Visible Light Laser Guidestar Experiments (ViLLaGEs) is a new Micro-Electro Mechanical Systems (MEMS)
based visible-wavelength adaptive optics (AO) testbed on the Nickel 1-meter telescope at Lick Observatory. Closed
loop Natural Guide Star (NGS) experiments were successfully carried out during engineering during the fall of
2007. This is a major evolutionary step, signaling the movement of AO technologies into visible light with a MEMS
mirror. With on-sky Strehls in I-band of greater than 20% during second light tests, the science possibilities have
become evident.
Described here is the advanced engineering used in the design and construction of the ViLLaGEs system, comparing
it to the LickAO infrared system, and a discussion of Nickel dome infrastructural improvements necessary for this
system. A significant portion of the engineering discussion revolves around the sizable effort that went towards
eliminating flexure. Then, we detail upgrades to ViLLaGEs to make it a facility class instrument. These upgrades
will focus on Nyquist sampling the diffraction limited point spread function during open loop operations,
motorization and automation for technician level alignments, adding dithering capabilities and changes for near
infrared science.
We investigate the non-modulating pyramid wave-front sensor's (P-WFS) implementation in the context of Lick
Observatory's 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
sensor's non-linear signal, is developed. Using Monte Carlo simulations, the iterative reconstruction method's photon
noise propagation behavior is compared to both the pyramid sensor used in slope-sensing mode, and the traditional
Shack Hartmann sensor's 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.
The Lick Observatory is pursuing new technologies for adaptive optics that will enable feasible low cost laser guidestar
systems for visible wavelength astronomy. The Villages system, commissioned at the 40 inch Nickel Telescope this past
Fall, serves as an on-sky testbed for new deformable mirror technology (high-actuator count MEMS devices), open-loop
wavefront sensing and control, pyramid wavefront sensing, and laser uplink correction. We describe the goals of our
experiments and present the early on-sky results of AO closed-loop and open-loop operation. We will also report on our
plans for on-sky tests of the direct-phase measuring pyramid-lenslet wavefront sensor and plans for installing a laser
guidestar system.
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.
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.
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