F. Y. Khattak

Creation of hot dense matter in short-pulse laser-plasma interaction with tamped titanium foils

Dense titanium plasma has been heated to an electron temperature up to 1300eV with a 100TW, high intensity short-pulse laser. The experiments were conducted using Ti foils (5μm thick) sandwiched between layers of either aluminum (1 or 2μm thick) or plastic (2μm thick) to prevent the effects of prepulse. Targets of two different sizes, i.e., 250×250μm2 and 1×1mm2 were used. Spectral measurements of the Ti inner-shell emission, in the region between 4and5keV, were taken from the front-side (i.e., the laser illuminated side) of the target. The data show large shifts in the Kα emission from open-shell ions, suggesting bulk heating of the sample at near solid density, which was largest for reduced mass targets. Comparison with collisional radiative and 2D radiation hydrodynamics codes indicates a peak temperature of Te,peak=1300eV of solid titanium plasma in ∼0.2μm thin layer. Higher bulk temperature (Te,bulk=100eV) for aluminum tamped compared to CH tamped targets (Te,bulk=40eV) was observed. A possible expla...

He-like x-ray line emission from laser irradiated sources

Photon yields for the 1s2–1s2p (He-α) transition of He-like ions have been measured for laser irradiated, thin foils of Ti, V and Fe. The laser pulses were of 0.527 μm wavelength and of either 80 or 300 ps duration. The data shows significant shot-to-shot variation but the Ti data is broadly consistent with previous results. In this work, we extend the previous results to include, new elements, longer pulse lengths and yields measured for emission from both surfaces of the foils. We compare our data to simulations using a hydrodynamic code and a collisional radiative model.

Optical Thomson scatter from a laser-ablated magnesium plume

We have carried out an optical Thomson scatter study of a KrF laser-ablated Mg plume. The evolution of the electron temperature and density at distances 2–5mm from the target surface has been studied. We have observed that the electron density falls more rapidly than the atomic density and believe that this is a result of rapid dielectronic recombination. A comparison of the electron density profile and evolution with simple hydrodynamic modeling indicates that there is a strong absorption of the laser in the plasma vapor above the target, probably due to photoionization. We also conclude that an isothermal model of expansion better fits the data than an isentropic expansion model. Finally, we compared data obtained from Thomson scatter with those obtained by emission spectroscopy under similar conditions. The two sets of data have differences but are broadly consistent.

Optical Thomson scatter from laser-ablated plumes

We have obtained density and temperature informations on an expanding KrF laser-ablated magnesium plume via optical Thomson scatter with a frequency doubled Nd:YAG laser. The electron temperature was found to decay with the expected T{sub e}{proportional_to}t{sup -1} dependence. However, we have found the electron density to have a time dependence n{sub e}{proportional_to}t{sup -4.95} which can be explained by strong recombination processes. We also observed atomic Raman satellites originating from transitions between the different angular momentum levels of the metastable {sup 3}P{sup 0} term in Mg I.

Scale-length optimizing of short pulse CuKα laser-plasma sources

The authors present experimental results showing how the use of a high contrast femtosecond laser system allows better optimization of Kα emission from a Cu target. The shorter scale-length preformed plasma is better optimized for resonance absorption of the laser light when the laser is moved away from best focus. The experimental data show a central peak of Kα emission at tight focus with strong secondary peaks at large offset. The use of these secondary peaks results in a much reduced hard x-ray background and should lead to shorter Kα pulses than at tight focus.

Development of Time Resolved X-ray Spectroscopy in High Intensity Laser-Plasma Interactions

This article discusses the design of a novel time resolved von Hamos Bragg spectrometer to provide spectra in the region around the titanium K-α and He-α lines. The instrument consists of a highly oriented pyrolitic graphite mosaic crystal coupled to a picosecond x-ray streak camera. Measurements of the time dependent behavior from Ti foils illuminated with intense laser pulses can be used to improve the understanding of recombination dynamics, electron transport, and phase transitions in strongly coupled dense plasma. This is important for the modeling of the compression phase in inertial confinement fusion research and the study of astrophysical environments.

X-ray scattering from dense plasmas

We review the potential of x-ray scattering as a dense plasma diagnostic and present data taken from experiments in which x-ray scattering from dense plasmas is developed as a diagnostic tool. In one type of experiment the scattered photons are detected as a function of angle using direct detection onto a CCD chip. Such experiments are designed primarily to observe the static ion–ion structure factor, which is expected to dominate the scattering for moderate to high Z plasmas at a few electronvolts temperature. In a second type of experiment we have used a curved crystal to observe spectrally resolved x-ray scattering at a fixed angle. This experiment was designed to observe the dynamical structure factor of the plasma.

Nonlinear electrostatic solitary pulses in magnetized quantum plasma with relative density effects of spin-up and spin-down electrons

A separated spin evolution quantum hydrodynamics model is employed to study low frequency electrostatic waves in plasmas having inertia-less degenerate electrons with spin-up n e ↑ and spin-down n e ↓ states and inertial classical ions. A two-dimensional plasma geometry is assumed having a uniform magnetic field, directed along the z-axis, i.e., B = B 0 z . A Zakharov-Kuznetsov (ZK) type equation is derived for the electrostatic potential via the Reductive Perturbation Technique. The parametric role of the spin density polarization ratio κ in the characteristics of solitary wave structures is investigated. We have observed that both the amplitude and width of the soliton are significantly affected by the spin polarization but the amplitude remains largely un-affected by variation in the magnetic field strength. We have also carried out pulse stability analysis and have found that the pulse soliton solution of the ZK equation is unstable to oblique perturbations. The dependence of the instability growth r...

Effects of plastic coating on Kα yield from ultra-short pulse laser irradiated Ti foils

A study of the Kα radiation emitted from Ti foils irradiated with intense, ~0.2 J, 67 fs, 800 nm laser pulses, scanning a range of intensities (~1015–1018 W cm−2), is reported. The brightness of single-shot Kα line emission from the front of the targets is recorded. The yield from bare titanium (Ti) is compared to that from plastic (parylene-E) coated Ti. It is demonstrated that, for a defocused beam, a thin layer of plastic increases the yield.

Emission Spectroscopy from an XUV Laser Irradiated Solid Target

We have used the XUV FLASH laser at DESY to irradiate solid targets with intense XUV pulse at 13.5nm and ~1016 Wcm−2. XUV emission spectroscopy using a grating spectrometer has been used to observe both continuum radiation and line emission from Al IV. We present some preliminary results that indicate time integrated temperatures of below 20eV while simulation indicates higher initial temperatures.