•100 W ps-laser ablation of mm-wave subwavelength structures on alumina and sapphire.•Average ablation rate larger than 20 mm3/min on alumina and sapphire.•Order of magnitude increase in average ...ablation rate of alumina and sapphire.•Modeling of ultrashort-pulse laser ablation for fabricating pyramid structures.
We use a 1030 nm laser with 7 ps pulse duration and average power up to 100 W to ablate pyramid-shape subwavelength structures (SWS) on alumina and sapphire. The SWS give an effective and cryogenically robust anti-reflection coating in the millimeter-wave band. We demonstrate average ablation rate of up to 34 mm3/min and 20 mm3/min for structure heights of 900 μm and 750 μm on alumina and sapphire, respectively. These rates are a factor of 34 and 9 higher than reported previously on similar structures. We propose a model that relates structure height to cumulative laser fluence. The model depends on the absorption length δ, which is assumed to depend on peak fluence, and on the threshold fluence ϕth. Using a best-fit procedure we find an average δ=630 nm and 650 nm, and ϕth=2.0-0.5+0.5 J/cm2 and 2.3-0.1+0.1 J/cm2 for alumina and sapphire, respectively, for peak fluence values between 30 and 70 J/cm2. With the best fit values, the model and data values for cumulative fluence agree to within 10%. Given inputs for δ and ϕth the model is used to predict average ablation rates as a function of SWS height and average laser power.
Spectrum technologies are shaping the way our world connects, communicates, and functions. Radio nodes connect through a nearly ubiquitous wireless mesh of other nodes, access points, satellites, and ...base stations to support an ever-expanding panorama of applications, spanning communication, autonomous navigation and transportation, radar-based geo-sciences, soil-sciences, renewable energy, space surveillance, environment and healthcare, smart buildings and grids, precision agriculture, consumer and industrial Internet-of-Things (IoT), and other elements of the emerging smart world. This paper offers an overview on the impact of the current and future diverse applications on the radio spectrum. Specific applications to be addressed include astronomy, health, atmospheric, geosciences, and wildfire monitoring. These applications along with many other emerging applications highlight the critical need of implementation of Intelligent Radios and dynamic spectrum access techniques that enable efficient spectrum management.
The Polar Mesospheric Cloud Turbulence (PMC Turbo) instrument consists of a balloon‐borne platform which hosts seven cameras and a Rayleigh lidar. During a 6‐day flight in July 2018, the cameras ...captured images of Polar Mesospheric Clouds (PMCs) with a sensitivity to spatial scales from ~20 m to 100 km at a ~2‐s cadence and a full field of view (FOV) of hundreds of kilometers. We developed software optimized for imaging of PMCs, controlling multiple independent cameras, compressing and storing images, and for choosing telemetry communication channels. We give an overview of the PMC Turbo design focusing on the flight software and telemetry functions. We describe the performance of the system during its first flight in July 2018.
Key Points
PMC Turbo, a balloon‐borne platform hosting seven cameras and a Rayleigh lidar, launched in July 2018
We describe the camera hardware and image capture methods used during the mission
We describe the design and performance of the flight control hardware and software
We quantify the level of polarization of the atmosphere due to Zeeman splitting of oxygen in the Earth’s magnetic field and compare it to the level of polarization expected from the polarization of ...the cosmic microwave background radiation. The analysis focuses on the effect at mid-latitudes and at large angular scales. We find that from stratospheric balloon borne platforms and for observations near 100 GHz the atmospheric linear and circular polarized intensities are about 10
−12 and 100
×
10
−9 K, respectively, making the atmosphere a negligible source of foreground. From the ground the linear and circular polarized intensities are about 10
−9 and 100
×
10
−6 K, making the atmosphere a potential source of foreground for the CMB E (B) mode signal if there is even a 1% (0.01%) conversion of circular to linear polarization in the instrument.
