Laser Spectroscopy of Exotic Helium Isotopescolloquium/2008S/_home_isaac... · June 15thth --...
Transcript of Laser Spectroscopy of Exotic Helium Isotopescolloquium/2008S/_home_isaac... · June 15thth --...
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NTHU Physics Colloquium, 2/27/2008
Laser Spectroscopy of Exotic Helium Laser Spectroscopy of Exotic Helium IsotopesIsotopes
王立邦
清華大學物理系
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Neutron HaloNeutron Halo
Discovery of neutron halo change our common view of nuclear structureHow is it discovered?
neutron proton stable nucleus3,4He, 6,7Li, 40,48Ca
neutron halo6,8He, 11Li, 14Be
proton halo8B, 17Ne(?)
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Nuclear Interaction Cross SectionNuclear Interaction Cross Section
Interaction cross section σI =π(Rtarget+Rbeam)2
First observation of “halo nuclei” by Tanihata, 1985
σI(6He) ~ σI(4He) + σ-2n(6He)
target
target
Radioactivebeam
Target nuclei
3.0
2.5
2.0
1.5
1.0
Inte
ract
ion
Rad
ius
(fm)
876543
Helium Mass Number A
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Nuclear ChartNuclear Chart
Neutron number
Pro
ton
num
ber
stable nuclei
unstable nuclei
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NeutronNeutron--rich rich 66He and He and 88HeHe
Charge radius probes “valence neutron correlation”
Isotope Half-life Spin Isospin Core + Valence
He-6 807 ms 0+ 1 α + 2n
He-8 119 ms 0+ 2 α + 4n
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Methods of Measuring Charge RadiiMethods of Measuring Charge Radii
( )
2sin4
)(42
222
θασ
E
cZdd
Rutherfordh
=Ω
222exp )(*2
cos*)()( qGdd
dd
ERutherfordθσσ
Ω=
Ω
02
22
arg2
2
)(6=
−=><q
Eech dq
qdGr h
Electron scattering
Nuclei with finite size:
R=1.21×A1/3 fm for non-deformed nucleiCan NOT apply to unstable (short-lived) nuclei
e beam
qpi
pf
θ
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NeutronNeutron--rich rich 66He and He and 88HeHe
Charge radius probes “valence neutron correlation”
Isotope Half-life Spin Isospin Core + Valence
He-6 807 ms 0+ 1 α + 2n
He-8 119 ms 0+ 2 α + 4n
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Nuclear ForceNuclear Force
Fundamental theory QCD not calculable in low-energy regime
Modern nuclear models use “effective potential”
Long range (~2 fm) attraction: one-pion exchange
Intermediate range (~1 fm) attraction: two-pion exchange
Short range repulsion: hard-core effect, quarks are fermions
QCD
q
q
qq
qq
N
N
Mesonexchangeq
qq
q
qq
N
N
π
qq
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Neutron Halo Nuclei 6He and 8HeNeutron Halo Nuclei 6He and 8HeIsotope Half-life Spin Isospin Core + Valence
He-6 807 ms 0+ 1 α + 2n
He-8 119 ms 0+ 2 α + 4n
4He
8He
6He
QuantumMonte Carlocalculation
Proton
NeutronPieper & Wiringa (2006)
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Charge Radius of Helium IsotopesCharge Radius of Helium Isotopes
Charge radii 4He < 6He ~ 8HeElectron scattering, not possible for 6He, 8HeElastic proton scattering involves strong interaction, cannot separate proton and neutronNo “Poisson equation” for QCD to relate strong force to nucleon distributionAtomic isotope shift, measure the difference
??1.673(1)1.964(1)AtomicIsotope shift
1.80(7)1.56(6)
2.09(9)1.95(8)1.79(4)
Protonscattering
1.676(8)1.96(3)Electron scattering
1.99(1)2.05(1)1.662(5)1.954(5)Theory
8He6He4He3He
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Atomic Isotope ShiftAtomic Isotope Shift
Mass shift: due to nucleus recoil
Isotope Shift δν = δνMS + δνFS
Field shift: due to nuclear size
δνMS ∝ ''
AAAA −
δνFS∝ [Ψ(0)]2 × δ< rc2 >
Nuclear mass precisely known Atomic structure Ψ(0) calculable,H, He, Li.
