Post on 30-Jan-2016
description
(Towards) Extreme Ultraviolet Frequency Comb Spectroscopy of Helium and Helium+ Ions
VU University, Netherlands
Kjeld Eikema
€ from
ECT* 28 September – 2 november 2012 "Proton size conundrum"
Jonas Morgenweg, Itan Barmes, Tjeerd PinkertDominik Kandula, Chirstoph Gohle,
Anne Lisa Wolf, Stefan Witte
Outline
Introduction To the XUV (at 51-85 nm) with frequency combs: Two-pulse “Ramsey Comb” excitation. The next generation: “Ramsey-Fourier-Frequency Comb” First signal with two-pulse two-photon excitation in Rb Summary en Outlook
Frequency comb laser activities @ LaserLaB
XUV comb metrology, QED tests:Jonas Morgenweg, Tjeerd Pinkert, Itan Barmes, Dominik Kandula, Christoph Gohle
Coherent control: Itan Barmes, Stefan Witte
Precision spectroscopy on ions:Anne Lisa Wolf, Jonas Morgenweg,Wim Ubachs, Steven v.d. Berg
Dual-comb spectroscopy &mid-IR combs: Axel Ruehl, AlissioGambetta, Marco Marangoni et al.
Precision dissemination over fiber: Tjeerd Pinkert, Jeroen Koelemeij
Precision frequency comb calibrations, collaborations with: Wim Ubachs, Jeroen Koelemeij, Rick Bethlem, and others.Wim Vassen: He 2 3S1 - 2 1S0 transition, Science 333, 196-198 (2011)
15
51 nm = 6 PHz
100µm
Introduction QED / Ry issues?
Hydrogen
1S
2S
243 nm
243 nm
Muonic-hydrogen
1S
2S
2 keV…
6 m
C.G. Parthey et al., PRL 107, 203001 (2011)
R. Pohl et al,Nature, vol. 466, pp. 213-216 (2010).
2P
1S-2S: 2 466 061 413 187 035 (10) Hz
Comparison normal vs. muonic matter
1S
2S
Ener
gy
2x 243 nm 1S
2S
2x 60 nm
He+H H
Ener
gy
He+
6 mm
0.6 nm(2 keV)
1S
2S2P
812 nm
0.15 nm(8.2 keV)
1S
2S
2P
The 1S-2S values for H and H
Theory
Experiment
1S-2S
L1S-2S
1S-2S
B60+B7i
L(R∞)1S-2S
Rel. acc. L1S-2S
Finite size(nucl. pol.)
Rel. L(R∞)
Z2
Z≥3.7
Z4r2
Z≥6
Z2
9.869...×1012
93 856 127(348)*62 079(295)
-543(185)(40 or 15**)
3.7 ppm****
not measured650.7 ppm
2.466...×1012
7 127 887(44)1102(44)
-8(3)(2)
6.3 ppm
246606143187.035(10)162.2 ppm
H (kHz) He+ (kHz)Scaling
Test B60+B7i 25% 7% or 4%***
1S-2S Z4 83×10-31.3×10-3
H 1S-2S from C.G. Parthey et al., PRL 107, 203001 (2011)
The experimental challenge
Hydrogen
1S
2S2x 243 nm
Helium+
1S
2S
2x 60 nm
Helium
1s2
1s2s
2x 120 nm51 nm
1s5p<30 nm
Frequency comb lasers
T
Frequency Comb laser
Mode-locked laser
Nobel Prize Physics 2005
J. Hall T.W. HänschR.J. Glauber
Frequency comb lasers
frequency
Int.
