77 research outputs found
Spectro-temporal shaping of seeded free-electron laser pulses
We demonstrate the ability to control and shape the spectro-temporal content
of extreme-ultraviolet (XUV) pulses produced by a seeded free-electron laser
(FEL). The control over the spectro-temporal properties of XUV light was
achieved by precisely manipulating the linear frequency chirp of the seed
laser. Our results agree with existing theory, which allows retrieving the
temporal properties (amplitude and phase) of the FEL pulse from measurements of
the spectra as a function of the FEL operating parameters. Furthermore, we show
the first direct evidence of the full temporal coherence of FEL light and
generate Fourier limited pulses by fine-tuning the FEL temporal phase. The
possibility to tailor the spectro-temporal content of intense short-wavelength
pulses represents the first step towards efficient nonlinear optics in the XUV
to X-ray spectral region and will enable precise manipulation of core-electron
excitations using the methods of coherent quantum control.Comment: 5 pages, 3 figure
Towards jitter-free pump-probe measurements at seeded free electron laser facilities
X-ray free electron lasers (FEL) coupled with optical lasers have opened unprecedented opportunities for studying ultrafast dynamics in matter. The major challenge in pump-probe experiments using FEL and optical lasers is synchronizing the arrival time of the two pulses. Here we report a technique that benefits from the seeded-FEL scheme and uses the optical seed laser for nearly jitter-free pump-probe experiments. Timing jitter as small as 6 fs has been achieved and confirmed by measurements of FEL-induced transient reflectivity changes of Si3N4 using both collinear and non-collinear geometries. Planned improvements of the experimental set-up are expected to further reduce the timing jitter between the two pulses down to fs level
24 mJ Cr+4:forsterite four-stage master-oscillator power-amplifier laser system for high resolution mid-infrared spectroscopy
We present the design of a Cr:forsterite based single-frequency master-oscillator power-amplifier laser system delivering much higher output energy compared to previous literature reports. The system has four amplifying stages with two-pass configuration each, thus enabling the generation of 24 mJ output energy in the spectral region around 1262 nm. It is demonstrated that the presented Cr:forsterite amplifier preserves high spectral and pulse quality, allowing a straightforward energy scaling. This laser system is a promising tool for tunable nonlinear down-conversion to the mid-infrared spectral range and will be a key building block in a system for high-resolution muonic hydrogen spectroscopy in the 6.8 \u3bcm rang
Improved stabilization scheme for extreme ultraviolet quantum interference experiments
Interferometric pump-probe experiments in the extreme ultraviolet (XUV)
domain are experimentally very challenging due to the high phase stability
required between the XUV pulses. Recently, an efficient phase stabilization
scheme was introduced for seeded XUV free electron lasers (FELs) combining
shot-to-shot phase modulation with lock-in detection. This method stabilized
the seed laser beampath on the fundamental ultraviolet wavelength to a high
degree. Here, we extend this scheme including the stabilization of the XUV
beampath, incorporating phase fluctuations from the FEL high gain harmonic
generation process. Our analysis reveals a clear signal improvement with the
new method compared to the previous stabilization scheme
High-Gain Harmonic Generation with temporally overlapping seed pulses and application to ultrafast spectroscopy
Collinear double-pulse seeding of the High-Gain Harmonic Generation (HGHG)
process in a free-electron laser (FEL) is a promising approach to facilitate
various coherent nonlinear spectroscopy schemes in the extreme ultraviolet
(XUV) spectral range. However, in collinear arrangements using a single
nonlinear medium, temporally overlapping seed pulses may introduce nonlinear
mixing signals that compromise the experiment at short time delays. Here, we
investigate these effects in detail by extending the analysis described in a
recent publication (Wituschek et al., Nat. Commun., 11, 883, 2020). High-order
fringe-resolved autocorrelation and wave-packet interferometry experiments at
photon energies > eV are performed, accompanied by numerical simulations.
It turns out that both the autocorrelation and the wave-packet interferometry
data are very sensitive to saturation effects and can thus be used to
characterize saturation in the HGHG process. Our results further imply that
time-resolved spectroscopy experiments are feasible even for time delays
smaller than the seed pulse duration.Comment: This is accepted version of the article. The Version of Record is
available online at https://doi.org/10.1364/OE.40124
Widely tunable two-colour seeded free-electron laser source for resonant-pump resonant-probe magnetic scattering
International audienceThe advent of free-electron laser (FEL) sources delivering two synchronized pulses of different wavelengths (or colours) has made available a whole range of novel pump–probe experiments. This communication describes a major step forward using a new configuration of the FERMI FEL-seeded source to deliver two pulses with different wavelengths, each tunable independently over a broad spectral range with adjustable time delay. The FEL scheme makes use of two seed laser beams of different wavelengths and of a split radiator section to generate two extreme ultraviolet pulses from distinct portions of the same electron bunch. The tunability range of this new two-colour source meets the requirements of double-resonant FEL pump/FEL probe time-resolved studies. We demonstrate its performance in a proof-of-principle magnetic scattering experiment in Fe–Ni compounds, by tuning the FEL wavelengths to the Fe and Ni 3p resonances
COMMISIONING OF THE FERMI@ELETTRA LASER HEATER*
Abstract The linac of the FERMI seeded free electron laser includes a laser heater to control the longitudinal microbunching instability, which otherwise is expected to degrade the quality of high brightness electron beam sufficiently to reduce the FEL power. The laser heater consists of a short undulator located in a small magnetic chicane through which an external laser pulse enters to modulate the electron beam energy both temporally and spatially. This modulation, which varies on the scale of the laser wavelength, together with the effective R52 transport term of the chicane increases the incoherent energy spread (i.e., e-beam heating). We present the first commissioning results of this system, and its impact both upon the electron beam phase space, and upon the FEL output intensity and quality
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