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Cryogenic Light Detectors
Patrick Huff
Max-Planck-Institut für Physik
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Applications of cryogenic LDs
Detection of the
• …energy of electromagnetic radiation
• …kinetic energy of a particle
• …biomolecules
• …single photons for quantum information
Range: meV < E < MeV
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Physical Principle
CTE
3 eV 3 µK
K
eV610
Absorption → Warming up
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Physical Principle
• 300 K: Cmetal (1 mm x 1 mm x 200 nm)
• 10 mK: Cmetal (1 mm x 1 mm x 200 nm)
K
eV12103
K
eV6101
4103 6103
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Ultra-Low-Temperatures
• T 10 mK
• macroscopic system
• arbitrary time period
3He/4He-Dilution Refrigerator
- Light source in the cryostat
- Light into the cryostat
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Low Temperature Measurement
• Measurement of µK @ 10 mK
→ e.g.: Transition Edge Sensor (TES)
ΔR
ΔT
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• material for TES:
→ TC 10 mK
pure metal
metal composition
→ proximity effect:
TC1 & TC
2 TC1<TC
12< TC2
e.g.: Ir/Au
magnetically doped superconductors
Low Temperature Measurement
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TES as Light Detector
• tungsten W
• 20 µm x 20 µm x 40 nm
• absorption probability
equal to PDE 50 %
in the optical band
• TC 80 mK
• FWHM = 0.15 eV @ 1 eV
• count rate: 30 kHz
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TES as Light Detector
• tungsten W
• 25 µm x 25 µm x 35 nm
• absorption probability
equal to PDE 50 %
in the optical band
• TC 125 mK
• FWHM = 0.28 eV @ 1 eV
• count rate: 20 kHz
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TES as Light Detector
• 250 µm x 250 µm
• Mo/Cu
• 1.5 µm Bi
absorber coating
• FWHM = 2.38 eV
• 400 µm x 400 µm
• FWHM = 2.9 eV
Mn-Kα2
Mn-Kα1
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• excellent energy resolution (sub-eV)
• good photon detection efficiency ( 50 %)
• response time 100 ns
• small absorption area (< 1 mm²)
TES as Light Detector
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TES with large absorption area
Enlargement of the absorption area:
→ Larger TES
sensitivity ~ 1/C
→ Array of TES
non active areas
# of wires and readout ~ # of TES
→ Multiplexing
→ Additional absorber with small heat capacity
non-metal crystal, e.g.: Si, SOS, Ge, …
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TES on Absorber
• diameter = 40 mm
• area increased by 104
• thickness = 0.46 mm
• signal threshold
5 photons (3 eV)
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TES on Absorber
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TES on Absorber
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CRESST Detector Module
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TES on Absorber
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TES on Absorber
Si-Absorber
Gold
continuous change of the index of refraction
due to the nano holes suppresses reflection
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TES on Absorber
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Summary
• Large PDE
• No dark counts
• No afterpulses
• Lower intrinsic radioactive background
• Not sensitive to overexposure
• Slow response time
• Not plug & play
(ultra-low temperature & Thermometer)