Complex far fields and optical singularities due to propagation beyond tight focusing: combined effects of wavefront curvature and aperture diffraction

TL;DR

This paper investigates the complex far-field optical phenomena caused by wavefront curvature and aperture diffraction after tight focusing, combining simulations and experiments to analyze their effects and potential mitigation strategies.

Contribution

It provides a detailed analysis of how wavefront curvature and aperture diffraction influence far-field optical singularities, offering new insights and experimental approaches.

Findings

Complex intensity profiles and optical singularities observed

Deviations are significant optical phenomena of fundamental interest

Strategies to minimize deviations are proposed

Abstract

All optical systems, which involve the collimation of a reflected, transmitted or scattered wave subsequent to tight focusing, are subject to two kinds of deviations. One is the wavefront curvature due to inaccurate focal placement of the interface or scatterer particle under consideration, and the other is the diffraction caused by the finite lens aperture. In the present paper we explore these phenomena in detail by considering a rigorous simulated model and an appropriate experimental setup. We hence demonstrate the complicated intensity profiles and optical singularity characteristics of the observed far field. Then we describe ways to minimize these deviations in a general experiment. But more importantly, our analysis proves that these deviations by themselves are significant optical phenomena of fundamental interest. The observed complex field profiles have similarities to standard diffraction-limited tight focal fields, though our field detection is different from the standard schemes. This indicates the relevance of these complex fields to a larger class of systems involving wavefront curvature and aperture diffraction. The detailed analysis and results of the present paper already serve as core explorations of these optical phenomena; and we also suggest future research directions where these system aspects can be purposefully created and explored further.