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For obtaining radiation less damageable laser mirrors, a preliminary optimization of film fabrication suitable for the analysis of laser damage mechanism has been done as the first step. Here, the optimization requires not only the stable fabrication process but also the ideal film structure i.e., the amorphous and smooth film structure simultaneously, eliminating latently unwanted secondary effects such as light scattering during laser damage test. For this purpose, we adopted the ion assisted deposition method and modified the deposition conditions for titanium and tantalum oxide films, both of which compose typical high index layers, and where SiO2 layers are also chosen as low index layers because of their amorphous and smooth nature, in alternative multilayer laser mirrors. Surface and cross sectional film structures and film crystallinity are compared and characterized, using a high resolution SEM and a x-ray diffractometer, respectively. The fabrication process and the film structures obtained even by IAD method for tantalum pentaoxide lack stability similar to those films by a conventional EB method. The fabrication process for titanium oxide films are stable even by a conventional EB method, but it produces the columnar film morphology and rough film surface and layer boundary simultaneously. Therefore, further optimization of titanium films, has been done by IAD method to improve the film morphology, introducing new fabrication parameters such as the determination of the best starting materials among various titanium oxides, adopting the new mixed gases of Ar and oxygen, suitable input power for ion gun, and arrival ratio of the ionized vapor ions. Then the structure of titanium oxides, adopting the new mixed gases of Ar and oxygen, suitable input power for ion gun, and arrival ratio of the ionized vapor ions. Then the structure of titanium oxide films deposition conditions of the ratios of oxygen and argon gases from 1:1 to 1:2 and ion power of 500 to 750 V during the titanium oxide deposition at the substrate temperature of 100 to 150 degrees C. Otherwise, the conventional EB and IAD methods with)2 gas only produce the columnar film structures and rougher boundaries than those by IAD with the mixed Ar + O2 gases. Related crystallinity and optical properties, such as refractive index, absorption, and index inhomogeneity, are also reported.
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