7 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 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
Abstraction and Idealization in Biomedicine: The Nonautonomous Theory of Acute Cell Injury
Neuroprotection seeks to halt cell death after brain ischemia and has been shown to be possible in laboratory studies. However, neuroprotection has not been successfully translated into clinical practice, despite voluminous research and controlled clinical trials. We suggested these failures may be due, at least in part, to the lack of a general theory of cell injury to guide research into specific injuries. The nonlinear dynamical theory of acute cell injury was introduced to ameliorate this situation. Here we present a revised nonautonomous nonlinear theory of acute cell injury and show how to interpret its solutions in terms of acute biomedical injuries. The theory solutions demonstrate the complexity of possible outcomes following an idealized acute injury and indicate that a “one size fits all” therapy is unlikely to be successful. This conclusion is offset by the fact that the theory can (1) determine if a cell has the possibility to survive given a specific acute injury, and (2) calculate the degree of therapy needed to cause survival. To appreciate these conclusions, it is necessary to idealize and abstract complex physical systems to identify the fundamental mechanism governing the injury dynamics. The path of abstraction and idealization in biomedical research opens the possibility for medical treatments that may achieve engineering levels of precision
The Simons Observatory: The Large Aperture Telescope (LAT)
The Simons Observatory is a Cosmic Microwave Background experiment to observe the microwave sky in six frequency bands from 30 to 290 GHz. The Observatory—at ∼5200 m altitude—comprises three Small Aperture Telescopes and one Large Aperture Telescope (LAT) at the Atacama Desert, Chile. This research note describes the design and current status of the LAT along with its future timeline