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Field (Volume) ShiftField (Volume) ShiftAA
FS rZe′
⋅ΨΔ⋅−= 222 )0(3
2 δπδν
1 10 1001E-3
0.01
0.1
1
10
100
| Iso
tope
Shi
ft |,
GH
zA tom ic num ber, Z
Mass shift
Field
shift
rE
s
p
V ~ - 1/r
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Gordon W.F. Drake (Can. J. Phys 84, 83 2006)
Non-relativistic wave functions fromvariational calculationsPerturbation theory for relativistic corrections, QED, finite nuclear mass and nuclear charge radiusQED terms “cancel” in isotope shift
Atomic Theory of HeliumAtomic Theory of Helium
Experimental confirmationTotal transition frequency4He Fine structure splitting3He-4He Isotope shift + HFS
3He 4He
33PJ
23S1
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Atomic Isotope ShiftAtomic Isotope Shift
Mass shift: due to nucleus recoil
Isotope Shift δν = δνMS + δνFS
Field shift: due to nuclear size
δνMS ∝ ''
AAAA −
δνFS∝ [Ψ(0)]2 × δ< rc2 >
Nuclear mass precisely known Atomic structure Ψ(0) calculable,H, He, Li.
For 23S1 – 33P2 transition @ 389 nm:
6He - 4He : δν6,4 = 43196.202(16) MHz + 1.008 (He4 - He6) MHz/fm28He - 4He : δν8,4 = 64702.410(70) MHz + 1.008 (He4 - He8) MHz/fm2
G.W.F. Drake, Univ. of Windsor, Nucl. Phys. A737c, 25 (2004)
100 kHz error in IS ~ 1% error in radius
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Helium Energy LevelHelium Energy Level
For noble gas atom, first excited state too high for laser excitation, (VUV)Exp. on metastable stateRF discharge by electron collision
A glow discharge He gas cell
23S1
11S0
389 nm
1083 nm
23P0,1,2
19.82 eV
33P0,1,2
He energy level
τ=106 ns
τ=98 ns
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Spectroscopy of Spectroscopy of 66HeHeTechnical challenges:
Short lifetime, small samples (~ 106 atom/s available)Difficult spectroscopy (Metastable efficiency ~ 10-5)Precision requirement (100kHz = Doppler shift @ 0.04 m/s)
Solution: Spectroscopy with cooled atoms in a magneto-optical trap
High resolution: cold atoms, Doppler width largely reducedHigh sensitivity: capable of detecting a single atom
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66He ProductionHe Production
Stripping reaction at ATLAS: 12C(7Li,6He)13N6He extraction rate ~ 3×106 /s
12C Target
7Li3+ 100 pnA60 MeV
β Counter
750 ºC
6He
Turbopump 6He→ 6Li+β-+ν
0 1 2 3 410
100
1000
Rat
e (c
ount
s/se
c)
Time (sec)
t1/2 ~ 800 mst1/2 ≈ 800 ms
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.01
10
100
Cou
nts
Energy (MeV)
3.5 MeV
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Experimental SetupExperimental Setup
6He from ATLASTransport time ~ 1 sec
PhotonCounter
RF discharge
4He, Kr
6He
He* Zeeman Slower MOT
TransverseCooling
389 nm 1083 nm
Mixingchamber
389 nm
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Single Single 66He Atom DetectionHe Atom Detection
0 5 10 15 200.0
0.2
0.4
0.6
0.8
1.0
1.2
Pho
ton
coun
t rat
e (k
Hz)
Time (s)
Capture efficiency ~ 2×10−8single atom detection necessary!
Imaging system and reducing background6He capture rate ~ 150 per hour
Trap
Detector
Aperture
Filter
Single
6He atom!
60 70 80 90
0
1
2
3
4
5
6
Pho
ton
coun
t rat
e (k
Hz)
Time (s)
4He test
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Spectroscopy of Trapped AtomsSpectroscopy of Trapped Atoms
Light shift and Zeeman shiftHeating and cooling effect: asymmetric line shape
single γ recoil: 440 kHz for 6He, 330 kHz for 8HeProbing laser power must be very low!M. Zhu, C. Oates, J. Hall, Opt. Lett., 18,1186 (1993)
-15 -10 -5 0 5 10 15 20
0
2
4
6
8
10
Phot
odet
ecto
r sig
nal (
a.u.
