The Actuator Design and the Experimental Tests of a New Technology Large Deformable Mirror for Visible Wavelengths Adaptive Optics

TL;DR

This paper presents the design and initial testing of a novel large deformable mirror actuator, VRALA, optimized for visible wavelength adaptive optics, achieving high speed, precision, and low thermal impact.

Contribution

The paper introduces VRALA, a new actuator with a magnetic core, dual-stator, and single-mover design, tailored for high-resolution, high-bandwidth visible wavelength adaptive optics.

Findings

Preliminary tests confirm the magnetic design meets power and force specifications.

The actuator achieves high speed and precision with negligible thermal impact.

Design addresses the demanding requirements of visible wavelength adaptive optics.

Abstract

Recently, Adaptive Secondary Mirrors showed excellent on-sky results in the Near Infrared wavelengths. They currently provide 30mm inter-actuator spacing and about 1 kHz bandwidth. Pushing these devices to be operated at visible wavelengths is a challenging task. Compared to the current systems, working in the infrared, the more demanding requirements are the higher spatial resolution and the greater correction bandwidth. In fact, the turbulence scale is shorter and the parameter variation is faster. Typically, the former is not larger than 25 mm (projected on the secondary mirror) and the latter is 2 kHz, therefore the actuator has to be more slender and faster than the current ones. With a soft magnetic composite core, a dual-stator and a single-mover, VRALA, the actuator discussed in this paper, attains unprecedented performances with a negligible thermal impact. Pre-shaping the current required to deliver a given stroke greatly simplifies the control system, whose output supplies the current generator. As the inductance depends on the mover position, the electronics of this generator, provided with an inductance measure circuit, works also as a displacement sensor, supplying the control system with an accurate feed-back signal. A preliminary prototype, built according to the several FEA thermo-magnetic analyses, has undergone some preliminary laboratory tests. The results of these checks, matching the design results in terms of power and force, show that the the magnetic design addresses the severe specifications.