Reconstructing Adaptive Optics Corrected Solar Images Using Phase-Diverse Speckle Imaging

1. Reconstructing Adaptive Optics Corrected Solar Images Using Phase-Diverse Speckle Imaging Christoph U. KellerNational Solar Observatory

2. Overview • Why high-resolution solar observations? • Differences to night-time astronomy • Low-order adaptive optics at 76-cm Dunn Solar Telescope (DST) • Phase-Diverse Speckle (PDS) • Speckle deconvolution applied to polarimetry • Outlook and Conclusions • Thanks to Thomas Rimmele for the adaptive optics at the DST • Thanks to Rick Paxman, John Seldin, and Dave Carrara for Phase-Diverse Speckle NOAO AO Data Analysis Workshop

3. Small-scale Structures on the Sun 1 Convective phenomena occur at scales down to 0.1 arcsec • shocks • vortices • interaction with magnetic flux • generation of global 5-minute oscillations Diffraction-limited white-light image of solar granulation and small-scale magnetic fields at 600 nm using adaptive optics at the Dunn Solar Telescope and phase-diverse speckle imaging arcsec NOAO AO Data Analysis Workshop

4. Small-scale Structures on the Sun 2 Speckle polarimetry revealed highly concentrated magnetic flux at the spatial limit of current solar telescopes: magnetic flux tubes • building blocks of network and active regions • most likely channels for transporting energy to upper atmosphere • affect convection, irradiance, oscillations, solar cycle NOAO AO Data Analysis Workshop

5. Small-scale Structures on the Sun 3 Sunspots • magneto-convection in umbral dots and penumbral filaments • combed penumbral fields, Evershed effect • relevance to other stars with huge spots NOAO AO Data Analysis Workshop

6. Transient eruptions: flares and coronal mass ejections Origin of solar variability Heating of chromosphere and corona, origin of solar wind Surface and atmosphere structure and dynamics Exploring the unknown High Spatial Resolution High Photon Flux Thermal Infrared Astrophysical Processes on the Sun • Important astrophysical scales (pressure scale height in photosphere, photon mean free path in photosphere) are on the order of 0.1 arcsec • Ohmic diffusion scale length for magnetic field diffusion is on the order of 0.001 arcsec NOAO AO Data Analysis Workshop

7. Differences to Night-time Astronomy • Extended source that is typically much larger than detector • No point sources • Low contrast source, rms intensity of a few percent • Fast temporal evolution, visible changes within 10 s at 0.1 arcsec resolution • Worse seeing (r0=10 cm is excellent seeing) • Small isoplanatic patch size (a few arcsec at most) • Resolution is so important that visible is used to reduce diffraction • Still relatively limited telescope apertures (<1.6 m) • Science requires spectroscopy and often polarimetry NOAO AO Data Analysis Workshop

8. Low-order Adaptive Optics at DST (Rimmele) NOAO AO Data Analysis Workshop

9. Correlating Shack-Hartmann Wavefront Sensor NOAO AO Data Analysis Workshop

10. Low-order Adaptive Optics NOAO AO Data Analysis Workshop

11. Low-order AO Properties • 76-cm telescope aperture • median seeing: 7 cm at 600 nm • 24 subaperture Shack-Hartmann • 80 by 80 PixelVision camera • 1600 Hz frame/update rate • 97-element Xinetics mirror With AO Without AO NOAO AO Data Analysis Workshop

12. Phase-Diverse Speckle Imaging (Paxman et al.) NOAO AO Data Analysis Workshop

13. PDS Processing NOAO AO Data Analysis Workshop

14. Small Field PDS Reconstruction Reconstruction with guard band 2 of 5 image pairs used (without AO) NOAO AO Data Analysis Workshop

15. PDS Large Field Reconstruction Reconstruction 3 of 10 image pairs with AO NOAO AO Data Analysis Workshop

16. Wavefront Estimates • Reconstruction occurs on small segments • Segment size comparable to isoplanatic patch • Wavefront is estimated for each segment • Object estimates of segment are combined into a single image NOAO AO Data Analysis Workshop

