Development of High Quality and High Laser-Resistive Multilayr Dielectric Thin Films by Means of Chemical Surface Reaction

用蒸发法制备具有高均匀性和高激光损伤阈值的米级多层光学薄膜是非常昂贵的。为了开发一种经济有效的方法，我们研究了一种应用原子层外延方法的表面化学反应技术。在化学表面反应中，通过交替引入反应物和氧化剂可以很容易地沉积薄膜，并且只需反应循环的次数就可以精确地控制薄膜的厚度，反应腔的尺寸与衬底的尺寸一样大。以三甲基铝(TMA)为反应气体，过氧化氢(H_2O_2)为氧化剂，制备了氧化铝(Al_2O_3)薄膜。利用四氯四氯化钛(TiCl4)和氢氧化物(H2O)作为高折射率薄膜材料，在玻璃基片上沉积了厚度在1%以内、厚度分布非常均匀的二氧化钛(TiO2)薄膜，厚度分布受腔型…的限制更大的尺码。结果表明，该方法能有效地生长出大尺寸光学元件的高均匀性、高厚度的薄膜。折射率强烈依赖于衬底温度，而生长速率依赖于残余气体的排气性能和氧化剂的引入压力。其他沉积参数对薄膜性能的影响不大。这些结果表明，这种方法可以在没有任何敏感控制的情况下，以稳定的、可重复的方式生长薄膜。制备了由Al_2O_3层和TiO_2层组成的增透膜，并对其光学性能进行了测试。所测试的增透膜适用于532 nm和1064 nm的光。获得了低于0.1%的剩余反射率，与设计值吻合较好。在1 ns、1064 nm激光脉冲下，Al_2O_3和TiO_2的激光损伤阈值分别为7J/cm~2和3.5J/cm~2。这些薄膜适用于激光器，但对于高功率激光器，如用于激光聚变，需要进行一些改进。总之，所开发的化学表面反应方法具有良好的厚度和均匀性可控性，适用于任何大型光学设备。这有望提高高功率激光器的激光损伤阈值。较少

It is very expensive to make meter size multilayr optical films with high uniformity and high laser damage threshold by an evaporation method. In order to develop a cost-effective method, we have studied a chemical surface reaction technique applied an atomic layr epitaxy method. In the chemical surface reaction, the films can be easily deposited by introducing a reactant and an oxidizer alternatively, and the thickness can be precisely controlled only by the number of reactive cycles with a reaction chamber of which size is as large as substrate size. Aluminium oxide (Al_2O_3) films were grown using trimethylaluminium (TMA) as a reactant gas and hydrogen peroxide (H_2O_2) as an oxidizer for a low refractive index layr. Titanium dioxide (TiO_2) films were grown using tetrachlorotitanium (TiCl_4) and hydrogen oxide (H_2O) for a high refractive index layr.The deposited film on glass plates showed very uniform distribution of thickness within 1% over 250-mm region which limited by a chamb … More er size. The results mean that this method is effective to grow the films with high uniformity and precise thickness for large optics. The refractive indices depended strongly upon the substrate temperature, and the growth rate depended upon the exhaust performance of the residual gas and upon the introduced pressure of oxidizers. The properties of films were not serious effected by other deposition parameters. These results suggest that this method can grow films by a stable and reproducible manor without any sensitive controls. Anti-reflective coatings consisting of Al_2O_3 and TiO_2 Layrs were deposited, and the optical characteristics were measured. The tested anti-reflective coatings are for 532-nm and 1064-nm light. Residual reflectivity of lower than 0.1% was easily obtained and was agreed well with the design value. The laser-induced damage threshold of Al_2O_3 and TiO_2 fulms was 7 J/cm^2 and 3.5 J/cm^2 at 1-ns, 1064-nm laser pulse, respectively. These films are applicable to lasers although some improvements are required for high power lasers such for laser fusion.In conclusion, the developed chemical surface reaction method showed an excellent controllability in thickness and uniformity and was applicable for any large optical apparatus. It is expected to improve laser damage threshold for high power lasers. Less