calibration of single-photon detectors from spontaneous parametric down-conversion
DESCRIPTION
Calibration of single-photon detectors from spontaneous parametric down-conversion. Justin Ripley Columbia University, New York, NY Fermi National Accelerator Laboratory, Batavia, IL Mentor: Carlos Escobar. August 9, 2012. Overview. What is Spontaneous Parametric Down-Conversion (SPDC)? - PowerPoint PPT PresentationTRANSCRIPT
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Calibration of single-photon detectors from spontaneous parametric down-conversion
Justin RipleyColumbia University, New York, NY
Fermi National Accelerator Laboratory, Batavia, ILMentor: Carlos Escobar
August 9, 2012
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Overview• What is Spontaneous Parametric Down-
Conversion (SPDC)?• Calibration using SPDC• What are Silicon Photomultipliers (SiPMs)?• Experimental set up• Preliminary Results• Current Work• Future Work
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SPDC: Basics• One photon (pump) enters a
nonlinear crystal; two photons (signal and idler) emerge
• Energy and momentum conserved
• ωp = ωs + ωi
• kp = ks + ki
kp ki
ks
θsignal
θidler
• “Spontaneous”: no final states in initial configuration ( ~ 1 in 109 photons down-converted)
• “Parametric”: crystal does not add/subtract energy/momentum from process (elastic scattering)
• “Down-Conversion”: frequency of pump photon lowered
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SPDC: Nonlinearity and Quantum Components
Nonlinear Component• Optical susceptibility tensor:
P(E) = χ(1)ijEj + χ(2)
ij’k’Ej’Ek’ + …
• Second order term: χ(2)ijkEjEk
Three wave mixing• Second order term: χ(2)
ijk EiEk
• Take two waves: (E(1)eiω1t + c.c. + E(2) eiω2t + c.c.)
• Run through crystal, among final wave states get:
• ~(E(1))(E(2))*ei(ω1 - ω2)t • ~(E(2))(E(1))*ei(ω2 – ω1)t
Quantum Component• Send in intense pump beam:
E(p)eiωpt + c.c.• Spontaneous fluctuations of
the vacuum state amplified in nonlinear crystal
(Ivano Ruo-Berchera, Advanced Science LettersVol. 2, 407–429, 2009)
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SPDC: Phase Matching• Select for specific exit angles
for signal beams at specified wavelengths
• kj = (2π/c)νjnjej
• νpnpep = νsnses + νiniei
• nj depends on orientation of optical axis (rotation of linear term χ(1))
• Crystal used is Beta-Barium Borate (BBO); is uniaxial (one optical axis)
kp
ki
ks
Θoptical axisΘidler
Θsignal
BBO Crystal*B. Boeuf, D. Branning, I. Chaperot, E. Dauler, S. Guérin, G. Jaeger, A. Muller, and A. Migdall, “Calculating characteristics of noncollinear phase matching in uniaxial and biaxial crystals,” Optical Engineering, vol. 39, no. 4, April 2000.
neee
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Calibration using SPDC
BBO Crystal
Pump Beam
Conjugate DetectorEfficiency: ηc
Z
Y X
Down-Converted Cone of Light
Idler
3˚
Trigger DetectorEfficiency: ηt
Signal
•Assume N down converted (correlated) photon pairs produced and reach Conjugate and Trigger detectors
Klyshko Method•Photons detected by trigger: Nt = Nηt
•Photons detected by conjugate given a detection by trigger : Nc = Nηtηc
•Efficiency of conjugate detector: ηc = Nc/Nt
•Absolute calibration•Modify for background counts
3˚
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Including sources of background in Calibration formula
• ηc = calibrated detector efficiency
• Nc = measured number of coincidence counts during calibration run
• Nt = measured number of single counts for trigger detector during calibration run
• Bc= Estimated background accidental coincidence counts
• Bt= Estimated background single trigger counts
• Background run– Measure background counting rate (Bt’) for trigger detector with no laser on
• Accidental coincidences run– Measure coincidence counting rate (Bc’) for detector with laser on with a time
delay• Calibration run
– Measure single counts on trigger, coincidence counts for time period T– Bc= Bc’T
– Bt= Bt’T
tt
ccc BN
BN
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What are SiPMs?
