Narrow-line output of a master oscillator (top) is amplified in an unstable-resonator amplifier (bottom), extracting energy from most of the unstable-resonator cavity. Components are (1) master oscillator rear reflector, (2) etalons, (3) apertures, (4) master oscillator output coupler, (5) prism, (6) rear unstable-resonator optic, (7) front unstableresonator optic. (Courtesy of Lumonics Inc.)