arXiv subjects

Grace E. Chesmore

Publications and source records attributed to Grace E. Chesmore.

22 records · Page 2Linked to original sources

arXiv2020

The Atacama Cosmology Telescope: Constraints on Cosmic Birefringence

We present new constraints on anisotropic birefringence of the cosmic microwave background polarization using two seasons of data from the Atacama Cosmology Telescope covering $456$ square degrees of sky. The birefringence power spectrum, measured using a curved-sky quadratic estimator, is consistent with zero. Our results provide the tightest current constraint on birefringence over a range of angular scales between $5$ arcminutes and $9$ degrees. We improve previous upper limits on the amplitude of a scale-invariant birefringence power spectrum by a factor of between $2$ and $3$. Assuming a nearly-massless axion field during inflation, our result is equivalent to a $2\,σ$ upper limit on the Chern-Simons coupling constant between axions and photons of $g_{αγ}<4.0\times 10^{-2}/H_I$ where $H_I$ is the inflationary Hubble scale.

astro-ph.CO↗

arXiv2018

Reflectometry Measurements of the Loss Tangent in Silicon at Millimeter Wavelengths

We report here on measurements of the reflectivity and loss tangent measured in the W-band (80-125 GHz) and D-band (125-180 GHz) in two samples of float zone silicon with intrinsic stoichiometry - one irradiated by neutrons, which increases the resistivity by introducing crystalline defects, and the other unperturbed. We find a loss tangent $\tan(δ)$ of 2.8e-4 and 1.5e-5 for neutron-irradiated silicon and intrinsic silicon, respectively, both with an index of refraction of 3.41. The results demonstrate the applicability of silicon as a warm optical component in millimeter-wave receivers. For our measurements, we use a coherent reflectometer to measure the Fabry-Perot interference fringes of the reflected signal from dielectric slabs. The depth of the reflection nulls provides a sensitive measurement of dielectric losses. We describe the test setup which can also characterize scattering and transmission, and can provide detailed characterization of millimeter wave materials.

astro-ph.IM↗

arXiv2018

The Simons Observatory: Instrument Overview

The Simons Observatory (SO) will make precise temperature and polarization measurements of the cosmic microwave background (CMB) using a set of telescopes which will cover angular scales between 1 arcminute and tens of degrees, contain over 60,000 detectors, and observe at frequencies between 27 and 270 GHz. SO will consist of a 6 m aperture telescope coupled to over 30,000 transition-edge sensor bolometers along with three 42 cm aperture refractive telescopes, coupled to an additional 30,000+ detectors, all of which will be located in the Atacama Desert at an altitude of 5190 m. The powerful combination of large and small apertures in a CMB observatory will allow us to sample a wide range of angular scales over a common survey area. SO will measure fundamental cosmological parameters of our universe, constrain primordial fluctuations, find high redshift clusters via the Sunyaev-Zel`dovich effect, constrain properties of neutrinos, and trace the density and velocity of the matter in the universe over cosmic time. The complex set of technical and science requirements for this experiment has led to innovative instrumentation solutions which we will discuss. The large aperture telescope will couple to a cryogenic receiver that is 2.4 m in diameter and nearly 3 m long, creating a number of technical challenges. Concurrently, we are designing the array of cryogenic receivers housing the 42 cm aperture telescopes. We will discuss the sensor technology SO will use and we will give an overview of the drivers for and designs of the SO telescopes and receivers, with their cold optical components and detector arrays.

astro-ph.IM↗

arXiv2015

Structure-function relationships of fullerene esters in polymer solar cells: unexpected structural effects on lifetime and efficiency

We report both transport measurements and spectroscopic data of polymer/fullerene blend photovoltaics using a small library of fullerene esters to correlate device properties with a range of functionality and structural diversity of the ester substituent. We observe that minor structural changes can lead to significant differences in device efficiency and lifetime. Surprisingly, we have found that isomeric R-groups in the fullerene ester-based devices we have studied have very different efficiencies. The characteristic lifetimes derived from both transport and spectroscopic measurements are generally comparable, however some more rapid effects in specific fullerene esters are not observed spectroscopically. Our results support using a library approach for optimizing device performance in these systems.

cond-mat.mtrl-sci↗