What is active optics? (1 Viewer)

[ro_2006]

Through the process of doing a syllabus based summary, i have come across the point
"outline methods by which the resolution and/or the sensitivity of ground-based systems can be improved, including:
-adaptive optics
-interferometry
-active optics"

i have been able to answer about the first 2 sub points, but i cant seem to be able to find information on the third in either of my texts (excel physics and "physics in context - the forces of life")

 

[passion89]

The simplest way to improve the sensitivity and resolution of a ground-based telescope would be to increase the size of the primary mirror. However, as the size of the mirror increases, it is much more inclined to be indistinct and distorted.

Active optics use a slow feedback system to correct deformities and defects in the primary mirror of a reflector telescope.

Active optics uses primary mirrors with extremely small thickness (compared to the diameter of the mirror). These thin mirrors are fitted with actuators that can push or pull the mirror into its correct shape.

When the light leaves the primary mirror, it is slowly sampled by a 'wavefront sensor' (a type of interferometer) which detects how the light has been changed or deformed by the mirror. This process is very slow and eliminates the effect of atmospheric turbulence. A computer then calculates the adjustments needed to be made to the mirror, and the actuators are moved as required.