@article{PismaZhETF.9.660,
    title = {Two-level Gas Laser with Coherent Optical Pumping},
    author = {Basov, N. G. and Letokhov, V. S.},
    journal = {Письма в ЖЭТФ},
    volume = {9},
    issue = {12},
    pages = {660},
    year = {1969},
    doi = {},
    url = {http://jetpletters.ru/ps/0/article_25423.shtml},
}