Studies On Third-order Nonlinear Optical Properties Of Bi-layer Structure Ferroelectirc Ceramic Films

Rapid development of information network makes higher requirements for the technique ofinformation processing and transmission, the basic of which is photo-electronic function device withexcellent photoelectric characteristic. Nonlinear optical materials have important application in thephoto-electronic function device of frequency change, Q-switched technique, optical limiter, opticalwaveguide and photo-switch etc. Generally, for example, photo-switch needs materials with largethird-order nonlinear refractive index and small linear or nonlinear absorption coefficient and Q-switcheddevice require material with large nonlinear absorption coefficient. Besides, the miniaturization andintegration development tendency of device gives a higher requirement of excellent thin films preparation.Hence, in recent year, the thing of exploring in excellent third-order nonlinear optical material is one of thehotspots in work of scientists concerned with, and obtained great achievements. By now, the third-ordernonlinear optical materials mainly focus on organic materials, inorganic semiconductor, metallic oxide,organic metallic compound and ferroelectric material etc.With both nonlinear optical characteristics and ferroelectric properties, ferroelectric materials are ableto content the requirements of device multi-function. Meanwhile, nonlinear optical theories of theferroelectric are more mature. Its maybe make out to excellent photoelectric function device rapidly.Therefore, researches in nonlinear optical properties of ferroelectric ceramic material have gotten greatattention. General ferroelectric and piezoelectric materials include lead, which do harmful to environmentand human health in their preparation and production process. So it isn’t conforms to the requirement ofsustainable development. Bi-layered ferroelectric ceramics film have obvious advantages in non-pollution,anti-fatigue and dielectric properties, so it as star materials in substitutes for tradition ferroelectric materials.But, Easy to volatile of bismuth atoms in the fabrication process of Bi-layer ferroelectric oxide burn atomvacancy, which hard to make high density of ceramic film and harm to the physical characteristics of thefilms. Therefore, explore the preparation technology and study the nonlinear optical properties becomingone of the researching hotspots in investigating the third-order nonlinear optical properties in Bi-layerferroelectric thin film. In this point, we have done some researches on the following aspects, obtaining some novel results and reported in two papers in the international important journals.Firstly, we fabricated well crystallized Bi_1.5Zn_1.0Nb_1.5O₇（BZN） and Bi_0.95La_0.05NbO₄（BLN） films onquartz substrates by pulsed laser deposition （PLD）, and obtained the optimization of process parameters.The crystal structure, surface morphology and roughness of the samples were measured by X-raydiffraction and atomic force microscope. Meanwhile, we obtained the transmittance spectra andfundamental optical constants by UV-Vis-NIR spectrophotometer.Secondly, with the single-beam Z-scan technique, we investigated third-order optical properties ofBZN ferroelectric ceranmic thin film at1064nm of laser wavelength for the first time and obtained novelresult. The results show that BZN ferroelectric ceranmic thin film has significant value in applications ofphotoelectronic integrated devices.In off-resonate region with1064nm38ps pulses excitation, BZN was found self-defocusing andsaturated absorption in exceed saturated light intensity excitation. Combining single-beam Z-scan theorywith experimental data, we obtained that third-order nonlinear refractive index γ and nonlinear absorptioncoefficient β of the BZN thin film were4.06×10^-15m²/W and-1.45×10^-9m/W, respectively. Meanwhile, wealso got the real part and the imaginary part of the third-order nonlinear susceptibities χ³were6.03×10^-9esu and1.82×10^-10esu, respectively. These results show that BZN thin film is one of the promising materialcandidates for optoelectronic device with excellent nonlinear optical properties. Our studies in this sectionwere published in Physica Status Solidi A.Thirdly, with the La₂O₃doping BiNbO₄technique, we prepared well crystallized BLN thin film andinvestigated the third-order nonlinear optical properties for first time. Study results show that BLN thinfilm has excellent nonlinear optical properties and possess potential value in photoelectronic integrateddevice.Experiment results show that La³⁺doping can progress the density of BiNbO₄ceramic material, andafter doping, the BLN showed excellent nonlinear optical properties too. In off-resonate region with1064nm38ps pulses excitation, BLN was found self-defocusing and third-photon absorption. Underclosed-aperture Z-scan technique, we obtained that third-order nonlinear refractive index γ and nonlinearabsorption coefficient β of the BLN thin film were4.34×10^-15m²/W and6.6×10^-9m/W, respectively. Andwe also got real part and imaginary part of the third-order nonlinear susceptibities χ³were6.77×10^-9esu and8.72×10^-10esu, respectively. These results show that BLN thin film is one of the promising materialcandidates for optoelectronic device with excellent nonlinear optical properties. Our studies in this sectionhave been submitted to Journal of the American Ceramic Society.