Direct femtosecond laser writing of birefringent microtracks in bulk fused silica

The characteristics of birefringent microtracks inscribed by ultrashort laser pulses with varied parameters in the volume of fused silica have been studied. In particular, the formation of birefringent microtracks with a phase shift of up to 150$^\circ$ degrees is observed, and the direction of the slow axis coincides with the direction of the linear polarization vector of the inducing laser radiation. The physical mechanisms of modification of fused silica using Raman scattering have been revealed. Using a spectrophotometer microscope, transmission and reflection spectra of birefringent regions consisting of microtracks were obtained.