title: Performance of photoelectron spin polarimeters with continuous and pulsed sources: from storage rings to free electron lasers.
abstract: In this work the experimental uncertainties concerning electron spin polarization (SP) under various realistic measurement conditions are theoretically derived. The accuracy of the evaluation of the SP of the photoelectron current is analysed as a function of the detector parameters and specifications, as well as of the characteristics of the photoexcitation sources. In particular, the different behaviour of single counter or twin counter detectors when the intensity fluctuations of the source are considered have been addressed, leading to a new definition of the SP detector performance. The widely used parameter called the figure of merit is shown to be inadequate for describing the efficiency of SP polarimeters, especially when they are operated with time-structured excitation sources such as free-electron lasers. Numerical simulations have been performed and yield strong implications in the choice of the detecting instruments in spin-polarization experiments, that are constrained in a limited measurement time. Our results are therefore applied to the characteristics of a wide set of state-of-the-art spectroscopy facilities all over the world, and an efficiency diagram for SP experiments is derived. These results also define new mathematical instruments for handling the correct statistics of SP measurements in the presence of source intensity fluctuations.
authors.affiliation: Dipartimento di Fisica, Università degli studi di Milano, Via Celoria 16, 20133 Milano, Italy.
authors.forename: T
authors.initials: T
authors.lastname: Pincelli
authors.affiliation: Dipartimento di Scienze Fisiche, Informatiche e Matematiche, Università degli Studi di Modena e Reggio Emilia, Via Campi 213/a, Modena, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Grasselli
authors.affiliation: Saint Petersburg State Polytechnical University, Politechnicheskaya Street 29, 195251, Russian Federation.
authors.forename: V N
authors.initials: VN
authors.lastname: Petrov
authors.affiliation: Laboratorio TASC, IOM-CNR, SS 14 km 163.5, Basovizza, 34149 Trieste, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Torelli
authors.affiliation: Dipartimento di Fisica, Università degli studi di Milano, Via Celoria 16, 20133 Milano, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Rossi
keywords: continuous source; intensity fluctuations; pulsed source; spin-polarimetry statistics; spin-resolved photoemission