Apurv Chaitanya, N.N.Apurv ChaitanyaJabir, M. V.M. V.JabirBanerji, JagannathJagannathBanerjiSamanta, Goutam KumarGoutam KumarSamanta2025-08-222025-08-222016-06-012331-8422http://arxiv.org/abs/1606.09005https://d8.irins.org/handle/IITG2025/18181Hollow 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.en-USe-Printe-Print123456789/615