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   Clouser, Benjamin W; Sarkozy, Laszlo C; Singer, Clare E; KleinStern, Carly C; Desmoulin, Adrien; Gaeta, Dylan; Khaykin, Sergey; Gabbard, Stephen; Shertz, Stephen; Moyer, Elisabeth J (September 2024, Atmospheric Measurement Techniques)

   We describe a new version of the Chicago Water Isotope Spectrometer (ChiWIS), designed for airborne measurements of vapor-phase water isotopologues in the dry upper troposphere and lower stratosphere (UTLS) aboard research aircraft. This version of the instrument is a tunable diode laser (TDL), off-axis integrated cavity output spectrometer (OA-ICOS). The instrument was designed to measure the HDO/H2O ratio in the 2017 Asian Summer Monsoon flight aboard the M-55 Geophysica during the StratoClim campaign, and so far has also flown aboard the WB-57F in the 2021 and 2022 ACCLIP campaigns. The spectrometer scans absorption lines of both H2O and HDO near 2.647 μm wavelength in a single current sweep, and has an effective path length of 7.5 km under optimal conditions. The instrument utilizes a novel non-axially-symmetric optical component which increases the signal-to-noise ratio by a factor of 3. Ultra-polished, 4-inch diameter cavity mirrors suppress scattering losses, maximize mirror reflectivity, and yield optical fringing significantly below typical electrical noise levels. In laboratory conditions, the instrument has demonstrated a 5-second measurement precision of 3.6 ppbv and 82 pptv in H2O and HDO, respectively. 

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2. Serpentine Integrated Grating Spectrometer

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4. Channel dispersed Fourier transform spectrometer

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5. Pair Spectrometer for FACET-II

   https://doi.org/10.18429/JACoW-IPAC2021-THPAB270  

   Naranjo, B.; Andonian, G.; Cavanagh, N.; Di Piazza, A.; Fukasawa, A.; Gerstmayr, E.; Holtzapple, R.; Keitel, C.; Majernik, N.; Meuren, S.; et al (August 2021, IPAC)

   We present the design of a pair spectrometer for use at FACET-II, where there is a need for spectroscopy of photons having energies up to 10 GeV. Incoming gammas are converted to high-energy positron-electron pairs, which are then subsequently analyzed in a dipole magnet. These charged particles are then recorded in arrays of acrylic Cherenkov counters, which are significantly less sensitive to background x-rays than scintillator counters in this case. To reconstruct energies of single high-energy photons, the spectrometer has a sensitivity to single positron-electron pairs. Even in this single-photon limit, there is always some low-energy continuum present, so spectral deconvolution is not trivial, for which we demonstrate a maximum likelihood reconstruction. Finally, end-to-end simulations of experimental scenarios, together with anticipated backgrounds, are presented. 

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