The Atacama Large Millimeter/submillimeter Array (ALMA) Band 10 receiver covering 787 to 950 GHz is the highest frequency receiver of the ten bands envisioned for the ALMA Front End system. The Band 10 receivers have been undergoing installation and commissioning since 2012. After the Band 10 receiver tuning scripts (Josephson currents suppression, LO power optimization) and operation procedures had been developed and implemented, astronomical verification procedures (radio pointing, focus, beam squint, and end-to-end spectroscopic verification) were established in single dish mode at the ALMA Operations Support Facility (OSF; 2900 m elevation). Subsequently, the first Band 10 astronomical fringes were achieved at the Array Operations Site in October 2013 (AOS; 5000 m elevation). This is the highest frequency ever achieved by a radio interferometer and opens up a new window into submillimeter astrophysics.
An enhanced version of the ”Polarimeter für bolometer Kameras” (PolKa) has been installed on the APEX telescope (Atacama Pathfinder EXperiment) in October 2009, to work in combination with LABOCA (the Large APEX Bolometer Camera). This polarimeter was included in the design of LABOCA’s optics from the beginning and it is now going through a commissioning and science verification phase. The combination of PolKa, LABOCA and APEX provides superior capabilities in mapping the polarization of the continuum at submillimeter wavelengths. We present here some preliminary results of the last commissioning run.
APEX, the Atacama Pathfinder EXperiment, is being operated successfully, now for five years, on Llano de Chajnantor
at 5107m altitude in the Chilean High Andes. This location is considered one of the worlds outstanding
sites for submillimeter astronomy, which the results described in this contribution are underlining. The primary
reflector with 12 m diameter is cautiously being maintained at about 15 μm by means of holography. This
allows to access all atmospheric submillimeter windows accessible from the ground, up to 200 μm. Telescope and
instrument performance, operational experiences and a selection of scientific results are given in this publication.
An enhanced version of the "Polarimeter f¨ur bolometer Kameras" (PolKa) has been installed on the APEX
telescope (Atacama Pathfinder EXperiment) in October 2009, to work in combination with LABOCA (the
Large APEX Bolometer Camera). This polarimeter was included in the design of LABOCA's optics from the
beginning and it is now going through a commissioning phase. Preliminary tests on sky have confirmed that the
combination of PolKa, LABOCA and APEX provides unprecedented capabilities in mapping the polarization of
the continuum emission at submillimeter wavelengths.
We present the experimental results and a bolometer model of the voltage-biased superconducting bolometer
on the low stress silicon nitride (Si<sub>3</sub>N<sub>4</sub>) membrane, developed in collaboration between the Max-Planck-Institut
fur Radioastronomie (MPIfR), Bonn and the Institute for Photonic Technology (IPHT), Jena, Germany. The
superconducting thermistor, deposited on the low stress silicon nitride membrane, is a bilayer of gold-palladium
and molybdenum and is designed for a transition temperature of 450 mK. Bolometers for the 1.2 mm atmospheric
window were designed, built and tested. The thermal conductance of the bolometer is tuned by structuring the
silicon nitride membrane into spider-like geometries. The incident radiation is absorbed by crossed dipoles
made from gold-palladium alloy with a surface resistance of 10 Ω/square. Using the COSMOS finite element analysis
package, the thermal conductance is obtained for the bolometers of different geometries. FEA simulations showed
that the deposition of a gold ring around the absorbing area could increase the sensitivity of the bolometer.
Therefore, a gold ring is deposited around the center absorbing patch of the silicon nitride membrane. For the
bolometer with a gold ring, the measured NEP is 1.7 X (see manuscript for formula)
Hz and the time constant is in the range
between 1.4 and 2 ms.
