Measurements of Speckle Lifetimes in Near-infrared Extreme Adaptive Optics Images for Optimizing Focal Plane Wavefront Control
AuthorGoebel, Sean B.
Hall, Donald N. B.
AffiliationUniv Arizona, Steward Observ
Univ Arizona, Coll Opt Sci
instrumentation: adaptive optics
instrumentation: high angular resolution
techniques: high angular resolution
MetadataShow full item record
PublisherIOP PUBLISHING LTD
CitationSean B. Goebel et al 2018 PASP 130 104502
Rights© 2018. The Astronomical Society of the Pacific. All rights reserved.
Collection InformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at firstname.lastname@example.org.
AbstractAlthough extreme adaptive optics (ExAO) systems can greatly reduce the effects of atmospheric turbulence and deliver diffraction-limited images, our ability to observe faint objects such as extrasolar planets or debris disks at small angular separations is greatly limited by the presence of a speckle halo caused by imperfect wavefront corrections. These speckles change with a variety of timescales, from milliseconds to many hours, and various techniques have been developed to mitigate them during observations and during data reduction. Detection limits improve with increased speckle reduction, so an understanding of how speckles evolve (particularly at near-infrared wavelengths, which is where most adaptive optics science instruments operate) is of distinct interest. We used a SAPHIRA detector behind Subaru Telescope's SCExAO instrument to collect H-band images of the ExAO-corrected point-spread function (PSF) at a frame rate of 1.68 kHz. We analyzed these images using two techniques to measure the timescales over which the speckles evolved. In the first technique, we analyzed the images in a manner applicable to predicting performance of real-time speckle-nulling loops. We repeated this analysis using data from several nights to account for varying weather and AO conditions. In our second analysis, which follows the techniques employed by Milli et al. (2016) but using data with three orders of magnitude better temporal resolution, we identified a new regime of speckle behavior that occurs at timescales of milliseconds. It is not purely an instrument effect and likely is an atmospheric timescale filtered by the ExAO response. We also observed an exponential decay in the Pearson's correlation coefficients (which we employed to quantify the change in speckles) on timescales of seconds and a linear decay on timescales of minutes, which is in agreement with the behavior observed by Milli et al. For both of our analyses, we also collected similar data sets using SCExAO's internal light source to separate atmospheric effects from instrumental effects.
Note12 month embargo; published online: 4 September 2018
VersionFinal accepted manuscript
SponsorsNSF [AST 1106391]; NASA Roses APRA award [NNX 13AC14G]; JSPS [23340051, 26220704, 23103002]; Astrobiology Center (ABC) of the National Institutes of Natural Sciences, Japan; Subaru Telescope; ERC [CoG 683029]