Controlling the electronic spin plays a critical role in the development of modern technology. Most established methods rely on electrical transport. Developing an all-optical approach will enable a non-invasive and potentially ultrafast method to initiate, control, and read the spin states, which will greatly advance the spintronics and quantum information device research. Although a circularly polarized photon carries a spin of ±h, direct magnet domain manipulation with light helicity has been challenging due to the weak angular momentum transfer between photons and magnetic ions. The recently discovered atomically-thin, two-dimensional (2D) magnets offer new possibilities with their rich electric and optical properties. In particular, novel interfacial effects within such 2D magnetic heterostructures can lead to new control capabilities of magnetic states. This proposal uses optical pump-probe spectroscopy to investigate the photon-induced magnetization modulation in 2D magnetic crystals and magnetic heterostructures. The project will develop a fundamental understanding of the non-equilibrium spin dynamics in 2D systems, and aims to achieve a full spin-flip and further coherent spin control with ultrafast laser pulses. The results will provide insights into emergent phenomena between different physical systems and stimulate 2D device development for high-speed spintronics and quantum operations.