Delta-doped electron-multiplying CCDs for FIREBall-2

Abstract

We present the status of ongoing detector development efforts for our joint NASA/ Centre National d'Études Spatiales balloon-borne UV multiobject spectrograph, the Faint Intergalactic Redshifted Emission Balloon (FIREBall-2; FB-2). FB-2 demonstrates a UV detector technology, the delta-doped electron-multiplying CCD (EMCCD), in a low-risk suborbital environment, to prove the performance of EMCCDs for future space missions and technology readiness level advancement. EMCCDs can be used in photon-counting mode to achieve extremely low readout noise (<1 electron). Our testing has focused on reducing clockinduced-charge (CIC) through wave shaping and well-depth optimization with a Nüvü V2 CCCP controller, measuring CIC at 0.001 e − ∕pixel∕frame. This optimization also includes methods for reducing dark current, via cooling, and substrate voltage levels. We discuss the challenges of removing cosmic rays, which are also amplified by these detectors, as well as a data reduction pipeline designed for our noise measurement objectives. FB-2 flew in 2018, providing the first time an EMCCD, was used for UV observations in the stratosphere. FB-2 is currently being built up to fly again in 2020, and improvements are being made to the EMCCD to continue optimizing its performance for better noise control.

End-to-end ground calibration and in-flight performance of the FIREBall-2 instrument

“…4.5. The detector performance is detailed further in the work by Kyne et al 14 Relevant to the present analysis, the detector shows sub-optimal charge transfer efficiency (CTE) due to the unusually low temperature selected to minimize the dark current. We think this can be improved by further optimization of the controller/parameter trade-off for the next flight.…”

“…The 2018 flight of FIREBall-2 performed the first space multi-object acquisition using an MOS, demonstrated the successful performance of all subsystems, and provided a test flight for several key technology innovations such as the EMCCD, 14 the sub-arcsecond pointing system, 15 or the aspherical grating. 13 In this paper, we have described the calibration of the second generation of the FIREBall instrument and its performance.…”

“…In addition to the science objectives described in Sec. 1, the flight of the FIREBall-2 instrument also validated many processes and state-of-the-art hardware components (UV EMCCD, 14 CNES pointing system, 15 cooling system, and large UV aspherical grating 13 ).…”

“…Smearing inversion algorithms can be applied, but there is an intrinsic limitation as these inversions always generate noise amplification. 14…”

“…It will be equipped with a new version of the detector controller (Nüvü v3), developed specifically by Nüvü Cameras for these EMCCD detectors. 14 The expected lower read noise provided by this controller combined with a slightly higher temperature should make the photon-counting algorithm more efficient. Data acquired with this new setup will allow further optimization of the temperature/smearing/ gain parameters in order to increase the SNR.…”