A method and system for determining a shape of an irradiance pulse to which a semiconductor wafer is to be exposed during a thermal cycle are disclosed. The method includes receiving, with a processor circuit, thermal cycle parameters specifying requirements of the thermal cycle, and determining, with the processor circuit, a shape of a heating portion of the irradiance pulse. Determining includes optimizing at least one parameter of a flux profile model of the heating portion of the irradiance pulse to satisfy the requirements while minimizing frequency-domain energy spectral densities of the flux profile model at resonant frequencies of the wafer, to minimize vibration of the wafer at the resonant frequencies when the wafer is exposed to the irradiance pulse.