Optical fibers are widely used in ground-based astrophysics, especially in the visible and near-infrared regimes. The use of fibers in other spectral regimes (such as the ultraviolet) and in the space environment has been limited due to the high absorption of most glasses in the UV and the radiation-induced degradation of glasses, respectively. Recently, we have demonstrated hollow-core optical fibers that transmit wavelengths as short as approximately 140 nm. Because oxygen and water vapor strongly absorb light with wavelengths shorter than 180 nm, we performed our transmission measurements in a chamber filled with high purity nitrogen. The fibers we measured show high transmission and low bend-induced losses in the 140 - 250 nm regime. Most recently, we have developed a vacuum system, capable of transmission measurements across the full FUV range (100 - 200 nm). Here, we present fiber transmission measurements in the 115 - 250 nm range and introduce some instrument concepts that are made possible by these FUV fibers.
Over the past several years, research and development surrounding hollow-core optical fibers has produced intriguing designs that feature low attenuation and precise polarization control. We present findings of polarization effects in symmetric, tapered, negative curvature fibers. The tested fibers feature twenty-two inner tubes that are much smaller than those in previous designs. Our tests involve transmitting light of varying wavelengths and linear polarization states through the fiber and imaging the fiber output with a microscopic camera. The camera that observes the transmitted light is positioned on a setup that can bend the fiber to observe any intensity or mode shape due to the bending, including any polarization dependence. These fibers may provide excellent polarization stability without the need for more complex designs, like those with nesting or asymmetric capillaries.
The SPRITE (The Supernova remnants, Proxies for Re-Ionization Testbed Experiment) 12U CubeSat mission, funded by NASA and led by the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado Boulder, will house the first Far-UV (100-175 nm) long-slit spectrograph with access to the Lyman UV (λ ⪅ 115 nm) and sub-arcminute imaging resolution. SPRITE will map the high energy emission from diffuse gas allowing for the study of star formation feedback in a critical, but rarely studied, Far-UV regime on both stellar and galactic scales. This novel capability is enabled by new UV technologies incorporated into SPRITE’s design. These technologies include more robust, high broadband reflectivity mirror coatings and an ultra-low background photon counting microchannel plate detector. The SPRITE science mission includes weekly calibration observations to characterize the performance of these key UV technologies over time, increasing their technology readiness level (TRL) to 7+ and providing flight heritage essential for future UV flagship space missions such as the Habitable Worlds Observatory (HWO). Currently, SPRITE is in the beginning stages of integration and testing of its flight assembly with a planned delivery date of fall of 2024. This proceeding will overview the current mission status, the schedule for testing and integration prior to launch, and the planned mission operations for SPRITE.
In this paper we discuss the testing setup, characterization, and applications of hollow core fiber optics designed to transmit light in the far-ultraviolet (FUV; λ ⪅ 200 nm). These hollow core fibers were developed at the University of Bath in collaboration with the University of Colorado (CU) Laboratory for Atmospheric and Space Physics (LASP) for potential use in a multiplexed spectrometer for future planetary science instruments. We present an update on the nitrogen-purged test chamber used for throughput and bend loss testing. We find that these fibers exhibit less than 3 dB loss at λ = 170 nm at a bend angle of 90 degrees and a 27 mm radius of curvature. The net transmission of the 20 cm fiber sample in this bend configuration remains greater than 10% for three of the four fiber samples tested, meeting initial requirements for a future prototype fiber-fed instrument. Two of the four fibers tested exceeded 30% transmission. We present these results in detail and provide an update on the development of the Testbed for Fiber-Fed Instrumentation (TUFFI) prototype in development at CU-LASP.
Observations of standard stars and calibration sources are critical to most astronomical observations. Many of the scientific goals and questions recently highlighted in the Decadal Survey on Astronomy and Astrophysics 2020 require more precise calibration of telescopes and instruments than is possible with current methods. We present the Calibration Satellite for Traceable Astrophysical Radiometric Standards (CSTARS) mission concept. CSTARS is a small space telescope and spectroradiometer, whose absolute spectral response is traceable to NIST standards with an uncertainty of < 0.3%. CSTARS will be able to characterize and monitor the absolute spectral energy distribution of dozens of stars, including the white dwarfs commonly used to calibrate the Hubble Space Telescope and the most stable G-type dwarfs found so far. Once characterized, these targets may be used to calibrate a wide range of astronomical telescopes and instruments, on the ground and in space.
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