.:T. Wakui, T. ShinozukaT. Wakui, T. ShinozukaT. Wakui, T. ShinozukaT. Wakui, T. Shinozuka

Meiji Univ.:Meiji Univ.:Meiji Univ.:Meiji Univ.:K. Imamura, Y. Yamaguchi,, Y. Mitsuya, S. Arai, M. MuramotoK. Imamura, Y. Yamaguchi,, Y. Mitsuya, S. Arai, M. MuramotoK. Imamura, Y. Yamaguchi,, Y. Mitsuya, S. Arai, M. MuramotoK. Imamura, Y. Yamaguchi,, Y. Mitsuya, S. Arai, M. Muramoto

Tokyo Univ. of Agriculture and Tech.Tokyo Univ. of Agriculture and Tech.Tokyo Univ. of Agriculture and Tech.Tokyo Univ. of Agriculture and Tech.：：：：A. HatakeyamaA. HatakeyamaA. HatakeyamaA. Hatakeyama

Spokesperson:Spokesperson:Spokesperson:Spokesperson:Takeshi FurukawaTakeshi FurukawaTakeshi FurukawaTakeshi Furukawa (Tokyo Metropolitan University)(Tokyo Metropolitan University)(Tokyo Metropolitan University)(Tokyo Metropolitan University), Yukari Matsuo , Yukari Matsuo , Yukari Matsuo , Yukari Matsuo (RIKEN)(RIKEN)(RIKEN)(RIKEN)

CNS, Univ. Tokyo:CNS, Univ. Tokyo:CNS, Univ. Tokyo:CNS, Univ. Tokyo:S. Kubono, Y. OshiroS. Kubono, Y. OshiroS. Kubono, Y. OshiroS. Kubono, Y. Oshiro

Tokyo Gakugei Univ.:Tokyo Gakugei Univ.:Tokyo Gakugei Univ.:Tokyo Gakugei Univ.:H. Tetsuka, Y.Tsutsui, Y. Ebara, M. Hayasaka, H. Tetsuka, Y.Tsutsui, Y. Ebara, M. Hayasaka, H. Tetsuka, Y.Tsutsui, Y. Ebara, M. Hayasaka, H. Tetsuka, Y.Tsutsui, Y. Ebara, M. Hayasaka,

Tokyo institute of Technology:Tokyo institute of Technology:Tokyo institute of Technology:Tokyo institute of Technology:Y. Ichikawa, K. Asahi, Y. Ichikawa, K. Asahi, Y. Ichikawa, K. Asahi, Y. Ichikawa, K. Asahi, N. YoshidaN. YoshidaN. YoshidaN. Yoshida, , , , H. ShiraiH. ShiraiH. ShiraiH. Shirai, Y. Kondo, Y. Kondo, Y. Kondo, Y. Kondo

Thank you for your kind attention !

spin polarization of atoms produced by laser excitation...

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