53 research outputs found
LEDs: Sources and Intrinsically Bandwidth-Limited Detectors
The increasing demand for light emitting diodes (LEDs) is driven by a number of application categories, including display backlighting, communications, signage, and general illumination. Nowadays, they have also become attractive candidates as new photometric standards. In recent years, LEDs have started to be applied as wavelength-selective photo-detectors as well. Nevertheless, manufacturers' datasheets are limited about LEDs used as sources in terms of degradation with operating time (aging) or shifting of the emission spectrum as a function of the forward current. On the contrary, as far as detection is concerned, information about spectral responsivity of LEDs is missing. We investigated, mainly from a radiometric point of view, more than 50 commercial LEDs of a wide variety of wavelength bands, ranging from ultraviolet (UV) to near infrared (NIR). Originally, the final aim was to find which LEDs could better work together as detector-emitter pairs for the creation of self-calibrating ground-viewing LED radiometers; however, the findings that we are sharing here following, have a general validity that could be exploited in several sensing applications
Aluminum-Titanium Bilayer for Near-Infrared Transition Edge Sensors
Transition-edge sensors (TESs) are single photon detectors attractive for applications in quantum optics and quantum information experiments owing to their photon number resolving capability. Nowadays, high-energy resolution TESs for telecommunication are based on either W or Au/Ti films, demonstrating slow recovery time constants. We report our progress on the development of an Al/Ti TES. Since bulk aluminum has a critical temperature (Tc) of ca. 1.2 K and a sufficiently low specific heat (less than 10(-4) J/cm³K²), it can be employed to produce the sensitive material for optical TESs. Furthermore, exploiting its high Tc, Al-based TESs can be trimmed in a wider temperature range with respect to Ti or W. A first Al/Ti TES with a Tc ≈ 142 mK, investigated from a thermal and optical point of view, has shown a response time constant of about 2 μs and single photon discrimination with 0.34 eV energy resolution at telecom wavelength, demonstrating that Al/Ti films are suitable to produce TESs for visible and NIR photon counting.Transition-edge sensors (TESs) are single photon detectors attractive for applications in quantum optics and quantum information experiments owing to their photon number resolving capability. Nowadays, high-energy resolution TESs for telecommunication are based on either W or Au/Ti films, demonstrating slow recovery time constants. We report our progress on the development of an Al/Ti TES. Since bulk aluminum has a critical temperature (Tc) of ca. 1.2 K and a sufficiently low specific heat (less than 10(-4) J/cm³K²), it can be employed to produce the sensitive material for optical TESs. Furthermore, exploiting its high Tc, Al-based TESs can be trimmed in a wider temperature range with respect to Ti or W. A first Al/Ti TES with a Tc ≈ 142 mK, investigated from a thermal and optical point of view, has shown a response time constant of about 2 μs and single photon discrimination with 0.34 eV energy resolution at telecom wavelength, demonstrating that Al/Ti films are suitable to produce TESs for visible and NIR photon counting
Simulation software for transition-edge sensor performance prediction
Transition-edge sensors (TES) are outstanding calorimeters based on the steep superconductive transition of ametallic film. Among other photon detectors, they are renowned for the fine energy resolution, the photon-number resolving(PNR) capability and an extremely low dark count rate. Due to the broad detection spectrum, from gamma-ray to visible and submillimetre wavelengths, TESs are highly sought-after in a great variety of fields, such as X-ray detection and quantum technologies. Each of these fields demands a step forward in TESs performance with regards to the recovery time and energy resolution. Here we present a program, primarily capable of predicting the performance of TESs. Using established theoretical and empirical methods we developed a software that allows the users to choose active area, thickness, and material composition of a TES and to calculate its performance. Furthermore, the software can simulate TES properties at different working points.The aim of the software is to minimize the production cost and speed up the overall process for the creation of new devices with improved performance
Dual-mode room temperature self-calibrating photodiodes approaching cryogenic radiometer uncertainty
The room temperature dual-mode self-calibrating detector combines low-loss photodiodes
with electrical substitution radiometry for determination of optical power. By using thermal
detection as a built-in reference in the detector, the internal losses of the photodiode can be
determined directly, without the need of an external reference. Computer simulations were
used to develop a thermal design that minimises the electro-optical non-equivalence in
electrical substitution. Based on this thermal design, we produced detector modules that we
mounted in a trap structure for minimised reflection loss. The thermal simulations predicted a
change in response of around 280 parts per million per millimeter when changing the position
