Hüning, M. JACoW Publishing Geneva, Switzerland 2226-0366 978-3-95450-194-6 10.18429/JACoW-LINAC2018-FR1A02 English 972-976 FR1A02 FEL diagnostics electron emittance beam-diagnostic Contribution to a conference proceedings 2019 2019-01 https://doi.org/10.18429/JACoW-LINAC2018-FR1A02 http://jacow.org/linac2018/papers/fr1a02.pdf Shorter and shorter bunch lengths (some 10 fs) require sophisticated bunch length measurent devices. Free electron lasers - but not only - use transverse deflecting systems. Employing suitable diagnostic tools measurements are not limited to bunch lengths but can be extended to longitudinal profiles and phase-space distributions, and slice emittances. Not only do successfully operated systems aid the commissioning and operation of FELs but they allow control over more sophisticated phase-space manipulations. The design and construction of such systems, actually operated at different RF frequencies, includes cavity design and fabrication, powerful RF systems, low level RF control, beam lines, diagnostics, and data analysis.