Light shining through wall experiments -...
Transcript of Light shining through wall experiments -...
Jan H. Põld DESY
Bethe Forum: Axions and the Low Energy Frontier 9. March 2016
Light shining through wall experiments
Jan H. Põld | LSW experiments | 9.March 2016 | Page
Outline
Overview LSW experiments
> key elements
> sensitivity
> source, magnets, detector
> cavities as an improvement for LSW experiments
The ALPS experiment
> history
> layout
> current status and performance
> future efforts
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Jan H. Põld | LSW experiments | 9.March 2016 | Page
What are the key elements of an LSW experiments?
> Source, magnet, wall, detector
> production and detection lab based
3Primakov effect
Jan H. Põld | LSW experiments | 9.March 2016 | Page
Sensitivity for ALP photon coupling
> probability for photon-ALP-photon conversion
> most effective improvements by increase of B and/or L
> coherent sources can be combined with resonators to raise the number of photons in front of the wall
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Jan H. Põld | LSW experiments | 9.March 2016 | Page
Sources
> Sources: sub THz (microwave), optical (532nm and 1064nm lasers), xray sources, proton beam (talk by Babette on Friday about beam dump experiments)
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CROWS STAX
ALPS I OSQAR
experiments at SPRING-8 ESRF
ALPS II
concluded under construction proposed
Jan H. Põld | LSW experiments | 9.March 2016 | Page
Magnets
> pulsed
> non-destructive: up to 60T and 15mm bore (MagLab)
> permanent
> e.g. 2.5T and 20mm bore (PVLAS)
> superconducting electromagnets
> 9 T and 50mm bore (LHC)
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Jan H. Põld | LSW experiments | 9.March 2016 | Page
Detectors
> single photon detection
> high conversion efficiency
> low background rates
> Transition edge sensor (subTHZ,visible,IR)
> CCD (visible)
> heterodyne readout scheme (visible, IR)
> Germanium (Xray)
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TES
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Cavities as improvement for LSW
> resonator: arrangement of optical components which allows a beam of light to circulate
> resonator modes: field distributions which reproduce themselves after one roundtrip
> high power lasers are expensive and hard to get with requirements for a certain beam quality
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Jan H. Põld | LSW experiments | 9.March 2016 | Page 9
0
0.2
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1
-0.5 0 0.5 1 1.5
Nor
mal
ized
Inte
nsity
FSR
Finesse=10Finesse=50
How to characterize an optical resonator?
> Finesse describes the quality (losses) of a cavity
> free spectral range
> full width at half maximum
> Intensity
(circulating)
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Pound-Drever-Hall locking
> published in 1983
> modulation/demodulation scheme to generate an error signal with a linear slope at the resonance
> feedback to the length of the cavity or the laser frequency possible
Jan H. Põld | LSW experiments | 9.March 2016 | Page
Production cavity
> increase number of photons in front of the wall
> high power buildup/ high Finesse
> in two mirror case a standing wave is produced inside the cavity
> only efficient with coherent source
> single frequency, single spatial mode source required
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Jan H. Põld | LSW experiments | 9.March 2016 | Page
Regeneration cavity
> waist needs to be in the middle to have efficient coupling
> the physics is the same it is just harder to imagine
> higher mode density ==> higher reconversion probability
> similar to Purcell effect for atoms (predicted 1946, experimental verification 1989)
> three independent publications about this technique (Hoogeveen and Ziegenhagen (1990), Fukuda et al. (1996), Sikivie (2007))
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Jan H. Põld | LSW experiments | 9.March 2016 | Page
Summary LSW experiments
> for a very sensitive LSW experiment you need
> strong magnets in a long string configuration
> low background rate detectors
> high power lasers and cavities
> sophisticated control systems
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Jan H. Põld | LSW experiments | 9.March 2016 | Page
