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Proceedings Paper

Thermo-optically driven adaptive mirror
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Paper Abstract

The ideal adaptive optical mirror combines large aperture with high spatial and temporal resolution and a phase shift of at least 2π. Further, a simple low-cost solution is preferred. No adaptive system can perfectly fulfill all these requirements. We present a system that has the potential to reach this goal with the exception of high temporal resolution. But even with a moderate temporal resolution of one second such a system can find practical applications. For example as a laser resonator mirror that allows to modify the intensity distribution of the emission, or to correct slowly varying aberrations of optical systems. Two possible mechanisms can be used to change the optical path length of the adaptive mirror: thermal expansion of the mirror substrate or the thermally induced change of the refractive index (thermal dispersion) of a medium in front of the mirror. Both mechanisms have been shown to lead to promising results. In both cases heating was performed by irradiation of light in the active medium. The thermal dispersion based adaptive mirror is built with a thin layer of a liquid in front of a mirror. To allow a modification of the refractive index by irradiation with a diode laser at 808 nm, a suitable absorber is dissolved in the water. With chopped irradiation a resolution of 3.8 Hz at 30 % contrast is measured. This mirror has been used in a laser resonator to modify the output distribution of the laser. The thermal expansion based adaptive mirror is built with a thin layer of a silicon elastomer with a gold coated front side. We present a preparation method to produce thin films of Sylgard on sapphire. With an irradiated intensity of only 370 mW/cm2 surface modulations of up to 350 nm are obtained. With a test pattern a resolution of 1.6 line-pairs per millimeter at 30 % contrast is measured. The temporal resolution is better than one second.

Paper Details

Date Published: 22 February 2006
PDF: 7 pages
Proc. SPIE 6101, Laser Beam Control and Applications, 61010A (22 February 2006); doi: 10.1117/12.645065
Show Author Affiliations
Felix Reinert, Univ. of Bern (Switzerland)
Willy Lüthy, Univ. of Bern (Switzerland)

Published in SPIE Proceedings Vol. 6101:
Laser Beam Control and Applications
Steven J. Davis; Alexis V. Kudryashov; Adolf Giesen; Detlef Nickel; Michael C. Heaven; Alan H. Paxton; Vladimir S. Ilchenko; J. Thomas Schriempf, Editor(s)

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