Future deep space missions will tax the ability of existing radio frequency systems to return all the data. In addition, these missions must be able to communicate around the clock, including when the spacecraft is near the Sun. This is especially true for crewed missions. Optical communication can solve these problems, and also offers the promise of being more compact and using less power and mass. Traditional deep space optical communication concepts require large diameter telescopes (<8m) to collect enough photons to provide adequate signal-to-noise ratio. Systems operating during the day will experience strong turbulence which results in large point spread functions. This necessitates photon counting detectors with a large field-of-view which are difficult to build. The large field-of-view also lets in excessive sky background which degrades the communication performance. Adaptive optics (AO) can mitigate this degradation by concentrating the light and thus not needing a large field of view. We present an AO system architecture capable of operating in the daytime and requiring only moderate performance. We present the architecture along with performance predictions of the system for different size telescopes. Finally we include a technology gap list, which will guide future development of the component technologies.
We present the development and testing of focal plane wavefront control techniques that utilize microwave kinetic inductance detectors (MKIDs) as a focal plane IFU. MKIDs are ideally suited to this application, as they are energy resolving, and have single photon sensitivity, zero read noise, and microsecond time resolution. These characteristics enable much higher feedback rates than conventional systems; for the first time, focal plane measurements may be used to correct atmospheric aberrations in addition to quasistatics. A variety of approaches are under development, including conventional speckle nulling, as well as more advanced approaches such as linear dark field control.
We have developed an MKID-specific speckle nulling code for DARKNESS, a 10,000 pixel MKID IFU behind the stellar double coronagraph (SDC) and PALM-3000 (P3K) AO system at Palomar observatory. Our code implements the algorithm described in (Bottom, et. al, 2016) with minor modifications. To facilitate high feedback rates on sky, the code is optimized for computational speed, and implements low-latency communications to both P3K and the MKID readout. It is also capable of integrating with P3K in closed loop operation. Using our code, we have demonstrated quasi-static speckle nulling at a 1 Hz feedback rate in the laboratory. We hope to demonstrate rates ~10-100 Hz in the near future.
In addition to continuing our work with DARKNESS, we will adapt our code to MEC, a 20,000 pixel MKID IFU behind the Subaru coronagraphic extreme adaptive optics system (SCExAO) at Subaru observatory. MEC is scheduled to commission in January 2018.
Deformable mirrors are at the heart of any adaptive optics system. We present the results of tests of deformable mirrors from Microscale. One of the key innovations of these deformable mirrors is that the facesheet is created from a silicon on insulator (SOI) wafer with integral posts for mechanical linkage to the actuators. This dramat- ically reduces the variability of the influence function. The facesheet is bonded to an array of piezoelectric stack actuators. The actuators are currently PZT, but single crystal PMN actuators are being developed. We present results of optical and electrical tests of the performance of the DM.
The Integrated Optical System (IOS) is an extreme adaptive optics system designed for NASA’s Laser Com- munication Relay Demonstration mission. There is a great deal of overlap between the requirements for laser communication AO and high-contrast exoplanet imaging AO systems. Both require very high Strehl ratios with narrow fields of view. This overlap allows the IOS to serve as a testbed and technology demonstrator for astronomical extreme adaptive optics systems. <p> </p>
There are several example technologies from the IOS that are already making the transition to astronomical AO systems. The first is that the real time controller based on Direct Memory Access transfer between the WFS camera link frame-grabber and a DSP board is being reused on the upgrade to PALM-3000 AO system at Palomar Observatory. This enables the system to minimize latency by bypassing the CPU and its inherent timing jitter. Technologies like this will be crucial to enabling high contrast imaging on the next generation of extremely large telescopes. In addition, the IOS measures Fried’s parameter from wavefraont measures in near real time. This technology has already been deployed to PALM-3000. The main function of Laser Communication AO systems is to couple the incoming light into single mode fiber. This is the same configuration that will be used by AO coupled radial velocity spectrographs. <p> </p>
The adaptive optics system is a woofer/tweeter design, with one deformable mirror correcting for low spatial frequencies with large amplitude and a second deformable mirror correcting for high spatial frequencies with small amplitude. The system uses a Shack-Hartmann wavefront sensor. The system has achieved first light and is undergoing commissioning. We will present an overview of the system design and initial performance.
