PURPOSE: To provide a process for producing high-purity thin films by selectively separating only one kind of element from raw materials contg. many elements.

CONSTITUTION: This process for forming high-purity thin films comprises irradiating atom beams 4 of the raw materials contg. ≥2 kinds of elements with pulse laser beams 1, 2 of first and second two different wavelength pulses set at the wavelengths in such a manner that only one kind of the atom is selectively excited to ionize only the desired atom by two-stages of resonance excitation processes applying an electric field to such light ionized regions and introducing the generated ions onto a substrate 8 placed in the clean space parted from the flow of the atom beams, thereby capturing and laminating the ions on the substrate 8. The atom beams 4 described above are held by a pair of mirrors 5, 6 and the pulse laser beams 1, 2 are moved back and forth plural times in the atom beams by these mirrors 5, 6.