)
R e la tive frequency (M H z)
6uw 150uw 650uw
Test using 4He trap
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Frequency Scanning StrategyFrequency Scanning Strategy
off
onoffon
8μs2μs
~ 12 μs
Frequency scan 12MHz
Trapping light
Probe laser
Fast switch & scan
Identification50 ms
Spectroscopy for 1 s
Two frequency-detuning trap (hot and cold)Balance between the two probe beams
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Systematic Effect StudySystematic Effect Study
PMT
liquid N2 cooledRF discharge
He*
transversecooling
He + Kr
4He fine structure splitting as a testAtomic Beam ExperimentVery different systematic effect
2 3S1
3 3PJ
389 nm
J=0
J=1
J=2ν12
ν01ν02
4He level
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44He Fine StructureHe Fine Structure
ReferencesLamb ‘57: I. Wieder and W.E. Lamb, Jr., Phys. Rev. 107, 125 (1957)Pipkin ‘78: P. Kramer and F. Pipkin, Phys. Rev. A18, 212 (1978)Metcalf ‘86: D.-H. Yang, P. McNicholl, and H. Metcalf, Phys. Rev. A33, 1725 (1986)This work: P. Mueller, L.-B. Wang, G.W.F. Drake, K. Bailey, R.J. Holt,
Z.-T. Lu, and T.P. O’Connor, Phys. Rev. Lett. 94, 133001(2005)
8113.6 8114.0658.4 658.8 8772.4 8772.8
Metcalf '86
Pipkin '78
Lamb '57
Drake '04
This work(trap)
ν12 ν01
Fine structure splitting, MHz
ν02
This work(atomic beam)
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66He SingleHe Single--Atom SpectroscopyAtom Spectroscopy
~150 6He atomsin one hour
IS = 43 194.772(56) MHz
1/2 = 2.054(14) fm (0.7%)Phys. Rev. Lett. 93, 142501 (2004)
0 2 4 6 8 10 12 14 16 18 2043194.0
43194.4
43194.8
43195.2
43195.6
Isot
ope
Shift
(MH
z)
# of Measurement
April Run May Run
Frequency (MHz)
Res
idua
l
- 8 -6 -4 -2 0 2 4 6 8-4 0
0
4 0
-8 -6 -4 -2 0 2 4 6 8-1 0 0
0
1 0 0
50
100
150
200
250
300
Pho
ton
coun
ts
0
300
600
900
1200
Phot
on c
ount
s 6He4He
Res
idua
l
Frequency (MHz)
(a) (b)
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Point Proton RadiusPoint Proton Radius
Theory:ms point-proton radius
rp
Experimental mean square charge radii:Proton 1/2 = 0.895(18) fm, [Sick, 2003]Neutron = −0.120(5) fm2, [Kopecky, 1997]
Experiment:ms charge radius
Rp
rc
Rn
>< 22
222 143 n
pppc RZ
NM
Rrr
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Comparison with TheoriesComparison with Theories
Neutron-halo structure confirmedUnderestimate in cluster modelsDisagree with nuclear collision
Reaction collision
Elastic collision
Isotope shift
Clustermodels
No-core shell
Quantum MC
1.8 1.9 2.0 2.1 2.2 2.3 2.4
Nuclear charge radius of 6He (fm)
[Tanihata, 1992]
[Alkhazov, 1997]
This work
[Csoto, 1993]
[Funada, 1994]
[Varga, 1994]
[Wurzer, 1997]
[Esbensen, 1997]
[Navratil, 2001]
[Pieper, 2005]
AIP Physics News Update, # 702-3, Sep. 2004
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Where to find Where to find 88He?He?
GANILCaen, France
Other possible sites:
TRIUMF in CanadaISOLDE @ CERNNSCL @ MSU
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88He @ GANILHe @ GANIL
2.15 3.15
1.85 0.75
1.65
5 m
Salle D2
6,8He+@ 20 keV
6,8Hethermal
Laser System
MOT
ECR Ion Source
Massseparator
75 MeV/u, 0.4 pμA 13C beamon 12C target
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Atom Trapping of Atom Trapping of 66He & He & 88He at GANILHe at GANIL
~1x108 6He+/s~5x105 8He+/s
PMT
Zeemanslower
MOTTransverse
cooling 389 nm 1083 nm
Atom Trap Setup
RF -Discharge
Xe
Capture efficiency1x10-7
Source~5x107 He-6/s,~1x105 He-8/s
Trap~5 He-6/s,
~30 He-8/hr
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Jan. 26th 2007
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… June 2007
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June 15June 15thth -- HeHe--8 Trapped!8 Trapped!
