Holographic recording using azo-polymers

高分子材料是电光器件和存储器件中最有前途的有机材料。在过去的几年里，在偶氮聚合物中直接制造浮雕结构已经有了报道。这种方法是一种一步制造技术。采用干涉条纹辐照的方法制备了表面浮雕结构。我们提出了一种利用偶氮聚合物薄膜表面变形的可逆性表面浮雕全息图。电晕充电可显著提高全息图的衍射效率，并受电晕充电电压的控制。侧链偶氮聚合物，聚橙汤姆-1异膦二异氰酸酯，用于本研究。图1显示了该材料的化学结构。玻璃化转变温度T_g为136℃。染料的吸收峰为440 nm，截止波长为560 nm。这种聚合物溶解在环己酮中。采用旋转镀膜法在玻片上制备了厚度为1 ~ 5μm的样品。在633 nm波长处，用m线技术测得薄膜的折射率为1.65。采用双光束干涉条纹辐照制备表面浮雕光栅。在接近或高于T_g的温度下，电晕充电增加表面浮雕结构的衍射效率和浮雕深度的机理尚不清楚，但我们认为浮雕深度的增加是电荷施加的库仑力的结果；从而提高了衍射效率。在电晕充电过程中，在T_g附近的温度下施加电压，聚合物薄膜被加热到电晕充电温度，因为在T_g以上的温度下，表面的起伏结构在没有施加电压的情况下被热擦除。

Polymeric materials are the most promising organic materials for electro-optic, and memory devices. In the past several years, direct fabrication of relief structures in azo-polymers has been reported. This method is a one step fabrication technique. A surface relief structure is fabricated by means of irradiation of interference fringes. We propose a new reversible surface relief hologram using photomduced surface deformation on azo-polymer films. The diffraction efficiency of the hologram is dramatically increased by corona charging, and it is controlled by applied voltage of the corona charging.The side-chain azo-polymer, poly orange tom-1 isophoronediisocyanate, is used in this study. Figure 1 shows the chemical structure the material. The glass transition temperature T_g is 136℃. The absorption peak and the cut-off wavelength of the dye are 440 nm and 560 nm, respectively. This polymer is dissolved in cyclohexanone. Samples of l〜5μm thickness are prepared by spin-coating on a slide glass plate. The refractive index of the film is measured as 1.65 at a wavelength of 633 nm by the m-line technique. The surface relief grating is fabricated by the irradiation of two-beam interference fringes.The mechanism of increasing the diffraction efficiency and the relief depth of a surface relief structure by corona charging at temperatures near or above its T_g is not clearly understood, but we consider that the relief depth increases as a result of the Coulomb force exerted by electric charge ; therefore the diffraction efficiency is increased. In the corona charging process, the voltage was applied at a temperature near T_g and the polymer film was heated to the corona charging temperature with the voltage applied, because the surface relief structure is thermally erased above T_g without the applied voltage.