Slated for launch in 2025, SPHEREx will be NASA’s next astrophysics explorer mission. Optimized to meet rigorous requirements to precisely map the Universe’s large scale structure, produce deep maps of the diffuse extra-galactic background, and to survey the Milky Way’s biogenic ice content, the SPHEREx telescope’s widefield optical design utilizes a series of custom near infrared linear variable filters to survey the entire sky spectroscopically. This unique instrument has now completed its construction phase and is fully assembled for flight. To precisely focus and calibrate the optical and spectroscopic properties of SPHEREx, a custom optical-cryogenic facility was developed and commissioned. In this overview, we describe the implementation of the recently completed instrument integration and testing campaign, delivering a well characterized imaging spectrometer to be integrated with the rest of the observatory.
The Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx) is an upcoming all-sky near-infrared spectroscopic survey satellite designed to address all three primary science goals of NASA’s Astrophysics Division. SPHEREx employs a series of Linear Variable Filters (LVFs) to create 102 spectral channels across the wavelength range of 0.75 to 5 µm, with spectral resolutions R between 35 and 120. This paper presents the spectral calibration setup used for SPHEREx and discusses the various challenges encountered during the measurement process. Ultimately, we demonstrate the spectral responses for all 25 million pixels in SPHEREx.
The SPHEREx satellite will survey the entire sky between 0.75 - 5.0 μm in over 100 wavelengths with spectral resolving power R = 35 to 130 to study cosmic inflation, the history of galaxy formation, and biogenic ices in the Milky Way. The instrument uses six HAWAII-2RG detectors and linear variable filters (LVF) that sort incoming photons into different wavelengths along one spatial direction of the detectors. To minimize the scattered light produced when sources outside of SPHEREx field of view land on the LVF mounting frame (also known as “dragon’s breath”), a scale model was tested to refine a double undercut edge design and coating recipe that halves the ghost size and reduces the ghost’ intensity by 10-fold. We present here the edge design, the scale model experiment, and the characterization of the ghost in the flight telescope.
SPHEREx is a NASA Medium Explorer mission planned for launch in early 2025. It will produce an all-sky near infrared spectral survey from 0.75µm to 5µm with 6.2”x 6.2” pixels and spectral resolving power ranging between R=35 and R=130.
Each focal plane assembly (FPA) comprises three 2048x2048 H2RG detector arrays. The H2RG detector is paired with a Linear Variable Filter, placed just above the detector, that defines a spectral response that varies over the detector along one spatial direction. Two FPAs view the sky through a dichroic beamsplitter, where the short-wave FPA uses three 2.5µm cutoff H2RGs and the mid-wave FPA uses three 5.3µm cutoff H2RGs. We developed a novel laboratory setup to carry out spectral response measurements of every pixel by coupling a cryogenic Winston Cone and integrating spheres to a grating spectrometer which allows us to measure the full 2x3.5°x11.3° field of view simultaneously. This presentation will present the design of the test apparatus and results.
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.
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