First He-8 AtomJune 15th 2007
t
f
-10 -8 -6 -4 -2 0 2 4 6 8 100
100
200
300
400
500
Cou
nts
per C
hann
el
Rel. Laser Frequency, MHz-10 -8 -6 -4 -2 0 2 4 6 8 10
0
20
40
60
80
100
Cou
nts
per C
hann
el
Rel. Laser Frequency, MHz
50 kHz
6He
~ 5 6He atoms/s
110 kHz60 atoms
8He
~ 30 8He atoms/hr
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0.4
0.5
0.6
0.7
0.8
0.9
-0.2
0.0
0.2
0.4
0.6
0.8
-1.6
-1.4
-1.2
-1.0
-0.8
-0.6
δν6,
4 - 4
3194
, MH
z
(b)
(a)
δν8,
4 - 6
4701
, MH
z
J = 0 J = 1 J = 2
(c)
6He8He
Fiel
d S
hift,
MH
z
J = 0 J = 1 J = 2
8He
6He
Isotope Shift and Field Shift : J Isotope Shift and Field Shift : J -- Dependence?Dependence?
2 3S1
389
nm
3 3P0,1,2
J=2J=1
J=0
J=1
Wang 04Argonne
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Experimental Uncertainties and CorrectionsExperimental Uncertainties and Corrections
74 kHz15 kHzNuclear Mass
97 kHz35 kHzTOTAL
45 kHz30 kHzZeeman Shift
15 kHz0 kHzProbing Power Shift
24 kHz2 kHzReference Laser Drift
12 kHz2 kHzLaser Alignment Drift
32 kHz8 kHzPhoton Counting
8He6He
Statistical {
Systematic {
-2(1) kHz-14(3) kHzNuclear Polarization
+165(0) kHz+110(0) kHzRecoil EffectCorrections
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66He & He & 88He RMS Point Proton RadiiHe RMS Point Proton Radii
0.4 %0.3 %- He-4: 1.460(8) fm1.0 %0.2 %- Mass Systematics0.6 %0.3 %- Trap Systematics
0.6 %0.1 %- Statistical1.3 %0.5 %Total Uncertainty
1.809(28)1.926(11)RMS Rpp, fm-0.916(95)-1.464(34)Field Shift, MHz
8He6He
PRL 99, 252501 (2007)
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66He & He & 88He Charge RadiiHe Charge Radii
AIP Physics News Update, # 851-2, Dec. 2007
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ConclusionConclusion
Hypothesis of neutron-halo structure confirmed model-independentlyDemonstrated trap spectroscopy with single atom sensitivity
OutlookTo further improve the precision and compare with theories:Nuclear polarizability and MEC (meson exchange current) correction necessary at this level of precisionNeed more precise value of proton radius Need more precise value of helium-4 radius See also recent laser spectroscopy work on Li-11 at GSI/TRIUMFNew He-8 mass measurement in Penning trap @ TRIUMF in Dec. ‘07
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CollaborationCollaborationK. Bailey, J.P. Greene, D. Henderson, R.J. Holt, R.
Janssens, C.L. Jiang, Z.-T. Lu, P. Mueller, T. O’Conner, R.C. Pardo, K.E. Rehm, J.P. Schiffer, I.
Sulai, X.D. Tang Argonne National Laboratory, USA
M.-G. Saint Laurent, J.-Ch. Thomas, A.C.C. Villari et al.- GANIL, Caen, France
G. W. F. Drake - University of Windsor, Canada
L.-B. Wang - Los Alamos National Laboratory, USA
P. Mueller L.-B. Wang I. Sulai Z.-T. Lu
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GFMC GFMC –– What happens to the Core?What happens to the Core?
