A method and apparatus are provided for attenuating an optical beam. The method includes selecting a level of attenuation to be applied to the optical beam. A pattern of on-state and off-state pixels in a two dimensional spatial light modulator (SLM) is selected such that the pattern will modulate the optical beam to provide the selected level of attenuation. Finally, the optical beam is directed onto the SLM while tile pixels are arranged in the selected pattern. The pattern is periodic along a first axis and symmetric along a second axis along which an intensity distribution of die optical beam extends.