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Brief Introduction
- Phasing Discontinuity Sensing (PDS) is a method of determining wavefront
aberrations using out of focus images. Currently we are investigating the
use of such a scheme as a alternative method of phasing the 36 segments
of the 10 meter Keck telescopes.
PDS is an active alternative to the passive Gerchberg phase reconstructor. While we have a working Gerchberg simulator, it is numerically intensive and time consuming. PDS, by contrast, requires only minimal computing power. It makes a series of moderately sized moves of modest accuracy, but continually corrects these by looking at the image (out of the focal plane) which each move produces. It is active in the sense that each move is communicated to the ACS, and a new picture is generated after each move.
Recent Data
- In November of 1997 we made our first attempt at phasing the Keck 1
telescope using the PDS method. We started with a phased and stacked mirror
from PCS. We dephased the mirror by random, but known, amounts. We then
ran our PDS algorithm. Each iteration of PDS took about 7 minutes.