Systems and methods for EUV Light Source metrology are disclosed. In a first aspect, a system for measuring an EUV light source power output may include a photoelectron source material disposed along an EUV light pathway to expose the material and generate a quantity of photoelectrons. The system may further include a detector for detecting the photoelectrons and producing an output indicative of EUV power. In another aspect, a system for measuring an EUV light intensity may include a multi-layer mirror, e.g., Mo/Si, disposable along an EUV light pathway to expose the mirror and generate a photocurrent in the mirror. A current monitor may be connected to the mirror to measure the photocurrent and produce an output indicative of EUV power. In yet another aspect, an off-line EUV metrology system may include an instrument for measuring a light characteristic and MoSi2/Si multi-layer mirror.