Spectrograph calibration at extreme ultraviolet wavelengths by comparison to a 'standard' spectrograph

The response of a grazing incidence spectrograph has been calibrated at several points in the extended wavelength range 2.5-18.2 nm by direct and by branching ratios comparison to the response of a grazing incidence spectrograph absolutely calibrated in the range 1.0-4.5 nm. CVI Lyman lines and a CV resonance line are used for the direct comparison and CVI Lymand and Balmer series line pairs for the branching ratios comparison. The radiation source used is the plasma formed by irradiating thin (diameter approximately 6.5 mu m) carbon fibres with a focused high power ( approximately 10 10 W) laser. Experimental results are presented for a compact one-meter spectrograph used with a 1200 line mm -1 gold-coated grating at angle of incidence 86 degrees . The reference or 'standard' spectrograph is a two-metre Hilger-Watts E580 spectrograph used with a 600 line mm -1 , platinum-coated grating at angle of incidence 88 degrees .