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Kroening J., R.K.Tyson. Adaptive Optics Engineering Handbook (M.Dekker,1999)(ISBN 0824782755)(T)(C)(348s)_EO_.djvu |
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Size 3.9Mb Date Jan 16, 2005 |
which required a "go to'" capability in the wavefront correctors...
Hence, when the actuator is subdivided into n
layers, the applied voltage on each layer is reduced by a factor of n, but the
actuator capacitance increases by a factor of n, and the current required to charge
the actuator in a particular time increases by the same factor...
Deformable Mirror Wavefront Correctors
187
contact
electrode
Figure 17 The alternation of the electrode patterns provides the means by which the
actuators are connected electrically in parallel but operate in series mechanically to provide
high stroke at low voltage...
The dried tapes are cut to size and the electrode pattern is applied using
standard screen printing processes...
Without further data available, one may conclude that in actua-
actuators, structural simplicity and reliability go hand in hand, but at the cost of re-
reduced performance...
By far the best approach is to perform all calibration functions digi-
digitally and to keep other requirements to an absolute minimum...
) which may or may
not have significant hysteresis, depending upon the composition of the actuator
material...
In the second case the wavefront is measured
directly using a self-referencing Mach-Zehnder interferometer utilizing a suitably
bright and tilt-stabilized speckle in one leg of the interferometer (Colucci 1994)...
The least-squares matrices are the
easiest to generate and do not require any a priori information about atmospheric
statistics, beacon brightness or photon noise levels, winds, etc...
Equation Bb) is
very straightforward to compute and avoids the necessity of using, or even know-
knowing how to use, singular value decomposition methods; in Matlab Bb) is found
by using the pinv(A) command...
Here we note that Тг(Г) is not an obvious statistical generalization
of Л because C) is the reconstruction error rather than the slope discrepancy in
A)...
Finding an optimal
M for finite range beacon АО systems, where focal anisoplanatism is known to
correlate with tilt anisoplanatism, may still best be done using a generalization
of F) explicitly incorporating these two quantities...
, Р
11 ,А'Мтргрт + *2Ау, ,,АтМтр
+ k-\\\i,, 2ATMTPTpT + Ar2A\j/,, ,АтМтрт-*'АрМХ„ьМтртрт
+ А-2Х„дМтртргр2 - ^AMX,,JVITpTpTp + к:Х„ Мтртр
- *3АМХ„яМтрт + к2Х„Мт + А-2Х„1гМтртр2 - ГАрМХ^ЛГр1
- Аг'АМХ^Мт^ртр + Ar2XniMTp2 - ^АрМХ^М7 - АчАМХ„гМтР
+ ^Х,,, Мтр - ^АМХ„„МТ + *2Хя„Мгртртр
- *'АМХ„иМтртрт + АггХ
where р = я„1р - ША, у„.„- = ЗХФтт...
At a loss
of on-axis Strehl performance, such a space-invariant M arises from minimizing
the norm
Г = <||/{ф(/,-ь 6)} - ф(Л, 0)|р> A2)
for some specified 9 > 90, or more generally, 9 > 9f, where we define 9f as the
effective isoplanatic angle, which is the angle at which there is a l-rad: mean-
square error between the on-axis and the off-axis wavefront...
For more points distributed within the patch there are correspondingly more terms
in the expression to accomplish the angular averaging...
Often a quadrant or
centroiding sensor (gradient or G-tilt) is used to measure these modes and a sepa-
separate servo drives the fast steering mirror...
The various KL modes can be projected in or out of the slopes or phases
as discussed above by replacing the matrix Z by K...
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