A superconducting microcalorimeter for low-flux detection of near-infrared single photons

Dreyling-Eschweiler, Jan

Dissertation / PhD Thesis

DESY-2014-03157

A superconducting microcalorimeter for low-flux detection of near-infrared single photons

Dreyling-Eschweiler, J. (Corresponding Author)DESY*

2014
DESY, Verlag Hamburg

Hamburg : DESY, Verlag 221 pp. (2014) [10.3204/DESY-THESIS-2014-016] = Dissertation, University of Hamburg, 2014

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Please use a persistent id in citations: doi:10.3204/DESY-THESIS-2014-016

Report No.: DESY-THESIS-2014-016

Abstract: This thesis covers the development and the characterization of a single photon detector based on a superconducting microcalorimeter. The detector development is motivated by the Any Light Particle Search II (ALPS II) experiment at DESY in Hamburg, which searches for weakly interacting sub-eV particles (WISPs). Therefore, a detection of low-fluxes of 1064 nm light is required. The work is divided in three analyses: the characterization of a milli-kelvin (mK) cryostat, the characterization of superconducting sensors for single photon detection, and the determination of dark count rates concerning 1064 nm signals.Firstly, an adiabatic demagnetization refrigerator (ADR) is characterized, which allows to reach mK-temperatures. During commissioning, the ADR cryostat is optimized and prepared to stably cool superconducting sensors at 80 mK ± 25 μK. It is found that sensors can be continuously operated for ∼20 h before recharging the system in <2 h. Furthermore, the adiabatic system reaches a chance of success of ∼80 % for a recharge without technical problems.Secondly, superconducting sensors are analyzed. The focus is on microcalorimetric transition-edge sensors (TESs) based on 20 nm Tungsten (W) films fabricated by the U.S. National Institute of Standards and Technology (NIST). NIST TESs have a near unity detection efficiency for 1064 nm light (literature value). The energy resolution for 1064 nm signals is measured to be <8 %. The exponential falling time of a photon pulse is 1.5 μs. Furthermore, by determining TES parameters, it is found that the linear TES theory describes measured photon pulses well. The TES response is read out by a superconducting quantum interference device (SQUID) fabricated by Physikalisch-Technische Bundesanstalt (PTB). The system bandwidth is measured to be 0.9 MHz. Finally, the operation in the ADR cryostat as well as the ALPS II laboratory is optimized. This setup forms the ALPS TES detector.Thirdly, the background is measured to obtain a dark count rate for 1064 nm signals. The ALPS TES detector is calibrated by a 1064 nm single photon source and methods are developed to analyze signals. In long-term measurements, background events are measured by using different optical setups. By operating the TES without an optical link outside mK-environment, intrinsic background components are observed and classified. This results in an intrinsic dark count rate for 1064 nm signals of 1.0 · 10^-4 s^-1 . By operating a fiber-coupled TES, it is found that the dark count rate for 1064 nm signals is dominated by pile-up events of near-infrared thermal photons coming through the fiber from the warm environment. Considering a detection efficiency of ∼18 %, a dark count rate of 8.6 · 10^-3 s^-1 is determined for 1064 nm ALPS photons.Concerning ALPS II, this results in a sensitivity gain compared to the ALPS I detector. Furthermore, this thesis is the starting point of TES detector development in Hamburg, Germany.

Keyword(s): Dissertation

Note: Dissertation, University of Hamburg, 2014

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