Controlling a spectral property of an output light beam produced by an optical source

A method for controlling a deep ultraviolet (DUV) light source comprising N optical oscillators, wherein N is an integer number greater than one and each optical oscillator is configured to produce a respective light beam, the method comprising:

• forming an output light beam based on M light beams produced by M respective optical oscillators, wherein M is an integer number that is greater than zero and is less than or equal to N;
• accessing data related to a spectral property of each of the M light beams;
• comparing a spectral property of each of the M light beams to a reference;
• and
• determining, based on the comparison, whether to control an aspect of any of the N optical oscillators to thereby adjust the spectral property of any of the N light beams.

A control system for a deep ultraviolet (DUV) light source comprising N optical oscillators, wherein N is an integer number greater than one and each optical oscillator is configured to produce a respective light beam, the control system configured to:

• control a first set of the N optical oscillators to generate a first set of light beams during a first time period such that an output light beam produced by the DUV light source during the first time period comprises the first set of light beams;
• control a second set of the N optical oscillators to generate a second set of light beams during a second time period such that the output light beam produced by the DUV light source during the second time period comprises the second set of light beams, wherein the second set of the N optical oscillators and the first set of N optical oscillators do not comprise the same one or ones of the N optical oscillators;
• and
• control a spectral adjustment apparatus of at least one of the N optical oscillators to increase uniformity of a spectral property of the N light beams.