Femtosecond Laser Induced Photonics Microstructures In Transparent Dielectrics

Photonics is now a rapidly developing discipline. It mainly studies a photon how to act as an information carrier for communication technology. The data storage capacity of photon as an information carrier is 3-4 larger than that of electron, and it has fast response and good spatial compatibility. Therefore, the development of photonics will significantly promote materials science, physics and other disciplines. Recently, much attention has been paid on the photonics microstructures induced by femtosecond laser. Due to its ultrashort pulse and ultrahigh peak power, nonlinear optical effects are dominant in the process of femtosecond laser interaction with dielectrics, and this process is strictly limited by the threshold intensity of incident laser. In this way, femtosecond laser may space-selectively induce various functional microstructures in materials.In this thesis, two different repetition (1 kHz and 250 kHz) femtosecond lasers are used to induce photonics microstructures in transparent dielectrics including glass and crystal. We focused on the following topics: the microstructures induced by femtosecond laser in Ag⁺-doped silicate glass, self-assembly void microstructure induced by femtosecond laser in borosilicate glass and CaF₂ crystal, the space-selectively precipitation of nonlinear optical crystal induced by high repetition femtosecond laser in similar glass matrix.We investigated the effect of Ce³⁺ on the precipitation of Ag nanoparticles in silicate glass via a femtosecond laser irradiation and successive annealing. Absorption spectra show that Ce³⁺ may absorb part of the laser energy via multiphoton absorption and release free electrons, resulting in an increase of concertration of Ag atoms, which influence precipitation of the Ag nanoparticles. In addition, we found that the formed Ago may reduce Ce⁴⁺ to Ce³⁺ during the annealing process, which inhibits the growth of the Ag nanoparticles.A kind of fluorescent Ag nanoparticles may be space-selectively induced in glass via femtosecond laser irradiation and successive annealing. Extinction spectra and fluorescence spectra show that a fraction of the Ag atoms generated from multiphoton reduction, and aggregated to form nanoparticles under thermal treatment. Red luminescence from the irradiated region is observed under blue or green laser excitation, which is very similar in fluorescence characteristics of semiconductor quantum dots. Therefore, this red fluorescence may be attributed to interband transitions within Ag nanoparticles. These fluorescent Ag nanoparticles are very stable at room temperature.Multiple refocusing of a tightly focused femtosecond laser due to the dynamic transformation between Kerr self-focusing and self-defocusing from plasma produced a quasi-periodic void microstructure in borosilicate glass and CaF₂ crystal. It is found that the diameter or interval of the periodic void increase with the increasing pulse energy of the laser. The detailed course for producing periodic voids is discussed by analyzing the damaged track induced by the tightly focused femtosecond laser,Nonlinear optical crystals Ba₂TiSi₂O₈, Sr₂TiSi₂O₈ and Ba₂TiGe₂O₈ may be arbitrarily induced by 250 kHz femtosecond laser inside the stoichiometric glass matrices of BaO-TiO₂-SiO₂, BaO-TiO₂-SiO₂ and BaO-TiO₂-SiO₂ compositions. The induced crystals show excellent nonlinear optical nonlinearity. A heat accumulation effect is proposed as an important contribution to crystal growth in the irradiated regions. The mechanism of crystal formation as follows: The glass will transform to plasma state via multiphoton ionization due to the ultrahigh field intensity of femtosecond laser, the optically dense plasma will also absorb the laser energy effectively. So there exists a temperature gradient field in the heat-affected zone. When the glass temperature exceeds the crystallization temperature T_c, the glass will be a phase change into a crystal. Finally, crystallization due to the heat accumulation is brought in the laser-irradiated regions.