The Mechanism Of Structural Change In Au～(3+)-doped BK7 Glass Irradiated By Femtosecond Laser

Femtosecond lasers have shown predominant advantages in the space-selective microscopic processing and formation of the three-dimension (3D) modified microstructures. Various kinds of integrated functional optical devices including 3D optical waveguide, optical memory, grating, coupler and photonic crystal etc. have been fabricated by the femtosecond laser processing. On the other hand, glasses doped with noble metallic nanoparticles have attracted considerable attention for their ultrafast nonlinear response and large third-order nonlinear susceptibility. For the applications related to integrated optoelectronics, a well-defined assembly and spatial distribution of nanoparticles in materials are essential. Recently, Qiu et. al. have reported that metallic nanoparticles could be precipitated near the focal point of the femtosecond pulsed laser beam inside metallic ion-doped glasses after irradiation with the femtosecond laser and successive heat treatment. But the research only focused on silicate glasses. BK7 glass is a borosilicate optical glass which is widely used in many kinds of optical devices. Here, we take BK7 glasses doped with noble metallic ions as our studying materials.In this dissertation, a grating structure was inscribed in a BK7 glass sample doped with noble metallic ions by a focused femtosecond laser, and metallic nanoparticles were space-selectively precipitatied inside silicate glasses by femtosecond laser irradiation and successive heat treatment. Absorption spectra and optical microscope were used to analyze the mechanisms. The diffraction efficiency of the inscribed grating was also measured. The content of this dissertation consists of four parts. The first part is about femtosecond laser induced micro-structure change in Ag⁺-doped BK7 glass and Au³⁺-doped BK7 glass. In the second part we used nanosecond laser to induce noble metal nanoparticles and micro structure change in the BK7 glass and take comparison with the phenomena induced by femtosecond laser. And in the third part, we discussed the effect of micro-crack on the precipitation of noble metal nanoparticles.In the first part , we chose BK7 glasses doped with Au³⁺or Ag⁺as samples. The optical microscope pictures of the micro structure change induced by femtosecond laser were taken. And the diffractive efficiency of the inscribed grating after annealing at various temperatures was measured. The induced-structure changedas the annealing temperature rose. And the diffraction efficiency of the grating decreased at first and then increased with the further increase of annealing temperature. It was the color centers and noble metal nanoparticles that caused the change of the diffraction efficiency. We can control the diffraction efficiency of the grating in conventional optical glasses by controlling the annealing temperature. This technique is useful to fabricate micro optical devices, such as ultrafast all-optical switching devices and three-dimensional optical memory with ultrahigh storage density system.In the second part, nanosecond laser was used to induce micro structure change in the BK7 glass doped with noble ions. We compared the micro structure changes induced by nanosecond laser and femtosecond laser. Nanosecond laser can also precipitate noble metal nanoparticals in relevant glasses after heat treatment. The features of the microstnicture changes induced by nanosecond laser and femtosecond laser were compared.And in the third part, we confirmed that micro cracks also play important role for the precipitation of noble metal nanoparticles in glasses. The mechanism is discussed and proposed.