Tighter spots of light with superposed orbital angular momentum beams

TL;DR

This paper demonstrates that superpositions of beams with opposite orbital angular momentum can achieve focal spot sizes smaller than traditional Gaussian beams, enhancing optical resolution.

Contribution

It introduces a comprehensive analysis of the smallest achievable focal features using superposed orbital angular momentum beams, including both scalar and vectorial models.

Findings

Lateral feature sizes smaller than Gaussian focus achieved

Both simulations and experiments confirm the smaller focal spots

Potential applications in nano-optics and high-resolution imaging

Abstract

The possibility of focusing light to an ever tighter spot has important implications for many applications and fields of optics research, such as nano-optics and plasmonics, laser-scanning microscopy, optical data storage and many more. The size of lateral features of the field at the focus depends on several parameters, including the numerical aperture of the focusing system, but also the wavelength and polarization, phase and intensity distribution of the input beam. Here, we study the smallest achievable focal feature sizes of coherent superpositions of two co-propagating beams carrying opposite orbital angular momentum. We investigate the feature sizes for this class of beams not only in the scalar limit, but also use a fully vectorial treatment to discuss the case of tight focusing. Both our numerical simulations and our experimental results confirm that lateral feature sizes considerably smaller than those of a tightly focused Gaussian light beam can be observed. These findings may pave the way for improving the resolution of imaging systems or may find applications in nano-optics experiments.