Imaging spin polarimeter for momentum microscopy

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We request an imaging spin polarimeter that will add spin resolution to an existing setup for energy-, time- and momentum-resolved photoemission-microscopy with fs-XUV radiation. This upgraded setup is at the core of most of the planned and ongoing research activities of the Cinchetti group, whose ultimate goal is the understanding and the optical manipulation of magnetic and electronic properties in solids on the shortest possible length- and time-scales. This proposal is the follow-up of two, already approved, major instrumentation proposals for the procurement of a femtosecond extreme ultraviolet (fs-XUV) source and of a time-of-flight momentum microscope system. The latter instrument will be upgraded with the here requested imaging spin polarimeter to realize an advanced setup for spin- angle- and time-resolved photoemission spectro-microscopy. This combination will allow us to perform the cutting-edge photoemission experiments that are planned in the ongoing as well as future research activities of our group. The ongoing activities include the ERC consolidator project hyControl as well as the FET-OPEN projects SINFONIA and INTERFAST, where it is planned to perform spin-resolved femtosecond molecular orbital mapping experiments. In addition, in project B9 of the DFG TRR 160, we will map the time evolution of the spin-polarized band structure of magnetically ordered 2D materials, throughout the whole Brillouin zone, with femtosecond time resolution. Finally, in a "MERCUR Kooperation" project we plan, together with Prof. Saraceno (RUB Bochum), to build an ultrafast spectroscopic tool with unique performance and flexibility based on state-of-the-art ultrafast laser technology specifically tailored for spin-resolved photoemission spectroscopy of molecular systems. Such ongoing projects, as well as the future research activities of our group (that include three projects planned for the third phase of the TRR160), pose a set of demanding requirements on the whole setup and on the imaging spin polarimeter. In particular, the instrument must allow for a seamless integration in the available momentum microscope system and enable on-demand switching to the spin-resolved mode of operation. Moreover, the device should allow in-parallel detection of the spin-filtered momentum-resolved photoemission intensity. As high-resolution spin-resolved momentum mapping is required to pursue our scientific goals, the polarimeter must employ a scattering target surface with low mosaic-spread and present a single-pixel figure of merit comparable with the state-of-the-art performance of conventional spin-polarized low-energy-electron-diffraction polarimeters. Finally, due to the generally small intensity of the time-resolved photoemission transients, the polarimeter must ensure prolonged periods of uninterrupted data acquisition, and rely on a scattering target with proven long-lifetime in ultra-high-vacuum conditions.