Proc. SPIE. 9912, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation II
KEYWORDS: Actuators, Monochromatic aberrations, Mirrors, Mirrors, Polishing, Polishing, Interfaces, Finite element methods, Chemical elements, Freeform optics, Active optics, Active optics, Disk lasers
We present two ways to generate or compensate for first order optical aberrations using smart warping harnesses. In these cases, we used the same methodology leading to replace a previous actuation system currently on-sky and to get a freeform mirror intended to a demonstrator. Starting from specifications, a warping harness is designed, followed by a meshing model in the finite elements software. For the two projects, two different ways of astigmatism generation are presented. The first one, on the VLT-SPHERE instrument, with a single actuator, is able to generate a nearly pure astigmatism via a rotating motorization. Two actuators are sufficient to produce the same aberration for the active freeform mirror, main part of the OPTICON-FAME project, in order to use stress-polishing method.
FAME is a four-year project and part of the OPTICON/FP7 program that is aimed at providing a breakthrough component for future compact, wide field, high resolution imagers or spectrographs, based on both Freeform technology, and the flexibility and versatility of active systems.
Due to the opening of a new parameter space in optical design, Freeform Optics are a revolution in imaging systems for a broad range of applications from high tech cameras to astronomy, via earth observation systems, drones and defense. Freeform mirrors are defined by a non-rotational symmetry of the surface shape, and the fact that the surface shape cannot be simply described by conicoids extensions, or off-axis conicoids. An extreme freeform surface is a significantly challenging optical surface, especially for UV/VIS/NIR diffraction limited instruments.
The aim of the FAME effort is to use an extreme freeform mirror with standard optics in order to propose an integrated system solution for use in future instruments. The work done so far concentrated on identification of compact, fast, widefield optical designs working in the visible, with diffraction limited performance; optimization of the number of required actuators and their layout; the design of an active array to manipulate the face sheet, as well as the actuator design.
In this paper we present the status of the demonstrator development, with focus on the different building blocks: an extreme freeform thin face sheet, the active array, a highly controllable thermal actuator array, and the metrology and control system.
We present the conception of an anamorphic and telecentric scale changer with no distortion, able to provide magnifications in the range of 2 to 30 without any interchangeable optics, dedicated to ground or space applications. Several optical designs are investigated and the final configuration is based on off-axis five mirrors system with no moving elements. Four active mirrors are adapted to four different zoom configurations. A specific mechanical profile with variable thickness distribution is simulated and optimized on each mirror to allow using a minimal number of actuators. An opto-mechanical design will be presented, showing the implementation of actuators on the system. This work is done in the frame of the ANR project OASIX and will produce a lab prototype in 2015.