Characterization of a Transition-Edge Sensor for the ALPS II Experiment
CCharacterization of a Transition-Edge Sensor forthe ALPS II Experiment
No¨emie Bastidon , Dieter Horns , Axel Lindner , University of Hamburg, Hamburg, Germany, Deutsches Elektronen-Synchrotron (DESY), Hamburg, Germany
DOI: w ill be assigned The ALPS II experiment, Any Light Particle Search II at DESY in Hamburg, will lookfor light (m < − eV) new fundamental bosons (e.g., axion-like particles, hidden photonsand other WISPs) in the next years by the mean of a light-shining-through-the-wall setup.The ALPS II photosensor is a Transition-Edge Sensor (TES) optimized for λ = 1064 nmphotons. The detector is routinely operated at 80 mK, allowing single infrared photondetections as well as non-dispersive spectroscopy with very low background rates. Thedemonstrated quantum efficiency for such TES is up to 95% at λ =1064 nm as shown in[1]. For 1064 nm photons, the measured background rate is < − sec − and the intrinsicdark count rate in a dark environment was found to be of 1 . · − sec − [2]. Latestcharacterization results are discussed. The ALPS II experiment will be looking for new fundamental bosons. Such a light-shining-through-the-wall experiment requires a high quantum efficiency low background single-photondetector [3]. A Tungsten Transition-Edge Sensor, which is optimized for low-background highquantum efficiency single photon detection, has been developed by NIST (National Institute ofStandards and Technology).
TESs are superconductive microcalorimeters measuring the temperature difference ∆T inducedby the absorption of a photon. They are operated in a strong negative electro-thermal feedbackcorresponding to a constant voltage bias.When a 1064 nm photon is absorbed by the tungsten chip, the sensor temperature raisesby 0.1 mK. Heating up of the detector brings it from its superconductive stage to close to itsnormal resistive stage with an increase of the resistance of ∆R ≈ ≈
70 nA. TESs are inductively coupled to a SQUID (SuperconductingQuantum Interference Device) that converts this current variation in a voltage difference of ∆V ≈ - 50 mV. Patras 2015 a r X i v : . [ phy s i c s . i n s - d e t ] S e p he ALPS II detector module is constituted of two TESs coupled to a SQUID. Both detec-tors are 25 × µ m large and 20 nm thick. A ceramic standard mating sleeve towers aboveeach detector, allowing coupling of a standard single-mode fiber. Transition-Edge Sensors are superconductive detectors. The detector needs to be placed ina bath at T bath = 80 mK ± µ K. In order to do so, the TES is placed in an AdiabaticDemagnetization Refrigerator (ADR).ADR cryostats can reach two low-temperature levels [4]. A temperature baseline of 2.5 Kat the colder stages of the cryostat is reached with the help of a compressor using helium anda pulse-tube cooler. This cool-down’s length in time is only limited by maintenance works andneeded modifications of the setup. Within a cool-down, many phases at 80 mK can be reachedin two hours through adiabatic degmanetization. Such a recharge lasts approximately 24 hours.
Figure 1: Infrared single-photon pulse shape.The average pulse shape for 1064 nm photons shows a Peak Height of PH ≈ -50 mV and aPeak Integral of PI ≈ -100 nVs (Fig. 1). A mask, corresponding to an average pulse, is fittedto the pulses for different scaling factors a and shift values j towards the trigger point [2]. The linearity of the ALPS II W-TESs was tested by analysing the detector response to differentphoton energies. Four different lasers were used to that purpose (1064, 645, 532, 405 nm). InFigure 2, the average PH is shown depending on the energy of the photons absorbed by thedetector. The sensors are linear in our region of interest (1.17 eV) [2]. The non-linearity athigher energies matches expectations (saturation of the detector). The energy resolution of thedetectors for these different wavelengths was measured to be ∆E/E <
8% [2].2
Patras 2015 .3 Stability
Detection stability over time is essential for the ALPS II experiment where long-term measure-ments will be performed. Stability during a cool-down as well as between different cool-downshas been checked successfully. The most essential characteristic of the detector is its stabilityduring a recharge-cycle corresponding to the data-taking period. The TES bias current (i.e.TES working point (Fig. 3)) has been measured to be reasonably stable with a maximumgradient < µ A . This variation in the TES bias current corresponds to a variation in thepeak height of ∆PH < Transition-Edge Sensors seem to ideally meet the ALPS II detector challenges. The characteri-zation of the sensors provided by NIST has demonstrated a good detector energy resolution aswell as a good stability of the pulse shape over long-term measurements. In addition to this,both detectors have shown a good linearity in the ALPS II region of interest (1.17 eV).In the near future, optimization of the detectors quantum efficiency as well as reduction ofthe background will be performed.
The authors are grateful to NIST, PTB and Entropy for their technical support. We would alsolike to thank J. Dreyling-Eschweiler and F. Januschek. Finally, we thank the PIER HelmholtzGraduate School for their financial travel support.
References [1] A. E. Lita, A. J. Miller and S. W. Nam, “Counting near-infrared single-photons with 95% efficiency,” Opticsexpress , 5 (2008).[2] J. Dreyling-Eschweiler et al. , “Characterization, 1064 nm photon signals and background events of a tung-sten TES detector for the ALPS experiment,” J. Mod. Opt. , 14 (2005) [arXiv:1502.07878 [hep-ex]].[3] R. B¨ahre et al. , “Any light particle search II Technical Design Report,” JINST , (2013) [arXiv:1302.5647v2[hep-ex]].[4] G. K. White, P. J. Meeson, “Experimental techniques in low-temperature physics,” Fourth Edition (2002). Patras 2015 R = 30 % R normal as a function oftime after the beginning of a recharge.4as a function oftime after the beginning of a recharge.4