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，人们试图在高折射率的金属氧化物如氧化铝(Al_2O_3)、氧化锆(ZrO_2)和二氧化钛(TiO_2)中形成明确的大孔。此外，利用相干后向散射和时间分辨透射法，分别以连续波脉冲激光和非垃圾脉冲激光为光源，计算了光在多孔介质中的平均传输自由程和扩散常数。主要研究结果如下：(1)通过溶胶-凝胶法结合相分离的方法，成功地制备出具有规整大孔的二氧化硅(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，在Y_3Al_5O_1-…等二元氧化物中可以形成双连续的大孔结构通过选择合适的原料和溶胶-凝胶体系的组成，制备了更多的2&gT；(YAG)和Y_2O_3掺杂的ZrO_2(YSZ)以及Al_2O_3、ZrO_2和TiO_2等单组分氧化物。在强散射介质中，相干后向散射峰对散射光的角度依赖性很大。为了测量散射光的角度依赖关系，并获得传输平均自由程，已经建立了自制的设备。此外，利用飞秒激光脉冲和条纹相机相结合，建立了测量时间分辨透过率的光学系统，从而可以计算扩散常数。研究发现，平均传输自由程随大孔尺寸的不同而不同，这表明散射强度可以由大孔的形态来系统地控制。在某些介质中，传输平均自由程比光的波长短。对时间分辨透射率分布的分析表明，它与经典的光扩散模型略有偏离，这表明了Anderson局域化的特征。为了弄清光的漫射态和定域态之间的相变，需要详细的实验和分析。较少

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