Description

Energy Spectrometers

A single energy spectrometer (PRESTO) is designed to acquire the FEL spectrum for both FEL1 and FEL2 in the wavelength range 100-3 nm. The optical part is made by three identical plane Silicon substrates. All of them have the central part ruled in order to realize a Variable Line Spacing (VLS) diffraction grating. Each grating is designed to deliver and focus a very small part of the incoming radiation (about 1%) onto a YAG crystal, imaged by a CCD detector, while most of the incoming photons (>97%) are reflected to the following beamlines. The grazing angle of incidence is fixed to 2.5°, while the distance from the source slightly depends on the selected wavelength, and is about 45 m. The focus position changes as a function of the photon energy for both angle and distance. The minimum and maximum collectable diffraction angles are limited by the mechanical system, and are 9° and 19°, respectively, while the focal distance ranges from 2500 to 3100 mm.
A similar spectrometer (TARDI) serves only MagneDYN, which receives light only from FEL2. There are two gratings covering the 60-2.1 nm range, working at a grazing incidence angle of 2°.
The gratings parameters are reported in the tables below (D0, D1, D2nad D3 are the groove density variation parameters).