@article{PismaZhETF.6.490,
    title = {Coherent Photon Decay in a Nonlinear Medium},
    author = {Klyshko, D. N.},
    journal = {Письма в ЖЭТФ},
    volume = {6},
    issue = {1},
    pages = {490},
    year = {1967},
    doi = {},
    url = {http://jetpletters.ru/ps/0/article_25244.shtml},
}