Pros• High gain• Single photon resolution• Good time resolution• Low Bias Voltage• Low power
consumption
Cons• High dark pulse rate• Cross talk• Lots of afterpulsing
• Matrix of silicon p-n junction diodes
• Operate in Geiger mode
(Pictures courtesy of SensL: http://www.sensl.com/downloads/ds/TN%20-%20Intro%20to%20SPM%20Tech.pdf )
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General Experimental Layout
(1) Ga-As laser (405nm)
(2) Iris
(5) BBO
(9) SiPM 1
(10) SiPM 2
(6)Beam Dump
(7) 810nm Filter
(8) 810nm Filter
TOP VIEW (not to scale)
1m
3˚
•Readout from detectors went to a FPGA SiPM general readout board (Rubinov and Fitzpatrick)
•Low bandwidth processing
(3) Iris
(4) Iris3˚
•BBO crystal optical axis aligned for 3 degree phase matching
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Experimental Set Up
(as of 8/1/2012)
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Preliminary Results (7/27/12)
Detection counts per second with alignment SiPMs (~7sec run)
Channel 0 Channel 1 Coincidences
Laser Off 179 500 (± 423) 173 344 (± 416) 158 859 (± 399)
Laser on, with BBO 1 613 297 (± 1 270) 2 995 289 (± 1 731) 286 846 (± 536)
Laser off, without BBO
1 579 296 (± 1 257) 4 180 864 (± 2 045) 609 153 (± 780)
•Detectors used for alignment•Single pixel SiPMs (100μm)•Calibrated detectors will have ~103 or more pixels
•Data processed in ~18.8 ns long bins•Channel 0: Trigger detector•Channel 1: Conjugate detector
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Preliminary Results (7/27/12)
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Preliminary Results (8/2/12)
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Current Work: Alignment • Align detector mounts
– “Scanning” alignment detectors and search for global maxima in count rates around calculated down-converted beam location
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Current Work: Noise• Electronic
– Hard to distinguish electronic signals from photons in a short time frame (ΔtΔν ~ 1)
• Low bandwidth board to cut high frequency noise• Measure background rates (should include electronic noise)• House FPGA in Faraday cage
• Background stray photons– Laser fluorescence
• Weaker laser• Mirrors with higher reflectivity in near ultraviolet• Dark box with 810nm filters covering beam entrances
• Dark Pulses, Afterpulsing– Intrinsic to SiPMs– Measure during accidentals and background calibration runs– Possibly cool down detectors
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Future Work/Goals
• Proof of principle with alignment of detectors along one axis
• Align detector mounts along two axis (x, y)• Initially calibrate SiPMs at 810nm• Calibrate other photodetectors
– Other wavelengths possible via rotation of crystal optical axis or use of shorter wavelength pump laser
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Newer Developments (8/6/12 onwards)
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Newer Developments (8/7/12)
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Newer Developments (8/8/12)Detection counts per second with alignment SiPMs (~7sec run)
Channel 0 Channel 1 Coincidences
Laser Off 7700 (± 87.7) 5361 (± 73.2) 1 (± 1.0)
Laser on, with BBO 7657 (± 87.5) 6567 (± 81.0) 2 (± 1.4)
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Newer Developments (8/9/12)
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Newer Developments (8/9/12)
Detection counts per second with alignment SiPMs (~7sec run)Channel 0 Channel 1 Coincidences
Laser Off 4876 (± 70.0) 1797 (± 42.3) 0.1 (± 0.3)
Laser on, with BBO 5063 (± 71.1) 4787 (± 69.1) 1.1 (± 1.0)
Laser off, without BBO
4833 (± 69.5) 4754 (± 68.9) 1.6 (± 1.3)
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BBO in the Dark
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Acknowledgements
• Carlos Escobar• Paul Rubinov• Adam Para• Donna Kubik• Paul Kwiat