A metrology system is used for measuring a spectral feature of a pulsed light beam. The metrology system includes: a beam homogenizer in the path of the pulsed light beam, the beam homogenizer having an array of wavefront modification cells, with each cell having a surface area that matches a size of at least one of the spatial modes of the light beam; an optical frequency separation apparatus in the path of the pulsed light beam exiting the beam homogenizer, wherein the optical frequency separation apparatus is configured to interact with the pulsed light beam and to output a plurality of spatial components that correspond to the spectral components of the pulsed light beam; and at least one sensor that receives and senses the output spatial components.