874 research outputs found
Composite infrared bolometers with Si_3N_4 micromesh absorbers
We report the design and performance of 300-mK composite bolometers that use micromesh absorbers and support structures patterned from thin films of low-stress silicon nitride. The small geometrical filling factor of the micromesh absorber provides 20× reduction in heat capacity and cosmic ray cross section relative to a solid absorber with no loss in IR-absorption efficiency. The support structure is mechanically robust and has a thermal conductance, G < 2 × 10^(−11) W/K, which is four times smaller than previously achieved at 300 mK. The temperature rise of the bolometer is measured with a neutron transmutation doped germanium thermistor attached to the absorbing mesh. The dispersion in electrical and thermal parameters of a sample of 12 bolometers optimized for the Sunyaev–Zel’dovich Infrared Experiment is ±7% in R (T), ±5% in optical efficiency, and ±4% in G
Superconducting On-chip Fourier Transform Spectrometer
The kinetic inductance effect is strongly nonlinear with applied current in NbTiN, TiN and NbN thin films. This can be utilized to realize novel devices. We present results from transmission lines made with these materials, where DC (current) control is used to modulate the phase velocity thereby enabling on-chip spectrometers. Utility of such compact spectrometers is discussed, along with their natural connection with parametric amplifiers
Numerical optimization of integrating cavities for diffraction-limited millimeter-wave bolometer arrays
Far-infrared to millimeter-wave bolometers designed to make astronomical observations are typically encased in integrating cavities at the termination of feedhorns or Winston cones. This photometer combination maximizes absorption of radiation, enables the absorber area to be minimized, and controls the directivity of absorption, thereby reducing susceptibility to stray light. In the next decade, arrays of hundreds of silicon nitride micromesh bolometers with planar architectures will be used in ground-based, suborbital, and orbital platforms for astronomy. The optimization of integrating cavity designs is required for achieving the highest possible sensitivity for these arrays. We report numerical simulations of the electromagnetic fields in integrating cavities with an infinite plane-parallel geometry formed by a solid reflecting backshort and the back surface of a feedhorn array block. Performance of this architecture for the bolometer array camera (Bolocam) for cosmology at a frequency of 214 GHz is investigated. We explore the sensitivity of absorption efficiency to absorber impedance and backshort location and the magnitude of leakage from cavities. The simulations are compared with experimental data from a room-temperature scale model and with the performance of Bolocam at a temperature of 300 mK. The main results of the simulations for Bolocam-type cavities are that (1) monochromatic absorptions as high as 95% are achievable with <1% cross talk between neighboring cavities, (2) the optimum absorber impedances are 400 Ω/sq, but with a broad maximum from ~150 to ~700 Ω/sq, and (3) maximum absorption is achieved with absorber diameters ≥1.5λ. Good general agreement between the simulations and the experiments was found
The AzTEC mm-Wavelength Camera
AzTEC is a mm-wavelength bolometric camera utilizing 144 silicon nitride
micromesh detectors. Herein we describe the AzTEC instrument architecture and
its use as an astronomical instrument. We report on several performance metrics
measured during a three month observing campaign at the James Clerk Maxwell
Telescope, and conclude with our plans for AzTEC as a facility instrument on
the Large Millimeter Telescope.Comment: 13 pages, 15 figures, accepted for publication in Monthly Notice
The BOOMERANG North America Instrument: a balloon-borne bolometric radiometer optimized for measurements of cosmic background radiation anisotropies from 0.3 to 4 degrees
We describe the BOOMERANG North America (BNA) instrument, a balloon-borne
bolometric radiometer designed to map the Cosmic Microwave Background (CMB)
radiation with 0.3 deg resolution over a significant portion of the sky. This
receiver employs new technologies in bolometers, readout electronics,
millimeter-wave optics and filters, cryogenics, scan and attitude
reconstruction. All these subsystems are described in detail in this paper. The
system has been fully calibrated in flight using a variety of techniques which
are described and compared. It has been able to obtain a measurement of the
first peak in the CMB angular power spectrum in a single balloon flight, few
hours long, and was a prototype of the BOOMERANG Long Duration Balloon (BLDB)
experiment.Comment: 40 pages, 22 figures, submitted to Ap
Interstellar dust in the BOOMERanG maps
Interstellar dust (ISD) emission is present in the mm-wave maps obtained by the BOOMERanG experiment at intermediate and high Galactic latitudes. We find that, while being sub-dominant at the lower frequencies (90,150, 240 GHz), thermal emission from ISD is dominant at 410 GHz, and is well correlated with the IRAS map at 100 µm. We find also that the angular power spectrum of ISD fluctuations at 410 GHz is a power law, and its level is negligible with respect to the angular power spectrum of the Cosmic Microwave Background (CMB) at 90 and 150 GHz
Limits on the Peculiar Velocities of Two Distant Clusters Using the Kinematic Sunyaev-Zel'dovich Effect
We report millimeter-wavelength observations of the Sunyaev-Zel'dovich (S-Z)
effect in two distant galaxy clusters. A relativistically correct analysis of
the S-Z data is combined with the results of X-ray observations to determine
the radial peculiar velocities v_r of the clusters. We observed Abell 2163
(z=.201) in three mm-wavelength bands centered at 2.1, 1.4, and 1.1 mm. We
report a significant detection of the thermal component of the S-Z effect seen
as both a decrement in the brightness of the CMB at 2.1 mm, and as an increment
at 1.1 mm. Including uncertainties due to the calibration of the instrument,
distribution and temperature of the IC gas, and astrophysical confusion, a
simultaneous fit to the data in all three bands gives v_r=+490 +1370/-880 km/s
at 68% confidence. We observed Abell 1689 (z=.181) in the 2.1 and 1.4 mm bands.
