Stimulated Raman-induced Beam Focusing

TL;DR

This paper explores how stimulated Raman scattering involving Laguerre-Gauss modes can modulate beam profiles, revealing limitations in super-resolution Raman imaging compared to stimulated emission depletion fluorescence microscopy.

Contribution

It demonstrates the modulation of amplitude and phase of higher-order Laguerre-Gauss beams via stimulated Raman processes and analyzes the resulting superposition effects on beam intensity distributions.

Findings

Significant modulation of pump and Stokes beams in Laguerre-Gauss modes.

Limitations identified in super-resolution Raman imaging with toroidal beams.

Contrast with no fundamental resolution limit in stimulated emission depletion microscopy.

Abstract

Stimulated Raman scattering, employing a pump and a Stokes beam, exhibits itself through both the Raman loss observed in the pump beam and the Raman gain in the Stokes beam. This phenomenon finds application in spectroscopy for chemical analyses and microscopy for label-free bioimaging studies. Recent efforts have been made to implement super-resolution Raman microscopy using a doughnut-shaped pump, Stokes, or depletion beam. In this study, it is shown that the amplitude and phase of the pump or Stokes beam undergo significant modulation through the stimulated Raman process when they are configured as one of the higher-order Laguerre-Gauss modes, achieved using appropriate spiral phase plates or spatial light modulators. The resulting intensity distributions of the pump and Stokes beams are determined by a superposition of multiple Laguerre-Gauss modes that are coupled through nonlinear Raman gain and loss processes. Calculation results are used to elucidate the limitations associated with super-resolution coherent Raman imaging with a toroidal pump or Stokes beam. This stands in contrast with the stimulated emission depletion fluorescence microscopy technique, which lacks a fundamental limit in the spatial resolution enhancement.