Ultraviolet (UV, 900−2000 Å) astrophysics plays a vital role in studying exoplanets and evaluating their potential habitability. One approach to understanding exoplanetary habitability is through the study of their absorption spectra, which can reveal not only the chemical composition and physical properties (e.g., mass-loss rate) of their atmosphere but also the UV environment around the host star. Using grating simulation software, we explored a grating-parameter space (blaze angle, grating period) to optimize the design parameters of a UV grating designed for observing key spectral features (e.g., H i, O i, C ii, etc.) in exoplanetary atmospheres. We use interferometric measurements to determine the grating’s groove placement accuracy, groove uniformity, and limiting resolution; and other metrology techniques to characterize the surface roughness. We quantify the expected performance of our UV gratings using these measurements. This work is part of an effort to leverage trends found between measured UV grating performance and the grating’s intrinsic, fabricated characteristics to estimate the expected performance of UV gratings as we fabricate larger gratings.
Errors in grating fabrication contribute to ghosting and reduce efficiency, decreasing the signal-to-noise ratio of observations. It has historically been challenging to quantify fabrication errors across large areas using common tools such as scanning electron microscopes due to time and automation constraints. Interferometry allows for direct, large area measurement of these characteristics as a metric for success. We present interferometric measurements of laminar which have been used to characterize and optimize EBL tool error (“stitch error”) over large areas and detail future measurements of the impact of KOH etching on the groove placement accuracy. Additionally we comment on future work replicating EBL gratings via nanoimprint lithography.
The EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) will constrain star formation over cosmic time by carrying out a blind and complete census of redshifted carbon monoxide (CO) and ionized carbon ([CII]) emission in cross-correlation with galaxy survey data in redshift windows from the present to z=3.5 with a fully cryogenic, balloon-borne telescope. EXCLAIM will carry out extragalactic and Galactic surveys in a conventional balloon flight planned for 2023. EXCLAIM will be the first instrument to deploy µ-Spec silicon integrated spectrometers with a spectral resolving power R=512 covering 420-540 GHz. We summarize the design, science goals, and status of EXCLAIM.
Ultraviolet (UV, 900−2000Å) spectroscopy simultaneously traces the most common elements (e.g., H, He, O, C, N) in many phases, in the form of ionic, atomic, and molecular lines. UV grating spectrometers hence offer unique insights into astrophysical systems and the impacts of their evolution. This work seeks to understand how we might best optimize certain grating designs for targeted astrophysical tracers. Our work is intended to guide proposers in determining the ideal grating parameters given their specific science objectives. We report on the results of the initial phase of the project, a thorough design phase to determine the ideal grating parameters and electron-beam lithography/potassium hydroxide patterning prescriptions for blazed UV gratings. We use grating simulation software to explore a grating-parameter space and determine the key performance expectations for gratings in next-generation UV space instruments. We present our results for a rough grid in grating-parameter space (blaze angle: ∼30°−76°, grating period: 100−5000 nm). Future work will explore specific cases that include the nominal grating prescriptions for current (e.g., Hyperion, PolStar, LUVOIR) and future mission designs.
This conference presentation was prepared for the Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray conference at SPIE Astronomical Telescopes and Instrumentation, 2022.
The experiment for cryogenic large-aperture intensity mapping (EXCLAIM) is a balloon-borne telescope designed to survey star formation in windows from the present to z = 3.5. During this time, the rate of star formation dropped dramatically, while dark matter continued to cluster. EXCLAIM maps the redshifted emission of singly ionized carbon lines and carbon monoxide using intensity mapping, which permits a blind and complete survey of emitting gas through statistics of cumulative brightness fluctuations. EXCLAIM achieves high sensitivity using a cryogenic telescope coupled to six integrated spectrometers employing kinetic inductance detectors covering 420 to 540 GHz with spectral resolving power R = 512 and angular resolution ≈4 arc min. The spectral resolving power and cryogenic telescope allow the survey to access dark windows in the spectrum of emission from the upper atmosphere. EXCLAIM will survey 305 deg2 in the Sloan Digital Sky Survey Stripe 82 field from a conventional balloon flight in 2023. EXCLAIM will also map several galactic fields to study carbon monoxide and neutral carbon emission as tracers of molecular gas. We summarize the design phase of the mission.
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