Submicrometer Space Control of Metal Oxides for Creating Optical Functions Based on Spontaneous Optical Resonator Formation

为了在可见光区获得强的光散射，人们尝试在高折射率金属氧化物如氧化铝（Al_O_3）、氧化锆（ZrO_2）和二氧化钛（TiO_2）中形成轮廓分明的大孔。此外，还分别以连续波和超短脉冲激光为光源，通过相干背散射和时间分辨透射测量，计算了光在多孔介质中的传输平均自由程和扩散常数。结果可总结如下。(1)采用溶胶-凝胶相分离法可以成功地制备出大孔SiO_2。然而，由于前体的高反应性，将这种合成技术推广到其他金属氧化物是非常困难的。研究表明，二元氧化物如Y_3Al_5O_（1 ...更多信息 2、通过合理选择溶胶-凝胶体系中的原料和组分，制备了YAG、Y_2O_3掺杂的ZrO_2（YSZ）以及Al_2O_3、ZrO_2、TiO_2等单组分氧化物。在强散射介质中，相干后向散射峰具有很宽的散射光角度依赖性。为了测量散射光的角度依赖性并获得输运平均自由程，自制了测量装置;此外，通过飞秒激光脉冲和条纹相机的组合，建立了测量时间分辨透射的光学系统，从而可以评估扩散常数。结果表明，输运平均自由程随大孔尺寸的变化而变化，表明散射强度可由大孔形貌系统地控制。在某些介质中，传输平均自由程比光的波长短。时间分辨透射曲线的分析表明，与经典的光扩散模型略有偏差，表明安德森本地化的签名。光的扩散态和局域态之间的相变需要详细的实验和分析来阐明。少

An attempt has been made to form well-defined macropores in high-refractive-index-metal oxides such as alumina (Al_O_3), zirconia (ZrO_2), and titania (TiO_2) in order to obtain strong light scattering in the visible region. In addition, the transport mean free path and diffusion constant of light in the resultant porous media have been evaluated by means of coherent backscattering and timeTesolved transmission measurements, in which the continuous wave and untrashort pulsed lasers ar used as the light sources, respectively. The results can be summarized as follows.(1) It is well established that silica (SiO_2) with well-defined macropores can be successfully prepared via the sol-gel process accompanied by the phase separation. However, it has been very hard to extend this synthetic technique to other metal oxides because of the high reactivity of precursors. In this study, it is shown that bicontinuous macroporous structures can be formed in binary-component oxides such as Y_3Al_5O_<1 … More 2> (YAG) and Y_2O_3 -doped ZrO_2 (YSZ) as well as single-component oxides such as Al_2O_3, ZrO_2, and TiO_2 by selecting the starting materials and compositions in the sol-gel systems adequately. In particular it is Sound that the SS of macropores in TiO_2 monoliths can be controlled over a wide range of 100 nm to 10 μm.In strongly scattering media, coherent backscattering peaks exhibit very wide angular dependence of scattering light. Home-made equipment has been built in order to measure the angle dependence of scattering light and also to obtain the transport mean free path. In addition, optical systems to measure the time-resolved transmission has been built by combining femtosecond laser pulses and a streak camera so that the diffusion constant can be evaluated. It is found that the transport mean free path varies with the size of macropores, indicating that the scattering strength can be systematically controlled by the macroporous morphology. In some media, the transport mean free path is shorter than the wavelength of light. Analysis of time-resolved transmission profiles shows the slight deviation from classical light diffusion model, suggesting the signature of Anderson localization. The detailed experiments and analysis are required to clarify the phase transition between the diffused and localized states of light. Less