Abstract: A wavelength converting device for converting a wavelength of a light is provided. The wavelength converting device includes: a substrate comprising MgO; a waveguide membrane comprising KNbO.sub.3, for guiding the light; a buffer membrane which is disposed between the substrate and the waveguide membrane and which comprises KTa.sub.x Nb.sub.(1-x) O.sub.3. A mixing rate of Ta in the KTa.sub.x Nb.sub.(1-x) O.sub.3 in the buffer membrane is in a range of 40 atom % to 60 atom % at a surface of the buffer membrane touching the substrate, and is 0 atom % at a surface of the buffer membrane touching the waveguide membrane.

Abstract: When a potassium-containing substance is formed in to a film using an organic potassium complex as a potassium source by the CVD method, it is prevented that the film formation rate is changed with the lapse of time, and the potassium content in the film thus formed is changed.As a potassium source for vaporization used for depositing the potassium-containing substance on a substrate by the CVD method, a .beta.-diketone complex of potassium that has been melted by heating to a temperature higher than its melting point and then cooled to be solidified is used.

Abstract: A method of subliming material is provided for use in a CVD film preparation method wherein a CVD precursor is sublimed from its solid state by heating to a temperature not exceeding its melting point, thereby producing a vapor of the precursor, and the vapor of the precursor is transported to a reactor. The method of subliming material comprises the steps of forming the solid-state compound into a film, covering a back surface of the film with a non-reactive support and exposing a front surface of the film to an atmosphere as a sublimation surface. The method maintains the exposed surface area of the solid compound constant during processing.