A metrology system includes an optical frequency separation apparatus in the path of the pulsed light beam and configured to interact with the pulsed light beam and output a plurality of spatial components that correspond to the spectral components of the pulsed light beam; a plurality of sensing regions that receive and sense the output spatial components; and a control system connected to an output of each sensing region. The control system is configured to: measure, for each sensing region output, a property of the output spatial components from the optical frequency separation apparatus for one or more pulses; analyze the measured properties including averaging the measured properties to calculate an estimate of the spectral feature of the pulsed light beam; and determine whether the estimated spectral feature of the pulsed light beam is within an acceptable range of values of spectral features.