Chronological observations of the formation of Raman-Nath diffraction gratings in photoreactive monomer base mixtures, A. Emoto, S. B. Baharim, T. Sasaki, A. Ogiwara, T. Shioda and H. Ono, Jpn. J. Appl. Phys. 49 (2010) 122502.


Taking several hours, the phase type diffractive gratings were growing in a photoreactive monomer base mixture. The gratings were inscribed by focusing and scanning of ultraviolet laser beam on the thin film of the mixture. Photopolymerization of the monomers and subsequent molecular migrations generate surface relief formation which results in transparent phase gratings, involving a refractive index modulation inside the film. The temporal changes of diffraction intensities exposed the pronounced behavior undergoing the grating formation, chronologically. The sequential formation can be explained with a time-dependent model described by theoretical formulation on the basis of Raman-Nath diffraction theory. Homogeneous irradiation of ultraviolet light during the growth enables us to fix the diffraction characteristics at the time, which allows resultant diffraction gratings to tailoring the specification. The sequential process could be applied for practical cases.

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