Image formation process with the solar gravitational lens

TL;DR

This paper models the image formation process using the solar gravitational lens, deriving analytical expressions for the intensity distribution in the focal plane of a telescope, with applications to exoplanet imaging.

Contribution

It provides a wave-optical analysis of the SGL, extending previous models to include off-axis positions and detailed image progression.

Findings

Derived analytic expressions for on-axis and off-axis image formation.

Identified transition from Einstein ring to dual bright spots with off-axis displacement.

Reproduced familiar microlensing expressions in the weak interference regime.

Abstract

We study image formation with the solar gravitational lens (SGL). We consider a point source that is positioned at a large but finite distance from the Sun. We assume that an optical telescope is positioned in the image plane, in the focal region of the SGL. We model the telescope as a convex lens and evaluate the intensity distribution produced by the electromagnetic field that forms the image in the focal plane of the convex lens. We first investigate the case when the telescope is located on the optical axis of the SGL or in its immediate vicinity. This is the region of strong interference where the SGL forms an image of a distant source, which is our primary interest. We derive analytic expressions that describe the progression of the image from an Einstein ring corresponding to an on-axis telescope position, to the case of two bright spots when the telescope is positioned some distance away from the optical axis. At greater distances from the optical axis, in the region of weak interference and that of geometric optics, we recover expressions that are familiar from models of gravitational microlensing, but developed here using a wave-optical treatment. We discuss applications of the results for imaging and spectroscopy of exoplanets with the SGL.