Adaptive optics with four laser guide stars: correction of the cone effect in large telescopes

Abstract

We study the performance of an adaptive optics (AO) system with four laser guide stars (LGSs) and a natural guide star (NGS). The residual cone effect with four LGSs is obtained by a numerical simulation. This method allows the adaptive optics system to be extended toward the visible part of the spectrum without tomographic reconstruction of three-dimensional atmospheric perturbations, resolving the cone effect in the visible. Diffraction-limited images are obtained with 17-arc ms precision in median atmospheric conditions at wavelengths longer than 600 nm. The gain achievable with such a system operated on an existing AO system is studied. For comparison, performance in terms of achievable Strehl ratio is also computed for a reasonable system composed of a 40 x 40 Shack-Hartmann wave-front sensor optimized for the I band. Typical errors of a NGS wave front are computed by use of analytical formulas. With the NGS errors and the cone effect, the Strehl ratio can reach 0.45 at 1.25 microm under good-seeing conditions with the Nasmyth Adaptive Optics System (NAOS; a 14 x 14 subpupil wave-front sensor) at the Very Large Telescope and 0.8 with a 40 x 40 Shack-Hartmann wave-front sensor.

Addressable Microlens Array to Improve Dynamic Range of Shack–Hartmann Sensors

“…The measured mechanical resonant frequencies of the MEMS-microlens units 1 The experimentally measured resonant frequencies deviate from their design values by as much as 17% due mainly to imprecision in control of the DRIE process as revealed by SEM measurements and shown in Fig. 14 and Table V.…”

“…The polymer-jet printing head used in our system is the Microfab MJ-AT-01-40, which operates at room temperatures. 1 The MJ-AT-01-40 requires that the viscosity of the printed material not exceed 40 cps . We used Epoxy Technology's uv-curable Epo-Tek OG146, which meets this requirement at room temperature.…”

“…They are fast, accurate, and, in contrast to interferometers, generally insensitive to vibrations. When they are used in conjunction with adaptive mirrors, Shack-Hartmann sensors are able to improve the image quality of astronomical telescopes by performing real-time corrections on the wavefront aberrations that are inherently generated as starlight traverses the earth's atmosphere [1]. Shack-Hartmann sensors have also proven to be the most suitable wavefront monitors for ophthalmic-analysis applications (such as preand/or post-LASIK surgery and keratoconus analysis) because measuring the optical aberrations in illumination passing through constantly moving human eyes requires fast measurement speed and high accuracy [2]- [6].…”

The influence of high-frequency phase and correction distance on the phase correction effect

“…The key factors that cause this phenomenon are the tilting of cavity mirrors [1,2], the thermal deformation of cavity mirrors [3,4], the non-uniformity of gain medium [5,6], etc. An adaptive optics (AO) system can effectively improve beam quality by using a Shack-Hartmann sensor (S-H) to measure the wavefront phase and an optical deformable mirror (DM) to compensate the distorted wavefront [7,8]. Nevertheless, in the process of correcting the distorted phases of the wavefront with the AO technology, we found that the correction effect became worse and worse when the output power of high-power chemical laser increased gradually, and the correction effects were different when the DM was placed in different positions.…”

Preliminary numerical simulation investigation of the cone effect in an adaptive optics system using a laser guide star

“…Viard and his colleagues studied the four-LGS method for improving the image quality when an AO system is used in an astronomical telescope. 7 Based on an analytical study, the residual cone effect with four LGSs was investigated and presented. Furthermore, in order to overcome the cone effect Buscher el al.…”