Laser-microwave double resonance methodin superfluid helium

for the measurement of nuclear moments

Takeshi FurukawaDepartment of Physics, Graduate School of Science,

Osaka University

CollaboratorY. Matsuo2, A. Hatakeyama3, T. Ito4, Y. Ota4,

Y.Fukuyama2, T. Kobayashi2, and T. Shimoda1

1Dept. Phys., Osaka Univ., 2RIKEN, 3Inst. Phys., Univ. of Tokyo, 4Dept. Phys., Meiji Univ.

1) Problems in measuring the nuclear moment

2) Double resonance method to cope with the problems

Contents

3) Present status of the development

4) Summary and future prospect

・ Low-yield, high-contamination, small-polarization of unstable nuclei

Laser spectroscopy & optical detection・ Double resonance method in He II

Optical pumping in He II(

・ Long atomic spin relaxation time in He II・ Hyperfine transition spectrum in He II

Scientific MotivationUnstable nuclei near the drip-line

Polarized RI nucleus

detectorstopper

Signals from RI detector

ex-NMR method

・ low-yield・ high-contamination・ small-polarization

Difficult to measure the nuclear moment

)Laser spectroscopy & optical detection of RI atoms

Optical pumping in He II

Measure the hyperfine structure

Determination of nuclear moments

Merit in Optical Detection

Pumping the RI atoms repeatedly.Detecting the LIF photons repeatedly.

The impurity atoms can not absorb the pumping laser.

Insensitive detection to the impurity atoms.Laser

RI beam

low yield, high contaminationLaser spectroscopic method is suitable for unstable nuclei.

Laser Induced Fluorescence (LIF) photon

Good S/N ratio

Useful to measurethe unstable nuclei

We plan to measure the h.f.s with the double resonance method.

LIF Intensity ∝ 1 - Pz

Double resonance method

Polarized atoms : Can not absorb circularly polarized laser light.

Measure the constant A, B of isotope mX and nXmXnX

=AmX ImXAnX InX

eQmX

eQnX

BmXBnX

=

Hyperfine Structure (J=1, I=3/2 case)

A=<B>/IJ B=eQ<V>I:nuclear spin, J:electronic angular momentum,: nuclear magnetic dipole moment,eQ: nuclear electric quadrupole moment,<B>:magnetic field produced by the electrons<V>:electric field gradient produced by the electros

J=1, I=3/2

F=5/2

F=3/2

F=1/2

5/2A

3/2A

5/2A+5/4B

3/2A-9/4B

LIF

inte

nsi

ty

microwave frequency

expected spectrum

Limited to

alkali-like atoms

Optical pumping is performedonly alkali-like atoms.

Optical pumping in He II

In vacuum In He II

Many lasers needed.Only one laser beaminduce to polarization.

Optical spectrum of atoms is dynamically broadened due to the influence of the surrounding He atoms.

Mg 3s3p 3P2,1,0 3s4s 3S1 Transition

In He II: possible to polarize various atoms with optical pumping

Possible to optically pump the atoms with complicated level structure using a single laser beam

Problem:How fast spin relaxes in He II ?

Spin polarization in He II

Long spin relaxation time are expected in He II !

Low temperatureSmall polarizabilitySpin-less atom

How long the relaxation time ?We have measured T1 of Cs atoms in He II

Spin relaxation of Cs atoms

relaxing time

Achieved polarization : ~90 % in Cs

Rela

tive p

ola

riza

tion

Optical pumping of the atoms other than alkalis is now in progress.

T. Furukawa et al., submitted to Phys. Rev. Lett.

He II is suitable to use with our method.

Hyperfine structure of 133CsHyperfine structure of 133Cs

Hyperfine structure of 133Cs atom

F=4

F=3

mF=+4~-4 9 levels

mF=-3~+3 7 levels

6s 2S1/2Hyperfine splitting energy

Eh.f.s = A ・ F = 4A

(A μ∝ I)

Double Resonance spectrum of Cs atoms in He IICheck the feasibility in He II

With σ+ pumping

With σ- pumping

mF=+4+3+2+10-1-2-3-4

F=4

F=3mF=+3+2+10-1-2-3

ν+

ν- ν0= (ν+ + ν-) /2

Details of 133Cs hyperfine transition

Measurement Result of Hyperfine SplittingMeasurement Result of Hyperfine Splitting

νσ+=9.257705(9) GHz νσ-=9.243484(4) GHz

ν0 = (νσ+ + νσ-)/2 = 9.2505945(98) GHz

∴ ∴ A = A = νν00 / F = 2.3126486(25) / F = 2.3126486(25)( in vacuum: 2.298157943 GHz )( in vacuum: 2.298157943 GHz )

~0.65% larger !!!~0.65% larger !!!

Preliminarily result

Pressure effect in He II

H

A = ν0 / F = 2.3126486(25)A = ν0 / F = 2.3126486(25)( in vacuum: 2.298157943 GHz )( in vacuum: 2.298157943 GHz ) ~0.65% larger !!!~0.65% larger !!!

A=<H>/IJ

Large <H> in He II

Because of compressed electron orbit

pressurized with surrounding He atoms

H’ (> H)

Pressurized by helium

No difference in isotopes ??

