Femtosecond laser induced space-selective precipitation of nonlinear optical crystals in rare-earth-doped glasses.

We report on space-selective precipitation of nonlinear optical crystals in an Er(3+)-doped BaO-TiO(2)-SiO(2) glass by using a focused femtosecond laser with 800 nm, 250 kHz and 150 fs. An intense green emission due to upconversion luminescence is observed around the focal point of the femtosecond laser beam at the initial stage of the laser irradiation. A blue emission due to second harmonic generation begins to emerge from the irradiation region after 40 s irradiation. Micro-Raman spectra indicate that nonlinear optical crystals (Ba(2)TiSi(2)O(8)) are precipitated after the laser irradiation. The irradiation time for crystallization in Er(3+)-doped BaO-TiO(2)-SiO(2) glasses is longer than that in BaO-TiO(2)-SiO(2) glasses under the same irradiation conditions. The mechanisms responsible for the observed phenomena are discussed.