Simultaneous ultra-high contrast imaging and determination of time-dependent, non-common path aberrations in the presence of detector noise

TL;DR

This paper presents a method for simultaneous high-contrast imaging and estimation of time-dependent non-common path aberrations using millisecond exposures, effectively mitigating detector noise and improving exoplanet detection.

Contribution

The study introduces a novel phase diversity technique capable of estimating dynamic NCPAs and scene information simultaneously at millisecond timescales, even with detector noise.

Findings

Simulations demonstrate successful estimation of NCPAs and planetary brightness.

Method effectively mitigates detector noise through exposure mixing.

Estimates include phase, amplitude, and frequency of NCPAs.

Abstract

Ground-based ultra-high contrast imaging, as required for direct imaging of exoplanets and other solar systems, is limited by difficulty of separating the planetary emission from the effects of optical aberrations that are not compensated by the adaptive optics (AO) system, so-called "non-common path aberrations" (NCPAs). Simultaneous ($\sim$ millisecond) exposures by the science camera and the AO system enable the use of "phase diversity" to estimate both the NCPAs and the scene via a processing procedure first described by the author (R. Frazin 2013, ApJ, 767, article id. 21). This method is fully compatible with more standard concepts used in long-exposure high-contrast imaging, such as angular differential imaging and spectral deconvolution. Long-exposure methods find time-dependent NCPAs, such as those caused by vibrations, particularly challenging. Here, an NCPA of the form of $\alpha \cos(k \cdot r - \omega t + \vartheta)$ is considered. It is shown that, when sampled at millisecond time-scales, the image plane data are sensitive to $\mbox{arg}(\alpha)$, $\vartheta$ and $\omega$, and, therefore such NCPAs can be simultaneously estimated with the scene. Simulations of observations with ms exposure times are reported. These simulations include substantial detector noise and a sinusoidal NCPA that places a speckle exactly at the location of a planet. Simulations show that the effects of detector noise can be mitigated by mixing exposures of various lengths, allowing estimation of the planet's brightness.