Ultrashort Free-electron Laser Pulses Research Articles

Impact of MoS2 Monolayers on the Thermoelastic Response of Silicon Heterostructures.

Understanding the thermoelastic response of a nanostructure is crucial for the choice of materials and interfaces in electronic devices with improved and tailored transport properties at the nanoscale. Here, we show how the deposition of a MoS2 monolayer can strongly modify the nanoscale thermoelastic dynamics of silicon substrates close to their interface. We demonstrate this by creating a transient grating with extreme ultraviolet light, using ultrashort free-electron laser pulses, whose ≈84 nm period is comparable to the size of elements typically used in nanodevices, such as electric contacts and nanowires. The thermoelastic response, featuring coherent acoustic waves and incoherent relaxation, is tangibly modified by the presence of monolayer MoS2. Namely, we observed a major reduction of the amplitude of the surface mode, which is almost suppressed, while the longitudinal mode is basically unperturbed, aside from a faster decay of the acoustic modulations. We interpret this behavior as a selective modification of the surface elasticity, and we discuss the conditions to observe such effect, which may be of immediate relevance for the design of Si-based nanoscale devices.

Ultra-Short Pulses Generation of Free Electron Laser

The major problem facing the development of civil and military laser applications lies in the attempts to obtain short pulses close to the length of the bond that connects the atoms of certain materials. In this paper, an executable program has been constructed to simulate and analyze the generation of ultra-short free electron laser pulses; it contains several parameters directing the creation of short pulses within a time duration of femtoseconds (fs). On analyzing the simulation results, it can be concluded that it is possible to generate ultra-short pulses with a duration of about 7.4 – 87.4 fs with the storage ring free-electron laser Fabry–Perot resonator with noticeably short wavelengths (11.4–190.2) for the output laser beam. KEYWORDS Homogenous broadening; SR-FEL; undulator; energy spread gain; Q- switching

Probing near-solid density plasmas using soft x-ray scattering

X-ray scattering using highly brilliant x-ray free-electron laser (FEL) radiation provides new access to probe free-electron density, temperature and ionization in near-solid density plasmas. First experiments at the soft x-ray FEL FLASH at DESY, Hamburg, show the capabilities of this technique. The ultrashort FEL pulses in particular can probe equilibration phenomena occurring after excitation of the plasma using ultrashort optical laser pumping. We have investigated liquid hydrogen and find that the interaction of very intense soft x-ray FEL radiation alone heats the sample volume. As the plasma establishes, photons from the same pulse undergo scattering, thus probing the transient, warm dense matter state. We find a free-electron density of (2.6 ± 0.2) × 1020 cm−3 and an electron temperature of 14 ± 3.5 eV. In pump–probe experiments, using intense optical laser pulses to generate more extreme states of matter, this interaction of the probe pulse has to be considered in the interpretation of scattering data. In this paper, we present details of the experimental setup at FLASH and the diagnostic methods used to quantitatively analyse the data.