**Devices and Techniques**

[25] Keller, C. U., Plymate, C., & Ammons, S. M. (2003). Low-cost solar adaptive optics in

the infrared. *Proc. SPIE*, 4853, 351-359.

40 Adaptive Optics Progress

**Chapter 3**

**Devices and Techniques for Sensorless Adaptive Optics**

Minimizing the aberrations is the basic concern of all the optical system designers. For this purpose, a large amount of work has been carried out and plenty of literature can be found on the subject. Until the last twenty years, the large majority of the optical design was relat‐ ed to "static" optical systems, where several opto-mechanical parameters, such as refractive index, shape, curvatures, etc. are slowly time dependent. In these systems, simple mecha‐ nisms can be adopted to change the relative position of one or more optical elements (for example, the secondary mirror of many astronomical telescopes), or slightly modify their shape and curvature (as in some synchrotron beamlines, where some optical surfaces are mechanically bent) to compensate defocusing. In the last years, a new type of optical sys‐ tems, that we may call "dynamical", have heavily occupied the interest of optical designers, opening the possibility of working also in situations where the system environment varies rather quickly with time, either in a controlled or not-controlled way. For this class of optical systems adaptive optics (AO) with a closed loop control system has to be implemented. The correction of dynamical systems was predicted by Babcock in the 1953 [1] and, then, the first prototypes were realized in the early 70s with the purpose of satellite surveillance and launching high power laser beams trough the atmosphere [2]. The most known scientific ap‐ plications of closed loop correction by means of AO is the acquisition of astronomical im‐ ages in ground-based telescopes [3] and *in-vivo* imaging of cone photoreceptor mosaic by AO enhanced Fundus Cameras [4]. In astronomy, to remove the so called "seeing effect", the star light twinkling due to local dynamic variations of the atmospheric density in the air column above the telescope, it is necessary to have the real time knowledge of the wavefront of the observed object. This can be realized, for instance, by means of a Shack-Hartmann wavefront sensing device coupled to a dedicated fast algorithm which returns the mathe‐ matical description of the wavefront aberration, typically through a Zernike series decompo‐

> © 2013 Bonora et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

© 2013 Bonora et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

distribution, and reproduction in any medium, provided the original work is properly cited.

S. Bonora, R.J. Zawadzki, G. Naletto,

Additional information is available at the end of the chapter

U. Bortolozzo and S. Residori

http://dx.doi.org/10.5772/53550

**1. Introduction**
