Recent theoretical and numerical studies of laser-driven femtosecond K *a sources are presented, aimed at understanding a recent experimental campaign to optimize emission from thin coating targets. ...Particular attention is given to control over the laser--plasma interaction conditions defined by the interplay between a controlled prepulse and the angle of incidence. It is found that the x-ray efficiency for poor-contrast laser systems in which a large preplasma is suspected can be enhanced by using a near-normal incidence geometry even at high laser intensities. With high laser contrast, similar efficiencies can be achieved by going to larger incidence angles, but only at the expense of larger x-ray spot size. New developments in three-dimensional modelling are also reported with the goal of handling interactions with geometrically complex targets and finite resistivity.
We have investigated the dynamics of femtosecond laser-induced ablation from the surface of various materials. Combining pump–probe techniques with optical microscopy we have monitored the structural ...modifications of the irradiated surfaces both in space
and time. In the fluence regime below the threshold for plasma formation ablation is caused by the hydrodynamic expansion of laser-heated material. Upon expansion into vacuum each of the investigated materials (Si, GaAs, Al, Au, Mg, Hg) evolves from the initial metallic state into an optically transparent phase with high index of refraction.
Time-resolved diffuse X-ray scattering with 50 fs, 9.5 keV X-ray pulses from the Linear Coherent Light Source was used to study the structural dynamics in materials undergoing rapid melting and ...ablation after fs laser excitation.
Intense ultrashort laser pulses enable the generation of subpico-second X-ray pulses in the multi-kilovolt range of photon energies. These X-ray pulses have opened the door to ultrafast time-resolved ...X-ray spectroscopy. Here, we report on the use of time-resolved X-ray diffraction to study ultrafast laser-induced order-to-disorder transitions and large amplitude picosecond acoustic transients that accompany the phase transitions.
Coherent imaging at FLASH Chapman, H N; Bajt, S; Barty, A ...
Journal of physics. Conference series,
09/2009, Letnik:
186, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We have carried out high-resolution single-pulse coherent diffractive imaging at the FLASH free-electron laser. The intense focused FEL pulse gives a high-resolution low-noise coherent diffraction ...pattern of an object before that object turns into a plasma and explodes. In particular we are developing imaging of biological specimens beyond conventional radiation damage resolution limits, developing imaging of ultrafast processes, and testing methods to characterize and perform single-particle imaging.
In the last few years, bent crystal x-ray mirrors have played an important role in time-resolved x-ray diffraction experiments when x-ray pulses from femtosecond laserproduced plasmas were used. ...Improvements in manufacturing techniques have significantly increased the quality of this type of mirror.
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