Relationships governing the cumulative effect in optical damage and its mechanism in the absence of subthreshold ionisation of a glass matrix

An investigation was made of the relationships governing the cumulative effect of optical damage to silicate glasses in the absence of subthreshold ionisation of the matrix. It was shown that in this case the damage threshold reduction in multiple irradiation of glasses is related to a reduction in the self-focusing threshold because of a change in the refractive index in the interaction region. This process occurs because of densification of the glass structure by a strong electrostriction pressure, which takes place without electronic excitation and is observed only when this pressure exceeds the striction pressure for the densification of glass.