A radiation source arrangement including: a radiation source operable to generate source radiation including source energy pulses; and at least one non-linear energy-filter operable to filter the source radiation to obtain filtered radiation including filtered energy pulses. The at least one non-linear energy-filter is operable to mitigate variation in energy in the filtered radiation by reducing the energy level of the source energy pulses which have an energy level corresponding to one of both extremities of an energy distribution of the source energy pulses by a greater amount than the source energy pulses which have an energy level corresponding to a peak of the energy distribution.