We present progress on a conceptual design for a new Keck multi-conjugate adaptive optics system capable of visible light correction with a near-diffraction-limited spatial resolution. The KOLA (Keck Optical LGS AO) system will utilize a planned adaptive secondary mirror (ASM), 2 additional high-altitude deformable mirrors (DMs), and ≳8 laser guide stars (LGS) to sense and correct atmospheric turbulence. The field of regard for selecting guide stars will be 2’ and the corrected science field of view will be 60”. We describe science cases, system requirements, and performance simulations for the system performed with error budget spreadsheet tools and MAOS physical optics simulations. We will also present results from trade studies for the actuator count on the ASM. KOLA will feed a new optical imager and IFU spectrograph in addition to the planned Liger optical + infrared (λ>850nm) imager and IFU spectrograph. Performance simulations show KOLA will deliver a Strehl of 12% at g’, 21% at r’, 53% at Y, and 87% at K bands on axis with nearly uniform image quality over a 40”×40” field of view in the optical and over 60”×60” beyond 1 μm. Ultimately, the system will deliver spatial resolutions superior to HST and JWST (∼17 mas at r’-band) and comparable to the planned first-generation infrared AO systems for the ELTs.
We present progress towards developing a science-grade, megapixel format linear-mode avalanche photodiode array for low background shortwave (1 - 2.4 um) infrared astronomy. Our latest results show outstanding performance, with dark current <1e-4 electrons/pixel/second and read noise reducing by 30% per volt of bias, reaching less than 1e-/pixel/frame in correlated double-sampling, and able to average down to ~0.3 e-/pixel/frame when using multiple non-destructive reads. We present some on-sky data as well as comment on prospects for photon counting and photon number resolution.
Spectroscopy and direct-imaging of ultra-faint targets such as Earth-like exoplanets and high redshift galaxies are among the primary goals of upcoming large scale astronomy projects like the Habitable World Observatory (HWO). Such objectives pose extreme instrumental challenges, in particular on detectors where dark currents lower than 1 e-/pixel/kilosecond and read noise less than 1 e-/pixel/frame will have to be achieved on large format arrays. Some technologies meet these requirements at optical wavelengths, but none do in the infrared. With this goal in mind, the University of Hawaii has partnered with Leonardo to develop linear-mode avalanche photodiodes (LmAPDs). In this paper, we report recent tests performed on LmAPDs, where we measure a ROIC glow of ∼0.01 e-/pixel/frame, without which the intrinsic dark current is essentially zero (<0.1 e-/pixel/kilosecond). We show that at high gain, these devices are capable of detecting single photons.
One of the primary goals of HgCdTe linear-mode avalanche photodiode arrays is to provide a 1kx1k pixels format, @15 μm pitch, near-infrared (0.9 to 2.5 μm) detector suitable for ultra-low background astronomical applications and long integration times. Such science goals impose very strict detector requirements, namely a dark current <0.001 [e−/pix/sec] and a sub-electron read noise. The Institute for Astronomy (IfA), University of Hawaii has partnered with Leonardo Company to develop such devices, using fine control of the photodiode process to enable noise-free amplification of the charge carriers and a readout circuit optimized for minimal glow. We discuss the first results of the tests conducted at the IfA on this new device operated in our cryogenic testbed. We report the values of dark current, read noise and conversion gain, as well as its cosmetic qualities that we have measured at a temperature of 50K. The measured dark current of these devices at low bias voltages is of ∼3 [e-/pix/ksec] (ksec=1000 seconds). We show that this dark current is dominated by the glow emitted by the ROIC of the detector when it is being read out. The intrinsic dark current of these devices is consistent with zero, with a best estimate of ∼0.1 [e-/pix/ksec]. The glow coming from the ROIC is measured to be ∼0.08 [e-/pix/frame], or 1 [e-/pix] every ∼12 frames. The read noise of these devices starts around ∼10 [e-/pix/frame] at a bias voltage of 3V, and decreases by a factor of 1.3 with each +1V increment of the bias voltage, in agreement with theory. It is reduced to ∼2 [e-/pix/frame] at a bias voltage of 8V.
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