Excited stale proton transfer lasers are considered. The working princ
iple of photochemical laser is described. The criteria of acid-base sy
stems selection for active media of photochemical lasers are stated. T
he list of acid-base laser systems, working conditions and radiation c
haracteristics of photochemical lasers are given. The specific losses
in photochemical lasers are analyzed. The method of tuning range incre
asing of photochemical laser radiation are described.