Calibration of an extreme-ultraviolet transmission grating spectrometer with synchrotron radiation

The responsivity of an extreme-ultraviolet transmission grating spectromete r with silicon photodiode detectors was measured with synchrotron radiation . The spectrometer was designed to record the absolute radiation flux in a wavelength bandpass centered at 30 nm. The transmission grating had a perio d of 200 nm and relatively high efficiencies in the +1 and the -1 diffracti on orders that were dispersed on either aide of the zero-order beam. Three photodiodes were positioned to measure the signals in the zero order and in the +1 and -1 orders. The photodiodes had aluminum overcoatings that passe d the desired wavelength bandpass centered at 30 nm and attenuated higher-o rder radiation and wavelengths longer than approximately 80 nm. The spectro meter's responsivity, the ratio of the photodiode current to the incident r adiation power, was determined as a function of the incident wavelength and the angle of the spectrometer with respect to the incident radiation beam. The spectrometer's responsivity was consistent with the product of the pho todiode responsivity and the grating efficiency, both of which were separat ely measured while removed from the spectrometer.