@article{PismaZhETF.56.301,
    title = {Strengthening of the photorefractive response in a ferroelectric $Ba_2NaNb_5O_{15}$ crystal in an alternating external field},
    author = {Nesterkin, O. R. and Shershakov, E. P. and Zel'dovich, B. Ya. and Novikov, A. D.},
    journal = {πΙΣΨΝΑ Χ φότζ},
    volume = {56},
    issue = {6},
    pages = {301},
    year = {1992},
    doi = {},
    url = {http://jetpletters.ru/ps/0/article_19489.shtml},
}