Direct Imaging of exoplanets is one of the most technically difficult techniques used to study exoplanets, but holds immense promise for not just detecting but characterizing planets around the nearest stars. Ambitious instruments at the world’s largest telescopes have been built to carry out this science: the Gemini Planet Imager (GPI), SPHERE at VLT, SCExAO at Subaru, and the P1640 and Stellar Double Coronagraph (SDC) at Palomar. These instruments share a common archetype consisting of an extreme AO system feeding a coronagraph for on-axis stellar light rejection followed by a focal plane Integral Field Spectrograph (IFS). They are currently limited by uncontrolled scattered and diffracted light which produces a coherent speckle halo in the image plane. A number of differential imaging schemes exist to mitigate these issues resulting in star-planet contrast ratios as deep as ~10^-6 at low angular separations. Surpassing this contrast limit requires high speed active speckle nullification from a focal plane wavefront sensor (FPWS) and new processing techniques.
MEC, the Microwave Kinetic Inductance Detector (MKID) Exoplanet Camera, is a J-band IFS module behind Subaru Telescope’s SCExAO system. MEC is capable of producing an image cube several thousand times a second without the read noise that dominates conventional high speed IFUs. This enables it to integrate with SCExAO as an extremely fast FPWS while eliminating non-common path aberrations by doubling as a science camera. Key science objectives can be further explored if longer wavelengths (H and K band) are simultaneously sent to CHARIS for high resolution spectroscopy. MEC, to be commissioned at Subaru in early 2018, is the second MKID IFS for high contrast imaging following DARKNESS’ debut at Palomar in July 2016.
MEC will follow up on young planets and debris disks discovered in the SEEDS survey or by Project 1640 as well as discover self-luminous massive planets. The increased sensitivity, combined with the advanced coronagraphs in SCExAO which have inner working angles (IWAs) as small as 0.03” at 1.2 μm, allows young Jupiter-sized objects to be imaged as close as 4 AU from their host star. If the wavefront control enabled by MEC is fully realized, it may begin to probe the reflected light of giant planets around some nearby stars, opening a new parameter space for direct imaging targeting older stars. While direct imaging of reflected light exoplanets is the most challenging of the scientific goals, it is a promising long-term path towards characterization of habitable planets around nearby stars using Extremely Large Telescopes (ELTs). With diameters of about 30-m, an ELT can resolve the habitable zones of nearby M-type stars, for which an Earth-sized planet would be at ~10^-7 contrast at 1 μm. This will complement future space-based high contrast optical imaging targeting the wider habitable zones of sun-like stars for ~10^-10 contrast earth analogs.
We will present lessons learned from the first few months of MEC’s operation including initial lab and on-sky (weather permitting) results. We already have preliminary data from Palomar testing a new statistical speckle discrimination post-processing technique using the photon arrival time measured with MKIDs. Residual stellar light in the form of a speckle masquerading as a planetary companion is pulled from a modified Rician distribution and can be statistically discerned from a true off-axis Poisson point source. Additionally, the progress of active focal plane wavefront control will be briefly discussed.
Proc. SPIE. 10709, High Energy, Optical, and Infrared Detectors for Astronomy VIII
KEYWORDS: Point spread functions, Light emitting diodes, Cameras, Sensors, Calibration, Organic light emitting diodes, Image sensors, Electron multiplying charge coupled devices, Scene simulation, Photometry, Tracking and scene analysis, RGB color model
Full characterization of imaging detectors involves subjecting them to spatially and temporally varying illumination patterns over a large dynamic range. Here we present a scene generator that fulfills many of these functions. Based on a modern smartphone, it has a number of good features, including high spatial resolution (13 um), high dynamic range (∼10<sup>4</sup> ), near-Poisson limited illumination stability over time periods from 100 ms to many days, and no background noise. The system does not require any moving parts and may be constructed at modest cost. We present the optical, mechanical, and software design, test data validating the performance, and application examples.
