The Neel Iram Kids Array (NIKA) is a prototype instrument devoted to millimetric astronomy that has been
designed to be mounted at the focal plane of the IRAM 30m telescope at Pico Veleta (Spain). After the runs
of 2009 and 2010, we carried a third technical run in October 2011. In its latest configuration, the instrument
consists of a dual-band camera, with bands centered at 150 GHz and 220 GHz, each of them equipped with
116 pixels based on Lumped Element Kinetic Inductance Detectors. During the third run we tested many
improvements that will play a crucial role in the development of the final, kilopixel sized camera. In particular,
a new geometry based on a Hilbert curve has been adopted for the absorbing area of the LEKIDs, that makes
the detectors dual-polarization sensitive. Furthermore, a different acquisition strategy has been adopted, which
has allowed us to increase the photometric accuracy of the measurements, a fundamental step in order to get
scientifically significant data. In this paper we describe the main characteristics of the 2011 NIKA instrument
and outline some of its key features, discusse the results we obtained and give a brief outlook on the future NIKA
camera which will be installed permanently on site.
We present latest developments of the millimetric Stationary Waves Integrated Fourier Transform Spectrometer
(SWIFTS) that uses the Kinetic Inductance Detectors (KID) technology. SWIFTs are on-chip autocorrelator
spectrometers where the incoming signal forms an interferogram by reflection in a short-circuited coplanar wave-guide.
By collecting electromagnetic (EM) energy along the guide, one can retrieve this interference pattern. A subsequent offline
Fourier transform gives spectral information with a moderate resolution (~500-1000). SWIFTS concept has already
been proven to work in the optical and microwave (<20 GHz) bands. It will be useful in any application where integrated
and broadband spectral analysis is needed, as an example it will be a practical alternative to Martin-Pupplet
interferometer. In practice, fabrication of such a device is very challenging mostly because the set of detectors has to
collect energy without destroying the interference pattern. As a consequence, design of the coupling parts is a crucial
problem that has to be tackled with the help of EM simulation tools. We present here the SWIFTS principle of operation,
details of fabrication, and the latest simulations results.
We present the design and the present development status of a 204 pixels mm-wave bolometric camera compatible with
the 30 meter IRAM telescope at Pico Veleta. Sequential and non-sequential ray-tracing and physical optics simulations
have been performed with ZEMAX, taking into account the IRAM mirrors and the telecentric camera. The focal plane is
made by an array of antenna-coupled NbSi microbolometers, described in brief. We present the cryostat design, and then
more in details the optics and the baffling system. We conclude with a brief discussion on the future perspectives toward
the multi-thousands pixels bolometric mm-wave camera at IRAM.
Bolometers cooled to very low temperature are currently the most sensitive detectors for low spectral resolution
detection of millimetre and sub-millimetre wavelengths. The best performances of the state-of-the-art bolometers allow
to reach sensitivities below the photon noise of the Cosmic Microwave Background for example. Since 2003, a french
R&D effort called DCMB ("Developpement Concerte de Matrices de Bolometres") has been organised between different
laboratories to develop large bolometers arrays for astrophysics observations. Funded by CNES and CNRS, it is intended
to get a coherent set of competences and equipments to develop very cold bolometers arrays by microfabrication. Two
parallel developments have been made in this collaboration based on the NbSi alloy either semi-conductive or
superconducting depending on the proportion of Nb. Multiplexing schemes have been developed and demonstrated for
these two options. I will present the latest developments made in the DCMB collaboration and future prospects.
Current noise measurements allow to enlighten the transport mechanisms in mesoscopic samples in a complementary way to conductance measurements. The noise gives directly access to the charge of the current carriers and is modified by interactions. This is particularly instructive in the context of hybrid superconductor-normal metal structures where charge pairs generated by Andreev reflection compete with quasiparticles in the current transport. We present investigations of current noise in various hybrid geometries at temperatures down to 50<i>mK</i> using a SQUID as fluctuations detector.
