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Electron-nuclear spin interactions by pulsed optical pumping have been found to polarize the nuclear spin system, leading to the nuclei building up an intrinsic magnetic field known as the Overhauser field. Studies have indicated an Overhauser field hysteresis effect dependent on the sweep direction of an externally applied magnetic field in negatively detuned periodically pumped Si-doped GaAs. Although predictions of bistable mode-locked electron spin precession frequency modes have been made for systems exhibiting this hysteresis, there have been no reports on the experimental observation of said bistable spin precession modes. This report details the evolution of bistable Overhauser field solutions leading to a hysteretic effect in negatively detuned optical excitation of Si-doped GaAs by magneto-optic pump–probe spectroscopy in the Voigt geometry and investigates the resulting consequence of this hysteresis acting on the electron spin system. One manifestation of the Overhauser field hysteresis acting on the electron spin system leads to the discretization of bistable mode-locked electron spin precession modes within a given band of externally applied magnetic fields. A method for preferentially accessing the two different and stable mode-locked spin precession modes within a given band of externally applied magnetic field is outlined, which may be of interest for communities utilizing electron and nuclear spins for information processing protocols. 

An experimental and computational optical pump-probe model is constructed, which utilizes two ultrafast pump pulses within the repetition period of a mode-locked laser to generate electron spin polarization. This report focuses on the effects of resonant spin amplification induced by an infinite train of the two-pump pulses. The first pump pulse is used to generate ordinary resonant spin amplification spectra, while the second pump pulse is used to manipulate the generated spectra. This model gives control of the accumulation of spin polarized electrons along a magnetic field by selecting the temporal separation of the two-pump pulses. The computational model accurately predicts and agrees with the experimental results, which shows manipulation of resonant spin peaks that are no longer entirely dependent on the external magnetic field. This two-pump model and the associated manipulations of resonant spin peaks can be used as a platform to construct and conceptualize resonant spin amplification-based optospintronic devices and applications.