phase retrieval in the focal plane
DESCRIPTION
Phase retrieval in the focal plane. Wolfgang Gaessler, Diethard Peter Clemens Storz MPIA, Heidelberg, Germany. Preface: Parallel sub-window read. Long exposure. Fast sub-windows in parallel. t win. t science. What the MPIA-Readout Electronic can do. MPIA-ROE3 - PowerPoint PPT PresentationTRANSCRIPT
Phase retrieval in the Phase retrieval in the focal planefocal plane
Wolfgang Gaessler, Diethard Peter Clemens Storz
MPIA, Heidelberg, Germany
June 22-26, 2009 AO4ELT: ‘Phase retrieval in the focal plane’ 2
Preface: Parallel sub-window readLong exposure Fast sub-windows
in parallel
tscience
twin
June 22-26, 2009 AO4ELT: ‘Phase retrieval in the focal plane’ 3
What the MPIA-Readout Electronic can do
o MPIA-ROE3 o 1 (3) Sub-windows
at science RON (5e-)- 25x25 Pixel- 135 Hz (50 Hz) - Up to 600Hz for one
sub-window with 3 times science RON
o Even with the old HAWAII 2 chips
o Currently, limited by some undersized Flash RAM
June 22-26, 2009 AO4ELT: ‘Phase retrieval in the focal plane’ 4
sCMOSo [email protected] Development on
back-illuminated
June 22-26, 2009 AO4ELT: ‘Phase retrieval in the focal plane’ 5
Focal plane AO
I = |Uf|2
—No unique solution—Non linear—Computation
intensive
Simple setup No additional parts As close as
possible to the science image
Bucci, et al. 1997
Methods using one image plane for phase retrieval.Methods using one image plane for phase retrieval.
June 22-26, 2009 AO4ELT: ‘Phase retrieval in the focal plane’ 6
Questions
o Could it increase sensitivity?o What’s already done?o Is the computation power the limit?o How could an implementation look
like?
June 22-26, 2009 AO4ELT: ‘Phase retrieval in the focal plane’ 7
Increased Sensitivity?
o Number of Photons ~ D2
o Number of Sub-Apertures ~ D2
o No gain for AO with larger diameter
o Doesn’t this change in focal plane? o Yes, but needs proper sampling.
Pixseeing/Pixdiff ~ D2
Solution: Dynamic binning
June 22-26, 2009 AO4ELT: ‘Phase retrieval in the focal plane’ 8
Dynamic binning
SNRbin,soft ~ D SNRbin,hard ~ D2
June 22-26, 2009 AO4ELT: ‘Phase retrieval in the focal plane’ 9
Solving I = |Uf|2
o Image sharpening algorithmo Intensity metrics maximizing
oMuller et. al. 1974 theoryoBuffington et. al. 1977
implementation in telescopeoRecently: Murray et. al. 2007, Both
et. al. 2005
o Iterative Fourier TransformoGerchberg Saxton
June 22-26, 2009 AO4ELT: ‘Phase retrieval in the focal plane’ 10
Image sharpening metrics
o Optimization metrics– S=∫In(x,y)dxdy n=2,3,4
maximize– S =∫ln(I(x,y))dxdy
maximize– Lukosz-Zernike metric minimize
•ρ = spot radius•NA = aperture•λ = wavelength•b = Lukosz-Zernike coefficient
June 22-26, 2009 AO4ELT: ‘Phase retrieval in the focal plane’ 11
Image sharpening algorithms
o Change shape of DM to minimize
o ADN -> N+1 iterations (Murray et. al.2007)o AD = actuator dynamic ~ >255, N = # actuator ~
>1000
o Time consuming for high order correction
DM
June 22-26, 2009 AO4ELT: ‘Phase retrieval in the focal plane’ 12
Gerchberg Saxon– Approximate amplitude constant in pupil – Inverse Fourier transform– Compare to PSF
– Fourier transform
June 22-26, 2009 AO4ELT: ‘Phase retrieval in the focal plane’ 13
Implementation by Bucci et. al. 1997
o Penalty algorithmo Representation in Zernikeo Minimizes the Intensity with a
gradient operatoro Stable and usual trapping problem
less relevant
o O(Nmode ln(Nmode) x Npix)
o Converge after some 100 iterationso For low order sensing feasable
June 22-26, 2009 AO4ELT: ‘Phase retrieval in the focal plane’ 14
Low order sensorNon common path error tracker
o Low order sensor (TT, focus, etc.)
o Time varying flexure and distortion
o Slow offload of non common path
WFC
WFS
DM
Telescope
Guide Star
WFC
WFS
DM
Telescope
Guide Star
Science Focal Plane
June 22-26, 2009 AO4ELT: ‘Phase retrieval in the focal plane’ 15
Conclusiono Phase retrieval in the focal plane is a
long known problem worked on with several solutions:– Image sharpening– Iterative Inverse Fourier transformation
o All are quite time consuming in computation
o Dynamic binning could gain some sensitivity and computation power
o Low order sensoro But also high order, shown by O. Guyon
June 22-26, 2009 AO4ELT: ‘Phase retrieval in the focal plane’ 16
What else…spectroscopy
– Slit viewer image (put all light into the slit) – Phase retrieval on the PSF of spectral lines
– Does this problem even compare to a
diffraction grating sensor?
June 22-26, 2009 AO4ELT: ‘Phase retrieval in the focal plane’ 17