An energy modulator for use with a particle source that provides a beam of particles includes a first block moveable between a first position and a second position, wherein when the first block is at the second position, it is in a path of the beam, and a second block moveable relative to the first block, wherein the second block and the first block are offset from each other in a direction of the beam, wherein the first block has a first energy absorption characteristic, and the second block has a second energy absorption characteristic that is different from the first energy absorption characteristic.