## 2 Micromagnetic Model  
In a typical AOS experiment, a ferromagnetic layer grown over a substrate is subjected to the action of trains of laser pulses (Figure 1a), with a typical duration (\(\tau_{L}\)) from hundreds of femtoseconds to several picoseconds. The laser spot is assumed to have a space Gaussian profile with a full-width at half-maximum (FWHM) defined by the diameter \(d_{0}\). Its temporal profile is assumed to be Gaussian, with \(\tau_{L}\) being its FWHM duration. Therefore, the space and temporal profile of the laser power is  
\[P(r,t)\ =\ P_{0}\exp\left[-\frac{r^{2}}{d_{0}^{2}/(4 ln2)}\right]\exp\left[- \frac{\left(t-t_{0}\right)^{2}}{\tau_{L}^{2}/(4 ln2)}\right] \tag{1}\]  
where \(r\ =\ \sqrt{x^{2}+y^{2}}\) is the distance from the center of the laser spot and \(t_{0}\) is the time at which the laser power reaches its maximum power (\(P_{0}\)) in the center of the laser spot. The maximum power of the laser is \(P_{0}\ =\ F/(t_{FM}\tau_{L})\), where \(F\) is the laser fluence and \(t_{FM}\) is the thickness of the ferromagnetic sample. Laser pulses heat the ferromagnetic sample. The temperature evolution in the system under the action of the laser pulses is described by the two Temperature Model (2 TM) in terms of two subsystems involving the electron (\(T_{e}\)) and the lattice (\(T_{l}\)) temperatures [28]. The temperature dynamics are given by the following coupled set of differential equations:  
\[ \begin{array}{rl}C_{e}\frac{\partial T_{e}}{\partial t}\ =&-k_{e}\
abla^{2}T_{e}-g_{el}(T_{e}-T_{l})+\eta \left(\overset{\rightarrow}{m},\sigma\right)\left(1-R\right)P\left(\overset{ \rightarrow}{r},t\right)\\ &C_{l}\frac{\partial T_{l}}{\partial t}\ =\ -k_{l}\
abla^{2}T_{l}-g_{d}(T_{l}-T_{e}) \end{array}  \tag{2}\]  
where \(e\) and \(l\) refer to electrons and lattice, respectively. \(C_{i}\) is the thermal capacity (in \(\left[J/\left(m^{3}K\right)\right]\)) and \(k_{i}\) is the thermal conductivity (in \(\left[W/\left(m\cdot K\right)\right]\)) of each subsystem (\(i:e,l\)). \(g_{el}\) is the coupling constant between electrons and lattice (in \(\left[W/m^{3}K\right]\)). \(P\left(\overset{\rightarrow}{r},t\right)\) is the laser power, which is absorbed by the sample in a magnitude that depends on reflectivity of the sample (\(R\)), the local magnetization and helicity (\(\sigma\)) when the MCD is considered through the coefficient \(\eta\left(\overset{\rightarrow}{m},\sigma\right)\). Note that above the Debye temperature, \(C_{l}\) can be considered as constant parameter, whereas, \(C_{e}\) is linear with the electron's temperature, \(C_{e}\ =\ \gamma_{e}T_{e}\) where \(\gamma_{e}\) is the electronic heat capacity (in \(J/m^{3}K^{2}\)). The influence of the substrate is taken into account by adding an additional Newton-like term to the right hand side of the second one of these equations, \((-C_{l}(T\ -\ T_{sub}))/\tau_{sub})\), where \(T_{sub}\) is the substrate temperature, and the \(\tau_{sub}\) is a characteristic time describing the heat transport to the substrate and the surrounding. As the laser pulse usually heats the sample close or even over its Curie temperature (\(T_{C}\)), the Landau-Lifshitz-Gilbert equation (LLG) cannot be used to describe the magnetization dynamics. Instead, the Landau-Lifshitz-Bloch (LLB) equation must be employed [27; 29].