Figure 1

Suppression of graphite in femtosecond laser induced modification at 500-kHz repetition rate.

(a) Transverse optical microscope image of single laser-induced track written with 500-kHz repetition rate, 50-mW average power and 0.5-mm/s scan speed. (b) μRaman spectra (532-nm excitation wavelength) at four different vertical positions inside the modification. ‘Out’ refers to a spectrum taken outside the track. The spectra have been normalized to the diamond peak to show the change in the relative intensity of the G-peak inside the structure. (c) μRaman spectra (normalized to the G-peak) in the center of modification tracks at repetition rates of 5 kHz, 25 kHz and 500 kHz, with pulse energy held constant (800 nJ) to produce a similar size modification at each repetition rate. (d) Tauc plot for diamond with tracks written over the entire sample at 50-μm depth and 20-μm line separation for 5-kHz and 500-kHz repetition rates. It is considered that the absorption in the visible region is only due to the modification tracks, with the rest of the sample being transparent.