Matthias Arndt

Time-Tagged Multiplexing of Serially Biased Superconducting Nanowire Single-Photon Detectors

We present a concept for a time-tagged multiplexed readout of several superconducting nanowire single-photon detector elements for small arrays in ultra-short pulsed laser applications. The detector elements were coupled in an array by a superconducting delay line giving each detector element a temporal signature. The complete detector chain is biased by one bias supply. The patterning concept and the first experimental proof of principle are demonstrated on two-detector element arrays with delay times of 86 and 156 ps each made from a 5-nm NbN film on sapphire. We discuss the propagation delay of a delay line taking the geometric and kinetic inductance into account. We show that mainly the normal conducting propagation velocity defines the characteristic time of the delay line and that the inductance dependent response pulse width currently limits the maximum number of detector elements.

Superconducting single-photon counting system for optical experiments requiring time-resolution in the picosecond range

We have developed a cryogenic measurement system for single-photon counting, which can be used in optical experiments requiring high time resolution in the picosecond range. The system utilizes niobium nitride superconducting nanowire single-photon detectors which are integrated in a time-correlated single-photon counting (TCSPC) setup. In this work, we describe details of the mechanical design, the electrical setup, and the cryogenic optical components. The performance of the complete system in TCSPC mode is tentatively benchmarked using 140 fs long laser pulses at a repetition frequency of 75 MHz. Due to the high temporal stability of these pulses, the measured time resolution of 35 ps (FWHM) is limited by the timing jitter of the measurement system. The result was cross-checked in a Coherent Anti-stokes Raman Scattering (CARS) setup, where scattered pulses from a β-barium borate crystal have been detected with the same time resolution.

Wide-Range Bolometer With RF Readout TES

To improve both scalability and noise-filtering capability of a transition-edge sensor (TES), a new concept of a thin-film detector is suggested, which is based on embedding a microbridge TES into a high-Q planar GHz-range resonator weakly coupled to a 50-Ω-readout transmission line. Such a TES element is designed as a hot-electron microbolometer coupled to a THz-range antenna and as a load of the resonator at the same time. A weak THz signal coupled to the antenna heats the microbridge TES, thus reducing the quality factor of the resonator and leading to a power increment in the readout line. The power-to-power conversion gain, an essential figure of merit, is estimated to be above 10. To demonstrate the basic concept, we fabricated and tested a few submicrometer-sized devices from Nb thin films for operation temperature about 5 K. The dc and RF characterization of the new device is made at a resonator frequency about 5.8 GHz. A low-noise high-electron mobility transistor amplifier is used in our TES experiments without the need for a SQUID readout. The optical sensitivity to blackbody radiation within the frequency band 600-700 GHz ismeasured as (2.7 ± 0.9) × 10-14 W/√Hz at Tc ≈ 5 K at bath temperature ≈1.5 K.

Investigation of the Electrical Field Sensitivity of Sub-μm Y–Ba–Cu–O Detectors

The behavior of submicrometer-sized thin-film YBa2Cu3O7-x (YBCO) detectors under illumination with picosecond terahertz (THz) pulses was investigated. Real-time measurements with a temporal resolution of 15 ps full width at half maximum were performed at ANKA, the synchrotron facility of Karlsruhe Institute of Technology, and the UVSOR-III facility at the Institute for Molecular Science in Okazaki, Japan. The capability of YBCO detectors to reproduce the shape of a several picosecond long THz pulse was demonstrated. Single-shot measurements adhering to a reversal of the direction of the electrical field of the THz radiation were carried out. They provided evidence for the electrical field sensitivity of the YBCO detector. Exploiting the electrical field sensitivity of the YBCO detector, the effect of microbunching was observed at UVSOR-III.

Novel Detection Scheme for Cryogenic Bolometers With High Sensitivity and Scalability

Cryogenic bolometers based on thin silicon nitride membranes show a very high sensitivity, which makes them ideal for ultrasensitive detector applications, particularly in the field of submillimeter-wave imaging. For that, transition-edge sensors (TESs) have been established as a viable approach toward developing multipixel sensor arrays. However, current multiplexer techniques as time- or code-division multiplexing do not scale well to multiplexing levels of several hundred detectors per channel. To achieve such a scalable readout solution, frequency-division multiplexing (FDM) would be an applicable way. For that, the temperature-sensing element of a bolometer has to be resonant or coupled to a resonance circuit, which changes its microwave behavior with the temperature of the absorber.

