arXiv subjects

Howard Hui

Publications and source records attributed to Howard Hui.

30 records · Page 2Linked to original sources

arXiv2025

The SPHEREx Sky Simulator: Science Data Modeling for the First All-Sky Near-Infrared Spectral Survey

We describe the SPHEREx Sky Simulator, a software tool designed to model science data for NASA's SPHEREx mission that will carry out a series of all-sky spectrophotometric surveys at $\sim$6'' spatial resolution in 102 spectral channels spanning 0.75 to 5 $μ$m. The Simulator software implements models for astrophysical emission, instrument characteristics, and survey strategy to generate realistic infrared sky scenes as they will be observed by SPHEREx. The simulated data includes a variety of realistic noise and systematic effects that are estimated using up-to-date astrophysical measurements and information from pre-launch instrument characterization campaigns. Through the pre-flight mission phases the Simulator has been critical in predicting the impact of various effects on SPHEREx science performance, and has played an important role guiding the development of the SPHEREx data analysis pipeline. In this paper, we describe the \skysim\ architecture, pre-flight instrument and sky models, and summarize high-level predictions from the Simulator, including a pre-launch prediction for the 5$σ$ point source sensitivity of SPHEREx, which we estimate to be $m_{\rm AB}$ 18.5--19 from 0.75 to 3.8~$μ$m and $m_{\rm AB}$ 16.6--18 from 3.8 to 5 $μ$m, with the sensitivity limited by the zodiacal light background at all wavelengths. In the future, on-orbit data will be used to improve the Simulator, which will form the basis of a variety of forward-modeling tools that will be used to model myriad instrumental and astrophysical processes to characterize their systematic effects on our final data products and analyses.

astro-ph.IM↗

arXiv2024

Cryogenic Focus Measurement System for a Wide-Field Infrared Space Telescope

We describe a technique for measuring focus errors in a cryogenic, wide-field, near-infrared space telescope. The measurements are made with a collimator looking through a large vacuum window, with a reflective cold filter to reduce background thermal infrared loading on the detectors and optics. The vacuum window and cold filter introduce wavefront error which we characterize using an autocollimating microscope. For the $200\textrm{ mm}$ diameter aperture $f/3$ space telescope, SPHEREx, we achieve a focus position measurement with a $\sim15 \textrm{ }μ\textrm{m systematic}$ and a $\sim 5\textrm{ }μ\textrm{m statistical}$ error.

astro-ph.IM↗

arXiv2024

Calibration Measurements of the BICEP3 and BICEP Array CMB Polarimeters from 2017 to 2024

The BICEP3 and BICEP Array polarimeters are small-aperture refracting telescopes located at the South Pole designed to measure primordial gravitational wave signatures in the Cosmic Microwave Background (CMB) polarization, predicted by inflation. Constraining the inflationary signal requires not only excellent sensitivity, but also careful control of instrumental systematics. Both instruments use antenna-coupled orthogonally polarized detector pairs, and the polarized sky signal is reconstructed by taking the difference in each detector pair. As a result, the differential response between detectors within a pair becomes an important systematic effect we must control. Additionally, mapping the intensity and polarization response in regions away from the main beam can inform how sidelobe levels affect CMB measurements. Extensive calibration measurements are taken in situ every austral summer for control of instrumental systematics and instrument characterisation. In this work, we detail the set of beam calibration measurements that we conduct on the BICEP receivers, from deep measurements of main beam response to polarized beam response and sidelobe mapping. We discuss the impact of these measurements for instrumental systematics studies and design choices for future CMB receivers.

