The extragalactic background light (EBL) is the integrated diffuse emissions from unresolved stars, galaxies, and intergalactic matter along the line of sight. The EBL is regarded as consisting of stellar emissions and thus an important observational quantity for studying global star formation history throughout cosmic time. Intensity and anisotropy in the near-infrared EBL as measured by the Cosmic Infrared Background ExpeRiment (CIBER), NASA’s sounding rocket experiment, and previous infrared satellites exceed the predicted signal from galaxy clustering alone. The objective of CIBER-2 is to unveil the EBL excess by observing it at extended wavelengths into the visible spectrum with an accuracy better than CIBER. The onboard instrument of CIBER2 comprises a 28.5-cm telescope cooled to 90K, and three HAWAII-2RG detectors coupled with dual-band filters for photometric mapping observations in six wavebands simultaneously and with linear variable filters for lowresolution spectroscopy. Although CIBER-2 made a successful first flight from White Sands Missile Range in New Mexico in 2021, technical problems such as contamination of thermal radiation from the rocket chassis and degradation of the mirror coat were recognized. Despite a successful second flight in 2023 solving the problems with the revised onboard instrument, the experiment was aborted because of trouble with the rocket tracking system. In this paper, we describe the parachute-recovered payload rebuilt after the second flight and the testing, and we report the successful flight on May 5th 2024.
Astrophysical measurements at far-infrared (FIR) wavelengths have many applications, including probing the fuel for cosmic star formation and understanding the role of dust in the interstellar medium. We are currently developing an on-chip spectrometer operable in the 100-200µm [50-100 cm−1 ] band with sub-micron spectral resolution coupled to a low-noise kinetic inductance detector (KID) array with planned noise equivalent power (NEP) < 10−19 WHz1/2 . Ultimately we will need to evaluate the spectral response of these chips at very low photon backgrounds. While the spectral performance can be simulated, it is crucial to make measurements of the as-built properties of the chip with a calibrator. To this end, we have designed and fabricated a cryogenic Fourier Transform Spectrometer (FTS). Since self-emission from the FTS at room temperature would dominate a cold black body source, the FTS optics are cooled to a temperature of 5K, which greatly reduces the photon background and simulates space-like conditions. The FTS is based on the Michelson design, with 6 fixed Aucoated Al mirrors, back-to-back moving mirrors that increase the effective optical path length by a factor of 2, and a kapton film beamsplitter. Light is coupled into the FTS using HDPE collimating lenses protected by bandpass filters, and the output beam is coupled directly into the device under test through a shared vacuum space. In this paper, we report on the FTS design and discuss its fabrication and testing plan.
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