Calibration of windowless photodiode for extreme ultraviolet pulse energy measurement

For energy measurement of extreme ultraviolet pulses, no universal commercially available device is available. Therefore, a co-axial setup of a vacuum photodiode was developed and tested. First its unsuccessful calibration at the National Institute of Standards and Technology (USA) is mentioned. Then our own single-wavelength (46.9 nm) calibration procedure is described in detail. It is based on tabulated photoemission efficiency and on measured (1) anode collection efficiency, (2) attenuation of Al filters, and (3) attenuation of measuring cables. Some other relevant attenuating factors are also taken into account.