Illumination subsystems of a metrology or inspection system, metrology systems, inspection systems, and methods for illuminating a specimen for metrology measurements or for inspection are provided. One illumination subsystem includes a light source configured to generate coherent pulses of light and a dispersive element positioned in the path of the coherent pulses of light, which is configured to reduce coherence of the pulses of light by mixing spatial and temporal characteristics of light distribution in the pulses of light. The illumination subsystem also includes an electro-optic modulator positioned in the path of the pulses of light exiting the dispersive element and which is configured to reduce the coherence of the pulses of light by temporally modulating the light distribution in the pulses of light. The illumination subsystem is configured to direct the pulses of light from the electro-optic modulator to a specimen.