Optimization of the Microwave Properties of the Kinetic-Inductance Bolometer (KIBO)

Silicon nitride membrane based cryogenic bolometers exhibit high sensitivity and enable ultra-sensitive detector applications. Multi-pixel instruments were already introduced as devices for submillimeter-wave imaging. Nevertheless, the numbers of pixels are limited by the readout process which is typically a time-division multiplexing or code-division multiplexing technique. To overcome this challenge, a replacement of the transition-edge sensor as thermometer by a lumped-element resonance circuit seems to be a promising solution. Therefore, one can benefit from the intrinsic capability of frequency-division multiplexing that allows the readout of large detector arrays simultaneously and in real-time. The number of pixels is then limited by the available readout bandwidth and the quality factors of each individual resonance circuit. We successfully demonstrated, based on our feasibility study, the principal operation of such a device, what we call kinetic-inductance bolometer (KIBO). But the overall performance of the achievable noise-equivalent power (NEP) was limited by implementation and operation temperature of KIBO. Therefore, improved KIBO designs were developed and fabricated with niobium thin-film technology. In this paper, we describe the improvement procedure and estimate the expected NEP value.

An Integrated Planar Array of Ultrafast THz Y–Ba–Cu–O Detectors for Spectroscopic Measurements

Detectors made from the high-Tc superconductor YBa2Cu3O7-x are well suited to detect the high-intensity pulsed-terahertz (THz) radiation emitted by synchrotron light sources and free-electron lasers due to their fast response times. We propose a detection system consisting of an integrated planar array with four superconducting detectors coupled to narrowband double-slot antennas for the frequencies 140 GHz, 350 GHz, 650 GHz, and 1.02 THz, respectively. With the ability for spectroscopic measurements, it has the potential to further improve the understanding of accelerator science and the future application of THz radiation. In this paper, we present a new antenna and array design that has been especially optimized to match the high impedance of sub-μm-sized detector bridges needed for high sensitivities, and measurements performed at the Diamond Light Source.

A Data Acquisition System for Kinetic-Inductance Detectors

Kinetic-inductance detectors (KIDs) combine high sensitivity with an intrinsic frequency-division readout capability. This kind of detector is ideal to build large arrays, which can be read out via frequency-division multiplexing. In order to precisely measure the detuning of the resonators, a highly specialized data acquisition system (DAQ) has to be used. We have developed a DAQ system, which is based on a XILINX Kintex 7 FPGA, with additional analog-to-digital/digital-to-analog converters. The analog signal chain is divided in a baseband with a bandwidth of 400 MHz and an RF band of 4-8.5 GHz, which can be adapted to different resonant frequencies of the detector array. To design a system with good linearity and noise performance, carefully selected analog components have to be used. To achieve a readout with video rate and high-frequency resolution, digital signal flow and signal processing are crucial. Therefore, clock synchronization is an important factor to achieve a dual-channel sampling rate of 1 GSPS. In order to obtain the upmost flexibility in signal processing, the digital signal processing is done completely in software on the PC. We will present the electrical characterization of the Kinetic-Inductance Readout Circuit (KIRC). Measurement results of a 20-pixel KID array will be shown and discussed in more detail.

Superconducting nanowire single-photon detectors for picosecond time resolved spectroscopic applications

Raman scattering spectroscopy allows the direct and fast study of molecules by analysis of their vibrational normal modes. However, for certain materials the scattered signal is superimposed by fluorescence, which - if present - overwhelms the intrinsically weak Raman signal by orders of magnitude. An approved method to resolve the instantaneous Raman signal of interest from the delayed fluorescence background is time-correlated single-photon counting (TCSPC). For that, a single-photon detector with fast dynamics is required. The, so-called, superconducting nanowire single-photon detector (SNSPD) is a promising candidate for TCSPC. We have developed an optical instrument using such a SNSPD for the TCSPC method. The detector is made from a 5 nm thick NbN film, patterned by electron-beam lithography in a meander line with a width of 100 nm and a filling-factor of 50 %, covering an active area of 4 × 4 μm2. As a proof of concept we have shown that it is possible to resolve low power optical signals (λ between 520 and 630 nm) with a timing jitter of about 35 ps. Based on our experimental results we will discuss perspectives and limits of SNSPD application for spectroscopy.