77 research outputs found
Simons Observatory: Broadband Metamaterial Anti-Reflection Cuttings for Large Aperture Alumina Optics
We present the design, fabrication, and measured performance of metamaterial
Anti-Reflection Cuttings (ARCs) for large-format alumina filters operating over
more than an octave of bandwidth to be deployed on the Simons Observatory (SO).
The ARC consists of sub-wavelength features diced into the optic's surface
using a custom dicing saw with near-micron accuracy. The designs achieve
percent-level control over reflections at angles of incidence up to 20.
The ARCs were demonstrated on four 42 cm diameter filters covering the 75-170
GHz band and a 50 mm diameter prototype covering the 200-300 GHz band. The
reflection and transmission of these samples were measured using a broadband
coherent source that covers frequencies from 20 GHz to 1.2 THz. These
measurements demonstrate percent-level control over reflectance across the
targeted pass-bands and a rapid reduction in transmission as the wavelength
approaches the length scale of the metamaterial structure where scattering
dominates the optical response. The latter behavior enables the use of the
metamaterial ARC as a scattering filter in this limit.Comment: 9 pages, 8 figures, submitted to Applied Optic
The Simons Observatory: Characterizing the Large Aperture Telescope Receiver with Radio Holography
We present near-field radio holography measurements of the Simons Observatory
Large Aperture Telescope Receiver optics. These measurements demonstrate that
radio holography of complex millimeter-wave optical systems comprising
cryogenic lenses, filters, and feed horns can provide detailed characterization
of wave propagation before deployment. We used the measured amplitude and
phase, at 4K, of the receiver near-field beam pattern to predict two key
performance parameters: 1) the amount of scattered light that will spill past
the telescope to 300K and 2) the beam pattern expected from the receiver when
fielded on the telescope. These cryogenic measurements informed the removal of
a filter, which led to improved optical efficiency and reduced side-lobes at
the exit of the receiver. Holography measurements of this system suggest that
the spilled power past the telescope mirrors will be less than 1% and the main
beam with its near side-lobes are consistent with the nominal telescope design.
This is the first time such parameters have been confirmed in the lab prior to
deployment of a new receiver. This approach is broadly applicable to millimeter
and sub-millimeter instruments.Comment: in proces
The Atacama Cosmology Telescope: Mitigating the impact of extragalactic foregrounds for the DR6 CMB lensing analysis
We investigate the impact and mitigation of extragalactic foregrounds for the
CMB lensing power spectrum analysis of Atacama Cosmology Telescope (ACT) data
release 6 (DR6) data. Two independent microwave sky simulations are used to
test a range of mitigation strategies. We demonstrate that finding and then
subtracting point sources, finding and then subtracting models of clusters, and
using a profile bias-hardened lensing estimator, together reduce the fractional
biases to well below statistical uncertainties, with the inferred lensing
amplitude, , biased by less than . We also show
that another method where a model for the cosmic infrared background (CIB)
contribution is deprojected and high frequency data from Planck is included has
similar performance. Other frequency-cleaned options do not perform as well,
incurring either a large noise cost, or resulting in biased recovery of the
lensing spectrum. In addition to these simulation-based tests, we also present
null tests performed on the ACT DR6 data which test for sensitivity of our
lensing spectrum estimation to differences in foreground levels between the two
ACT frequencies used, while nulling the CMB lensing signal. These tests pass
whether the nulling is performed at the map or bandpower level. The
CIB-deprojected measurement performed on the DR6 data is consistent with our
baseline measurement, implying contamination from the CIB is unlikely to
significantly bias the DR6 lensing spectrum. This collection of tests gives
confidence that the ACT DR6 lensing measurements and cosmological constraints
presented in companion papers to this work are robust to extragalactic
foregrounds.Comment: Companion paper to Qu et al and Madhavacheril et a
The Simons Observatory Large Aperture Telescope Receiver
The Simons Observatory (SO) Large Aperture Telescope Receiver (LATR) will be
coupled to the Large Aperture Telescope located at an elevation of 5,200 m on
Cerro Toco in Chile. The resulting instrument will produce arcminute-resolution
millimeter-wave maps of half the sky with unprecedented precision. The LATR is
the largest cryogenic millimeter-wave camera built to date with a diameter of
2.4 m and a length of 2.6 m. It cools 1200 kg of material to 4 K and 200 kg to
100 mk, the operating temperature of the bolometric detectors with bands
centered around 27, 39, 93, 145, 225, and 280 GHz. Ultimately, the LATR will
accommodate 13 40 cm diameter optics tubes, each with three detector wafers and
a total of 62,000 detectors. The LATR design must simultaneously maintain the
optical alignment of the system, control stray light, provide cryogenic
isolation, limit thermal gradients, and minimize the time to cool the system
from room temperature to 100 mK. The interplay between these competing factors
poses unique challenges. We discuss the trade studies involved with the design,
the final optimization, the construction, and ultimate performance of the
system
The Simons Observatory: Modeling Optical Systematics in the Large Aperture Telescope
We present geometrical and physical optics simulation results for the Simons
Observatory Large Aperture Telescope. This work was developed as part of the
general design process for the telescope; allowing us to evaluate the impact of
various design choices on performance metrics and potential systematic effects.
