Study of a spatio-temporal sensor for turbulence characterisation and wavefront sensing (Conference Presentation)

Abstract

We introduce the use of an event based image sensor as a versatile device for characterisation of turbulence and for wavefront Sensing at unusually high rates. This type of sensor presents the changes in the intensity field with time that integrate to a threshold level before output, rather than the traditional integrate for a specified time period. As a result a time sequence of activity tagged to spatial location and time is provided. This information can be signal processed in novel ways to ascertain high speed imagery, or more importantly directly provide fundamental descriptors of the turbulence field related to phase structure function, and possibly determining the power spectrum parameters of Cn2 , Fried’s coherence length r0 , anisoplanatic angle and the changes in these over ensemble average timescales. The likes of the lenslet array used in Shack-Hartmann sensors can present the optical field to the sensor upon which it may provide location of the centroid by occurrence of light accumulating to a threshold, or highest temporal rate of occurrences in the region of interest behind the lenslet. In this way the Shack-Hartmann sensors it is not limited to one star per lenslet, and can respond to stationarity changes, and can facilitate investigations of chaos in the timeseries of aberrations. We explore these thoughts upon data collected on-sky from both streaming Shack-Hartmann sensor and the direct light field incident onto the sensor, and the sensor behind a lenslet array. In fact we present on-sky data from two event based sensors (ATIS and Davis 240c), alongside the traditional integration video camera. Data is acquired both with and without an image intensifier.