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MesonMeson--Exchange Current CorrectionExchange Current Correction
Mesons mediating strong force carry electric chargeExpected to be different among 4He, 6He and 8HeIn H−D isotope shift, MEC correction ~0.2% of deuteron charge radiusSmall but NOT negligible at this precision
⇒ further theoretical investigation necessary
MECnp
ppc rRZN
MRrr >< 222
222 143
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Cluster Models for Cluster Models for 66HeHe
Assume α core not affected much by the two neutronsEmpirical form of n-n, n-α potential, parameterized by scattering phase shiftCluster modelsTriton + triton channel used
α
C.M.
n n
r1R1C.M.
α
n n
r2 R2
α
n n
R3
r3
t
t
R4
(a) (d)(c)(b)
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MuonicMuonic Atom XAtom X--ray Spectroscopyray Spectroscopy
mμ/me ~ 200
Bohr radius
Energy level
Wave function
Energy shift due to nuclear size
~
Sensitivity ~ (mμ/me)3
muon decay μ νν− −→ e
nucleus μ-em
a 1~0
2~ nmE en −
Muonic 4He+ Energy Level
δν(2S1/2-2P3/2)=1.813 −0.102 eV811.68(15)nm ⇒ 1/2(4He)=1.673(1) fm
Carboni et al., Nucl. Phys. A278, (1977)
Muonic hydrogen in PSI ⇒ proton radius1 S1/2
2 P3/2
8.2 keVX ray
2 S1/2
1.5 eV 812 nm
4% in metastable state
( ) 220 rδΨΔ
( ) 0/2/30~ arear −−Ψ
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Atomic Theory of HeliumAtomic Theory of Helium
Solve 3-body Schrödinger Equation
2×10-96×10-31×10-78×10-85×10-47×10-49×10-44
Z4 (RN/ao)2Z4 α3ln αZ4 α2 μ/MZ2(μ/M)2Z2μ/MZ4 α3Z4α2Z2Magnitude
Relativistic correctionAnomalous magnetic moment
Nonrelativistic energy
Second-order mass polarizationMass polarization (SMS)
Finite Nuclear SizeQED correction (Lamb shift)Finite mass correction (NMS)
Contribution
Error
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Binding Energy of Light NucleiBinding Energy of Light Nuclei
α+2n 6He+2n8He+2n
S. Pieper and R. Wiringa, Annu.Rev. Nucl. Part. Sci. 51, 53(2001)
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Monte Carlo CalculationMonte Carlo Calculation
Argonne v18 two-body potential:
∑ ∑<
+++=i ji
Rijijiji vvvKH
πγ
EM OPE TPE+HC
• Coupling strength to fit NN scattering data• Problem: binding energy of most light nuclei too small
Illinois 3-body potential:
Rijkijkijkijk VVVV ++=
ππ 32
Urbana IX Illinois 1-5
•In nuclei A>3, excitation of the excited state of nucleons•Parameters to fit 3H, 3He binding energy• Isospin dependant, Neutron-rich light nuclei, e.g. 6He
S. Pieper and R. Wiringa, Annu.Rev. Nucl. Part. Sci. 51, 53(2001)
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NuclearNuclear--Medium CorrectionMedium Correction
Electron does NOT see the bare nucleus ⇒ Nuclear polarizabilityThe energy shift in the helium 23S1−33P2 transition:
)()()( 087 2
46
HαHeαHeαkHz.δν
E
EE −×=
∑≠ −
=0 0
20
32
N NE EE
DNαα ∫∞
=+0
22
)(21 ω
ωωσ
πβα γ dME
G.W.F. Drake, private communication
αE(6He) = 0.68 − 0.74 fm3 by Esbensen αE(6He) ~ 0.8 fm3 by BaccaαE(2H) = 0.63 fm3 by Friar
10 kHz shift expectedIncrease 6He 1/2 by 0.1%
Baldin-Lapidus sum rule
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389 nm Spectroscopy Laser Setup389 nm Spectroscopy Laser Setup
389 nmoutput
Diode Laser 1@ 778 nm
Diode Laser 2@ 778 nm
lock to I2 transition
TaperedAmplifier
measure beatfrequency
I2 spectrum near 777.946 nm
2S-3P 389 nm Frequency (GHz)40.6-44.6 0
3He I2×24He 6He
-2.5
Frequencydoubling
0 200 400 600 800 1000 1200 1400 1600
-3
-2
-1
0
1
2
3
Sign
al (a
rb. u
nit)
Relative Frequency (MHz)
used for laser locking
AOM
Fast frequency scan for spectroscopy