Light transmissive member, light source device, method of producing light transmissive member, and method of producing light source device

A method of producing a light transmissive member comprising a first film, a second film, and a third film, the method comprising:

• providing a light transmissive base member having a first surface, and a second surface on a side opposite the first surface;
• forming a light transmissive aluminum oxide film covering at least part of the first surface and at least part of the second surface, the light transmissive aluminum oxide film containing aluminum oxide having a crystallinity lower than a crystallinity of α-alumina;
• obtaining an intermediate structure by forming a light transmissive third film covering the aluminum oxide film on the second surface;
• and
• hydrating the intermediate structure such that the aluminum oxide film becomes the first film covering at least part of the first surface and containing hydrous alumina, and becomes the second film covering at least part of the second surface and containing the aluminum oxide having a crystallinity lower than the crystallinity of α-alumina.