Insight into the thermionic emission regimes under gold film thermal relaxation excited by a femtosecond pulse

► We investigated the role of the two temperature relaxation and the thermal diffusion relaxation participating in ultrafast thermionic emission processes. ► The thermionic emission rate profiles would emerge as alternative shapes of single peak or two-part structure, depending on the laser parameters. ► There exists a transition between two thermionic emission regimes under the peculiar laser conditions.