Studies On Femtosecond Laser Induced Microstructures And Nonlinear Optical Materials Of Inorganic-Organic Hybrid

Femtosecond (fs) lasers with high peak power and ultrashort pulse width have been used to make microscopic modifications to many kinds of materials through multiphoton absorption, which has become a new research field in materials and information science. Hybrid inorganic-organic materials with unique properties offered by the two components play an important role in the development of photonic devices. The microscopic modifications of hybrid inorganic-organic materials have become a hot research topic in the field of materials, physics, and infomations science.This thesis focuses on fs laser induced microstructures and nonlinear optical materials of hybrid inorganic-organic. We studied fs laser induced birefringence, ultrafast optical Kerr effect, microgratings and nonresonant all-optical poling in hybrid inorganic-organic materials and PMMA polymers doped with azodyes, laser dyes, and phthalocyanines.The photoinduced birefringence induced by a fs laser in hybrid inorganic-organic materials and PMMA polymers doped with azodyes was experimentally demonstrated. The probe transmittances for the induced birefringence in these two kinds of materials were estimated to be 92% and 21%, respectively. The characteristic kinetics of growth and decay of the indued birefringence was investigated by measuring the probe transmittance for the photoinduced birefringence. It is evidenced experimentally that the photoinduced birefringence for the azodyes-doped PMMA polymers is mainly due to the reorientation of the azodye molecules, while the photoinduced birefringence for the azodyes-doped hybrid inorganic-organic materials is mainly due to the trans-cis isomerization of the azodye molecules.The research of the effects of writing conditions on the probe transmittance for the photoinduced birefringence in the azodyes-dopedPMMA polymers confirmed that writing conditions had great impact on the growth rate and saturation value of the photoinduced birefringence. Four cases of writing conditions on the growth kinetics of the probe transmittance for the photoinduced birefringence were sdudied. In the following three conditions: (1) fixing the pulse width and repetition rate of the pulses with variation in the writing power, (2) fixing the writing power and repetition rate with variation in the pulse width and (3) fixing the writing power and pulse width with variation in the repetition rate, the peak power is the dominating parameter. When fixing the energy of the pulses or the incident energy, however, the writing power becomes the dominating parameter. The research of the effects of sample thickness on the probe transmittance for the photoinduced birefringence in the azodyes-doped hybrid inorganic-organic materials confirmed that sample thickness had great impact on the growth rate and saturation value of the photoinduced birefringence. The growth rate remarkably becomes fast and the saturation value increases with a longer saturation time with increasing the sample thickness and that the decay of the probe transmittance for the photoinduced birefringence in thicker sample becomes slower. In addition, the probe transmittance for the saturated photoinduced birefringence â–³n_sat is saturated at 80% after reaching a critical sample thickness, while the effect of the sample thickness on the permanent photoinduced birefringence â–³n_perm is not as sensitive as that for â–³n_sat. We propose a novel method for optical srotage based on the photoinduced birefringence in hybrid inorganic-organic materials. The recorded image can be stored for several weeks.Ultrafast optical Kerr effect (～200 fs) in the order of the time-resolution of the experiment dominating over the decay process was demonstrated in lead (II) phthalocyanine (PbPc)-doped hybrid inorganic-organic materials. The research of the influence of pumping power on optical Kerr signal intensity confirms that the optical Kerr effect origins from third-order nonlinear optical properties of the PbPc molecules. By investigating the dependence of optical Kerr signal intensity on the polarization angle between the pumping beam and the probing beam, we have identified the origin of the optical Kerr effect indetail that the ultrafast response process should be attributed to self-diffraction of the pump pulse by the fs laser indued transient gratings.To increase the diffraction efficiency of the microgratings, a new method of fabricating microgratings in hybrid inorganic-organic materials and PMMA polymers doped with azodyes or phthalocyanines was developed. Holographic one-dimentional volume microgratings with high first-order Bragg diffraction efficiency (greater than 35%) were fabricated in the laserdyes-doped hybrid inorganic-organic materials by two-beam interference of fs pulses. The micrograting depth was greater than 450 μm. Based on one-dimensional volume microgratings, holographic two-dimensional volume microgratings were also fabricated in the azodyes- or phthalocyanines-doped materials by four-beam interference of fs pulses. Under the same writing conditions, the linewidth of the strip of the two-dimensional microgratings fabricated in the azodye-doped PMMA polymers is narrower than that of the strip of the two-dimensional microgratings in the azodye-doped hybrid inorganic-organic materials. The photodecomposition of the dyes doped is responsible for the microgratings.Nonresonant all-optical poling in the azodye-doped hybrid inorganic-organic materials was demonstrated. The characteristic kinetics of growth and decay of the photoinduced second-order nonlinear optical effect was measured by second-harmonic generation. It is evidenced experimentally that the nonresonant all-optical poling of the azodyes-doped hybrid inorganic-organic materials is mainly due to the trans-cis isomerization of the azodye molecules. The second-order nonlinear optical coefficient d₃₃ is determined to be 10^-3 pm/V. The decay for the photoindcued second harmonic intensity is improved when increasing the power of the seeding beams, with the intensity ratio between the fundamental and the second harmonic light kept at 750: 1.