Hollow Gaussian beam generation through nonlinear interaction of photons with orbital angular momentum.

N Apurv Chaitanya,G K Samanta,J Banerji,M V Jabir

doi:10.1038/srep32464

Abstract

Hollow Gaussian beams (HGB) are a special class of doughnut shaped beams that do not carry orbital angular momentum (OAM). Such beams have a wide range of applications in many fields including atomic optics, bio-photonics, atmospheric science, and plasma physics. Till date, these beams have been generated using linear optical elements. Here, we show a new way of generating HGBs by three-wave mixing in a nonlinear crystal. Based on nonlinear interaction of photons having OAM and conservation of OAM in nonlinear processes, we experimentally generated ultrafast HGBs of order as high as 6 and power >180 mW at 355 nm. This generic concept can be extended to any wavelength, timescales (continuous-wave and ultrafast) and any orders. We show that the removal of azimuthal phase of vortices does not produce Gaussian beam. We also propose a new and only method to characterize the order of the HGBs.

Highlights

For theoretical understanding of nonlinear generation of HGBs we consider sum frequency generation (SFG) of two pump vortex beams with transverse electric field amplitude given as[1]
As a proof of principle, here we report, for the first time to the best of our knowledge, nonlinear generation of HGBs
From the coupled wave equations of SFG process[23] under perfect-matching, the transverse electric field amplitude of the generated field can be represented in the form, E3(ρ, φ)

Summary

Introduction

Given that the nonlinear frequency conversion processes[23,24,25] satisfy OAM conservation[26,27], one can in principle, remove the azimuthal phase term of the generated beam through annihilation of OAM modes of the interacting beams in three wave-mixing process. When the pump beams have same OAM orders but opposite helicity (l1 = −l2 = l, as schematically shown in Fig. 1a), the field amplitude of the generated beam (Eq 2) will have the form of a HGB5, E

Results

Conclusion