Phase-Matched Wavelenght-Conversion in Nonlinear-Optical Waveguide of Organic Crystal Based on Thickness Control of LB Film

从有机非线性光学晶体导层顶层厚度控制的角度研究了LB膜。作为顶层的LB膜可以逐层堆叠，并且可以精确地控制厚度，因为通常LB层具有nm级的厚度。在实验上，我们采用多层LB膜的方法实现了在实际大容差的厚度控制相位匹配条件下的光学二次谐波产生（SHG），并从理论上设计了在给定的导层厚度下，如何获得较大容差的导-导模式SHG。我们尝试在LiNbO_3基片上外延生长的无机非线性光学LiTaO_3上，堆积N-二十二烷基-N ^-（4-硝基苯基）脲（DONPU）的Z型LB膜。结果表明，在LiTaO_3层厚度为45 nm的范围内，在可容忍的相位匹配下，可以实现倍频，这比通常的1 nm量级的厚度范围要宽得多。在理论上，我们将有机非线性光学材料（-）2-（α-甲基苄基氨基）-5-硝基吡啶（MBANP）和3，5-二甲基-1-（4-硝基苯基）吡唑（DMNP）作为玻璃基片上的导向层，并加入适当的缓冲层。我们可以预测，宽的引导层厚度范围可以提供可容忍的相位匹配的SHG，其中相位匹配是通过根据引导层的厚度逐层堆叠DONP膜来控制的。

We studied Langmuir-Blodgett (LB) films in a viewpoint of thickness control of top layrs on guideing layrs of organic nonlinear-optical crystals. The LB film as a top layr can be stacked layr by layr and the thickness can be precisely controlled, since, generally, on LB layr has thickness of nm-order. In the research, by means of stacking LB layrs, we experimentally achieved optical second-harmonic generation (SHG) under the condition of thickness-controlled phase-matching with practcally large tolerance and theoretically designed how to obtain larger tolerance in guided-to-guided mode SHG for given thickness of the guiding layre.In the experiment, we tried to stack Z-type LB layrs of N-dococyl-N^1- (4-nitrophenyl) urea (DONPU) on the inorganic nonlinear-optical LiTaO_3 epitaxially grown on the inorganic LiNbO_3 substrate. As a result, we could attain SHG under the tolerable phase-matching within a thickness range of 45 nm of the LiTaO_3 layr, which is wide enough in comparison with the usual thickness range of 1 nm-order. We also found that the stearic acid has to be used as the intermediate layr on the LiTaO_3, since DONPU can be stacked on the hydrophobic substrate.In the theory, we treated the organic nonlinear-optical (-) 2- (alpha-methylbenzylamino) -5-nitrophyridine (MBANP) and 3,5-dimethyl-1- (4-nitrophenyl) pyrazole (DMNP) as the guiding layrs on the glass substrates with the appropriate buffer layrs. We could predict that the wide thickness-range of the guiding layr can provide the tolerably phase-matched SHG,where the phase matching is controlled by stacking the DONP film layr by layr according to the thickness of the guiding layr.