The two-dimensional (2D) magnetic semiconductor CrSBr shows great potential for spintronic and optoelectronic device applications due to its intrinsic ferromagnetism and a large magnetic anisotropy. In this study, the phononassociated excitonic dynamics in CrSBr is studied using ultrafast reflectance spectroscopy. The signatures of coherent optical phonons (COPs) and coherent acoustic phonons (CAPs) relaxation dynamics were observed in various spectral ranges. The COPs are mainly generated by a spontaneous multi-body excitation, which corresponds to three Raman peaks and exhibits pronounced phononexciton couplings at two resonances corresponding to the exciton magnetic polariton. Remarkably, CAPs predominantly generated by an electronic stress mechanism exhibit wavelength-dependent frequency dispersion ranging from $\sim 24.57\mathrm{GHz}$ at 660 nm to $\sim 9.28\mathrm{GHz}$ at 1400 nm within the same sample, which can be visualized as concentric ripple patterns through spatially resolved femtosecond transient absorption (TA) imaging of surface acoustic waves (SAWs). These observations provide fundamental insights into the exciton magnetic polaron formation in the 2D CrSBr multilayer structure with its anisotropic magnetic profiles and establish a framework for magnonphononmediated quantum information processing devices.

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• Spin-phonon coupling
• Two-dimensional electron system
• van der Waals systems
• Femtosecond laser spectroscopy