astro-ph.CO↗

arXiv2024

SPHEREx: NASA's Near-Infrared Spectrophotmetric All-Sky Survey

SPHEREx, the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and ices Explorer, is a NASA MIDEX mission planned for launch in 2024. SPHEREx will carry out the first all-sky spectral survey at wavelengths between 0.75 micron and 5 micron with spectral resolving power ~40 between 0.75 and 3.8 micron and ~120 between 3.8 and 5 micron At the end of its two-year mission, SPHEREx will provide 0.75-to-5 micron spectra of each 6.2"x6.2" pixel on the sky - 14 billion spectra in all. This paper updates an earlier description of SPHEREx presenting changes made during the mission's Preliminary Design Phase, including a discussion of instrument integration and test and a summary of the data processing, analysis, and distribution plans.

astro-ph.IM↗

arXiv2023

Noise Reduction Methods for Large-scale Intensity-mapping Measurements with Infrared Detector Arrays

Intensity mapping observations measure galaxy clustering fluctuations from spectral-spatial maps, requiring stable noise properties on large angular scales. We have developed specialized readouts and analysis methods for achieving large-scale noise stability with Teledyne 2048$\times$2048 H2RG infrared detector arrays. We designed and fabricated a room-temperature low-noise ASIC Video8 amplifier to sample each of the 32 detector outputs continuously in sample-up-the-ramp mode with interleaved measurements of a stable reference voltage that remove current offsets and $1/f$ noise from the amplifier. The amplifier addresses rows in an order different from their physical arrangement on the array, modulating temporal $1/f$ noise in the H2RG to high spatial frequencies. Finally, we remove constant signal offsets in each of the 32 channels using reference pixels. These methods will be employed in the upcoming SPHEREx orbital mission that will carry out intensity mapping observations in near-infrared spectral maps in deep fields located near the ecliptic poles. We also developed a noise model for the H2RG and Video8 to optimize the choice of parameters. Our analysis indicates that these methods hold residual $1/f$ noise near the level of SPHEREx photon noise on angular scales smaller than $\sim30$ arcminutes.

astro-ph.IM↗

arXiv2023

High-sensitivity transition-edge-sensed bolometers: improved speed and characterization with AC and DC bias

We report on efforts to improve the speed of low-G far-infrared transition-edged-sensed bolometers. We use a fabrication process that does not require any dry etch steps to reduce heat capacity on the suspended device and measure a reduction in the detector time constant. However, we also measure an increase in the temperature-normalized thermal conductance (G), and a corresponding increase in the noise-equivalent power (NEP). We employ a new near-IR photon-noise technique using a near-IR laser to calibrate the frequency-domain multiplexed AC system and compare the results to a well-understood DC circuit. We measure an NEP white noise level of 0.8 aW/rtHz with a 1/f knee below 0.1 Hz and a time constant of 3.2 ms.

physics.app-ph↗

arXiv2022

SPHERExLabTools (SLT): A Python Data Acquisition System for SPHEREx Characterization and Calibration

Selected as the next NASA Medium Class Explorer mission, SPHEREx, the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer is planned for launch in early 2025. SPHEREx calibration data products include detector spectral response, non-linearity, persistence, and telescope focus error measurements. To produce these calibration products, we have developed a dedicated data acquisition and instrument control system, SPHERExLabTools (SLT). SLT implements driver-level software for control of all testbed instrumentation, graphical interfaces for control of instruments and automated measurements, real-time data visualization, processing, and data archival tools for a variety of output file formats. This work outlines the architecture of the SLT software as a framework for general purpose laboratory data acquisition and instrument control. Initial SPHEREx calibration products acquired while using SLT are also presented.

astro-ph.IM↗

arXiv2022

Snowmass2021 Cosmic Frontier: Cosmic Microwave Background Measurements White Paper

This is a solicited whitepaper for the Snowmass 2021 community planning exercise. The paper focuses on measurements and science with the Cosmic Microwave Background (CMB). The CMB is foundational to our understanding of modern physics and continues to be a powerful tool driving our understanding of cosmology and particle physics. In this paper, we outline the broad and unique impact of CMB science for the High Energy Cosmic Frontier in the upcoming decade. We also describe the progression of ground-based CMB experiments, which shows that the community is prepared to develop the key capabilities and facilities needed to achieve these transformative CMB measurements.