17. Adaptive Optics and Phase Diversity • AO at DST • Phase Diverse Speckle • 10-nm spectral bandpass • One camera in focus, one out of focus • Zurich IMaging POLarimeter I • Piezo-Elastic Modulator at 42 kHz • Synchronous demodulation with specially masked CCDs • Works with adaptive optics and image reconstruction techniques • 3 frames per second per camera • 20 ms exposure time • Universal Birefringent Filter • CaI 6103 Å • Bandwidth 180 mÅ from 76-cm DST AO polarization modulation UBF in-focus CCD camera narrow-band CCD camera out-of-focus CCD camera NOAO AO Data Analysis Workshop

18. Optical Setup and Raw Data white light line wing intensity magnetogram NOAO AO Data Analysis Workshop

19. Speckle Deconvolution • Formation of broad-band and narrow-band images through turbulent atmosphere in Fourier space:I is Fourier transform of observed imageO is true objectS is optical transfer function • * indicates conjugate complex<…> indicate ensemble average • SNR in narrow-band reconstruction is proportional to geometric mean of SNR in broad-band and narrow-band channels (gain of about 10)! NOAO AO Data Analysis Workshop

20. Data Reduction Techniques • Phase Diverse Speckle: • select 20 best frames • use 20 white-light in and out-of-focus images to determine object and (remaining) wavefront aberrations • Speckle Deconvolution: • use 100 in-focus white light images and PDS reconstruction to determine 100 spatially varying point spread functions • deconvolve 100 simultaneous Stokes I and V images in small (isoplanatic) segments • magnetogram = Stokes V/I • Movies: • destretching • subsonic filtering < 5km/s out of focus in focus narrow-band Phase Diversity Speckle Deconvolution white light Stokes I Stokes V/I NOAO AO Data Analysis Workshop

21. Results • plage close to disk center • most flux is clumped in large, stationary areas with little overall motion • some flux is in small, highly dynamic elements NOAO AO Data Analysis Workshop

22. Diffraction-Limited Polarimetry • some magnetic elements have apparent sizes at the diffraction limit • distance between the two elements is 0.3 arcsec • diffraction-limit of telescope at this wavelength is 0.16 arcsec NOAO AO Data Analysis Workshop

23. Outlook • High-order AO systems • Long-slit spectroscopy • Advanced Technology Solar Telescope (ATST) NOAO AO Data Analysis Workshop

24. Adaptive Optics at 1.6 m McMath-Pierce • measure wavefront errors with Shack-Hartmann at about 1m • correct wavefront adequately from 2 to 5 m • wavefront measurements tested with up to 306 subapertures NOAO AO Data Analysis Workshop

25. Adaptive Optics at 1.6 m McMath-Pierce • deconvolution from wavefront sensing provides AO-like results • 106 subapertures over 1m aperture at 950 nm at McMath-Pierce telescope NOAO AO Data Analysis Workshop

26. Deconvolution of Long-Slit Spectroscopy • Deconvolution in 3-dimensional x, y, λ space • Each wavelength was reconstructed separately • Velocity amplitudes are amplified as expected for higher spatial resolution raw reconstructed NOAO AO Data Analysis Workshop

27. Advanced Technology Solar Telescope NOAO AO Data Analysis Workshop

28. Conclusions • Low-order adaptive optics works well on the sun in the visible part of the spectrum • Phase-Diverse Speckle (PDS) imaging works well to correct remaining aberrations in AO-corrected images • PDS extends diffraction-limited performance over much larger field of view than even high-order AO could provide • Speckle Deconvolution provides significant SNR gains for narrow-band and polarimetric observations • Tools are ready to make use of high resolution to be provided by 4-m ATST NOAO AO Data Analysis Workshop

29. Isoplanatic Patch Size NOAO AO Data Analysis Workshop