0
fn = f0 + n.frep
frep = 1/Tf0 = frep x φCE / 2
time
φCE= /2φCE= 0
vg ≠ vφ
T
R. Holzwarth et al. PRL 85, 2264 (2000), D.J. Jones et al. Science 288, 635 (2000)
Frequency comb lasers as optical rulers
T
Experimentbeat note measurement;f = f0 + n frep + fbeat
Single-modelaser freq. f
Frequency Comb laser
Direct frequency comb excitation
T
Experiment
Experiment
beat note measurement;f = f0 + n frep + fbeat
Single-modelaser freq. f
Frequency Comb laser
Upconversion through high-harmonic generation
IR pulses XUV (<100 nm)
1014 W/cm2
NIR (800 nm) DUV
frequency
VUV XUV X-RAYharmonicconversion
UV
Noble gas jet
3rd 5th 7th 9th 333rd…
High-harmonic generation (HHG)
Corkum & Krausz, Nature Physics 3, 381 (2007)
IR ~1014 W/cm2
Phase coherence of HHG
Other experiments: E.g. excitation Kr continuum @ 88 nm, delays~ 100 fs – ps rangeCavalieri et al., PRL 13, 133002 (2002)A. Pirri et al. PRA 78, 043410 (2008) and more
Phase XUV ~ - IIR
Frequency comb up-conversion
IR
DUV
frequency
VUV XUV
X-RAY
harmonicconversion
XUV
UV
fn = f0 + n frep fn = p f0 + m frep
pth harmonic:Near-Infrared:
XUV comb generation methods
HHG in resonator(MPQ, JILA, Arizona, etc.)
C. Gohle et al. Nature 436, 234 2005 A. Ozawa et al., PRL 100, 253901 (2008) R.J. Jones et al. PRL 94, 193201 (2005)I.Hartl et al. Opt. Lett. 32, 2870 (2007),Etc.
A. Cingoz et al., Nature 842, 68 (2012)Argon spectroscopy at 82 nm, 3 MHz acc.
HHG after amplification(LaserLaB Amsterdam)
S. Witte et al. Science 30, 400 (2005)Zinkstok et al. PRA 73, 061801(R) (2006)T.J. Pinkert et al. OL 36, 2026 (2011)(argon 85 nm, neon 60 nm, helium 51 nm)D. Kandula et al. PRA 84, 062512 (2011)
D. Kandula et al. PRL 105, 063001 (2010)Helium spectroscopy at 51 nm, 6 MHz acc.
Frequency comb lasers – infinite pulse train
frequency
Int.
0
fn = f0 + n.frep
frep = 1/Tf0 = frep x φCE / 2
time
φCE= /2φCE= 0
vg ≠ vφ
T
Frequency comb lasers - two pulses
frequency
Int.
0
fn = f0 + n.frep
frep = 1/Tf0 = frep x φCE / 2
time
φCE= /2φCE= 0
vg ≠ vφ
T
p, kp
pump
idler
signalc(2)
fluorescence cone
seeds, ks
sp
i
i = p – s
Parametric chirped pulse amplification
BBO crystals pumped by 532 nm at intensities of 7 GW/cm2
Tuning over 700-1000 nm with little effort Bandwidth adjustable from 300 nm to 5 nm No memory effect Two comb pulses amplified by two synchronized equal pump pulses; microradian pointing sensitivity!
HHG of two pulses
IR pulses – mJ level XUV pulses
few nJ levelDivergence <2 mrad
<1014 W/cm2
f=50 cm
IXUV ~ IIR9
At the 15th harmonic to excite He
15
HHG
15
fCE ~ /3006 MHz
6.6 nsHelium
1S2
1S2S
51.6 nm
1S5P
(51 nm)
Principle and setup schematic overview
Ramsey comb excitation of helium at 51 nm
Contrast up to 60% at higher rep-rate: 50 as jitter
121 MHz
D. Kandula et al. PRL 105, 063001 (2010)D. Kandula et al. PRA 84, 062512 (2011)
He ground state measurement systematics
IR phase shifts in OPA Pulse phase front tilt Spectral/temporal phase difference between pulses Doppler shift: varying speed using He, He/Ne, He/Ar & tune angle Ionization: varying density, pulse intensity ratio Adiabatic shift in HHG shift in HHG due to excitation AC Stark shifts (IR, XUV, ioniz. l.), DC Stark (field free) Self-phase modulation (pulse ratio). Recoil shift 18.5 MHz for 5p Many more efects!:
Tests of chirp, HHG focus position, f0, out-of-centre phase, ....etc.