astro-ph.CO↗

arXiv2021

Plastic Laminate Antireflective Coatings for Millimeter-wave Optics in BICEP Array

The BICEP/Keck series of experiments target the Cosmic Microwave Background at degree-scale resolution from the South Pole. Over the next few years, the "Stage-3" BICEP Array (BA) telescope will improve the program's frequency coverage and sensitivity to primordial B-mode polarization by an order of magnitude. The first receiver in the array, BA1, began observing at 30/40 GHz in early 2020. The next two receivers, BA2 and BA3, are currently being assembled and will map the southern sky at frequencies ranging from 95 GHz to 150 GHz. Common to all BA receivers is a refractive, on-axis, cryogenic optical design that focuses microwave radiation onto a focal plane populated with antenna-coupled bolometers. High-performance antireflective coatings up to 760 mm in aperture are needed for each element in the optical chain, and must withstand repeated thermal cycles down to 4 K. Here we present the design and fabrication of the 30/40 GHz anti-reflection coatings for the recently deployed BA1 receiver, then discuss laboratory measurements of their reflectance. We review the lamination method for these single- and dual-layer plastic coatings with indices matched to various polyethylene, nylon and alumina optics. We also describe ongoing efforts to optimize coatings for the next BA cryostats, which may inform technological choices for future Small-Aperture Telescopes of the CMB "Stage 4" experiment.

astro-ph.IM↗

arXiv2018

BICEP Array: a multi-frequency degree-scale CMB polarimeter

BICEP Array is the newest multi-frequency instrument in the BICEP/Keck Array program. It is comprised of four 550 mm aperture refractive telescopes observing the polarization of the cosmic microwave background (CMB) at 30/40, 95, 150 and 220/270 GHz with over 30,000 detectors. We present an overview of the receiver, detailing the optics, thermal, mechanical, and magnetic shielding design. BICEP Array follows BICEP3's modular focal plane concept, and upgrades to 6" wafer to reduce fabrication with higher detector count per module. The first receiver at 30/40 GHz is expected to start observing at the South Pole during the 2019-20 season. By the end of the planned BICEP Array program, we project $σ(r) \sim 0.003$, assuming current modeling of polarized Galactic foreground and depending on the level of delensing that can be achieved with higher resolution maps from the South Pole Telescope.

astro-ph.IM↗

arXiv2011

Properties of a Variable-delay Polarization Modulator

We investigate the polarization modulation properties of a variable-delay polarization modulator (VPM). The VPM modulates polarization via a variable separation between a polarizing grid and a parallel mirror. We find that in the limit where the wavelength is much larger than the diameter of the metal wires that comprise the grid, the phase delay derived from the geometric separation between the mirror and the grid is sufficient to characterize the device. However, outside of this range, additional parameters describing the polarizing grid geometry must be included to fully characterize the modulator response. In this paper, we report test results of a VPM at wavelengths of 350 microns and 3 mm. Electromagnetic simulations of wire grid polarizers were performed and are summarized using a simple circuit model that incorporates the loss and polarization properties of the device.

astro-ph.IM↗

arXiv2008

The Hertz/VPM polarimeter: Design and first light observations

We present first results of Hertz/VPM, the first submillimeter polarimeter employing the dual Variable-delay Polarization Modulator (dual-VPM). This device differs from previously used polarization modulators in that it operates in translation rather than mechanical rotation. We discuss the basic theory behind this device, and its potential advantages over the commonly used half wave plate (HWP). The dual-VPM was tested both at the Submillimeter Telescope Observatory (SMTO) and in the lab. In each case we present a detailed description of the setup. We discovered nonideal behavior in the system. This is at least in part due to properties of the VPM wire grids (diameter, spacing) employed in our experiment. Despite this, we found that the dual-VPM system is robust, operating with high efficiency and low instrumental polarization. This device is well suited for air and space-borne applications.

astro-ph↗