# Focusing light with a deep parabolic mirror

## TL;DR

This paper investigates how a deep parabolic mirror can focus light to a near-ideal point, comparing its performance with conventional methods and analyzing the effects of aberrations.

## Contribution

It introduces a detailed calculation of electric energy density in the focus of a parabolic mirror and compares it with traditional high-NA illumination techniques.

## Key findings

- Deep parabolic mirrors can achieve near-ideal focusing conditions.
- Comparison shows advantages over conventional nearly 4pi illumination.
- Aberrations due to misalignment significantly affect focus quality.

## Abstract

The smallest possible focus is achieved when the focused wave front is the time reversed copy of the light wave packet emitted from a point in space (S. Quabis et al., Opt. Commun. 179 (2000) 1-7). The best physical implementation of such a pointlike sub-wavelength emitter is a single atom performing an electric dipole transition. In a former paper (N. Lindlein et al., Laser Phys. 17 (2007) 927-934) we showed how such a dipole-like radiant intensity distribution can be produced with the help of a deep parabolic mirror and appropriate shaping of the intensity of the radially polarized incident plane wave. Such a dipole wave only mimics the far field of a linear dipole and not the near field components. Therefore, in this paper, the electric energy density in the focus of a parabolic mirror is calculated using the Debye integral method. Additionally, a comparison with "conventional nearly 4pi" illumination using two high numerical aperture objectives is performed. The influence of aberrations due to a misalignment of the incident plane wave is discussed.

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Source: https://tomesphere.com/paper/1905.05997