The New IRAM KID Array (NIKA) is a dual-band camera operating with frequency multiplexed arrays of Lumped Element Kinetic Inductance Detectors (LEKIDs) cooled to 100 mK. NIKA is designed to observe the intensity and polarisation of the sky at 1.25 and 2.14 mm from the IRAM 30 m telescope. We present the improvements on the control of systematic effects and astrophysical results made during the last observation campaigns between 2012 and 2014.
We present the latest improvements of lumped element kinetic inductance detectors (LEKIDs) for the NIKA camera at the 30-m telescope of IRAM at Pico Veleta (Spain) . LEKIDs are direct absorption detectors for millimeter wavelength and represent a particularly efficient concept of planar array continuum detectors for the millimeter and submillimeter wavelength range. To improve the detector radiation coupling over a wider frequency range, a combination of backplane reflector and a supplementary layer of dielectric between silicon substrate and backplane has been successfully explored. To this end we apply deep silicon etching to the substrate in order to decrease its effective dielectric constant in an intermediate layer. In the first generation of LEKIDs array, the response is disturbed by the presence of slot-modes in the frequency multiplexing coplanar feed/readout line, an effect which was reduced when applying wire bonding across the readout line. Superconducting air-bridges can be integrated into the array fabrication process. The suppression of slot-modes also reduces undesired cross-talk between pixels. Our current KID detectors are made of very thin aluminum films, but with a thickness of less than 20 nm we have reached some limitations concerning the layout and material processing. Following the results from Leduc et al. , we developed non-stoichiometric titanium nitride (TiN) at IRAM as an alternative material. We focus on the work done to achieve reproducible and homogenous films with the required transition temperature for mm-wave detection. We present characterization techniques that allow room temperature measurements to be correlated to the transition temperature of TiN<sub>x</sub> and first measurements on a test sample.
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 the concept for the GISMO-2 bolometer camera, which we build for background-limited operation at the
IRAM 30 m telescope on Pico Veleta, Spain. GISMO-2 will operate simultaneously in the 1 mm and 2 mm
atmospherical windows. The 1 mm channel uses a 32 x 40 TES-based Backshort Under Grid (BUG) bolometer array, the
2 mm channel operates with a 16 x 16 BUG array. The camera utilizes almost the entire full field of view provided by
the telescope. The optical design of GISMO-2 was strongly influenced by our experience with the GISMO 2 mm
bolometer camera which is successfully operating at the 30m telescope. GISMO is accessible to the astronomical
community through the regular IRAM call for proposals.
Lumped-element kinetic inductance detectors (LEKIDs) have recently shown considerable promise as direct-absorption
mm-wavelength detectors for astronomical applications. One major research thrust within the Néel Iram Kids Array (NIKA)
collaboration has been to investigate the suitability of these detectors for deployment at the 30-meter IRAM telescope located
on Pico Veleta in Spain.
Compared to microwave kinetic inductance detectors (MKID), using quarter wavelength resonators, the resonant circuit of
a LEKID consists of a discrete inductance and capacitance coupled to a feedline. A high and constant current density
distribution in the inductive part of these resonators makes them very sensitive. Due to only one metal layer on a silicon
substrate, the fabrication is relatively easy.
In order to optimize the LEKIDs for this application, we have recently probed a wide variety of individual resonator and
array parameters through simulation and physical testing. This included determining the optimal feed-line coupling, pixel
geometry, resonator distribution within an array (in order to minimize pixel cross-talk), and resonator frequency spacing.
Based on these results, a 32-pixel Aluminum array was fabricated and tested in a dilution fridge with optical access, yielding
an average optical NEP of ~7.2 x 10-16 W/Hz^1/2. In October 2009 a first prototype of LEKIDs has been tested at the IRAM
30 m telescope and first astronomical results have been achieved.
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.