Generation of femtosecond radial-mode vortex pulses from a solid-state oscillator

Laguerre-Gaussian (LG) vortex beams with non-zero radial indices provide an additional spatial degree of freedom beyond conventional azimuthal-order vortices, yet their generation in the femtosecond regime has remained experimentally challenging. Here, we report the direct generation of femtosecond radial-mode LG vortex pulses enabled by a mode-locked solid-state oscillator. Higher-order Hermite-Gaussian (HG) pulses are stably excited inside a SESAM-based Yb:KGW oscillator through controlled off-axis pumping and subsequently converted into LG p,l vortex pulses via astigmatic mode transformation. This scheme allows precise and reproducible control over both the radial and azimuthal orders of the generated pulses. The resulting vortex pulses feature multi-ring transverse profiles and pulse durations below 400 fs. Our approach provides a compact and robust platform for producing femtosecond structured light with multiple degrees of freedom, opening avenues for ultrafast optical manipulation, three-dimensional microfabrication and high-dimensional photonics.