Altermagnetism represents a novel magnetic phase combining zero net magnetization with momentum-dependent spin splitting. Here, we theoretically investigate the Landau levels and magneto-optical conductivity in $d$-wave altermagnets, explicitly incorporating the orientation of the anisotropic spin-split Fermi surfaces. We derive exact analytical solutions for the system in the absence of spin-orbit coupling. Although the Landau-level energy spectrum remains isotropic, the optical response retains the anisotropic nature of the altermagnet, manifesting as a $\pi$-periodic modulation. Additionally, we investigate the topological phase transitions arising from the interplay of Rashba spin-orbit coupling and the Dirac mass. We demonstrate that the magneto-optical conductivity spectrum provides characteristic signatures such as the sign reversal of the circular conductivity and anomalous peak splitting. Our findings demonstrate that magneto-optical spectroscopy can serve as a versatile probe for detecting both the altermagnetic orientation of the spin-split Fermi surfaces and topological phase transitions, providing theoretical guidance for future optospintronic applications.

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• Altermagnetism
• Electrical conductivity
• Landau levels
• Magneto-optics
• Magnetotransport
• Quantum transport
• Spin-orbit coupling
• 2-dimensional systems
• Altermagnets
• Linear response theory