Ye Dai

Micromodification of element distribution in glass using femtosecond laser irradiation

We report micromodification of Eu element distribution in a silicate glass with femtosecond laser irradiation. Elemental analysis shows that the content of Eu decreased at the focal point and increased in a ring-shaped region around the focal point, which indicates migration of Eu ions has been induced by the femtosecond laser irradiation. Confocal fluorescence spectra demonstrate that the fluorescence intensity of Eu(3+) ions increased by 20% in the laser-induced, Eu-enriched, ring-shaped region compared with that for nonirradiated glass. The mechanism for the laser induced change in fluorescence properties of Eu(3+) has been investigated.

Direct writing three-dimensional Ba2TiSi2O8 crystalline pattern in glass with ultrashort pulse laser

The nonlinear optical crystal Ba2TiSi2O8 is induced three-dimensionally inside a glass by a femtosecond pulse laser with 800nm, 250kHz, and 150fs. Micro-Raman and photoluminescence spectra confirm that crystals can grow in the focal point of the laser beam. Continuous crystalline lines were written through moving the focal point of the laser beam inside the glass. The results demonstrate a convenient method to engrave three-dimensional patterns of crystals with nonlinear optical properties for integrated optical devices.The nonlinear optical crystal Ba2TiSi2O8 is induced three-dimensionally inside a glass by a femtosecond pulse laser with 800nm, 250kHz, and 150fs. Micro-Raman and photoluminescence spectra confirm that crystals can grow in the focal point of the laser beam. Continuous crystalline lines were written through moving the focal point of the laser beam inside the glass. The results demonstrate a convenient method to engrave three-dimensional patterns of crystals with nonlinear optical properties for integrated optical devices.

Femtosecond laser-induced oriented precipitation of Ba 2 TiGe 2 O 8 crystals in glass

Ba(2)TiGe(2)O(8) crystals were selectively precipitated on femtosecond laser irradiated BaO-TiO(2)-GeO(2) glass surface. Furthermore, the crystal could grow from the surface of glass to the interior towards the laser movement direction when the laser focus was continuously moved. The laser-induced crystal was confirmed to be Ba(2)TiGe(2)O(8) phase by x-ray diffraction analysis and micro-Raman spectra. We also observed blue light due to double-frequency conversion of the 800nm incident laser in the crystallized regions. We propose the observed phenomena resulted from the femtosecond laser-assisted orientation of precipitation of crystal.

Formation mechanism of self-organized voids in dielectrics induced by tightly focused femtosecond laser pulses

In this paper, we briefly summarize two typical morphology characteristics of the self-organized void array induced in bulk of fused silica glass by a tightly focused femtosecond laser beam, such as the key role of high numerical aperture in the void array formation and the concentric-circle-like structure indicated by the top view of the void array. By adopting a physical model which combines the nonlinear propagation of femtosecond laser pulses with the spherical aberration effect (SA) at the interface of two mediums of different refractive indices, reasonable agreements between the simulation results and the experimental results are obtained. By comparing the fluence distributions of the case with both SA and nonlinear effects included and the case with only consideration of SA, we suggest that spherical aberration, which results from the refractive index mismatch between air and fused silica glass, is the main reason for the formation of the self-organized void array.

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.

Femtosecond laser induced coordination transformation and migration of ions in sodium borate glasses

We report on the coordination transformation of B3+ ions and migration of Na+ and O2− ions in sodium borate glasses, induced by 250kHz, 800nm femtosecond laser irradiation. Micro-Raman spectra show that the ratio of the integrated intensity of the two peaks at 806 and 774cm−1 decreases at first and then increases with increasing distance from the center of the laser modified zone. Electron dispersive x-ray spectra show that a portion of Na+ and O2− ions migrate from the vicinity of focal point after the femtosecond laser irradiation. A possible mechanism is proposed to explain the observed phenomena.

Femtosecond laser writing of Er 3+ -doped CaF 2 crystalline patterns in glass

We report on the use of 800 nm, 250 kHz femtosecond laser pulses to precipitate Er(3+)-doped CaF(2) crystals inside oxyfluoride glass, which was confirmed with x-ray diffraction analysis. Confocal upconversion luminescence spectra show that the precipitated crystals have greatly enhanced upconversion luminescence intensity in comparison with unmodified glass. We demonstrate the possibility of three-dimensional optical data storage in the glass by the use of the confocal upconversion luminescence imaging.

Femtosecond laser induced rotated 3D self-organized nanograting in fused silica.

Formation of rotated 3D self-organized nanograting inside fused silica is demonstrated by using a femtosecond pulse laser. The difference of birefringence signal of non-reciprocal writing lines indicates that the excited pulses may possess a finite tilt of intensity front, which produces an electric field vector parallel to the incident direction to modulate the excited electron plasma. We suggest that the orientation of nanograting depends on the correlation between the polarization plane azimuth and the tilted intensity front based on previous investigations. The result provides an opportunity to control the rotation of self-organized nanograting in three-dimensional space.

Self-formation of quasiperiodic void structure in CaF2 induced by femtosecond laser irradiation

We report the self-formation of quasiperiodic void structure with the length of several hundred micrometers inside the CaF2 crystal. The quasiperiodical voids along the propagation direction of the laser beam were formed spontaneously after the irradiation of a single femtosecond laser beam which was focused at a fixed point inside the crystal sample. The length of the void array varied with the focal depth beneath the sample surface. The possible mechanism of the self-formed void structure was discussed.

Crystalline phase distribution of Dy 2 (MoO 4 ) 3 in glass induced by 250 kHz femtosecond laser irradiation

Spatial precipitation of Dy2(MoO4)3 crystal in the glass is achieved by using 800 nm, 250 kHz femtosecond laser. Micro-Raman spectra show that multiple crystalline phases of Dy2(MoO4)3 can be formed in femtosecond laser-modified region. Their distributions depend mainly on femtosecond laser-induced temperature field, which is asymmetric along the light propagation direction. This phenomenon results from an inhomogeneous intensity distribution of the incident pulse due to both of self-focusing effect and spherical aberration effect. Furthermore, the EPMA mapping demonstrates that the O element concentration is reduced in the center of the modified region, while the Mo element one increases. The composition change is according strongly with the phase transformation of Dy2(MoO4)3 crystal. The present study implies that the asymmetry of the temperature field is an important factor to influence the crystal precipitation.