The SAPHIRA is currently the only astronomical device capable of counting photons in the NIR while showing other performance easily comparable to the ubiquitous HAWAII arrays. Photon counting was previously only available in astronomy with high dark currents, prohibiting observation of many astronomical targets. Initiated by the European Southern Observatory for work on the VLT’s GRAVITY instrument, it was further developed by the University of Hawai’i and greatly improved, including a reduction of dark current by 3+ orders of magnitude. Development continues, with further improvements in dark current relative to avalanche gain and larger array sizes to be shown. Since initial deployments, it has now become a vital device in several astronomical instruments, and remains the only array capable of counting NIR photons for low-background astronomical targets.
We report on initial results from the largest infrared AO direct imaging survey searching for wide orbit (≳ 100 AU) massive exoplanets and brown dwarfs as companions around young nearby stars using Robo-AO at the 2.1-m telescope on Kitt Peak, Arizona. The occurrence rates of these rare substellar companions are critical to furthering our understanding of the origin of planetary-mass companions on wide orbits. The observing efficiency of Robo-AO allows us to conduct a survey an order of magnitude larger than previously possible. We commissioned a low-noise high-speed SAPHIRA near-infrared camera to conduct this survey and report on its sensitivity, performance, and data reduction process.
We present results from several years of laboratory characterization and telescope deployment of the near infrared
(NIR) avalanche photodiode (APD) array SAPHIRA from Leonardo S.p.A. Dark current has fallen by three orders
of magnitude and we have demonstrated NIR photon counting. Tunnel-tunnel current dominates measured dark
current at high bias voltages for temperatures ≤ 65K. At higher temperatures, tunnel-thermal dominates. At low
temperatures and bias voltages, dark is glow-limited and not responsive to either temperature or bias voltage.
Histograms of individual avalanche events show a broad distribution but allow for photon-counting. Several
deployments of the SAPHIRA have also been conducted.
We present the measured characteristics of the most recent iteration of SAPHIRA HgCdTe APD arrays, and
with suppressed glow show them to be capable of a baseline dark current of 0:03e-/s. Under high bias voltages
the device also reaches avalanche gains greater than 500. The application of a high temperature anneal during
production shows great improvements to cosmetic performance and moves the SAPHIRA much closer to being
science grade arrays. We also discuss investigations into photon counting and ongoing telescope deployments of
the SAPHIRA with UH-IfA.
The primary goal of the HAWAII 4RG-15 (H4RG-15) development is to provide a 16 megapixel 4096x4096 format at significantly reduced price per pixel while maintaining the superb low background performance of the HAWAII 2RG (H2RG). The H4RG-15 design incorporates several new features, notably clocked reference output and interleaved reference pixel readout, that promise to significantly improve noise performance while the reduction in pixel pitch from 18 to 15 microns should improve transimpedance gain although at the expense of some reduction in full well and possible increase in crosstalk. We report the results of very preliminary characterization of a science grade Phase 2 λc ~ 2.5 μm H4RG-15 operated in both conventional and Interleaved Reference Pixel (IRP) 32-output mode and have demonstrated that the CDS averaged read noise at 200 kHz pixel rate is comparable to, and possibly slightly below, that of the best Phase 1 H4RG-15s. We have also investigated the characteristics of pixels exhibiting RTN in the IRP frames.
The Robo-AO Kepler Planetary Candidate Survey is observing every Kepler planet candidate host star (KOI) with laser adaptive optics imaging to hunt for blended nearby stars which may be physically associated companions. With the unparalleled efficiency provided by the first fully robotic adaptive optics system, we perform the critical search for nearby stars (0.15" to 4.0" separation with contrasts up to 6 magnitudes) that dilute the observed planetary transit signal, contributing to inaccurate planetary characteristics or astrophysical false positives. We present 3313 high resolution observations of Kepler planetary hosts from 2012-2015, discovering 479 nearby stars. We measure an overall nearby star probability rate of 14.5±0.8%. With this large data set, we are uniquely able to explore broad correlations between multiple star systems and the properties of the planets which they host, providing insight into the formation and evolution of planetary systems in our galaxy. Several KOIs of particular interest will be discussed, including possible quadruple star systems hosting planets and updated properties for possible rocky planets orbiting with in their star's habitable zone.
We present measurements of the evolutionary timescales of speckles around adaptive optics-corrected PSFs. We placed a SELEX SAPHIRA HgCdTe detector behind the SCExAO instrument at Subaru Telescope. We analyzed the behavior of speckles at radial distances of 2-8 λ/D away from the diffraction-limited PSF in H-band (∼1.6μm) images collected at ∼1 kHz framerates. Speckles evolve with a variety of timescales, and these have not previously been studied at near-infrared wavelengths. Ultimately we would like to image reflected-light exoplanets, which necessitates a fast speckle control loop. Based on our measurements, we calculate the parameters of an optimized control loop that would enable such observations.
We report the performance of Selex ES' SAPHIRA APD arrays from both laboratory characterization and telescope deployment. The arrays are produced using the MOVPE production method, allowing for solid state engineering and thus produce superior performance to similar liquid phase epitaxy efforts. With an avalanche gain slightly over 50 and read noise of ~9e-, the detectors are easily capable of single-frame sub-electron read noise, and the 32 output readout and flexible windowing allow an excellent readout speed. Gain-corrected dark current/glow is found to be 10-20 e-/s at low bias, and drops below basline at high avalanche gains. The detectors were also tested on-sky at both IRTF on Maunakea and the 1.5-m telescope at Palomar Observatory, demonstrating that the SAPHIRA is an ideal device for both tip-tilt NGS guiding and infrared lucky imaging, in the latter providing diffraction-limited resolution for the 3-meter IRTF without the benefit of adaptive optics correction.
The prototype Robo-AO system at the Palomar Observatory 1.5-m telescope is the world's first fully automated laser adaptive optics instrument. Scientific operations commenced in June 2012 and more than 12,000 observations have since been performed at the ~0.12" visible-light diffraction limit. Two new infrared cameras providing high-speed tip-tilt sensing and a 2' field-of-view will be integrated in 2014. In addition to a Robo-AO clone for the 2-m IGO and the natural guide star variant KAPAO at the 1-m Table Mountain telescope, a second generation of facility-class Robo-AO systems are in development for the 2.2-m University of Hawai'i and 3-m IRTF telescopes which will provide higher Strehl ratios, sharper imaging, ~0.07", and correction to λ = 400 nm.
The primary goal of the HAWAII 4RG-15 (H4RG-15) development is to provide a 16 megapixel 4096x4096 format at
significantly reduced price per pixel while maintaining the superb low background performance of the HAWAII 2RG
(H2RG). The H4RG-15 design incorporates several new features, notably clocked reference output and interleaved
reference pixel readout, that promise to significantly improve noise performance while the reduction in pixel pitch from
18 to 15 microns should improve transimpedance gain although at the expense of some degradation in full well and
crosstalk. During the Phase-1 development, Teledyne has produced and screen tested six hybrid arrays. In preparation for
Phase-2, the most promising of these are being extensively characterized in the University of Hawaii’s (UH) ULBCam
test facility originally developed for the JWST H2RG program. The end-to-end performance of the most promising array
has been directly established through astronomical imaging observations at the UH 88-inch telescope on Mauna Kea. We
report the performance of these Phase-1 H4RG-15s within the context of established H2RG performance for key
parameters (primarily CDS read noise), also highlighting the improvements from the new readout modes.