Microwave Kinetic Inductance Detectors, or MKIDS, have the ability to simultaneous resolve the wavelength of individual photons and time tag photons with microsecond precision. This opens up a number of exciting new possibilities and efficiency gains for optical/IR astronomy. In this paper we describe a plan to take the MKID technology, which we have demonstrated on the Palomar, Lick, and Subaru Telescopes, out of the realm of private instruments usable only by experts. Our goal is to incorporate MKIDs into a facility-class instrument at the Keck 1 Telescope that can be used by a large part of the astronomical community. This new instrument, the Keck Radiometer Array using KID ENergy Sensors (KRAKENS), will be a 30 kpix integral field spectrograph (IFS) with a 42.5” x 45” field of view, extraordinarily wide wavelength coverage from 380-1350 nm, and a spectral resolution R=λ/▵λ > 20 at 400 nm. Future add on modules could enable polarimetry and higher spectral resolution. KRAKENS will be built using the same style MKID arrays, cryostat, and similar readout electronics to those used in the successful 10 kpix DARKNESS instrument at Palomar and 20 kpix MEC instrument at Subaru, significantly reducing the technical risk.
An exoplanet mission based on a high-altitude balloon is a next logical step in humanity’s quest to explore Earthlike planets in Earthlike orbits orbiting Sunlike stars. The mission described here is capable of spectrally imaging debris disks and exozodiacal light around a number of stars spanning a range of infrared excesses, stellar types, and ages. The mission is designed to characterize the background near those stars, to study the disks themselves, and to look for planets in those systems. The background light scattered and emitted from the disk is a key uncertainty in the mission design of any exoplanet direct imaging mission, thus, its characterization is critically important for future imaging of exoplanets.
Microwave Kinetic Inductance Detectors, or MKIDs, have proven to be a powerful cryogenic detector technology
due to their sensitivity and the ease with which they can be multiplexed into large arrays. An MKID is an energy
sensor based on a photon-variable superconducting inductance in a lithographed microresonator. It is capable
of functioning as both a photon detector across the electromagnetic spectrum and a particle detector. We have
recently demonstrated the world's first photon-counting, energy-resolving, ultraviolet, optical, and near infrared
MKID focal plane array in the ARCONS camera at the Palomar 200" telescope. Optical Lumped Element (OLE)
MKID arrays have significant advantages over semiconductor detectors such as charge coupled devices (CCDs).
They can count individual photons with essentially no false counts and determine the energy (to a few percent)
and arrival time (to ≈1μs) of every photon, with good quantum efficiency. Initial devices were degraded by
substrate events from photons passing through the Titanium Nitride (TiN) material of the resonator and being
absorbed in the substrate. Recent work has eliminated this issue, with a solution found to be increasing the
thickness of the TiN resonator from 20 to 60 nm.
ARCONS, the Array Camera for Optical to Near-infrared Spectrophotometry, was recently commissioned at the
Coude focus of the 200-inch Hale Telescope at the Palomar Observatory. At the heart of this unique instrument
is a 1024-pixel Microwave Kinetic Inductance Detector (MKID), exploiting the Kinetic Inductance effect to
measure the energy of the incoming photon to better than several percent. The ground-breaking instrument is
lens coupled with a pixel scale of 0.23"/pixel, with each pixel recording the arrival time (< 2 _μsec) and energy of
a photon (~10%) in the optical to near-IR (0.4-1.1 microns) range. The scientific objectives of the instrument
include the rapid follow-up and classi_cation of the transient phenomena