Automatic sensitivity adjustment for a curvature sensor

Abstract

There are different techniques to sense the wavefront phase-distortions due to atmospheric turbulence. Curvature sensors are practical in their sensitivity being adjustable to the prevailing atmospheric conditions. Even at the best sites, the turbulence intensity has been found to vary at times over only a few minutes and regularly over longer periods. Two methods to automatically adjust the sensitivity of a curvature sensor are proposed: First, the defocus distance can be adjusted prior to the adaptive-optics (AO) loop through the acquisition of a long exposure image and can then be kept constant. Secondly, the defocus distance can be changed during the AO loop, based on the voltage values sent to the deformable mirror. We demonstrate that the performance increase -assessed in terms of the image Strehl-ratio -can be significant.

InnoPOL: an EMCCD imaging polarimeter and 85-element curvature AO system on the 3.6-m AEOS telescope for cost effective polarimetric speckle suppression

“…[25][26][27][28] Curvature adaptive optics has provided some advantages to pursuing faint objects in SSA such as the noise-less wavefront sensing, system flexibility to adapt in changing conditions as well as a convenient platform for upgrades to both the hardware and control systems. [29][30][31][32][33] The core H85 curvature AO components including the wavefront sensor (lenslet array, membrane mirror, avalanche photo diode array), deformable mirror (DM) and all associated control systems were reused in a new instrument design for the AEOS f/200 beam in coudé experiment room 3. The optical design was required to use only off-the shelf mirrors with short lead time spheres and parabolas.…”

Frequency analysis of a wavefront curvature sensor: selection of propagation distance

“…One of the most important factors in TIE technology is to determine the propagation distance, because the distance dominates the sensitivity [13,14], accuracy [15][16][17][18] and dynamic range of the wavefront sensor. Different authors have offered different qualitative criteria for selecting the distance [1,6,[17][18][19][20][21].…”