22 September 1997 Improved UV photorefractive LiNbO3 crystals and their applications in Ca K-line narrow-bandwidth imaging filters
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We present experimental results of holographic grating recording in the near ultra-violet (UV) in photorefractive LiNbO3 crystals. The UV wavelength limits of Fe-doped LiNbO3 crystals for UV grating filters have been established by characterizing the grating diffraction efficiency versus recording wavelength ranging from 300 to 400 nm. Methods for improving the UV performance of LiNbO3 have also been investigated. It has been shown that the material absorption loss of Fe:LiNbO3 crystals can be reduced and the grating efficiency can be a significantly improved by using proper post-grown oxidization treatment. Using the improved UV LiNbO3 crystal, a sub-Angstrom bandwidth holographic grating imaging filter for solar observation at the Ca K-line (393.3 nm) has also been fabricated. Narrow bandwidth (22 pm, FWHM), large numerical aperture (f/15), large field-of-view (35 mrad), large aperture (15 mm in diameter) and high in-band diffraction efficiency (25%) have been successfully demonstrated. These results indicate an improved performance at a reduced cost as compared with currently available Lyot filters for solar magnetic field sensing at Ca K-line. Applications of the UV photorefractive holographic grating devices include solar and planetary observing, lidar receiving sub-systems for Earth remote sensing and atmospheric monitoring, and high density UV optical data storage.
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Feng Zhao, Feng Zhao, Koichi Sayano, Koichi Sayano, Harold E. Miller, Harold E. Miller, Jason Corwin, Jason Corwin, Nicolette Werner, Nicolette Werner, } "Improved UV photorefractive LiNbO3 crystals and their applications in Ca K-line narrow-bandwidth imaging filters", Proc. SPIE 3137, Photorefractive Fiber and Crystal Devices: Materials, Optical Properties, and Applications III, (22 September 1997); doi: 10.1117/12.287784; https://doi.org/10.1117/12.287784

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