J. Bueno

Fluctuations in the electron system of a superconductor exposed to a photon flux

In a superconductor, in which electrons are paired, the density of unpaired electrons should become zero when approaching zero temperature. Therefore, radiation detectors based on breaking of pairs promise supreme sensitivity, which we demonstrate using an aluminium superconducting microwave resonator. Here we show that the resonator also enables the study of the response of the electron system of the superconductor to pair-breaking photons, microwave photons and varying temperatures. A large range in radiation power (at 1.54 THz) can be chosen by carefully filtering the radiation from a blackbody source. We identify two regimes. At high radiation power, fluctuations in the electron system caused by the random arrival rate of the photons are resolved, giving a straightforward measure of the optical efficiency (48±8%) and showing an unprecedented detector sensitivity. At low radiation power, fluctuations are dominated by excess quasiparticles, the number of which is measured through their recombination lifetime.

Thermal desorption of circumstellar and cometary ice analogs

Context. Thermal annealing of interstellar ices takes place in sever al stages of star formation. Knowledge of this process comes from a combination of astronomical observations and laboratory simulations under astrophysically relevant conditions. Aims. For the first time we present the results of temperature progr ammed desorption (TPD) experiments with pre-cometary ice analogs composed of up to five molecular components: H 2O, CO, CO2, CH3OH, and NH3. Methods. The experiments were performed with an ultra-high vacuum chamber. A gas line with a novel design allows the controlled preparation of mixtures with up to five molecular components . Volatiles desorbing to the gas phase were monitored using a quadrupole mass spectrometer, while changes in the ice structure and composition were studied by means of infrared spectroscopy. Results. The TPD curves of water ice containing CO, CO2, CH3OH, and NH3 present desorption peaks at temperatures near those observed in pure ice experiments, volcano desorption peaks after water ice crystallization, and co-desorption peaks w ith water. Desorption peaks of CH3OH and NH3 at temperatures similar to the pure ices takes place when their abundance relative to water is above ∼ 3 % in the ice matrix. We found that CO, CO2, and NH3 also present co-desorption peaks with CH3OH, which cannot be reproduced in experiments with binary water-rich ice mixtures. These are extensively used in the study of thermal desorption of interstellar ices. Conclusions. These results reproduce the heating of circumstellar ices i n hot cores and can be also applied to the late thermal evolution of comets. In particular, TPD curves represent a benchmark for the analysis of the measurements that mass spectrometers on board the ESA-Rosetta cometary mission will perform on the coma of comet 67P/Churyumov-Gerasimenko, which will be active before the arrival of Rosetta according to our predictions.

Anomalous response of superconducting titanium nitride resonators to terahertz radiation

We present an experimental study of kinetic inductance detectors (KIDs) fabricated of atomic layer deposited TiN films and characterized at radiation frequencies of 350 GHz. The responsivity to radiation is measured and found to increase with the increase in radiation powers, opposite to what is expected from theory and observed for hybrid niobium titanium nitride/aluminium (NbTiN/Al) and all-aluminium (all-Al) KIDs. The noise is found to be independent of the level of the radiation power. The noise equivalent power improves with higher radiation powers, also opposite to what is observed and well understood for hybrid NbTiN/Al and all-Al KIDs. We suggest that an inhomogeneous state of these disordered superconductors should be used to explain these observations.

Full characterisation of a background limited antenna coupled KID over an octave of bandwidth for THz radiation

We present the design, fabrication, and full characterisation (sensitivity, beam pattern, and frequency response) of a background limited broadband antenna coupled kinetic inductance detector covering the frequency range from 1.4 to 2.8 THz. This device shows photon noise limited performance with a noise equivalent power of 2.5 × 10−19 W/Hz1∕2 at 1.55 THz and can be easily scaled to a kilo-pixel array. The measured optical efficiency, beam pattern, and antenna frequency response match very well the simulations.

Performance verification of a double-slot antenna with an elliptical lens for large format KID arrays

Microwave Kinetic Inductance Detectors (MKIDs) are becoming a very promising candidate for next generation imaging instruments for the far infrared. A MKID consists of a superconducting resonator coupled to a feed-line used for the readout. In the devices presented here radiation coupling is achieved by coupling the MKID directly to planar antenna. The antenna is placed in the focus of an elliptical lens to increase the filling factor and to match efficiently to fore-optics. In this paper we present the design and the optical performance of MKIDs optimized for operation at 350 GHz. We have measured a device consisting of 14 pixels, characterized the coupling efficiency, antenna-lens frequency response and beam pattern and compared these to theoretical simulations. The optical efficiency has been measured by means of a black body radiator mounted in an ADR cryostat, through the variation of the black body temperature a variable illumination of each pixel (from 0.1 fW to 2 pW) is achieved. The frequency response and beam pattern have been directly measured in a He3 cryostat directly via the cryostat window and without the use of intermediate optics.

Eliminating stray radiation inside large area imaging arrays

With increasing array size, it is increasingly important to control stray radiation inside the detector chips themselves. We demonstrate this effect with focal plane arrays of absorber coupled Lumped Element microwave Kinetic Inductance Detectors (LEKIDs) and lens-antenna coupled distributed quarter wavelength Microwave Kinetic Inductance Detectors (MKIDs). In these arrays the response from a point source at the pixel position is at a similar level to the stray response integrated over the entire chip area. For the antenna coupled arrays, we show that this effect can be suppressed by incorporating an on-chip stray light absorber. A similar method should be possible with the LEKID array, especially when they are lens coupled.

Large Angle Optical Access in a Sub-Kelvin Cryostat

The development of lens-antenna-coupled aluminum-based microwave kinetic inductance detectors (MKIDs) and on-chip spectrometers needs a dedicated cryogenic setup to measure the beam patterns of the lens-antenna system over a large angular throughput and broad frequency range. This requires a careful design since the MKID has to be cooled to temperatures below

A kilo-pixel imaging system for future space based far-infrared observatories using microwave kinetic inductance detectors

300\,\hbox {mK}