Re: ATM Diffraction limited newt mirrors

[eedbrcu@eede.ericsson.se (Bratislav Curcic)]

> Strehl ratio is defined as how much of the theoretically possible amount
> of light from a point source is getting into the Airy disk. If a mirror
> gets 80% of the theoretical amount into the Airy disk, it's considered
> diffraction limited. A Strehl ratio of 100% means you got a perfect
> mirror.

Just a small correction. Strehl ratio is defined as the ratio of energy
at the CENTER of the Airy disc compared to the _ideal_ mirror. It is
relatively easy to "pack" all the rays into the Airy disc (you just
need to get transverse abberation smaller than 2*rho), but to get
really perfect mirror all rays must be directed to the very center
of Airy disc. And that is much, much more difficult (impossible).

Bratislav