Embedded nanogratings in germanium dioxide glass induced by femtosecond laser direct writing

From random inhomogeneities to periodic nanostructures induced in bulk silica by ultrashort laser

“…8(b)]. In addition, by varying energy from 0.2 to 1 μJ, no changes in nanogratings period are observed, as experimentally reported in [2,11,91,104]. However, beyond the energy of 1 μJ, high densities above the critical value are created in the center of tightly focused region, erasing the nanogratings at their initial state.…”

“…A good agreement between the periods obtained numerically and experimentally [2][3][4][5] is achieved. It is worth noting that the proposed mechanism of nanograting self-organization also explains possible coexistence of several characteristic periods [11,105] as well as the nanostructures separated by subwavelength periods shorter (around λ/3n) [1,8,18,27,59] at higher number of pulses and larger (around λ/n) [9,10,106,107] than λ/2n. According to numerical calculations, a uniform concentration profile of inhomogeneities is the most probable in the experiments, probably because of the strong arrangement (1)- (5) taken at the end of the pulse duration θ = 240 fs (FWHM) and laser wavelength of 800 nm with laser beam energy: (a) E = 50 nJ (smooth modification), (b) E = 500 nJ (birefringent modification), and (c) E = 2 μJ (disrupted modification).…”

“…A multiple irradiation of bulk fused silica by ultrashort laser pulses is known to induce volume nanogratings (VNGs) in fused silica [1][2][3][4][5][6][7][8] and a few other materials [9][10][11][12][13][14][15]. First observed in 2003 by using a fixed focused femtosecond laser beam [1], these nanoplanes are found to be oriented perpendicular to the laser polarization.…”

“…In particular, it was found that laser electric field direction controls their alignment for any scan direction [2], enabling the imaging of complex polarization states [16] and the inscription of rotated nanogratings [17]. The nanoplanes are spaced by half of the wavelength in the medium independently of pulse energy [2,8,11]. The period was shown to decrease continuously with the number of the applied pulses [1,8,10,13,18,19].…”

Direct writing of birefringent elements by ultrafast laser nanostructuring in multicomponent glass

“…15 Furthermore, doping of pure silica glass with Ge, F, and P was demonstrated to affect the threshold for nanograting formation. 16 Recently, evidence for femtosecond laser-induced nanogratings has been observed in glasses other than SiO 2 , including several studies reported nanogratings in GeO 2 glass, [17][18][19] binary titanium silicate glass (ULE, Corning), 20,21 and two multicomponent borosilicate glasses (BK7 and Borofloat 33, Schott). 20,22 Germanium dioxide is formed by a three-dimensional network of [GeO 4 ] tetrahedra with all bridging oxygen atoms, whereas ULE glass also possesses structure similar to pure SiO 2 24 were not revealed using scanning electron microscopy despite the induced retardance was of the same level as in Borofloat 33.…”