Renate Kupke

First results from the UCSC Laboratory for Adaptive Optics multi-conjugate and multi-object adaptive optics testbed

We present first results from the Multi-Conjugate and Multi-Object Adaptive Optics (MCAO and MOAO) testbed, at the UCO/Lick Laboratory for Adaptive Optics (LAO) facility at U.C. Santa Cruz. This testbed is constructed to simulate a 30-m telescope executing MCAO and/or open loop MOAO atmospheric compensation and imaging over 5 arcminutes. It is capable of performing Shack-Hartmann wavefront sensing on up to 8 natural or laser guide stars and 2-3 additional tip/tilt stars. In this paper, we demonstrate improved on-axis correction relative to ground layer adaptive optics (~ 15% Strehl relative to ~ 12%) with a simulated 28-m aperture at a D/r0 corresponding to a science wavelength of 2.6 microns using three laser guide stars on a simulated 41 arcsec radius with a central science object and one deformable mirror at the ground layer.

Pyramid wavefront sensing: theory and component technology development at LAO

Pyramid wavefront sensors offer an alternative to traditional Hartmann sensing for wavefront measurement in astronomical adaptive optics systems. The Pyramid sensor has been described as a slope sensor with potential sensitivity gains over the Shack Hartmann sensor, but in actuality seems to exhibit traits of both a slope sensor and a direct phase sensor. The original configuration, utilizing glass pyramids and modulation techniques, is difficult to implement. We present results of laboratory experiments using a Pyramid sensor that utilizes a micro-optic lenslet array in place of a glass pyramid, and does not require modulation. A group of four lenslets forms both the pyramid knife-edge and the pupil reimaging functions. The lenslet array is fabricated using a technique that pays careful attention to the quality of the edges and corners of the lenslets. The devices we have tested show less than 1 micron edge and corner imperfections, making them some of the sharpest edges available. We finish by comparing our results to theoretical wave optic predictions which clearly show the dual nature of the sensor.

Concept for the Keck Next Generation Adaptive Optics system

The Next Generation Adaptive Optics (NGAO) system will represent a considerable advancement for high resolution astronomical imaging and spectroscopy at the W. M. Keck Observatory. The AO system will incorporate multiple laser guidestar tomography to increase the corrected field of view and remove the cone effect inherent to single laser guide star systems. The improvement will permit higher Strehl correction in the near-infrared and diffraction-limited correction down to R band. A high actuator count micro-electromechanical system (MEMS) deformable mirror will provide the on-axis wavefront correction to a number of instrument stations and additional MEMS devices will feed multiple channels of a deployable integral-field spectrograph. In this paper we present the status of the AO system design and describe its various operating modes.

ShaneAO: an enhanced adaptive optics and IR imaging system for the Lick Observatory 3-meter telescope

The Lick Observatory 3-meter telescope has a history of serving as a testbed for innovative adaptive optics techniques. In 1996, it became one of the first astronomical observatories to employ laser guide star (LGS) adaptive optics as a facility instrument available to the astronomy community. Work on a second-generation LGS adaptive optics system, ShaneAO, is well underway, with plans to deploy on telescope in 2013. In this paper we discuss key design features and implementation plans for the ShaneAO adaptive optics system. Once again, the Shane 3-m will host a number of new techniques and technologies vital to the development of future adaptive optics systems on larger telescopes. Included is a woofer-tweeter based wavefront correction system incorporating a voice-coil actuated, low spatial and temporal bandwidth, high stroke deformable mirror in conjunction with a high order, high bandwidth MEMs deformable mirror. The existing dye laser, in operation since 1996, will be replaced with a fiber laser recently developed at Lawrence Livermore National Laboratories. The system will also incorporate a high-sensitivity, high bandwidth wavefront sensor camera. Enhanced IR performance will be achieved by replacing the existing PICNIC infrared array with an Hawaii 2RG. The updated ShaneAO system will provide opportunities to test predictive control algorithms for adaptive optics. Capabilities for astronomical spectroscopy, polarimetry, and visible-light adaptive optical astronomy will be supported.

Laser guidestar uplink correction using a MEMS deformable mirror: on-sky test results and implications for future AO systems

By inserting a MEMS deformable mirror-based adaptive optics system into the beam transfer optics of the Shane 3-meter telescope at Mt. Hamilton, we actively controlled the wavefront of the outgoing sodium laser guidestar beam. It was possible to show that a purposefully aberrated beam resulted in poorer performance of the Adaptive Optics system located behind the primary, though bad seeing conditions prevented us from improving the system’s performance over its nominal state. A silver-coated Iris AO deformable mirror was subjected to approximately 9.5 hours of exposure to a sodium laser guidestar of 3.5 Watts average output power and showed no signs of permanent damage or degradation in performance. Future applications of the uplink-AO system for correcting atmospheric turbulence and in generating custom laser guidestar asterisms are also discussed.

