Diffraction limited telescope: angular
resolution=λ/D
Strehl ratio: measure of contrast = ratio of peak
intensity to perfect optical system
Point Spread Function: image of a point source
Slide 5
Slide 5 text
Atmospheric Turbulence
Fried's coherence length r
0
is level of turbulence:
5-20 cm usually
Kolmogorov model: kinetic energy air > dissipated
as heat
Greenwood frequency: how quickly atmospheric
turbulence changes
Coherence time τ
0
= coherence length/wind
velocity ~ milliseconds
atmospheric structure constant C
n
2 is measure of
strength of turbulence
Slide 6
Slide 6 text
Phase Conjugation of Light
amplitude A, phase Φ
light wave: Ae(-iΦ)
cancel with: Ae(+iΦ)
e(+iΦ -iΦ) = e(0) = 1
think of it like noise cancelling headphones,
but with light instead of sound!
The Math for Closed Loop Control
Φ
k+1
= Φ
k
+ Bu
k
+ d
k
y
k
= Φ
k
+ v
k
and u
k
= -Ry
k
Φ: wavefront aberrations vector
B: mirror's influence matrix
u: actuator commands vector
d: wavefront turbulence vector
v: measurement noise vector
WANT reconstructor R = B-1
Inverse for non-square matrix calculated using
least-squares by SVD or Moore-Penrose