In a beam lithography operation the relative motion between a work piece and the exposure beam produces variations in linear speed at different regions of the work piece surface. For example, if a disk work piece rotates with a constant angular velocity (CAV) relative to the beam, the linear surface speed relative to the beam impact point increases in proportion to increasing radial distance of that point from the center of the disk. To provide uniform exposure dose, the duty cycle of pulses of the exposure beam are varied in accord with radial distance.