A new facility instrument, the Large APEX Bolometer Camera (LABOCA), developed by the Max-Planck-Institut f&diaeru;r Radioastronomie (MPIfR, Bonn, Germany), has been commissioned in May 2007 for operation on the Atacama Pathfinder Experiment telescope (APEX), a 12 m submillimeter radio telescope located at 5100 m altitude on Llano de Chajnantor in northern Chile. For mapping, this 295-bolometer camera for the 870 micron atmospheric window operates in total power mode without wobbling the secondary mirror. One LABOCA beam is 19 arcsec FWHM and the field of view of the complete array covers 100 square arcmin. Combined with the high efficiency of APEX and the excellent atmospheric transmission at the site, LABOCA offers unprecedented capability in large scale mapping of submillimeter continuum emission. Details of design and operation are
We present the experimental results of voltage-biased superconducting bolometers (VSB) on silicon nitride
(Si<sub>3</sub>N<sub>4</sub>) membranes with niobium wiring developed in collaboration between the Institut fur Physikalische
Hochtechnologie (IPHT), Jena, Germany and the Max-Planck-Institut fur Radioastronomie (MPIfR), Bonn,
Germany. The bolometer current is measured with the superconducting quantum interference device (SQUID),
and as expected, the current responsivity is proportional to the inverse of the bias voltage. The experiments
were performed with bilayer gold-palladium molybdenum thermistor at 300 mK <sup>3</sup>He cooled cryostat and the
desired transition temperature of T<sub>c</sub> = 450 mK is achieved. The strong negative electro-thermal feedback of
the VSB maintains the constant bolometer temperature and reduces the response time from 4 ms to 100 μs. We
have tested thermistors of various size and shape on a continuous membrane and achieved a noise equivalent
power (NEP) of 3.5 × 10<sup>-16</sup> W/√Hz. The measured NEP is relatively high due to the comparatively high
background and high thermal conductance of the unstructured silicon nitride (Si<sub>3</sub>N<sub>4</sub>) membrane. We have
fabricated 8-leg spider structured membranes in three different geometries and the relation between the
geometry and the thermal conductance (<i>G</i>) is studied. Using the COSMOS finite element analysis tool,
we have modeled the TES bolometers to determine the thermal conductance for different geometries and
calculated the various parameters. Due to the demands of large number pixel bolometer camera we plan to
implement multiplex readout with integrated SQUIDs in our design.
Ever since the first proposal of the voltage-biased transition-edge bolometer the astrophysics community desired bolometer arrays with as many pixels as possible. With respect to the technical problem due to the need of lots of readout SQUID sensors only with multiplexing it is possible to go beyond a few hundred pixel. A technology which allows the manufacture of detector and readout on one chip would simplify this task substantially. Here we demonstrate the fabrication of a transition edge sensor based on a thermistor out of a molybdenum / gold-palladium bilayer. The alloy of gold-palladium (Au-Pd), which allows the tuning of molybdenum's critical temperature by one order of magnitude, is taken from our foundry process for SQUID manufacturing. Au-Pd can further be used for shunt resistances, absorber patterns and bond pads, and, therefore, it is a good choice for a combined technology. The thermistor is placed on a moderately patterned silicon nitride membrane in the shape of an 8-legged spider. The radiation band of interest is coupled via a conical feed horn to a simple grid of dipole-like antenna patterns. This removes the need for the poorly reproducible high-resistance absorption films for the matching of the free space impedance. The simple detector technology is compatible with the SQUID manufacturing. Hence, some of the SQUID layers can be merged with the corresponding detector layer, i.e. the thermistor wiring and the SQUID washer are made in a single niobium layer. The concept of feed horn coupling eases the design requirements, consequently the SQUID can be placed close to the detector, thereby allowing a simpler wiring to be used and in theory a better performance to be obtained.
APEX, the Atacama Pathfinder Experiment, has been successfully commissioned and is in operation now. This novel submillimeter telescope is located at 5107 m altitude on Llano de Chajnantor in the Chilean High Andes, on what is considered one of the world's outstanding sites for submillimeter astronomy. The primary reflector with 12 m diameter has been carefully adjusted by means of holography. Its surface smoothness of 17-18 μm makes APEX suitable for observations up to 200 μm, through all atmospheric submm windows accessible from the ground.