A three-dimensional model of the field in the vicinity of a spherical inclusion in fused silica illuminated by a laser beam is established based on Mie scattering theory, and intensity distributions of the scattered field modulated by the inclusion are studied. The effects of refractive index and the radius of inclusion on light intensity enhancement factor (LIEF) and the position of the maximum intensity are analyzed. The results show that modulation effect of inclusion can be considered ineffective when inclusion radius is below 40 nm. When the radius is above 40 nm, inclusions (voids, Al, Fe, ZrO2) act as positive or negative lenses for the incident laser. Maximum light intensity is two orders of magnitude larger than the incident wave intensity in some parts distance away from inclusion. For a non-dissipative inclusion, maximum LIEF increases with the increasing difference between refractive index of inclusion and fused silicon. With the increasing of refractive index, the point of the maximum intensity moves from the backward to the forward of the inclusion. For a dissipative inclusion, with the increasing of the imaginary part of the refractive index, real part of the refractive index has less effect on LIEF. LIEF increases with increasing radius, and the points of maximum intensity move from the forward to the backward of the inclusion.