"Adaptive Optics for Subaru Telescope: Wavefront Sensing and Measurement in Astronomical Observations"

Prof. Masanori Iye, National Astronomical Observatory of Japan

Optical and infrared astronomical observations from ground are hindered by turbulent atmosphere. Temperature disturbance in the atmosphere produces wavefront distortion of the light beam fed in the telescope and blurs the images of stars to about 1 arcsec in diameter. The 8.2m Subaru Telescope (http://subarutelescope.org/index.html) has achieved image quality, as sharp as 0.2 arcsec in infrared K-band (2.2 um) and 0.3 arcsec in optical R-band (0.65um) under the best condition. This owes much to its superb site (Mauna Kea, 4200m), thermal designing to suppress the turbulence near and inside the telescope enclosure, and the actively controlled primary mirror to keep its figure and optical alignment at 1Hz.

Adaptive Optics (AO) is a rapidly growing optical engineering technology to measure and correct the remaining wavefront disturbance at about 1kHz to achieve the diffraction limited image size, 0.07 arcsec at K-band. We developed an AO system with 36 avalanche photodiodes and a thin deformable mirror driven by 36 bimorph piezo electrodes and are developing another AO system with 188 APDs and 188 electrodes. Additional new feature is a development of a laser guide star system to produce an artificial light spot at 90 km above the atmosphere, that is used as a light source to measure the atmospheric turbulence.

Some scientific achievements with AO system and the plan for the forthcoming 30m class telescope will also be introduced together with the principles of the AO system.