Next plan : Check the difference of <H’> between 85,87Rb

Summary and Future prospect

Double Resonance in He IIMeasurement Method for the nuclei near the drip-line

Merit・Detecting the LIF photons repeatedly

・ Insensitive to the impurity atoms

・ Long spin preservation, high polarization

Future prospectOptical detection from low-yield RI atoms

Optical pumping of various atoms other than alkalis (Mg, Al, ..)Measure the moments of various nuclei (22Al, 21Mg,...)

Problems・ low-yield

・ high-contamination・ small-polarization

・High polarization, long spin reservation, and precise resonance spectrum are confirmed in He II

Additional OHP

Hyperfine InteractionHyperfine Interaction

W(F, mF)= A ・ K/2 + B ・ {3K(K+1)/4 –I(I+1)J(J+1)}/{2(2I-1)(2J-1)IJ}

[K=F(F+1)-I(I+1)-J(J+1)]

Measure the constant A, B of isotope mX and nX

A=<B>/IJ B=eQ<V>I:nuclear spin, J:electronic angular momentum,: nuclear magnetic dipole moment,eQ: nuclear electric quadrupole moment,<B>:magnetic field produced by the electrons<V>:electric field gradient produced by the electros

mXnX

=AmX ImXAnX InX

eQmX

eQnX

BmXBnX

=

Timing Chart of MeasurementTiming Chart of Measurement

Pumping laser polarization

linearly

circularly

linearly

Counting gate

Count1 Count2 Count3

LIF

Inte

nsi

ty

With microwave resonance

∝NCs ∝NCs∝NCs(1-PlaserPatom)

LIF ratio :

count2

(count1 count3) 2(1 Plaser Patom ) Patom→small (with M.R.)

Ratio→Large

Experimental Setup

Atomic level energy

W = WJ + A ・ K/2 + WB + gFμBBmF

In 133Cs case ( |F, mf ＞ : |4, +4 ＞ → |3, +3 ＞ )….

ΔWσ+ = W(4, +4) - W(3, +3) = A ・ F + gJμBB×7/8

ΔWσ- = W(4, -4) - W(3, -3) = A ・ F - gJμBB×7/8

K = F(F+1) - I(I+1) - J(J+1)

Hyperfine Splitting of Hyperfine Splitting of 133133CsCsHyperfine Splitting of Hyperfine Splitting of 133133CsCs

Timing ChartTiming Chart

原子供給 on

off

50m

s 50m

s

EOM

Photon count

gate

Gate width:

1ms

on

2.5m

s

40 ms

0.5ms 1ms

Count1 Count2 Count3

LIF ratio : Count2 / { (Count1 + Count3) /2 }

Double Resonance MethodNeed more effective measurement method!Laser Double Resonance Method in He II is suitable for the measurement.

Laser Induced Fluorescence　　（ LIF ）

Len ｓ

LensOptical filter

Double resonance method a sort of laser spectroscopy

Bubble Model

Atoms in He II: repel the surrounding helium atoms(by Pauli repulsion)

Deform

Deform

absorb the photon

emit the photon

Energ

y

Like as bubble

absorption emissio

n

Bubble radius

Energy levels in the ground state and excited stateas a function of bubble radius.

Physics motivation

22Al : proton halo?

21Mg : Isospin symmetry?

22Al = 21Mg + p

21Mg-21F mirror pair in T = 3/2

35Ca : Z=20 magic?

Optical Pumping of Metastable Mg atoms21Mg atomic energy diagram Observable resonance line

(Assume I = 5/2)

3s3p 3P2 F=9/2 ⇔ F=7/2

[h.f.s = (9/2)A + (27/40)B]

F=7/2 ⇔ F=5/2 [h.f.s = (7/2)A + (7/40) B]

( 3s3p 3P1 F=7/2 ⇔ F=5/2 )

Relaxation in the Dark Method

Timing chart

Measured LIF intensity

Measured LIF intensity

Spin Relaxation Mechanism

◯s-state electron(s) (2S1/2

electron in Cs,Rb)magnetic interaction (spin-orbit interaction etc...)

σ …≒10 -14-15cm 2

J>1 electron(s) (3P electrons in Mg)electrostatic interaction

σ …≒10 -19-26cm 2 ex) Cs 2S1/2

: 2.5× １０-24cm2

ex) Hg 3P1 : 1.1× １０-15cm2

σ …≒10 -16-17cm 2

2P1/2

electron(s) (2P1/2

electron in Cs,Rb)virtual transition to 2P

3/2& electrostatic interaction

ex) Tl 2P1/2

: 6.0× １０-19cm2 Cs 2P1/2

: 2.1× １０-16cm2

2P1/ 2

- 2P3/ 2

Δ E ： 7793cm-1 554cm-1

M.R. Spectrum in He II

Peak frequency:959.5(5) kHz

Double Resonance spectrum of Cs atoms in He II(Zeeman sublevel transition, Magnetic field : ~ 3 G)

Energy level of g.s Cs atom

...F=4

F=3

6s1/2

Zeeman transition

Hyperfine transition

Observing hyperfine resonance same as that

Nuclear moments can be determined precisely

Check the feasibility in He II

(preliminary)