Spintronics, the use of electron spin for technological applications, is a rapidly evolving field. Its potential to enable faster, more energy-efficient devices has driven the search for materials with novel spin-related properties. In the modern condensed matter physics, spin-resolved electron spectroscopy is a cornerstone technique, which enables the exploration of materials' spin-dependent electronic structures. This thesis contributes to advancing this field through two complementary approaches: the development of a multichannel Mott polarimeter (iMott) and an experimental study of the altermagnetic material a-MnTe.

The first part of the thesis focuses on the iMott - a prototype of a Mott polarimeter designed for two-dimensional polarization measurements. The working principles of iMott's electron optics were systematically analyzed through numerical simulations and experimental calibration. The device demonstrates the ability to transfer electron images from a hemispherical analyzer (HSA) to position-sensitive detectors with minimal resolution degradation. Despite the inherent inefficiency of Mott scattering, the multichannel design provides significant advantages, including faster signal accumulation, as well as post-measurement adjustable resolution and count rate. Preliminary calibration with unpolarized electrons has been performed. Challenges such as the detector frame rates, high-voltage insulation, and ultra-high vacuum (UHV) compatibility were identified, offering a roadmap for future instrumental progress of the iMott.

The second part presents an in-depth spin- and angle-resolved photoemission spectroscopy (SARPES) study of a-MnTe - a candidate for hosting the recently discovered altermagnetic phase. This research explores altermagnetic-driven band splitting and spin textures arising from non-relativistic and relativistic phenomena. g-wave band splitting, arising from nonrelativistic lifted Kramer's spin degeneracy, was observed and corresponding antisymmetric (with respect to the zone center) spin polarization was detected. d-wave relativistic spin splitting, driven by both spin-orbit coupling and altermagnetic symmetry, was also observed. Symmetry-resolved domain mapping and polarization measurements suggest selective photoemission excitation based on the Néel vector orientation. These findings substantiate the altermagnetic nature of a-MnTe in qualitative agreement with theoretical models.

By bridging the gap between novel magnetic materials and advancements in experimental instrumentation, this thesis contributes to the growing understanding of altermagnetic materials and the tools required to study them. Together, they highlight the importance of technological innovation in uncovering the fundamental properties of new materials and driving their applications in spintronics.