Volumetric modifications in fused silica using Gaussian and Bessel femtosecond laser beams

In this work we present the results on volumetric fused silica modifications using femtosecond Gaussian and Gaussian-Bessel laser beams. We show that for specific photonic device, like volume Bragg grating, fabrication, Bessel beams are more superior to Gaussian, as the recording process is much faster and fabricated devices have better efficiencies. Also Gaussian beam tend to be more efficient in formation of nanogratings that causes the appearance of birefringence in modified zones. This reduces optical quality of fabricated device and limits overall recording velocity. We have successfully fabricated volume Bragg gratings in the bulk of fused silica that had absolute diffraction efficiencies reaching ~90% using femtosecond Gaussian-Bessel beam, while gratings made with Gaussian beam reached only 60%.