Figure 6
(a)The normalized Raman spectra of modified regions irradiated by fs laser single and double pulses in fused silica. The pulse delay of the double pulses is 350 fs. Dashed lines below the D2 peaks are baselines used in the peak area measurement in (b). The inset is the schematic diagram of 4- and 3-membered ring structures. (b) The percent area of the total reduced Raman spectrum under the D2 line versus different pulse delays. The total fluence is fixed at 9.46 J/cm2 and each site is irradiated by 500 shots. The measurements are conducted in a regions located 5 μm below the surface.
