On-sky performance verification of near infrared eAPD technology for wavefront sensing at ground based telescopes, demonstration of e-APD pixel performance to improve the sensitivity of large science focal planes and possibility to use this technology in space

Abstract

On-sky performance verification of near infrared eAPD technology for wavefront sensing at ground based telescopes, demonstration of e-APD pixel performance to improve the sensitivity of large science focal planes and possibility to use this technology in G. FingerABSTRACT Ground based near infrared adaptive optics as well as fringe tracking for coherent beam combination in optical interferometry required the development of high-speed sensors. Because of the high speed, a large analog bandwidth is needed. The short exposure times result in small signal levels which require noiseless detection. Both of these conflicting requirements cannot be met by state-of-the-art conventional CMOS technology of near infrared arrays as has been attempted previously[1] [2]. The HgCdTe electron avalanche photo diode (eAPD) technology is the only way to overcome the limiting CMOS noise barrier of near infrared sensors. Therefore, ESO funded the development of the near infrared SAPHIRA 320x256 pixel e-APD arrays at LEONARDO [3][4][5][6] [7]. SAPHIRA arrays have now become the devices of choice for control loops with unsurpassed performance [21]. This has also been demonstrated by the four wavefront sensors and the fringe tracker deployed in the VLTI instrument GRAVITY which set a new sensitivity standard in infrared interferometry [8] [9]. It has also been demonstrated that APD arrays have extremely low dark current (1E-3 electrons/s/pixel) and may outperform conventional CMOS arrays for 100 second integrations when operated with moderate APD gains. For AO systems of extremely large telescopes and for co-phasing segmented mirror telescopes larger formats are needed. Therefore, a 512x512 pixel SAPHIRA array with 64 parallel video outputs optimized for pyramid wavefront sensing is in development. Since the SAPHIRA array has successfully passed radiation hardness testing it soon may be used for future instruments in space. Apart from the large array common voltage for high APD gain it can also be operated with voltages compatible with the space qualified SIDECAR ASIC [10].

Performance characterization and near-realtime monitoring of MUSE adaptive optics modes at Paranal

“…The upgraded IRLOS detector (dubbed IRLOS+) uses a SAPHIRA Mark14b detector with sub-electron readout noise. 8 During commissioning this was shown to add at least two magnitudes to the limit for the wavefront sensing while simultaneously increasing the correction rate to 500 Hz. The 500 Hz small scale mode (compared to the old small scale mode operated at 200 Hz) of the IRLOS+ system is in operations with a fully automated acquisition sequence since the beginning of Period 107, with a limiting magnitude of J=16.0 for point sources.…”

Infrared Wavefront Sensing for Adaptive Optics Assisted Galactic Center Observations with the VLT Interferometer and GRAVITY: Operation and Results

“…Due to their high frame rates, high sensitivity, low noise, and low dark current, Saphira detectors [25][26][27][28][29][30] have characteristic properties, especially for applications in astronomical adaptive optics, which were not available 10 years ago. The Saphira detector used in CIAO is a 320 × 256 pixel HgCdTe avalanche photodiode array with 24 µm square pixels.…”

“…Unfortunately, with the installed ROIC of the CIAO wavefront sensors, the duty cycle is only 50%. A newer version of the ROIC, which can readout and reset the detector on a row by row basis (so-called rolling shutter mode), no longer has this problem [26,28,29].…”

Infrared wavefront sensing for adaptive optics assisted Galactic Center observations with the VLT interferometer and GRAVITY: operation and results

“…Due to their high frame rates, high sensitivity, low noise, and low dark current, Saphira detectors [24][25][26][27][28][29] have characteristic properties, especially for applications in astronomical adaptive optics, which were not available 10 years ago. The Saphira detector used in CIAO is a 320 x 256 pixel HgCdTe avalanche photodiode array with 24 µm square pixels.…”

“…A newer version of the ROIC, which can readout and reset the detector on a row by row basis (so called rolling shutter mode), no longer has this problem. 25,27,28 Additionally, to further reduce readout noise, each pixel can be multiple times converted to digital values and then averaged. As mentioned above, for the CIAO sub-region, 28 non-destructive readouts are theoretically possible during a 2 ms exposure, e.g.…”