Femtosecond laser three-dimensional isotropic inscription in glass enabled by high-speed rotating slit beam shaping

We demonstrate a high-speed rotating slit beam shaping method for femtosecond (fs) laser three-dimensional (3D) isotropic inscription in glass materials. By integrating fs laser direct writing with a real-time rotating slit mechanism, a 3D symmetric spherical focal field distribution is created in the laser-irradiated regions of transparent substrates. The corresponding focal field distribution is theoretically calculated and validated by examining the features of laser-inscribed lines in glass samples. Moreover, we investigate the influences of laser writing speed and slit rotational speed on the fabrication resolution in glass, and discuss the formation mechanism of the generated periodic microstructures. To showcase its powerful capability for 3D isotropic fabrication, the high-speed rotating slit beam shaping method is applied to create straight optical waveguides, bending optical waveguides, and hollow microchannels in the glass. The proposed method holds great potential for the facile manufacture of diverse 3D isotropic microstructures and devices within transparent materials across various applications, including advanced photonics, microoptics, micro-electromechanical systems, and microfluidics.