The advent of free electron lasers (FELs) in the soft and hard X-ray spectral region has opened the possibility to probe electronic, magnetic and structural dynamics, in both diluted and condensed matter samples, with femtosecond time resolution. In particular, FELs strongly enhanced the capabilities of several analytical techniques, which took advantage of the high degree of transverse coherence provided. FELs based on the harmonic up-conversion of an external seed laser are characterised also by a high degree of longitudinal coherence, since electrons inherit the coherence properties of the seed. At the present state of the art, the shortest wavelength delivered to user experiments by an externally seeded FEL light source is about 4 nm. We show here that pulses with a high longitudinal degree of coherence (first and second order) covering the water window and with photon energy extending up to 790 eV can be generated by exploiting the so-called nonlinear harmonic regime, which allows generation of radiation at harmonics of the resonant FEL wavelength.

Moreover, we report the results of two proof-of-principle experiments: one measuring the oxygen K-edge absorption in water ($\sim$ 530 eV), the other analysing the spin dynamics of Fe and Co through magnetic small angle x-ray scattering at their L-edges (707 eV and 780 eV)

Speakers:
Giuseppe Penco
(),
Alberto Simoncig
(Elettra-Sincrotrone Trieste S.C.p.A.),
Alessandro Gessini
(Elettra-Sincrotrone Trieste S.C.p.A.),
Alexander Brynes
(),
Enrico Allaria
(),
Alexander Demidovich
(),
Antonio Caretta
(Elettra-Sincrotrone Trieste S.C.p.A.),
Boris Vodungbo
(Sorbonne Université, CNRS, Laboratoire de Chimie Physique – Matière et Rayonnement, LCPMR, Paris 75005, France),
Carlo Callegari
(Elettra-Sincrotrone Trieste S.C.p.A.),
Carlo Spezzani
(),
Claudio Masciovecchio
(),
Dario De Angelis
(Elettra-Sincrotrone Trieste S.C.p.A.),
Eléonore Roussel
(),
Emanuele Pedersoli
(Elettra-Sincrotrone Trieste S.C.p.A.),
Emiliano Principi
(Elettra-Sincrotrone Trieste S.C.p.A.),
Emmanuelle Jal
(Sorbonne Université, CNRS, Laboratoire de Chimie Physique – Matière et Rayonnement, LCPMR, Paris 75005, France),
Filippo Bencivenga
(Elettra-Sincrotrone Trieste S.C.p.A.),
Filippo Sottocorona
(University of Trieste, Elettra Sincrotrone Trieste),
Flavio Capotondi
(),
Gabor Kurdi
(Elettra-Sincrotrone Trieste S.C.p.A.),
Giovanni De Ninno
(Elettra-Sincrotrone Trieste S.C.p.A.),
Giovanni Perosa
(University of Trieste, Elettra Sincrotrone Trieste),
Giulio Gaio
(Elettra-Sincrotrone Trieste S.C.p.A.),
Ivaylo Nikolov
(Elettra-Sincrotrone Trieste S.C.p.A.),
Jan Luning
(Sorbonne Université, CNRS, Laboratoire de Chimie Physique – Matière et Rayonnement, LCPMR, Paris 75005, France),
Laura Badano
(),
Laura Foglia
(Elettra-Sincrotrone Trieste S.C.p.A.),
Luca Giannessi
(Elettra-Sincrotrone Trieste S.C.p.A.),
Marcel Hennes
(Sorbonne Université, CNRS, Laboratoire de Chimie Physique – Matière et Rayonnement, LCPMR, Paris 75005, France),
Marco Malvestuto
(Elettra-Sincrotrone Trieste S.C.p.A.),
Marco Zangrando
(),
Mauro Trovo
(Elettra-Sincrotrone Trieste S.C.p.A.),
Michele Manfredda
(Elettra-Sincrotrone Trieste S.C.p.A.),
Miltcho Danailov
(Elettra-Sincrotrone Trieste S.C.p.A.),
Paolo Cinquegrana
(Elettra-Sincrotrone Trieste S.C.p.A.),
Pelli Cresi Stefano
(Elettra-Sincrotrone Trieste S.C.p.A.),
Primoz Rebernik Ribic
(Elettra-Sincrotrone Trieste S.C.p.A.),
Riccardo Mincigrucci
(Elettra-Sincrotrone Trieste S.C.p.A.),
Simone Di Mitri
(Elettra-Sincrotrone Trieste S.C.p.A.),
Simone Spampinati
(Elettra-Sincrotrone Trieste S.C.p.A.),
Valentin Chardonnet
(Sorbonne Université, CNRS, Laboratoire de Chimie Physique – Matière et Rayonnement, LCPMR, Paris 75005, France),
Benedikt Roesner
(),
Christian David
(),
Panagiota Bougiatioti
(),
Maurizio Sacchi
(),
Simone Dal Zilio
(CNR-IOM, Istituto Officina dei Materiali)