By focusing femtosecond laser pulses in the bulk of a quartz wafer, sub-surface waveguides were microexploded. The material around the femtosecond laser induced microexplosive zone was densified, which altered local refractive index. Changes in material density can take corresponding variations in nanomechanical properties, which were proved by the depth dependent modulus and hardness variations tested by nanoindentation in the area around the microexplosive zone. Changes in refractive index were correlated with residual strains along radial direction of the waveguide cross section. An equation of residual strain in such area that based on nanoindentation data was set up, so as to discover density and refractive index variations in the adjacent areas of femtosecond laser microexplosive zone indirectly.