article epub_ahead Veronika Sunko author 23cb1cf6-2c7a-11ef-91a4-f72fc19f20b30000-0003-2724-3523 J. Orenstein author VeSu department Altermagnets are a class of collinear magnets that exhibit non-relativistic spin splitting (NRSS) of electronic bands in the absence of net magnetization. Their potential to generate large spin polarization without spin-orbit coupling has created strong interest in probes that access the underlying order parameter directly. In this Perspective, we show that linear magneto-birefringence (LMB) provides a natural and broadly applicable route to detecting altermagnetic order. Building on the correspondence between the momentum-space structure of NRSS and the ferroic ordering of magnetic multipoles in real space, we demonstrate how $d$-wave and $g$-wave NRSS textures yield distinct LMB responses. We present a symmetry-based framework that identifies the optical geometries and field configurations required to isolate specific multipole components, enabling domain imaging and providing benchmarks for theoretical models of LMB. Springer Nature2026 eng 2397-4648 2511.1642110.1038/s41535-026-00901-8 Sunko V, Orenstein J. 2026. Linear magneto-birefringence as a probe of altermagnetism. npj Quantum Materials. Sunko, Veronika, and J. Orenstein. “Linear Magneto-Birefringence as a Probe of Altermagnetism.” <i>Npj Quantum Materials</i>, Springer Nature, 2026, doi:<a href="https://doi.org/10.1038/s41535-026-00901-8">10.1038/s41535-026-00901-8</a>. Sunko, Veronika, and J. Orenstein. “Linear Magneto-Birefringence as a Probe of Altermagnetism.” <i>Npj Quantum Materials</i>. Springer Nature, 2026. <a href="https://doi.org/10.1038/s41535-026-00901-8">https://doi.org/10.1038/s41535-026-00901-8</a>. Sunko, V., &#38; Orenstein, J. (2026). Linear magneto-birefringence as a probe of altermagnetism. <i>Npj Quantum Materials</i>. Springer Nature. <a href="https://doi.org/10.1038/s41535-026-00901-8">https://doi.org/10.1038/s41535-026-00901-8</a> V. Sunko, J. Orenstein, Npj Quantum Materials (2026). V. Sunko and J. Orenstein, “Linear magneto-birefringence as a probe of altermagnetism,” <i>npj Quantum Materials</i>. Springer Nature, 2026. Sunko V, Orenstein J. Linear magneto-birefringence as a probe of altermagnetism. <i>npj Quantum Materials</i>. 2026. doi:<a href="https://doi.org/10.1038/s41535-026-00901-8">10.1038/s41535-026-00901-8</a> 214372026-03-11T10:40:08Z2026-06-24T10:31:05Z