Sidelobe modeling and mitigation for a three mirror anastigmat cosmic microwave background telescope.

Telescopes measuring cosmic microwave background (CMB) polarization on large angular scales require exquisite control of systematic errors to ensure the fidelity of the cosmological results. In particular, far-sidelobe contamination from wide angle scattering is a potentially prominent source of systematic error for large aperture microwave telescopes. Here we describe and demonstrate a ray-tracing-based modeling technique to predict far sidelobes for a three mirror anastigmat telescope designed to observe the CMB from the South Pole. Those sidelobes are produced by light scattered in the receiver optics subsequently interacting with the walls of the surrounding telescope enclosure. After comparing simulated sidelobe maps and angular power spectra for different enclosure wall treatments, we propose a highly scattering surface that would provide more than an order of magnitude reduction in the degree-scale far-sidelobe contrast compared to a typical reflective surface. We conclude by discussing the fabrication of a prototype scattering wall panel and presenting measurements of its angular scattering profile.

Simons Observatory: broadband metamaterial antireflection cuttings for large-aperture alumina optics.

We present the design, fabrication, and measured performance of metamaterial antireflection cuttings (ARCs) for large-format alumina filters operating over more than an octave of bandwidth to be deployed at the Simons Observatory (SO). The ARC consists of subwavelength features diced into the optic's surface using a custom dicing saw with near-micrometer 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 to 170 GHz band and a 50 mm diameter prototype covering the 200 to 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 use of the metamaterial ARC as a scattering filter in this limit.

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 4 K, 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 300 K 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 sidelobes 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 sidelobes 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 submillimeter instruments.

Simons Observatory HoloSim-ML: machine learning applied to the efficient analysis of radio holography measurements of complex optical systems.

Near-field radio holography is a common method for measuring and aligning mirror surfaces for millimeter and sub-millimeter telescopes. In instruments with more than a single mirror, degeneracies arise in the holography measurement, requiring multiple measurements and new fitting methods. We present HoloSim-ML, a Python code for beam simulation and analysis of radio holography data from complex optical systems. This code uses machine learning to efficiently determine the position of hundreds of mirror adjusters on multiple mirrors with few micrometer accuracy. We apply this approach to the example of the Simons Observatory 6 m telescope.

The Simons Observatory: metamaterial microwave absorber and its cryogenic applications.

Controlling stray light at millimeter wavelengths requires special optical design and selection of absorptive materials that should be compatible with cryogenic operating environments. While a wide selection of absorptive materials exists, these typically exhibit high indices of refraction and reflect/scatter a significant fraction of light before absorption. For many lower index materials such as commercial microwave absorbers, their applications in cryogenic environments are challenging. In this paper, we present a new tool to control stray light: metamaterial microwave absorber tiles. These tiles comprise an outer metamaterial layer that approximates a lossy gradient index anti-reflection coating. They are fabricated via injection molding commercially available carbon-loaded polyurethane (25% by mass). The injection molding technology enables mass production at low cost. The design of these tiles is presented, along with thermal tests to 1 K. Room temperature optical measurements verify their control of reflectance to less than 1% up to 65∘ angles of incidence, and control of wide angle scattering below 0.01%. The dielectric properties of the bulk carbon-loaded material used in the tiles is also measured at different temperatures, confirming that the material maintains similar dielectric properties down to 3 K.

CC chemokine receptor 2 promotes recruitment of myeloid cells associated with insulin resistance in nonalcoholic fatty liver disease.

Nonalcoholic fatty liver disease (NAFLD) is a common disease, closely associated with obesity and insulin resistance. We investigated the presence of a subset of myeloid cells associated with metabolic disturbance in the liver of patients with NAFLD and a murine model of obesity-induced liver disease. Gene and protein expression in liver and serum was investigated with RT-PCR or ELISA and correlated to clinical disease. Liver-infiltrating immune cells were isolated from normal or diseased human liver for flow cytometric analysis. In animal experiments, mice were fed a high-fat diet (60% of calories from fat) for 16 wk, or high-fat diet with 30% fructose for 32 wk to induce steatohepatitis and fibrosis. A small molecule inhibitor of CC chemokine receptor 2 (CCR2), CCX872, was administered to some mice. A subset of CD11c+CD206+ immune cells was enriched in human liver tissue, and greater infiltration was observed in NAFLD. The presence of CD11c+CD206+ myeloid cells correlated with systemic insulin resistance. CD11c+CD206+ cells expressed high levels of CCR2, and liver CC chemokine ligand 2 (CCL2) expression was increased in nonalcoholic steatohepatitis and correlated with disease activity. In mice, CCR2 inhibition reduced infiltration of liver CD11b+CD11c+F4/80+ monocytes, which are functional homologs of human CD11c+CD206+ cells, and improved liver injury and glycemic control. A role for CCR2/CCL2 in human NAFLD has long been postulated. These data confirm a role for this chemokine/receptor axis, through mediating adipose and hepatic infiltration of myeloid cells. Inhibition of CCR2 improved hepatic inflammation and fibrosis in murine models of NAFLD. These data confirm the rationale for targeting CCR2 to treat NAFLD. NEW & NOTEWORTHY These data show for the first time that CD11c+CD206+ myeloid cells, previously associated with human adipose tissue inflammation, infiltrate into liver tissue in nonalcoholic fatty liver disease. These cells express CCR2. Inhibition of CCR2 in mice inhibits hepatic inflammation caused by a murine homolog of these myeloid cells and improves experimental liver disease.

Evidence of lensing of the cosmic microwave background by dark matter halos.

We present evidence of the gravitational lensing of the cosmic microwave background by 10(13) solar mass dark matter halos. Lensing convergence maps from the Atacama Cosmology Telescope Polarimeter (ACTPol) are stacked at the positions of around 12 000 optically selected CMASS galaxies from the SDSS-III/BOSS survey. The mean lensing signal is consistent with simulated dark matter halo profiles and is favored over a null signal at 3.2σ significance. This result demonstrates the potential of microwave background lensing to probe the dark matter distribution in galaxy group and galaxy cluster halos.