Simulation of microscale densification during femtosecond laser processing of dielectric materials

It has been demonstrated that femtosecond laser pulses can be used to process dielectric materials such as optical glass. One of the applications of this process is to produce sub-diffraction-limit structures whose index of refraction is different from that of the host medium. Due to the small size of these 'bits', it has been proposed to use this technique for high-density optical data storage. This paper is concerned with the mechanisms of the change of the index of refraction in such a small domain. We propose that the laser-induced strain field is responsible for the localized change of the index of refraction. It is demonstrated that the compressive strain field could be smaller than the area where the laser energy is absorbed in the glass.