Commissioning ShARCS: the Shane adaptive optics infrared camera-spectrograph for the Lick Observatory Shane 3-m telescope

We describe the design and first-light early science performance of the Shane Adaptive optics infraRed Camera- Spectrograph (ShARCS) on Lick Observatory’s 3-m Shane telescope. Designed to work with the new ShaneAO adaptive optics system, ShARCS is capable of high-efficiency, diffraction-limited imaging and low-dispersion grism spectroscopy in J, H, and K-bands. ShARCS uses a HAWAII-2RG infrared detector, giving high quantum efficiency (<80%) and Nyquist sampling the diffraction limit in all three wavelength bands. The ShARCS instrument is also equipped for linear polarimetry and is sensitive down to 650 nm to support future visible-light adaptive optics capability. We report on the early science data taken during commissioning.

Evidence that wind prediction with multiple guide stars reduces tomographic errors and expands MOAO field of regard

We explore the extension of predictive control techniques to multi-guide star, multi-layer tomographic wavefront measurement systems using a shift-and-average correction scheme that incorporates wind velocity and direction. In addition to reducing temporal error budget terms, there are potentially additional benefits for tomographic AO systems; the combination of wind velocity information and phase height information from multiple guide stars breaks inherent degeneracies in volumetric tomographic reconstruction, producing a reduction in the geometric tomographic error. In a tomographic simulation of an 8-meter telescope with 3 laser guide stars over 2 arcminute diameter, we find that tracking organized wind motion as it flows into metapupil regions sampled by only one guide star improves layer estimates beyond the guide star radius, allowing for an expansion of the field of view. For this case, we demonstrate improvement of layer phase estimates of 3% to 12%, translating into potential gains in the MOAO field of regard area of up to 40%. The majority of the benefits occur in regions of the metapupil sampled by only 1-2 LGSs downwind at high altitudes.

Opto-mechanical design of ShaneAO: the adaptive optics system for the 3-meter Shane Telescope

A Cassegrain mounted adaptive optics instrument presents unique challenges for opto-mechanical design. The flexure and temperature tolerances for stability are tighter than those of seeing limited instruments. This criteria requires particular attention to material properties and mounting techniques. This paper addresses the mechanical designs developed to meet the optical functional requirements. One of the key considerations was to have gravitational deformations, which vary with telescope orientation, stay within the optical error budget, or ensure that we can compensate with a steering mirror by maintaining predictable elastic behavior. Here we look at several cases where deformation is predicted with finite element analysis and Hertzian deformation analysis and also tested. Techniques used to address thermal deformation compensation without the use of low CTE materials will also be discussed.

Performance assessment of a candidate architecture for real-time woofer-tweeter controllers: simulation and experimental results

We evaluate the performance of a woofer-tweeter controller architecture for the new 3-meter Shane Telescope (Lick Observatory) laser guidestar adaptive optics (AO) system. Low order, high stroke phase correction is performed using the normal modal basis set of the Alpao woofer deformable mirror (DM). Since the woofer and tweeter DMs share the same wavefront sensor, the projected woofer phase correction is offloaded from the high-order, low stroke phase aberrations corrected by the tweeter DM. This ensures the deformable mirrors complementarily correct the input phase disturbance and minimizes likelihood of the tweeter actuators saturating. Preliminary analysis of on-sky closed-loop deformable mirror telemetry data from currently operating AO systems at Mt. Hamilton, as well as statistically accurate Kolmogorov phase screens, indicate that correction of up to 34 woofer modes results in all tweeter actuators remaining within their stroke limit.

Implementation of the pyramid wavefront sensor as a direct phase detector for large amplitude aberrations

We investigate the non-modulating pyramid wave-front sensors (P-WFS) implementation in the context of Lick Observatorys Villages visible light AO system on the Nickel 1-meter telescope. A complete adaptive optics correction, using a non-modulated P-WFS in slope sensing mode as a boot-strap to a regime in which the P-WFS can act as a direct phase sensor is explored. An iterative approach to reconstructing the wave-front phase, given the pyramid wave-front sensors non-linear signal, is developed. Using Monte Carlo simulations, the iterative reconstruction methods photon noise propagation behavior is compared to both the pyramid sensor used in slope-sensing mode, and the traditional Shack Hartmann sensors theoretical performance limits. We determine that bootstrapping using the P-WFS as a slope sensor does not offer enough correction to bring the phase residuals into a regime in which the iterative algorithm can provide much improvement in phase measurement. It is found that both the iterative phase reconstructor and the slope reconstruction methods offer an advantage in noise propagation over Shack Hartmann sensors.