Grazing-incidence flat-field spectrometer for high-order harmonic diagnostics

The design and performances of an EUV spectrometer for diagnostics of high- order harmonics generated by an ultrashort (<30 fs) pulsed laser focused on to a gas jet are presented. The system consists of a toroidal mirror, an en trance slit, a spherical variable-line-spaced grating and a bidimensional d etector. The mirror focuses astigmatically the radiation from the gas jet, with the tangential focus on the entrance slit. The grating diffracts the r adiation coming out from the slit, spectrally focusing the 5 to 40 nm wavel ength range in an almost straight focal curve, where the detector is locate d. The latter is a 40 mm diameter microchannel-plate intensifier. The spati al focal point of the toroidal mirror lies before the spectral focal plane of the spectrometer, so measurement of the height of the spectral lines giv es the beam divergence. The spectral resolution of the spectrometer was mea sured using the narrow line spectra obtained by a microfocus soft x-ray sou rce. Also the absolute response of the system, that is grating efficiency p lus detector efficiency, was measured. (C) 2001 Society of Photo-Optical In strumentation Engineers.