## 1 Introduction  
It has been reported that circularly polarized femtosecond laser pulses can deterministically switch the orientations of magnetization of certain materials [1; 2; 3; 4; 5], including rare-earth transition metal alloys [3; 6], CoPt [7; 8; 9], and their multilayer films [10]. However, the fundamental mechanism remains an open question that impedes the further development of study. All-optical magnetic switching is phenomenologically explained as a combination of effects derived from the inverse Faraday effect (IFE) [11; 12; 13] and heat described as the two-temperature model [5; 14; 15; 16; 17; 18], and all can be treated as effective magnetic fields [5; 19; 20; 21]. However, in a microscopic scale, the origin of IFE and the interaction between laser pulses and magnetic materials is only studied in few publications [12; 22]. The early attempt carried out by [PERSON] et al. [11] in 1961 theoretically predicted the existence of IFE in the frame of a thermodynamic potential. The first experimental observation of IFE was published by [PERSON] et al. [13] in 1965; [PERSON] et al. [12] explained the origin of the IFE from the view of quantum mechanics, and gave a quantitative expression for the IFE field. However, the derived effective Hamiltonian and standard magnetic field by [PERSON], \(\mathrm{M}_{(\mathrm{t})}\propto\mathrm{E}_{(\mathrm{t})}*\mathrm{E}_{( \mathrm{t})}^{*}\), is not applicable for sub-picosecond and high-intensity laser scenarios, because the research assumed that the variation of the pulse amplitude is negligible during the magnetization switching process. The two-temperature model is proposed to reconcile the contradiction between the time scale and the magnitude of magnetic field [4]. However, heat alone can only demagnetize the magnetic materials [23], if the material is not an anti-ferromagnetic system. To suitably fit the study for the process of ultra-fast magnetization reversal, IFE derived by stimulated Raman scattering (SRS) was proposed by [PERSON] [24; 25] who deduced the effective magnetic field from the second order of the time-dependent Hamiltonian. In her study, SRS stimulates the electron transition and changes the spin state, which is helicity dependent, in magnetic materials. Instead of the Schrodinger picture, we are going to use the density matrix formalism to describe the transitions which allows introducing the decay rate easily. In recent studies, the Rashba effect [26; 27; 28] is engineered to be coupled to laser schemes [29; 30; 31]. The circularly polarized laser-induced Rashba effect produces an effective magnetic field on CoPt [31]. The effective field is opposite to the magnetization direction; however, the magnitude of the effective field is helicity dependent. For left-handed circularly polarized light and magnetization along the z direction that is normal to the sample, the effective field is much greater than the right-handed circularly polarized laser-induced effective field. During the oscillation of electronic dipole transition, the angular moment should obey conservation law, which forbids the transitions with spin flips. The effective field induced by the Rashba effect contributes to the angular moment injection of the three-level system during the transitions, besides the function of splitting the energy band. According to [PERSON] and [PERSON] et al., the inverse Faraday field consists of two processes: (1) the light is directly interacted with magnetic materials, and (2) this interaction produces a quasi-stationary relaxed state, which leads to the birth of magnetization in the sample. In this paper, SRS is discussed both qualitatively and quantitatively in the transient process, which corresponds to the direct interaction of light with materials. The Rashba effect, the sub-picosecond time scale process [32], is treated as the builder of the quasi-stationary state. Here, we utilize the ab initio theorem with the two effects mentioned above to get the insight of transient process of magnetization switching on a femtosecond scale.