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Supercontinuum based birefringence characterization set-up.
Retardance dependence on the average power and writing speed for nanogratings induced with 515 nm (left) and 1030 nm (right). The steep increase of retardance at 300–400 mW indicates phase transition from Type I to Type II modification.
Losses for group of samples written at a 10 mm/s translation speed with first and second harmonics (1030 nm and 515 nm). The legend indicates the range of average power used during writing procedure. The large separation between structures written at 200 mW and 300–800 mW indicates the presence of Type I (isotropic refractive index increase) and Type II (nanograting) modifications. The dotted curves were measured after annealing the sample at 450 °C for 2 h.
Dichroism (scattering and absorption) exhibited by nanogratings induced with first harmonic. The shaded area indicates a region there dichroism was measured for various writing speeds (2–10 mm/s) and pulse energies (2–4 μJ).
(Top) Spectral dependence retardance induced with 2 μJ femtosecond laser pulses in fused silica glass. The legend indicates light wavelength. Oscillations seen on the short wavelength side are due to the interference of a light source used in the experiments. The dashed lines indicate independent measurements performed with 3 different laser sources at 515 nm, 1030 nm, and 1550 nm. (Bottom) Spectral retardance dependence before and after annealing measured with the ellipsometer. The target retardance values were half, quarter, and eighth of 1000 nm. The graph was built after correcting the data for phase discontinuity.
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