Thomas R. Rimmele

First results from the NSO/NJIT solar adaptive optics system

The National Solar Observatory and the New Jersey Institute of Technology have developed two 97 actuator solar adaptive optics (AO) systems based on a correlating Shack-Hartmann wavefront sensor approach. The first engineering run was successfully completed at the Dunn Solar Telescope (DST) at Sacramento Peak, New Mexico in December 2002. The first of two systems is now operational at Sacramento Peak. The second system will be deployed at the Big Bear Solar Observatory by the end of 2003. The correlating Shack-Hartmann wavefront sensor is able to measure wavefront aberrations for low-contrast, extended and time-varying objects, such as solar granulation. The 97-actuator solar AO system operates at a loop update rate of 2.5 kHz and achieves a closed loop bandwidth (0dB crossover error rejection) of about 130 Hz. The AO system is capable of correcting atmospheric seeing at visible wavelengths during median seeing conditions at both the NSO/Sacramento Peak site and the Big Bear Solar Observatory. We present an overview of the system design. The servo loop was successfully closed and first AO corrected images were recorded. We present first results from the new, high order AO system.

Evaluation of seeing-induced cross talk in tip-tilt-corrected solar polarimetry.

We reanalyze the effects of atmosphere-induced image motions on the measurement of solar polarized light using a formalism developed by Lites. Our reanalysis is prompted by the advent of adaptive optics (AO) systems that reduce image motion and higher-order aberrations, by the availability of liquid crystals as modulation devices, and by the need to understand how best to design polarimeters for future telescopes such as the Advanced Technology Solar Telescope. In this first attempt to understand the major issues, we analyze the influence of residual image motion (tip-tilt) corrections of operational AO systems on the cross talk between Stokes parameters and present results for several polarization analysis schemes. Higher-order wave-front corrections are left for future research. We also restrict our discussion to the solar photosphere, which limits several important parameters of interest, using some recent magnetoconvection simulations.

High speed low latency solar adaptive optics camera

This paper describes a versatile camera designed to operate at high frame rates of > 2kHz. Such high frame rates are required to reduce the latency, i.e., achieve high bandwidth in a solar adaptive optics application. The camera was designed around a 1280x1024 pixel CMOS 10-bit sensor with a readout rate of 2 microseconds per row. The output is switchable between a standard Camera Link interface with four 10-bit ports (standard camera mode) and a non-standard Camera Link interface with twelve 8-bit ports (adaptive optics mode). The programmable camera interface maps blocks of pixels to output ports enabling multiple regions of interest. This mode is of particular interest for solar multi-conjugate adaptive optics (MCAO). The speed of the camera is determined by the number of rows of pixels needed in the application. For example, a 200x200 pixel sub-array that is needed for the 97-actuator solar adaptive optics system at the Dunn Solar Telescope can be read out at a rate of 2.5kHz. Camera design and performance will be discussed.

The Diffraction Limited Spectro-Polarimeter: a new instrument for high-resolution solar polarimetry

The National Solar Observatory in collaboration with the High-Altitude Observatory is developing a new solar polarimeter, the Diffraction Limited Spectro-Polarimeter. In conjunction with a new high-order adaptive optics system at the NSO Dunn Solar Telescope, the DLSP design facilitates very high angular resolution observations of solar vector magnetic fields. This project is being carried out in two phases. As a follow-on to the successful completion of the first phase, the ongoing DLSP Phase II implements a high QE CCD camera system, a ferro-electric liquid crystal modulator, and a new opto-mechanical system for polarization calibration. This paper documents in detail the development of the modulator system and its performance, and presents preliminary results from an engineering run carried out in combination with the new NSO high-order AO system.

Expected performance of solar adaptive optics in large aperture telescopes

We study the performance of solar adaptive optics (AO) in large aperture telescopes and find that the extended field-of-view of the wavefront sensor and large zenith angle operations can compromise the quality of the AO correction.