Broadband wavefront correction algorithm for high-contrast imaging systems

Abstract

Great strides have been made in recent years toward the goal of high-contrast imaging with a sensitivity adequate to detect earth-like planets around nearby stars. It appears that the hardware -optics, coronagraph masks, deformable mirrors, illumination systems, thermal control systems -are up to the task of obtaining the required 10 −10 contrast. But in broadband light (e.g., 10% bandpass) the wavefront control algorithms have been a limiting factor. In this paper we describe a general correction methodology that works in broadband light with one or multiple deformable mirrors by conjugating the electric field in a predefined region in the image where terrestrial planets would be found. We describe the linearized approach and demonstrate its effectiveness through laboratory experiments. This paper presents results from the Jet Propulsion Laboratory High Contrast Imaging Testbed (HCIT) for both narrow-band light (2%) and broadband light (10%) correction.

Speckle suppression and companion detection using coherent differential imaging

“…A more powerful but model-dependent sensing and correction method is called "electric field conjugation," or EFC (Give'on et al 2007). The EFC algorithm uses pairs of small actuator displacements to perturb the electric field at the focal plane, in a specified control region.…”

Instantaneous phase retrieval with the vector vortex coronagraph

“…Owing to the mask imperfection, a maximum nulling of 10 −5 on the stellar peak seems to be feasible for an input Strehl ratio of 99.6%. The proposed method can handle various instrumental limitations and is sufficiently flexible to be coupled with the EFC algorithm (Give'on et al 2007) to minimize the electric field in a desired region of the focal plane.…”

“…In the classical phase diversity algorithm (Gonsalves 1982;Blanc et al 2003), the estimation of the entrance aberrations from the sole focused image does not ensure the uniqueness of the solution. Indeed, two different aberrations can produce the same PSF in the image plane.…”

“…Many coronagraphs have been proposed to suppress the starlight diffracted light, but all of them are limited by the imperfections of the entrance wavefront: residual speckle patterns are the dominant source of noise in the high-contrast imaging. Even when using high-order or extreme adaptive optics (XAO), the performance of coronagraphs is still limited by the phase and the amplitude knowledge used for the dark-hole generation, and maintenance while acquiring science data (Bordé & Traub 2006;Give'on et al 2007). We propose to measure the speckle phase and amplitude simultaneously with the science integration using the polarization properties of the vectorial vortex coronagraph (VVC), Mawet et al (2005), Mawet et al (2009).…”

SPICES a small space coronagraph to characterize giant and telluric planets in reflected light

“…The optical quality of the telescope is not drastic (typically 10 nm rms at mid frequencies on the primary). The wavefront control is achieved with the Electric Field Conjugation [6], a specific algorithm to measure the aberrations, and a deformable mirror (DM) to correct the wavefront, providing a quality/stability on the order of tens of picometers. Our goal is to implement a more promising technique, the Self Coherent Camera [5], which for now has a lower Technology Readiness Level but will allow a better discrimination of planets and speckles [2] while it requires little modification in a coronagraph.…”