Pulse energy of the extreme-ultraviolet free-electron laser at SPring-8 determined using a cryogenic radiometer

The pulse energy of an extreme-ultraviolet free-electron laser (EUV-FEL) has been directly measured using a cryogenic radiometer installed in an experimental station. The laser provided 21.0, 18.0, and 19.5 mu J/pulse at wavelengths of 51, 55, and 61 nm, respectively. The contribution of higher harmonics was estimated by measuring the attenuation of the average pulse energy with increasing At gas pressure in a gas cell. The ratio of the intensity of the higher harmonics to that of the fundamental was estimated to be about 1%. (C) 2009 Elsevier B.V. All rights reserved.