An indication of an output of an optical source of a photolithography system is accessed; an indication of an input provided to the optical source is accessed, the provided input being associated with the accessed indication of the output of the optical source; an output error is determined from an expected amount of output and the accessed indication of the output of the optical source; a local gain associated with the accessed indication of the input provided to the optical source is estimated; a gain error is determined from the estimated local gain and an expected local gain; a current value of one or more operating metrics of the optical source is estimated based on one or more of the output error and the gain error; and a gain relationship for the optical source is updated based on the estimated current value of the one or more operating metrics.