Sean Goebel (IfA)

SAPHIRA deployment at SCExAO

In this tech talk I will present some of the highlights of the deployment 
of the SAPHIRA detector array on the SCExAO instrument at Subaru 
Telescope. SAPHIRA is a 320x256 pixel avalanche photodiode detector array 
sensitive to 0.8-2.5 μm light and is intended for photon counting (the 
signal of an individual photon is less than the read noise) and high 
(~kHz) frame rates. SCExAO is a coronagraphic extreme adaptive optics 
instrument at Subaru used for high-contrast imaging of targets such as 
exoplanets and protoplanetary disks. It utilizes a 2000-element deformable 
mirror updating at 3.5 kHz to produce near-infrared Strehl ratios 
approaching 90%. Unlike GPI and SPHERE, SCExAO is continuously in 
development and frequently undergoes changes to take advantage of the 
latest technologies and techniques. In recent observing runs, we have 1) 
used SAPHIRA to conduct studies of the fast temporal evolution of the 
speckle halos surrounding diffraction-limited PSFs, 2) used it to 
iteratively null slowly-evolving speckles caused by static aberrations and 
diffraction within the optical train, and 3) put pyramid wavefront sensor 
optics in front of SAPHIRA to test the feasibility of using it for 
pupil-plane wavefront sensing at wavelengths nearer to those of the 
science instrument. I will also discuss future efforts involving SAPHIRA 
on the SCExAO instrument, including the development of the Pizza Box 
electronics for greatly improved readout rates, efforts to use SAPHIRA for 
on-sky nulling of quickly evolving speckles, and the potential to use it 
as the primary WFS detector on future ELTs.