of the beam along the centre line of the photodiode, and we were able to reproduce this change
experimentally. We report on dual-mode internal loss estimation measurements with radiation
of 488 nm at power levels of 500 μW, 875 μW and 1250 μW, using two different methods of
electrical substitution. In addition, we present three different calculation algorithms for
determining the optical power in thermal mode, all three showing consistent results. We
present room temperature optical power measurements at an uncertainty level approaching that
of the cryogenic radiometer with 400 ppm (k = 2), where the type A standard uncertainty in
the thermal measurement only contributed with 26 ppm at 1250 μW in a 6 hour long
measurement sequenc
Quantum characterization of superconducting photon counters
We address the quantum characterization of photon counters based on
transition-edge sensors (TESs) and present the first experimental tomography of
the positive operator-valued measure (POVM) of a TES. We provide the reliable
tomographic reconstruction of the POVM elements up to 11 detected photons and
M=100 incoming photons, demonstrating that it is a linear detector.Comment: 3 figures, NJP (to appear
Micro-SQUIDs based on MgB2 nano-bridges for NEMS readout
We show the results obtained from the fabrication and characterisation of MgB2 loops with two nano-bridges as superconducting weak links. These ring structures are made to operate as superconducting quantum interference devices and are investigated as readout system for cryogenics NEMS resonators. The nano-constrictions are fabricated by EBL and ion beam milling. The SQUIDs are characterised at different temperatures and measurements of the noise levels have been performed. The devices show high critical current densities and voltage modulations under applied magnetic field, close to the critical temperatures
Development of highly sensitive nanoscale transition edge sensors for gigahertz astronomy and dark matter search
Terahertz and sub-terahertz band detection has a key role both in fundamental
interactions physics and technological applications, such as medical imaging,
industrial quality control and homeland security. In particular, transition
edge sensors (TESs) and kinetic inductance detectors (KIDs) are the most
employed bolometers and calorimeters in the THz and sub-THz band for
astrophysics and astroparticles research. Here, we present the electronic,
thermal and spectral characterization of an aluminum/copper bilayer sensing
structure that, thanks to its thermal properties and a simple miniaturized
design, could be considered a perfect candidate to realize an extremely
sensitive class of nanoscale TES (nano-TES) for the giga-therahertz band.
Indeed, thanks to the reduced dimensionality of the active region and the
efficient Andreev mirror (AM) heat confinement, our devices are predicted to
reach state-of-the-art TES performance. In particular, as a bolometer the
nano-TES is expected to have a noise equivalent power (NEP) of
W/ and a relaxation time of ns
for the sub-THz band, typical of cosmic microwave background studies. When
operated as single-photon sensor, the devices are expected to show a remarkable
frequency resolution of 100 GHz, pointing towards the necessary energy
sensitivity requested in laboratory axion search experiments. Finally,
different multiplexing schemes are proposed and sized for imaging applications.Comment: 12 page, 7 figure
Detector Array Readout with Traveling Wave Amplifiers
Reducing noise to the quantum limit over a large bandwidth is a fundamental requirement for future applications operating at millikelvin temperatures, such as the neutrino mass measurement, the next-generation X-ray observatory, the CMB measurement, the dark matter and axion detection, and the rapid high-fidelity readout of superconducting qubits. The read out sensitivity of arrays of microcalorimeter detectors, resonant axion-detectors, and qubits, is currently limited by the noise temperature and bandwidth of the cryogenic amplifers. The Detector Array Readout with Traveling Wave Amplifers project has the goal of developing high-performing innovative traveling wave parametric amplifers with a high gain, a high saturation power, and a quantum-limited or nearly quantum-limited noise. The practical development follows two diferent promising approaches, one based on the Josephson junctions and the other one based on the kinetic inductance of a high-resistivity superconductor. In this contribution, we present the aims of the project, the adopted design solutions and preliminary results from simulations and measurements
Bimodal Approach for Noise Figures of Merit Evaluation in Quantum-Limited Josephson Traveling Wave Parametric Amplifiers
The advent of ultra-low noise microwave amplifiers revolutionized several
research fields demanding quantum-limited technologies. Exploiting a
theoretical bimodal description of a linear phase-preserving amplifier, in this
contribution we analyze some of the intrinsic properties of a model
architecture (i.e., an rf-SQUID based Josephson Traveling Wave Parametric
Amplifier) in terms of amplification and noise generation for key case study
input states (Fock and coherents). Furthermore, we present an analysis of the
output signals generated by the parametric amplification mechanism when thermal
noise fluctuations feed the device.Comment: 5 pages, 6 figure
- …