“…Alternatively, electrons can be trapped in the UV or valence bands, modifying electronic properties of the material, and consequently changing its refractive index. These processes and similar ones happen in glasses (Courrol et al, 2008), crystals (Martynovich et al, 2008;Orlando et al, 2010), and polymers , and when these defects are created with spatial control inside the material, structures such as waveguides (Nolte et al, 2003), diffraction gratings (Hirao & Miura, 1998) and photonic devices (Florea & Winick, 2003;Minoshima et al, 2001) can be manufactured by the ultrashort pulses. Once again, all these processes benefit from the minimized heat generation that preserves the material properties in the surroundings of the created structures.…”