Zero Focal Shift in High Numerical Aperture Focusing of a Gaussian Laser Beam through Multiple Dielectric Interfaces

TL;DR

This paper investigates how the focal shift of a Gaussian laser beam focused through multiple dielectric interfaces can be controlled or eliminated by adjusting refractive index mismatches, enabling precise focus positioning.

Contribution

It demonstrates that focal shift can be nullified across various depths by selecting suitable refractive indices, providing a method to eliminate focal shift in high NA focusing systems.

Findings

Focal shift varies with refractive index mismatch.

Focal shift can be positive or negative.

Focal shift can be eliminated by choosing appropriate media.

Abstract

In this paper, focal shift of a Guassian laser beam tightly focused through several planar dielectric interfaces is discussed. It is shown that the focal shift and focus point can be changed by variation of refractive index mismatch and this shift could be positive or negative, and it is proportional to refractive index mismatch between coverglass and immersion medium. It is shown also that for every immersion medium(coverglass), focal shift could be removed for a continuous range of depths by choosing a coverglass (immersion medium) with appropriate refractive index.