ALPS@DESY
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> ALPS I (concluded 2010)
ALPS: Any light particle search
> ALPS IIa (currently being set up)
> ALPS IIc (2019)
> Best effort with existing magnets and facilities
Jan H. Põld | LSW experiments | 9.March 2016 | Page
ALPS I
> LSW experiment at DESY
> most sensitive LSW experiment at its time (recently surpassed by OSQAR)
> first experiment with production cavity
> used frequency doubled 1064nm laser
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3.5·1021 1/s < 10-3 1/s
PLB Vol. 689 (2010), 149, or http://arxiv.org/abs/1004.1313
Jan H. Põld | LSW experiments | 9.March 2016 | Page
ALPS II
> LSW experiment with long baseline cavities in the HERA tunnel
> three orders of magnitude better than ALPS I
> surpassing CAST by a factor of three
> ALPS IIa is a pathfinder experiment to test the optical concept of ALPS IIc
16ALPS IIa (20m lab)
ALPS IIc in HERA tunnel
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> Optics: high power cw 35W laser; light enhancement by high Finesse cavities
> Detector: Transition edge sensor ▪ very sensitive at 1064nm (in comparison to a CCD camera)
▪ Tungsten film kept at the transition to superconductivity at 80 mK; Sensor size 25µm x 25µm x 20nm
▪ dark background: 10-4 counts/second
> Magnets: 20 straightened, superconducting HERA dipole magnets (B=5.3 Tesla, LMagnet=8.8m)
Subsystems overview of ALPS II
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Cavity Parameters FSR≈7.5 MHz linewidth ≈ 0.9 kHz ROCin = 20 m ROCout= 20 m beam radius = 1.8 mm Tin = 750 ppm Tout= 750 ppm anticipated PB ≈ 1300 anticipated Finesse ≈ 4100
ALPS IIa
> current setup in the lab at DESY
> to maintain a high power buildup PDH lock needs to be stable and the input beam has to overlap with the cavity eigenmode
> cavity mirrors on two separate optical tables
> 10mW send into the cavity
PDH
DWS
EOMDWS
Piezo actuated mirror
20m PD trans
quadrant photo detector
Jan H. Põld | LSW experiments | 9.March 2016 | Page
Results of the cavity characterization measurements
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> control signal displays the frequency noise of the cavity at low Fourier frequencies
> seismic noise is the dominant noise source
> common movement of optical tables at low frequencies
100 101 102 103 104 10510−4
10−2
100
102
104
106
Fourier frequency [Hz]
Freq
uenc
y N
oise
[Hz/
rtHz]
NPROerror signalcontrol signalseismic noise (geophone)
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-60
-40
-20
0
10-3 10-2 10-1 100
mag
nitu
de (d
B)
frequency (FSR)
exact transfer functionfirst-order lowpass filter
Performance of the cavity: Pole frequency
> resonator characteristics: acting like a low pass with pole frequency at the half width at half maximum for power fluctuations on the input beam
> low pass approximation is good for a high finesse cavity
Jan H. Põld | LSW experiments | 9.March 2016 | Page
> power buildup: 891
> verified by independent ringdown measurement
> 230 ppm unexplained losses
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frequency region of this measurement disappeared. This was presumably caused by thermaleffects and resonant higher order spatial modes. Considering the mirror transmission mea-surement we end up with 230 ppm of unexplained losses and a power buildup of 891. Thetheoretical throughput with 230 ppm of losses due to impedance mismatch is 98.66%. There-fore the higher order spatial mode content of the beam injected to the cavity is less than 4.16%.
-20
0
100 1k 10k
ma
gn
itud
e (
dB
)
Power modulation transfer function from upstream to downstream of the 20m cavity
measurementfit (f0 = 1184 Hz, F = 3166, FSR = 7.5 MHz)
-90
0
100 1k 10k
ph
ase
(d
eg
)
frequency (Hz)
Figure 1: Pole frequency measurement
5 Polarization dependence of cavity parameters
Turning the half waveplate in front of the cavity did not have any effect on the performance.
6 Length noise of cavity (spectra and time series)
The frequency noise measurement (see Fig. 2) is similar to what Reza and Marian measured.It is dominated by seismic noise for lower Fourier frequencies and by electronics noise forhigher frequencies. We will try to improve the signal-to-noise ratio and not be electronicsnoise limited any more.
