J.-C. Gauthier

Finite temperature dense matter studies on next-generation light sources

The construction of short-pulse tunable soft x-ray free electron laser sources based on the self-amplified spontaneous emission process will provide a major advance in capability for dense plasma-related and warm dense matter (WDM) research. The sources will provide 1013xa0photons in a 200-fs duration pulse that is tunable from approximately 6 to 100 nm. Here we discuss only two of the many applications made possible for WDM that has been severely hampered by the fact that laser-based methods have been unavailable because visible light will not propagate at electron densities of ne≥1022xa0cm-3. The next-generation light sources will remove these restrictions.

High Sensitivity Microwave Gated Radiometer for Low Temperature Plasma Afterglow Studies

We describe a new microwave gated radiometer for traveling wave measurement of the radiation temperature of low temperature plasma afterglows independent of plasma absorptivity and reflection coefficients. Since this radiometer is unaffected by a medium power heating microwave, it is particularly well suited for keeping a close control on temperature during microwave cross modulation experiments.

Modeling of the transient nickellike silver x-ray laser

Recent high-temporal-resolution nickellike x-ray laser experiments have yielded important insights into the output characteristics of picosecond-pumped x-ray lasers. However, current experimental observations do not fully explain the plasma dynamics, which is critical to gain generation within the x-ray laser medium. A numerical study of the nickellike silver x-ray laser has therefore been undertaken to complement our experimental results in an attempt to further our understanding of the processes at work in yielding the observed x-ray laser output. High gain coefficients existing with picosecond lifetimes are predicted, which is consistent with the short x-ray laser durations experimentally observed. The late onset of the continuum emission relative to the temporal peak of the x-ray laser output is explained as a sign of high electron density evolution near the target surface.

X-ray line polarization spectroscopy of He-like Si satellite line spectra

Laser-produced plasmas driven by high-intensity, femtosecond-duration pulsed lasers have been recognized as sources of short-duration x-ray line emissions. Electron kinetics simulations of such transient and nonequilibrium plasmas predict non-Maxwellian electron distributions and even the presence of electron beams. X-ray line polarization spectroscopy is a diagnostic that can be used to study the directionality of the electron distribution function and thus test electron kinetics simulation results. To this end, we use a time-dependent, collisional-radiative atomic kinetics model of magnetic sublevels to understand the underlying processes and mechanisms leading to the formation of polarized x-ray line emission in Si plasmas driven by high-intensity, ultrashort duration pulsed lasers. We focus on the polarization properties of the He-like Si satellites of the Lyα line. In the cases under consideration, the relevant line emissions last less than 1 ps during which the plasma undergoes a rapid development. ...

Multi-keV picosecond x-ray source development from ultra-intense kHz laser-cluster interaction

Multi-keV X-ray source from intense laser-cluster interaction was experimentally studied. A special effort was first made in order to characterize the cluster target. K-shell emission of Argon clusters (around 3 keV) was then studied when irradiated by kHz, 30 fs, 1017 W.cm-2 laser pulses. High-resolution spectra are presented, in this spectral range, as a function of laser duration and average cluster size. Signature of very highly charged ions (Ar16+) was observed with relatively low intensity laser pulses (few 1015 W.cm-2). This feature is not yet clearly understood nor reproduced by simulations. Optimal laser pulse duration was observed for X-ray production, depending on the cluster size. For the first time to our knowledge, the duration of K-shell X-ray bursts was measured with a home-made streak camera to be on the picosecond scale.