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FERMI is a single-pass FEL user-facility designed to cover the wavelength range from 100 nm to 4 nm. It uses a linear accelerator to generate a beam of relativistic electrons that is made to propagate through a long series of undulators. A conventional laser superposed to the electron beam in the first undulator (seeding) is utilized to induce coherent emission, which is exponentially amplified when the electrons propagate through the following undulator magnetic field. Among existing FEL sources FERMI is unique in many respects. The implemented seeded FEL scheme guarantees the generation of high transversely and longitudinally coherent pulses and the use of APPLE II-type undulators allows for variable polarization, from completely linear both horizontally and vertically to circular in both directions.

FERMI light source

Free Electron Laser

FERMI implements two externally, seeded free electron sources that produce coherent, ultrafast pulses.
Read more about seeding

Facility Overview

FERMI entered in operation for users since January 1st 2019, at the conclusion of its construction and commissioning phase. Here is a description of FEL’s single components, together with an overview of intermediate achieved goals.


Conceptual Design Report

The FERMI Conceptual Design Report.
See the document



The Macro-activity
FERMI Calendar


Historic Milestones

FERMI during the commissioning with external users was continuously improved and upgraded.
Milestone list


Papers published on conference proceedings and journals.
Machine Bibliography


Related Links

Last Updated on Wednesday, 28 April 2021 15:05