Fabris, Nicola (2019) Instrumentation for Photon Handling of XUV and Soft X-ray Ultrafast Pulses. [Ph.D. thesis]
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Abstract (italian or english)
The recent availability of ultrafast coherent sources in the extreme ultraviolet (XUV) and soft X-ray spectral regions, such as high-order laser harmonics and free-electron lasers made possible time-resolved studies of electron and molecules dynamics on sub-femtosecond time scales. Simultaneously, the increasing demand of optical technologies suitable for photon handling and conditioning of this type of sources is a field where a strong collaboration between research and industry is required, in order to reach new results. This thesis concerns the design, realization and characterization of different monochromators dedicated to the selection of a portion of the spectrum generated by ultrafast sources.
The first contribution regards the comparison in terms of overall efficiency between two widely adopted single diffraction grating monochromators geometries, specifically the classical (CDM) and off-plane (OPM) mounts. A subsequent comparison with AFM-based simulations has been performed in order to validate the experimental results. Remarkably, the OPM diffraction efficiency is measured to about 2 times and 7 times higher than the CDM at the XUV energies of 100 eV and 310 eV. Efficiencies as high as 45 % at 100 eV and 35 % at 310 eV have been measured for OPM gratings.
The second contribution consists in the software and optical setup of a double grating time-delay compensated monochromator. This monochromator will be soon inserted and ready for the alignment at the Extreme Light Infrastructure - Attosecond Light Pulse Source, ELI-ALPS, European ultra-high brightness laser facility (Hungary). The chosen parameters of the monochromator, in order to obtain the requested spectral bandwidth and temporal performances are analyzed in detail. The XUV monochromator simulated temporal resolution is lower than 15 fs at low energy resolution mode and lower than 30 fs at high energy resolution.
The third contribution consists in the characterization results achieved in terms of aberrations minimization, resolution and efficiency by designing a novel monochromator with a new three-optical-elements layout. The measured spectral resolving power is in the 3700-5200 range (output bandwidth <10 meV) over the spectral region of 12-50 eV. This is comparable to spectral resolving powers achieved on synchrotron beamlines. Excellent XUV monochromator performances has been obtained throughout by using simple optical components, which are available off the shelf on the market with high optical quality; although at modest prices.
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