Theory and experiment
blue = experiments and red = theory
DrakePachucki
S. Bergeson et al.Eikema et al.
Accuracy 6 MHz (8 fold improvement)
History of the He ground state energy accuracy
Blue = experimentRed = theory
Tunable XUV Ramsey frequency comb
Argon Neon Helium
~84 nm(9th harm. in Xe)
~51 nm(15th harm. in Kr)
~60 nm(13th harm. in Kr)
T.J. Pinkert et al. OL 36, 2026 (2011)
View of the lab
HHG and excitation apparatus
Apparent two-pulse limitation: T and s
Signal = cos(tr T – s)
T
sAn error in s gives a frequency
error in tr of tr = s / T
The magic of Fourier transformation
Signal = cos(tr T – s)
T
s
FFT
tr
The magic of Fourier transformation
Signal = cos(tr T – s)
T
s
FFT
tr
T
s
2T
FFT
tr
rep
rep = 2/T
s
FC-FTS vs. FC Full-rep-rate excitation
T
s
2T
FFT
tr
rep
rep = 2/T
T 2Ttr
rep
rep = 2/T
Full rep. rate coherent addition
Two-pulse incoherent addition
s
s s s
AC-Stark shift
T
Stark
2T
FFT
tr
rep
rep = 2/T
T 2Ttr
rep
rep = 2/T
Full rep. rate coherent addition
Two-pulse incoherent addition
Stark Stark
Stark
Stark
FC-FTS features and requirements
Accuracy and resolution equivalent to full-rep rate excitation FC-FFT more easily tunable at extreme wavelengths AC-Stark shift 'free', in contrast to full-rep rate excitation With more than 1 transition: ’interference’ effects, but possible
to model. Simulations for T=160 ns show ~10 kHz accuracy
Requirements:
IR FC pulses must be amplified with constant phase and energy, ideally < /1000 and <1% energy fluctuation,irrespective of the time delay between the pulses!
The old situation with a delay line
D. Kandula et al., Opt. Express, 16, 7071-7082 (2008)
power amp.2 x 200 mJ
SHGsync.
7 ps osc.1064 nm
comb laser ~780 nm
frep=150 MHz 2x 2 mJ200 fs @ 30 Hz
Relay imaging
3-stageNOPCPA
regen amp.2 mJ
The old situation with a delay line
SHGsync.
comb laser ~780 nm
frep=125 MHz
3-stageNOPCPA
The new system
SHGsync.
comb laser ~780 nm
frep=125 MHz 2x 2 mJ 10-200 fs, T=8 ns to >10 srep. rate 300 Hz
3-stageNOPCPA
10 ps osc.1064 nm
power amp.2 x 120 mJ
'bounce' amp2 x 1 mJEOM/AOM
pulse picking & scaling
T
J. Morgenweg and K.S.E. Eikema, OL 37, 208 (2012)J. Morgenweg and K.S.E. Eikema, Las. Phys. Lett. 5, 1 (2012)
New pump laser front-end
t = 8 ns to >10 sRep. rate < 1 kHz
30 Hz rep. rate (300 Hz in prep.)
2x 1 mJ
2x 100 mJ
(Bounce) amplifier performance
(n=7; Tosc ~ 8 ns)
(n=35)
(n=160)
Amplified comb pulses - phase measurement
Single shot differential spectral interferometry
Single shot SNR sufficient for 10-20 mrad rms stability
Inaccuracy < 5mrad
BS 50 %
BS10%
OPCPA
NG
CCD Camera
Oscillator
BS 5%
PC
PC
HHG Spectr.
