Local Formation of Birefringent Structures in Alkali-Silicate Glass by Femtosecond Laser Beam

It is demonstrated that a femtosecond laser beam forms in alkali-silicon glass with different Na2O concentration microregions that possess birefringence associated with the formation of nanolattices. The phase shift of such regions is determined as a function of the number and energy of the laser pulses. The minimum number of pulses required for birefringence to appear increases with increasing Na2O concentration. At 107 pulses the phase shift reaches approximately the same maximum value for all glass compositions, which indicates that the diffusion of alkali ions in the process of formation of nanolattices plays a leading role in such glasses.