We assess the uncertainty with which a balloon-borne experiment, nominally called Tau Surveyor (τS), can measure the optical depth to reionization σ(τ) with given realistic constraints of instrument ...noise and foreground emissions. Using a τS fiducial design with six frequency bands between 150 and 380 GHz, with white and uniform map noise of 7 μK arcmin, achievable with a single midlatitude flight, and including Planck's 30 and 44 GHz data, we assess the error σ(τ) obtained with three foreground models and as a function of sky fraction f sky between 40% and 54%. We carry out the analysis using both parametric and blind foreground separation techniques. We compare the σ(τ) values to those obtained with low-frequency and high-frequency versions of the experiment called τS-lf and τS-hf, which have only four and up to eight frequency bands with narrower and wider frequency coverage, respectively. We find that with τS, the lowest constraint is σ(τ) = 0.0034, obtained for one of the foreground models with f sky = 54%. σ(τ) is larger, in some cases by more than a factor of 2, for smaller sky fractions, with τS-lf, or as a function of foreground model. The τS-hf configuration does not lead to significantly tighter constraints. The exclusion of the 30 and 44 GHz data, which give information about synchrotron emission, leads to significant τ misestimates. Decreasing noise by an ambitious factor of 10, while keeping f sky = 40%, gives σ(τ) = 0.0031. The combination of σ(τ) = 0.0034, baryon acoustic oscillation data from DESI, and future cosmic microwave background B-mode lensing data from the CMB-S3/CMB-S4 experiments could give σ(∑m v) = 17 meV.
We fabricated a 302 mm diameter low-pass filter made of alumina that has an anti-reflection coating (ARC) made with laser-ablated sub-wavelength structures (SWS). The filter has been integrated into ...and is operating with the MUSTANG2 instrument, which is coupled to the Green Bank Telescope. The average transmittance of the filter in the MUSTANG2 operating band between 75 and 105 GHz is 98%. Reflective loss due to the ARC is 1%. The difference in transmission between the s- and p-polarization states is less than 1%. To within 1% accuracy we observe no variance in these results when transmission is measured in six independent filter spatial locations. The alumina filter replaced a prior MUSTANG2 Teflon filter. Data taken with the filter heat sunk to its nominal 40 K stage show performance consistent with expectations: a reduction of about 50% in filters-induced optical power load on the 300 mK stage, and in in-band optical loading on the detectors. It has taken less than 4 days to laser-ablate the SWS on both sides of the alumina disk. This is the first report of an alumina filter with SWS ARC deployed with an operating instrument, and the first demonstration of a large area fabrication of SWS with laser ablation.
We report new polarimetric and photometric maps of the massive star-forming region OMC-1 using the HAWC+ instrument on the Stratospheric Observatory for Infrared Astronomy. We present continuum ...polarimetric and photometric measurements of this region at 53, 89, 154, and 214 m at angular resolutions of 5″, 8″, 14″, and 19″ for the four bands, respectively. The photometric maps enable the computation of improved spectral energy distributions for the region. We find that at the longer wavelengths, the inferred magnetic field configuration matches the "hourglass" configuration seen in previous studies, indicating magnetically regulated star formation. The field morphology differs at the shorter wavelengths. The magnetic field inferred at these wavelengths traces the bipolar structure of the explosive Becklin-Neugebauer/Kleinman-Low outflow emerging from OMC-1 behind the Orion Nebula. Using statistical methods to estimate the field strength in the region, we find that the explosion dominates the magnetic field near the center of the feature. Farther out, the magnetic field is close to energetic equilibrium with the ejecta and may be providing confinement to the explosion. The correlation between polarization fraction and the local polarization angle dispersion indicates that the depolarization as a function of unpolarized intensity is a result of intrinsic field geometry as opposed to decreases in grain alignment efficiency in denser regions.
We report on polarimetric maps made with HAWC+/SOFIA toward ρ Oph A, the densest portion of the ρ Ophiuchi molecular complex. We employed HAWC+ bands C (89 μm) and D (154 μm). The slope of the ...polarization spectrum was investigated by defining the quantity R(sub DC) = p(sub D)/p(sub C), where p(sub C) and p(sub D) represent polarization degrees in bands C and D, respectively. We find a clear correlation between R(sub DC) and the molecular hydrogen column density across the cloud. A positive slope (R(sub DC) > 1) dominates the lower-density and well- illuminated portions of the cloud, which are heated by the high-mass star Oph S1, whereas a transition to a negative slope (R(sub DC) < 1) is observed toward the denser and less evenly illuminated cloud core. We interpret the trends as due to a combination of (1) warm grains at the cloud outskirts, which are efficiently aligned by the abundant exposure to radiation from Oph S1, as proposed in the radiative torques theory; and (2) cold grains deep in the cloud core, which are poorly aligned owing to shielding from external radiation. To assess this interpretation, we developed a very simple toy model using a spherically symmetric cloud core based on Herschel data and verified that the predicted variation of R(sub DC) is consistent with the observations. This result introduces a new method that can be used to probe the grain alignment efficiency in molecular clouds, based on the analysis of trends in the far-infrared polarization spectrum.
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