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Quality of 20m cavity
Jan H. Põld | LSW experiments | 9.March 2016 | Page
Auto alignment of input beam
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101 102 103
−60
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Mag
nitu
de [d
B]
Auto−alignment control loops
1x1y2x2y
101 102 103−180−135−90−45
04590
135180
Phas
e [d
eg]
Frequency [Hz]
PDH
DWS
EOMDWS
Piezo actuated mirror
20m PD trans
quadrant photo detector
> long term alignment of input beam with cavity eigenmode
> speed of the control loop is limited by Piezo resonances
Jan H. Põld | LSW experiments | 9.March 2016 | Page
Performance of automatic alignment
> alignment jitter on the input of a cavity produces power fluctuation in transmission of it
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100 101 102
10−5
10−4
10−3
Frequency (Hz)
RIN
/ rtH
z
Auto−AlignmentNo Auto−AlignmentLaser Power Noise
100 101 102
10−4
10−3
Frequency (Hz)
RIN
/ rtH
z
Auto−Alignment EngagedNo Auto−Alingment EngagedNPRO
aligned not optimized
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Status and next steps for ALPS IIa
> stable lock of the 20m cavity over the course of days -done
> control loops are running robustly -done
> characterization in vacuum -in progress
> reaching high power buildup and high circulating power in production cavity
> coherence measurements and noise mitigation
> implementation of central breadboard with aligned optics -in progress
> stable lock of production and regeneration cavity
> implementation and test of light connections and shutter concept
> integration of detector
Jan H. Põld | LSW experiments | 9.March 2016 | Page
Optical layout of ALPS II
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Figure12.Layoutofthe
ALPS-IIb
andA
LPS-IIcopticaltables.
differentialwavefrontsensing
(DW
S)andPD
Hsensing
schemes
togenerate
errorsignalsforthe
–27
–
Jan H. Põld | LSW experiments | 9.March 2016 | Page
Optical layout of ALPS II
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Figure12.Layoutofthe
ALPS-IIb
andA
LPS-IIcopticaltables.
differentialwavefrontsensing
(DW
S)andPD
Hsensing
schemes
togenerate
errorsignalsforthe
–27
–
> we have shown that our subsystems work independently, but we have not implemented the central part to ALPS IIa
Jan H. Põld | LSW experiments | 9.March 2016 | Page
How to control a cavity “without” light?
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150kWPC RC
single photondetector
SHG
PDH
DWS
EOM
EOM
DWS
PDH
DWS
DWS
Piezo actuated mirror
quadrant photo detector
common optical cavity axis1064nm laser beam532nm laser beam
100m 100m
> different transmission coefficient for green light ==> less power buildup
> lock of both cavities has been tested in a 1m experiment at Hannover
> PDH lock and automatic alignment techniques the similar for PC and RC
Jan H. Põld | LSW experiments | 9.March 2016 | Page 30
• Positions of cavity eigenmodes defined by central optics
• Positioning optics with autocollimator • Must be better than 13.1µrad for ALPSIIa and
8.8µrad for ALPSIIc • Long term measurements look very promising
and meet the requirements
Accurate positioning of central breadboard mirrors
Jan H. Põld | LSW experiments | 9.March 2016 | Page
Seismic noise in HERA hall
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• experiment should rest on the fundament of the HERA hall
• high seismic noise and long term drifts reduce effective free aperture of the beam pipe and eventually degrade the power buildup due to aperture losses
Jan H. Põld | LSW experiments | 9.March 2016 | Page
Limitations
> aperture size
> beam divergence angle
> intensity on mirrors
> wavelength
> actuator bandwidth
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101 102 103 104
−20
0
20
Mag
nitu
de [d
B]
TF PZT z−axis ==> control signal of PDH control loop
101 102 103 104−180−135−90−45
04590
135180
Phas
e [d
eg]
Frequency [Hz]
measurement
Jan H. Põld | LSW experiments | 9.March 2016 | Page
Is it feasible what we are aiming for?