The first two types of structures involve one superconductor in contact with a diffusive normal metal reservoir. To obtain a nearly perfect contact between a superconductor and the normal metal (high transmittive contact), we used niobium as a superconductor and copper as normal metal. Then, the current transport is mediated by charge pairs induced from the superconductor (proximity effect) and the noise is doubled <i>S</i>=2/3x2<i>eI</i>, compared to the case where the two electrodes are normal <i>S</i>=1/3x2<i>eI</i> (where <i>I</i> is the mean bias current and <i>e</i> the electron charge). The 1/3 reduction from the full Poisson noise (<i>S</i>=2<i>eI</i>), observed e.g. in a tunnel junction between two normal reservoirs, is due to the diffusive character of the normal metal. The noise doubling is observed as long as the voltage drop at the junction is smaller than the superconducting gap. Above the gap the shot noise has the same behavior as in the normal case.
In the second type of structures under study, where a superconductor (here TiN) is in contact with a strongly disordered metal (heavily doped silicon), the contact is degraded because of the Schottky barrier that forms at the interface (low transmittive junctions). The noise in such junctions is also doubled, but is twice the full Poisson noise <i>S</i>=<b>2</b>x2<i>eI</i> since the noise is mainly generated at the interface barrier. This confirms that the enhancement of the conductance observed at low bias voltage is due to coherent backscattering of quasiparticles towards the interface by the strong disorder in the silicon (reflectionless tunneling). When this excess of subgap conductance vanishes at finite voltage, the noise slope crosses over to the Poisson value <b>2e</b> indicating a large quasiparticle contribution to the current.
The third type of structures investigated is a long diffusive S/N/S junction made of aluminum and copper. The noise is enhanced compared to the N/N/N-case due to the confinement of the electron gas between the two superconducting reservoirs and the current transport involve Incoherent Multiple Andreev Reflections. Inelastic processes are important in our samples because the lengths of the junctions (4, 10, and 60 μm) are of the same order of magnitude as the inelastic scattering length. We analyze the results quantitatively with recent semi-classical theory taking into account electron-electron interaction and heat transfer through the SN interfaces in the context of S/N/S junctions. For the longer junctions, we also considered electron-phonon-interaction as a possible cooling mechanism. Finally we show that the energy dependence of the re-entrance of the resistance, observed at low voltage, is essentially due to the increasing effective temperature of the quasiparticles in the normal metal.
In this paper we review various improvements that we made in the development of multilayer mirror optics for home-lab x-ray analytical equipment in recent years. For the detection of light elements using x-ray fluorescence spectrometry, we developed a number of new multilayers with improved detection limits. In detail, we found that La/B4C multilayers improve the detection limit of boron by 29 % compared to the previous Mo/B<sub>4</sub>C multilayers. For the detection of carbon, TiO<sub>2</sub>/C multilayers improve the detection limit also by 29 % compared to the V/C multilayers previously used. For the detection of aluminum, WSi<sub>2</sub>/Si or Ta/Si multilayers can lead to detection limit improvements over the current W/Si multilayers of up to 60 % for samples on silicon wafers. For the use as beam-conditioning elements in x-ray diffractometry, curved optics coated with laterally d-spacing graded multilayers give rise to major improvements concerning usable x-ray intensity and beam quality. Recent developments lead to a high quality of these multilayer optics concerning beam intensity, divergence, beam uniformity and spectral purity. For example, x-ray reflectometry instruments equipped with such multilayer optics have dynamic ranges previously only available at synchrotron sources. Two-dimensional focusing multilayer optics are shown to become essential optical elements in protein crystallography and structural proteomics.
The silicon microstrips tracker for CMS at LHC demands fast, radiation-hard electronics. An original solution was proposed for the processing of signals from silicon detectors. This technique allows precise reconstruction of the arrival time of the particles, even with a 'slow' shaping time and a limited power budget. This idea was already implemented in the APV6 circuit, designed in a bulk CMOS technology from Harris.In this paper, we present the version (APVD) designed in the CMOS SOI radiation hard technology DMILL by a French-British collaboration. The APVD is a 128-channel mixed analogue-digital: each channel includes a low-noise charge preamplifier, a CR-RC shaper with a peaking time of 50 ns, an analogue pipeline where the signal is sampled at 40 MHz, an analogue pulse shape processor and a current output multiplexer. The circuit integrates an 12C interface for easy control of the operating parameters. All the control current and voltages as well as a calibration pulse are generated internally by dedicated blocks. The design and first experimental results from the first version of the 128-channel APVD, will be presented in this paper. They show the circuit is fully functional and can be used for the CMS experiment.