In 1955, Prokhorov started his research in the field of electron paramagnetic resonance (EPR). He focused on relaxation times of ions of the iron group elements in a lattice of aluminium oxide, but also investigated other, "non-optical", topics, such as magnetic phase transitions in DPPH.A. M. Prokhorov and V.B. Fedorov, Soviet Physics JETP 16 (1963) 1489. In 1957, while studying ruby, a chromium-doped variation of aluminium oxide, he came upon the idea of using this material as an active medium of a laser. As a new type of laser resonator, he proposed, in 1958, an "open type" cavity design, which is widely used today. In 1963, together with A. S. Selivanenko, he suggested a laser using two-quantum transitions. For his pioneering work on lasers and masers, in 1964, he received the Nobel Prize in Physics shared with Nikolay Basov and Charles Hard Townes.