The primary goal of the simulations was to evaluate the final design of the
reflectors and the cold optics which are now being built. We describe
non-sequential ray tracing used to inform the design of the cold optics,
including absorbers internal to each optics tube. We discuss ray tracing
simulations of the telescope structure that allow us to determine geometries
that minimize detector loading and mitigate spurious near-field effects that
have not been resolved by the internal baffling. We also describe physical
optics simulations, performed over a range of frequencies and field locations,
that produce estimates of monochromatic far field beam patterns which in turn
are used to gauge general optical performance. Finally, we describe simulations
that shed light on beam sidelobes from panel gap diffraction.Comment: 15 pages, 13 figure
The Atacama Cosmology Telescope: A Measurement of the DR6 CMB Lensing Power Spectrum and its Implications for Structure Growth
We present new measurements of cosmic microwave background (CMB) lensing over
sq. deg. of the sky. These lensing measurements are derived from the
Atacama Cosmology Telescope (ACT) Data Release 6 (DR6) CMB dataset, which
consists of five seasons of ACT CMB temperature and polarization observations.
We determine the amplitude of the CMB lensing power spectrum at
precision ( significance) using a novel pipeline that minimizes
sensitivity to foregrounds and to noise properties. To ensure our results are
robust, we analyze an extensive set of null tests, consistency tests, and
systematic error estimates and employ a blinded analysis framework. The
baseline spectrum is well fit by a lensing amplitude of
relative to the Planck 2018 CMB power spectra
best-fit CDM model and relative to
the best-fit model. From our lensing power
spectrum measurement, we derive constraints on the parameter combination
of
from ACT DR6 CMB lensing alone and
when combining ACT DR6 and Planck NPIPE
CMB lensing power spectra. These results are in excellent agreement with
CDM model constraints from Planck or
CMB power spectrum measurements. Our lensing measurements from redshifts
-- are thus fully consistent with CDM structure growth
predictions based on CMB anisotropies probing primarily . We find no
evidence for a suppression of the amplitude of cosmic structure at low
redshiftsComment: 45+21 pages, 50 figures. Prepared for submission to ApJ. Also see
companion papers Madhavacheril et al and MacCrann et a
The Atacama Cosmology Telescope: High-resolution component-separated maps across one-third of the sky
Observations of the millimeter sky contain valuable information on a number
of signals, including the blackbody cosmic microwave background (CMB), Galactic
emissions, and the Compton- distortion due to the thermal Sunyaev-Zel'dovich
(tSZ) effect. Extracting new insight into cosmological and astrophysical
questions often requires combining multi-wavelength observations to spectrally
isolate one component. In this work, we present a new arcminute-resolution
Compton- map, which traces out the line-of-sight-integrated electron
pressure, as well as maps of the CMB in intensity and E-mode polarization,
across a third of the sky (around 13,000 sq.~deg.). We produce these through a
joint analysis of data from the Atacama Cosmology Telescope (ACT) Data Release
4 and 6 at frequencies of roughly 93, 148, and 225 GHz, together with data from
the \textit{Planck} satellite at frequencies between 30 GHz and 545 GHz. We
present detailed verification of an internal linear combination pipeline
implemented in a needlet frame that allows us to efficiently suppress Galactic
contamination and account for spatial variations in the ACT instrument noise.
These maps provide a significant advance, in noise levels and resolution, over
the existing \textit{Planck} component-separated maps and will enable a host of
science goals including studies of cluster and galaxy astrophysics, inferences
of the cosmic velocity field, primordial non-Gaussianity searches, and
gravitational lensing reconstruction of the CMB.Comment: The Compton-y map and associated products will be made publicly
available upon publication of the paper. The CMB T and E mode maps will be
made available when the DR6 maps are made publi
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