> scaling from 20m to 200m: reducing the aperture and moving the mirrors further apart
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ALPS IIa 20m cavitySeptember 2015
ALPS IIa 20m cavityFebruary 2016
ALPS IIadesign sensitivity
ALPS IIcdesign sensitivity
plot from LIGO T-1400226-v6
Jan H. Põld | LSW experiments | 9.March 2016 | Page
Major challenges (for optics)
> thermal effects when going to higher circulating power (e.g. spatial higher order modes are resonant, change in ROC)
> lock both cavities with high bandwidth
> simultaneous, robust lock of production and regeneration cavity
> alignment of the beam in long baseline magnet string
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150kWPC RC
single photondetector
SHG
PDH
DWS
EOM
EOM
DWS
PDH
DWS
DWS
Piezo actuated mirror
quadrant photo detector
common optical cavity axis1064nm laser beam532nm laser beam
100m 100m
Jan H. Põld | LSW experiments | 9.March 2016 | Page
Current timeline
> Formal approval by DESY in summer 2016?
> First results on hidden photons from a prototype experiment without magnets in spring 2017.
> Construction could start 2017.
> ALPS II would be finished in 2020.
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Jan H. Põld | LSW experiments | 9.March 2016 | Page
Possible improvements beyond ALPS II
> ALPS III/ JURA
> requires dedicated magnet development
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table by Axel Lindner
Jan H. Põld | LSW experiments | 9.March 2016 | Page
Conclusion
> ALPS II is the best approach for a next generation LSW experiment
> most vital subsystems have already been tested
> ALPS IIa is progressing well
> we are eager to see results of the first hidden photon run with ALPS IIa
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Jan H. Põld | LSW experiments | 9.March 2016 | Page
(growing) collaboration
3838
ALPS II is a joint effort of
> DESY,
> Hamburg University,
> AEI Hannover (MPG & Hannover Uni.),
> Mainz University,
> University of Florida(Gainesville)
with strong support from
> neoLASE, PTB Berlin, NIST (Boulder), AIST (Japan).
Jan H. Põld | LSW experiments | 9.March 2016 | Page 40
• 35W cw output power • 2W non-planar-ring-oscillator
(NPRO) and four stage Nd:YVO4 amplifier
• high fundamental mode content • low frequency noise due to NPRO • very reliable
High power laser
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Differential wavefront sensing
• deviation of a beam with respect to a reference beam (e.g. resonator eigenmode)
ε =δxω0
$
%&
'
()
2
+δαΘD
$
%&
'
()
2
Jan H. Põld | LSW experiments | 9.March 2016 | Page
Performance of the cavity: Storage time
> cavity storage time via ring down measurements
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−100 −50 0 50 100 150 200 250 300 350
−0.2
0
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0.6
0.8
1
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1.8
time (µs)
Ampl
itude
(a.u
.)
Transmisson SignalExponential Fit τ = 134 µs
> fitted Finesse 3158
> F=t/(pi*FSR)
Jan H. Põld | LSW experiments | 9.March 2016 | Page 43
Accurate positioning of central breadboard mirrors
4 bewill/talks/15Alps_Cbfab_Aug
Autocollimator
� TRIOPTICS TA300-57 (accuray 0.75 arcsec)
19 bewill/talks/15Alps_Cbfab_Aug
32 day trend pitch (M9 mounted on grinded surface)
18 bewill/talks/15Alps_Cbfab_Aug
32 day trend yaw – with data gap projections
19 bewill/talks/15Alps_Cbfab_Aug
32 day trend pitch (M9 mounted on grinded surface)
18 bewill/talks/15Alps_Cbfab_Aug
32 day trend yaw – with data gap projections
Jan H. Põld | LSW experiments | 9.March 2016 | Page
ALPs: Astrophysical hints
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> Improve sensitivity for g, the ALPS-photon-photon coupling strength,by > 1,000.
The experiment measures a rate ~ g4:
> The experimental sensitivity is to increased by a factor 1012!
slide from Axel Lindner’s presentation
Jan H. Põld | LSW experiments | 9.March 2016 | Page
Problems with old cavity mirrors
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4
center
4
center
• 1000 ppm Losses in long cavity
• < 300 ppm Losses in short cavity
• Features size > 0.25 mm
• Rms surface fluctuations ~ 2.7 nm
> Insufficient power buildup in the PC
‣ 10 cm cavity with smaller eigenmode achieve full power build up
‣ Possible scattering from large features on substrate
> Surface profile measurement