MZ-Interferometer
Pulse separation
Analysis
SP-FilterFiber
Phase of the amplified comb pulses
Average phase equal within 5 mrad (/1200) and pulse energy equal within 1% for a 2-pulse delay (16 ns) to 32-pulse delay (256 ns)
Laser shots
Delay
Doppler-’free’ comb excitation in Rb
CW lasers: Hansch et al., OC 11, 1 (1974)
Nanosecond pulses: Biraben et al., PRL 32, 12 (1974)
Picosecond pulses: Fendel et al., OL 32, 6 (2007)
Femtosecond pulses, and withspatial coherent control: I. Barmes et al., to be published in Nature Photonics
V-shaped phase
100µm
100µm
Transform-limited
Elimination of background by coherent control
Two-photon two-pulse Fourier-Ramsey-Comb Excitation of Rb (5S – 7S)
Inter-pulse delay T in femtoseconds
n=2; T=15.9 ns
n=4; T=31.8 ns
n=2; T=63.5 ns
Fluo
resc
ence
sig
nal
Summary and Outlook XUV frequency comb metrology demonstrated, 85-50 nm Ground state energy of helium with an accuracy of 6 MHz Fourier-Ramsey Frequency Comb Excitation with 2 pulses New system and first spectroscopy in Rb shown Few mrad variation over 256 ns; potentially <kHz XUV accuracy
Outlook: He+ in an ion trap with Be+ cooling for 1S-2S spectr., Two-photon (2*120 nm) in Helium with coherent control, Two-photon in H2 to improve ionization potential to <100 kHz Delay extension up to 100’s of s for Hz-level accuracy?
D. Kandula et al. PRL 105, 063001 (2010)D. Kandula et al. PRA 84, 062512 (2011)
T.J. Pinkert et al. Opt. Lett. 36, 2026 (2011) J. Morgenweg et al. Opt. Lett. 37, 208 (2011)
I. Barmes et al., Nature Photonics, to be published
Ions in a Paul trap
The people
Itan Barmes
Tjeerd Pinkert
JonasMorgenweg
WimUbachs
ChristophGohle
RoelZinkstok
AxelRuehl
StefanWitte
DominikKandula
AmandineRenault
Anne LisaWolf
From here on additional slides
Coherent control for Doppler-reduced excitation
Full spatial coherent control
Spatial and atom selective excitation
To be published in Nature Photonics
Enhanced signal to noise
15 kHz absoluteaccuracy
Abs. calibration2.6x betterthan previousmeasurements
Hyperfine &Isotope shiftup to 10xbetter than before
Flat phase
V-phase85Rb(3-3)
87Rb(1-1)
85Rb(2-2)
87Rb(2-2)
Full measurement series, frep=121.5 MHz
PureHe
Neseeded
Arseeded
OPA: Pump laser influence on phase
Requirements:
– Pump pulse wave fronts equal to </20– Pump pulse intensity equal within few %
Then:– Comb amplified wave fronts equal to /300
dLconversionkz ss '')0()(
k = kp – ks - ki
2-pulse ‘Ramsey’ comb principle
Phase coherent pulse excitation: Ramsey (1949), Hänsch and coworkers (1976/77), Chebotayev et al. (1976), Snadden et al. (1996), Bellini et al. (1997, 1998), ....
Time domain Frequency domain
T = 1/T
t
t
He ground state ionization energy
Theory position (Pachucki, PRA 2010)
Direct comb spectroscopy in Ca+ for a search of variation
• Dipole allowed: 4s 2S1/2-4p 2P1/2 or 3/2
• Forbidden: 4s 2S1/2-3d 2D5/2
• All wavelengths of interest accessible with frequency comb at full repetition rate: equilibrium!
Ca+ ion
Relative to: 411 042 129 776 393.2 (1.0) Hz as measured byChwalla et al, PRL 102, 023002 (2009)
Lifetime 3d 2D5/2 = 1 second
Comb excitation of the 729 nm clock transition
A.L. Wolf et al., Opt. Lett. 36, 49 (2011)