arXiv subjects

Alex Zehnder

Publications and source records attributed to Alex Zehnder.

4 recordsLinked to original sources

arXiv2006

Imaging of single infrared, optical, and ultraviolet photons using distributed tunnel junction readout on superconducting absorbers

Single-photon imaging spectrometers of high quantum efficiency in the infrared to ultraviolet wavelength range, with good timing resolution and with a vanishing dark count rate are on top of the wish list in earth-bound astronomy, material and medical sciences, or quantum information technologies. We review and present improved operation of a cryogenic detector system potentially offering all these qualities. It is based on a superconducting absorber strip read out with superconducting tunnel junctions. The detector performance is discussed in terms of responsivity, noise properties, energy and position resolution. Dynamic processes involved in the signal creation and detection are investigated for a basic understanding of the physics, and for possible application-specific modifications of device characteristics.

physics.ins-det↗

arXiv2005

Distributed readout detectors using superconducting tunnel junctions

Superconducting tunnel junctions (STJs) are able to measure the energy of single photons in the range from near infrared to X-rays. They provide simultaneous information of the impact time and wavelength of an absorbed photon. The main difficulty of these detectors compared with conventional imaging detectors lies in their limited pixel number. Each STJ has to be connected independently and therefore the wiring becomes technologically more demanding as the number of STJs increases. One approach to solving this problem is to use a single large absorber and to distribute STJs for position sensitive signal readout. This configuration is able to detect single optical photons with an energy resolution close to that of a single STJ pixel. We have produced a Ta absorber strip with Ta/Al/AlOx/Al/Nb/Ta junctions at either end. The energy and position of single photons were measured simultaneously. The energy resolving power approaches the theoretical limit. We will present a simple Monte Carlo simulation which reproduces the measurement exactly.

physics.ins-det↗

arXiv2005

Self-cooling cryogenic microcalorimeters made of SINIS junctions

High quality low leakage SINIS devices made of Al-AlMn-Al layers were fabricated for energy dispersive single photon detection. Information on different heat flow channels was extracted from the measured dynamics of detector signals due to X-ray events. At the optimum operation point, the extracted effective electron temperature decreased from 88 mK down to 43 mK due to self-cooling, roughly doubling the detector sensitivity.

physics.ins-det↗

arXiv2005

New frequency-modulation readout based on relaxation oscillations

Scaling of multi-pixel cryogenic detectors for imaging becomes increasingly difficult with size due to complexity of readout circuitry and cryogenic constraints (thermal load from wiring). We propose and demonstrate a new readout scheme based on a highly stable RF oscillator composed of a superconducting tunnel junction which exhibits relaxation oscillations. The oscillation frequency is almost linear with the analog bias signal over a wide operation range. The frequency signals from different detectors can be combined into one single readout line. The current noise of an optimized circuit is about 5 pA/sqrt(Hz), which is comparable to standard SQUID amplifiers. We show experimental data from `stand-alone' operation as well as response to microcalorimeter X-ray signals.

physics.ins-det↗