PACS:42.65.Hw, 42.79.Bh, 42.30.−d (all) DOI:10.1070/PU1992v035n06ABEH002243 URL: https://ufn.ru/en/articles/1992/6/d/ Citation: Kulagin O V, Pasmanik G A, Shilov A A "Amplification and phase conjugation of weak signals" Sov. Phys. Usp.35 (6) 506–519 (1992)