Here we discuss advances in UV technology over the last decade, with an emphasis on photon counting, low noise, high eﬃciency detectors in sub-orbital programs. We focus on the use of innovative UV detectors in a NASA astrophysics balloon telescope, FIREBall-2, which successfully ﬂew in the Fall of 2018. The FIREBall-2 telescope is designed to make observations of distant galaxies to understand more about how they evolve by looking for diﬀuse hydrogen in the galactic halo. The payload utilizes a 1.0-meter class telescope with an ultraviolet multi-object spectrograph and is a joint collaboration between Caltech, JPL, LAM, CNES, Columbia, the University of Arizona, and NASA. The improved detector technology that was tested on FIREBall-2 can be applied to any UV mission. We discuss the results of the ﬂight and detector performance. We will also discuss the utility of sub-orbital platforms (both balloon payloads and rockets) for testing new technologies and proof-of-concept scientiﬁc ideas.
We present the latest developments in our joint NASA/CNES suborbital project. This project is a balloon-borne UV multi-object spectrograph, which has been designed to detect faint emission from the circumgalactic medium (CGM) around low redshift galaxies. One major change from FIREBall-1 has been the use of a delta-doped Electron Multiplying CCD (EMCCD). EMCCDs can be used in photon-counting (PC) mode to achieve extremely low readout noise (¡ 1e<sup>-</sup>). Our testing initially focused on reducing clock-induced-charge (CIC) through wave shaping and well depth optimisation with the CCD Controller for Counting Photons (CCCP) from N<i>ü</i>v<i>ü</i>. This optimisation also includes methods for reducing dark current, via cooling and substrate voltage adjustment. We present result of laboratory noise measurements including dark current. Furthermore, we will briefly present some initial results from our first set of on-sky observations using a delta-doped EMCCD on the 200 inch telescope at Palomar using the Palomar Cosmic Web Imager (PCWI).
The Faint Intergalactic-medium Redshifted Emission Balloon (FIREBall-2) is an experiment designed to observe low density emission from HI, CIV, and OVI in the circum-galactic medium around low-redshift galaxies. To detect this diffuse emission, we use a high-efficiency photon-counting EMCCD as part of FIREBall-2's detector. The flight camera system includes a custom printed circuit board, a mechanical cryo-cooler, zeolite and charcoal getters, and a Nüvü controller, for fast read-out speeds and waveform shaping. Here we report on overall detector system performance, including pressure and temperature stability. We describe dark current and CIC measurements at several temperatures and substrate voltages, with the flight set-up.
The Keck Cosmic Web Imager (KCWI) is a new facility instrument being developed for the W. M. Keck Observatory
and funded for construction by the Telescope System Instrumentation Program (TSIP) of the National Science
Foundation (NSF). KCWI is a bench-mounted spectrograph for the Keck II right Nasmyth focal station, providing
integral field spectroscopy over a seeing-limited field up to 20"x33" in extent. Selectable Volume Phase Holographic
(VPH) gratings provide high efficiency and spectral resolution in the range of 1000 to 20000. The dual-beam design of
KCWI passed a Preliminary Design Review in summer 2011. The detailed design of the KCWI blue channel (350 to
700 nm) is now nearly complete, with the red channel (530 to 1050 nm) planned for a phased implementation contingent
upon additional funding. KCWI builds on the experience of the Caltech team in implementing the Cosmic Web Imager
(CWI), in operation since 2009 at Palomar Observatory. KCWI adds considerable flexibility to the CWI design, and will
take full advantage of the excellent seeing and dark sky above Mauna Kea with a selectable nod-and-shuffle observing
mode. In this paper, models of the expected KCWI sensitivity and background subtraction capability are presented,
along with a detailed description of the instrument design. The KCWI team is lead by Caltech (project management,
design and implementation) in partnership with the University of California at Santa Cruz (camera optical and
mechanical design) and the W. M. Keck Observatory (program oversight and observatory interfaces).
The Wide-field Infrared Survey Explorer is a NASA Midex mission launching in late 2009 that will survey the entire
sky at 3.3, 4.7, 12, and 23 microns (PI: Ned Wright, UCLA). Its primary scientific goals are to find the nearest stars
(actually most likely to be brown dwarfs) and the most luminous galaxies in the universe. WISE uses three dichroic
beamsplitters to take simultaneous images in all four bands using four 1024×1024 detector arrays. The 3.3 and 4.7
micron channels use HgCdTe arrays, and the 12 and 23 micron bands employ Si:As arrays. In order to make a
1024×1024 Si:As array, a new multiplexer had to be designed and produced. The HgCdTe arrays were developed by
Teledyne Imaging Systems, and the Si:As array were made by DRS.
All four flight arrays have been delivered to the WISE payload contractor, Space Dynamics Laboratory. We present
initial ground-based characterization results for the WISE arrays, including measurements of read noise, dark current,
flat field and latent image performance, etc. These characterization data will be useful in producing the final WISE data
product, an all-sky image atlas and source catalog.