Including the same detailed accounting of uncertainty, a simultaneous fit to
the data in both bands gives v_r=+170 +815/-630 km/s. The limits on the
peculiar velocities of A2163 and A1689 correspond to deviations from the
uniform Hubble flow of <= 2-3%.Comment: 21 pages, 13 postscript figures, LaTeX(aaspptwo.sty), ApJ(in press
Bolocam Survey for 1.1 mm Dust Continuum Emission in the c2d Legacy Clouds. II. Ophiuchus
We present a large-scale millimeter continuum map of the Ophiuchus molecular
cloud. Nearly 11 square degrees, including all of the area in the cloud with
visual extinction more than 3 magnitudes, was mapped at 1.1 mm with Bolocam on
the Caltech Submillimeter Observatory (CSO). By design, the map also covers the
region mapped in the infrared with the Spitzer Space Telescope. We detect 44
definite sources, and a few likely sources are also seen along a filament in
the eastern streamer. The map indicates that dense cores in Ophiuchus are very
clustered and often found in filaments within the cloud. Most sources are
round, as measured at the half power point, but elongated when measured at
lower contour levels, suggesting spherical sources lying within filaments. The
masses, for an assumed dust temperature of 10 K, range from 0.24 to 3.9 solar
masses, with a mean value of 0.96 solar masses. The total mass in distinct
cores is 42 solar masses, 0.5 to 2% of the total cloud mass, and the total mass
above 4 sigma is about 80 solar masses. The mean densities in the cores are
quite high, with an average of 1.6 x 10^6 per cc, suggesting short free-fall
times. The core mass distribution can be fitted with a power law with slope of
2.1 plus or minus 0.3 for M>0.5 solar masses, similar to that found in other
regions, but slightly shallower than that of some determinations of the local
IMF. In agreement with previous studies, our survey shows that dense cores
account for a very small fraction of the cloud volume and total mass. They are
nearly all confined to regions with visual extinction at least 9 mag, a lower
threshold than found previously.Comment: 47 pages, 16 figures, accepted for Ap
A strained silicon cold electron bolometer using Schottky contacts
We describe optical characterisation of a strained silicon cold electron bolometer (CEB), operating on a 350 mK stage, designed for absorption of millimetre-wave radiation. The silicon cold electron bolometer utilises Schottky contacts between a superconductor and an n++ doped silicon island to detect changes in the temperature of the charge carriers in the silicon, due to variations in absorbed radiation. By using strained silicon as the absorber, we decrease the electron-phonon coupling in the device and increase the responsivity to incoming power. The strained silicon absorber is coupled to a planar aluminium twin-slot antenna designed to couple to 160 GHz and that serves as the superconducting contacts. From the measured optical responsivity and spectral response, we calculate a maximum optical efficiency of 50% for radiation coupled into the device by the planar antenna and an overall noise equivalent power, referred to absorbed optical power, of 1.1×10−16 W Hz−1/2 when the detector is observing a 300 K source through a 4 K throughput limiting aperture. Even though this optical system is not optimized, we measure a system noise equivalent temperature difference of 6 mK Hz−1/2. We measure the noise of the device using a cross-correlation of time stream data, measured simultaneously with two junction field-effect transistor amplifiers, with a base correlated noise level of 300 pV Hz−1/2 and find that the total noise is consistent with a combination of photon noise, current shot noise, and electron-phonon thermal noise
A Search for Cosmic Microwave Background Anisotropies on Arcminute Scales with Bolocam
We have surveyed two science fields totaling one square degree with Bolocam
at 2.1 mm to search for secondary CMB anisotropies caused by the Sunyaev-
Zel'dovich effect (SZE). The fields are in the Lynx and Subaru/XMM SDS1 fields.
Our survey is sensitive to angular scales with an effective angular multipole
of l_eff = 5700 with FWHM_l = 2800 and has an angular resolution of 60
arcseconds FWHM. Our data provide no evidence for anisotropy. We are able to
constrain the level of total astronomical anisotropy, modeled as a flat
bandpower in C_l, with frequentist 68%, 90%, and 95% CL upper limits of 590,
760, and 830 uKCMB^2. We statistically subtract the known contribution from
primary CMB anisotropy, including cosmic variance, to obtain constraints on the
SZE anisotropy contribution. Now including flux calibration uncertainty, our
frequentist 68%, 90% and 95% CL upper limits on a flat bandpower in C_l are
690, 960, and 1000 uKCMB^2. When we instead employ the analytic spectrum
suggested by Komatsu and Seljak (2002), and account for the non-Gaussianity of
the SZE anisotropy signal, we obtain upper limits on the average amplitude of
their spectrum weighted by our transfer function of 790, 1060, and 1080
uKCMB^2. We obtain a 90% CL upper limit on sigma8, which normalizes the power
spectrum of density fluctuations, of 1.57. These are the first constraints on
anisotropy and sigma8 from survey data at these angular scales at frequencies
near 150 GHz.Comment: 68 pages, 17 figures, 2 tables, accepted for publication in Ap
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