Efficient nonlinear generation of high power, higher order, ultrafast "perfect" vortices in green

TL;DR

This paper demonstrates an efficient method for generating high-power, higher-order ultrafast perfect vortices at green wavelengths using nonlinear optical processes, achieving record conversion efficiencies and high-quality vortex beams.

Contribution

It introduces a novel approach combining Fourier transformation and quasi-phase matching for high-order vortex generation with unprecedented efficiency.

Findings

Achieved 1.2 W green vortex power at order 12 with 27% efficiency.

Generated vortices up to order 12 with high beam quality.

Demonstrated highest single-pass SHG efficiency for non-Gaussian beams.

Abstract

We report on efficient nonlinear generation of ultrafast, higher order "perfect" vortices at the green wavelength. Based on Fourier transformation of the higher order Bessel-Gauss beam generated through the combination of spiral phase plate and axicon we have transformed the Gaussian beam of the ultrafast Yb-fiber laser at 1060 nm into perfect vortices of power 4.4 W and order up to 6. Using single-pass second harmonic generation (SHG) of such vortices in 5-mm long chirped MgO-doped, periodically poled congruent LiNbO$_3$ crystal we have generated perfect vortices at green wavelength with output power of 1.2 W and vortex order up to 12 at single-pass conversion efficiency of 27% independent of its order. This is the highest single-pass SHG efficiency of any optical beams other than Gaussian beams. Unlike the disintegration of higher order vortices in birefringent crystals, here, the use of quasi-phase matching process enables generation of high quality vortices even at higher orders. The green perfect vortices of all orders have temporal and spectral width of 507 fs and 1.9 nm, respectively corresponding to a time-bandwidth product of 1.02.