Optical pump-probe setups are commonly used for the excitation and investigation of spin dynamics in various types of magnetic materials. However, spatially homogeneous excitation is usually considered. In the present study, we describe an approach to optical excitation of nonuniform THz spin dynamics and to probing its spatial distribution inside a magnetic crystal. We propose to illuminate a crystal with laser pulses of properly adjusted polarization to benefit from the strong optical birefringence inherent in the crystal. This results in unusual behavior of the effective magnetic field generated by the pulses due to the inverse Faraday effect and the peculiar sign-changing dependence of the direct Faraday effect inside the crystal. The study is performed for an yttrium orthoferrite crystal as an example, although the proposed approach is applicable to various magnetic materials with optical anisotropy.

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• Birefringence
• Faraday effect
• Magnetization dynamics
• Spintronics
• Ultrafast magnetic effects
• Antiferromagnets
• Pump-probe spectroscopy
• Terahertz techniques