Measurement of absolute diffraction efficiency of a variable line spaced grating using reflectivity beamline

First and second order diffraction efficiency of a variable line spacing grating of average 1200 lines/mm density is measured at the reflectivity beam line of Indus-1. This grating is blazed at 3.2 deg. and has a blaze wavelength of 10 nm. The measurement has been carried out in the spectral range of 4.5 nm to 80 nm at 3o grazing angle of incidence. The maximum diffraction efficiency of the first order at ∼10 nm has been found to be ∼ 23% and for the second order it is ∼13%.