Higher-harmonics suppressor was designed for Beamline U26 at NSRL in order to improve the spectral purity of the monochromatic light over the wavelength region of 45–115nm.An investigation revealed that at certain incidence angle

the reflectivity of Al or Si

varying with the wavelength

has obvious cut-off wavelength that increases with decreasing incidence angle.And silicon was chosen as the mirror material for designing a two-mirror higher-harmonic suppressor.The system consists of four pairs of parallel mirrors

each of which works at a different wavelength range.Optimal incidence angle of each pair of reflector was determined.The calculated results show that suppression ratio of the system is greater than 100 over the 45–115 nm range.