The use of targets with surface structures for laser-driven particle acceleration has potential to significantly boost the particle and radiation energies because of enhanced laser absorption. We investigate, via experiment and particle-in-cell simulations, the impact of micron-scale surface-structured targets on the spectrum of electrons and protons accelerated by a picosecond laser pulse at relativistic intensity. Our results show that, compared with flat-surfaced targets, structures on this scale give rise to a significant enhancement in particle and radiation emission over a wide range of laser–target interaction parameters. This is due to the longer plasma scale length when using micro-structures on the target front surface. We do not observe an increase in the proton cutoff energy with our microstructured targets, and this is due to the large volume of the relief.

The use of laboratory experiments as plasma creating sources is a valuable tool for understanding astrophysical observations. Recently plasma created through irradiation by lasers with relativistic intensities has been used to study effects of hot electrons and X-ray pumping on X-ray formation of multiply charged ions spectra. This paper discusses the formation of K-shell Fe spectra recorded from a plasma irradiated by 35 fs pulses with intensities of 1021 W/cm2. Modeling of the spectra suggests three different regions of plasma radiation including a cold ~10 eV region, a mild ~700 eV region, and a hot ~3500 eV region. The influence of hot electrons and X-ray pumping is discussed and a comparison with K-shell Fe spectra from a 1 MA X-pinch experiment is included to highlight the differences due to the shorter time frame of the laser–plasma interaction experiment.

The overview of the recent results for discovery and investigations of a very exotic phenomenon – optical mirage in the X-ray spectral range – is presented. It was found that the mirage could be created in the form of coherent virtual point source, emerging in the vicinity of the second plasma in two-stage oscillator-amplifier X-ray laser. The X-ray source-mirage, rigidly phased with the initial radiation of generator, occurs only when amplification takes place in the amplifier plasma and leads to the appearance of the interference pattern in the form of concentric rings in the spatial profile of the output X-ray laser beam. The equation describing the emergence of X-ray mirage was found, numerical solution of which shows that its formation is similar to that of the optical mirages observed at propagation of light rays through an inhomogeneously heated air. Obtained results have already demonstrated novel comprehension into the physical nature of amplification of X-ray radiation, opening additional opportunities for X-ray interferometry, holography, and other applications, which require multiple rigidly phased sources of coherent radiation.

The two-temperature, 2D hydrodynamic code Hydro–ELectro–IOnization–2–Dimensional (HELIO2D), which takes into account self-consistently the laser energy absorption in a target, ionization, heating, and expansion of the created plasma is elaborated. The wide-range two-temperature equation of state is developed and used to model the metal target dynamics from room temperature to the conditions of weakly coupled plasma. The simulation results are compared and demonstrated a good agreement with experimental data on the Mg target being heated by laser pulses of the nanosecond high-energy laser for heavy ion experiments (NHELIX) at Gesellschaft fur Schwerionenforschung. The importance of using realistic models of matter properties is demonstrated.

It is shown that various spectroscopic methods based on measurements of X-ray spectra radiated from cluster targets can be used for estimation of the destruction degree of clusters by laser prepulses. These methods allow insight to be gained regarding the important issue of preservation of the dense cluster core at the moment of the arrival of the main laser pulse. In addition, they can be used for quantitative estimation of the size of the undestroyed parts of the clusters and also for measuring the temperature and density of the preplasmas produced by the laser prepulses.

K-shell emission from copper target was observed by focusing femtosecond laser pulses very close to the target surface-air interface. It was shown that mechanism of X-ray emission is connected with generation of fast electrons in the air plasma area. Experiments demonstrated that moderate intensity of laser radiation (IL < 1015 W/cm2) was enough to produce considerable flux of X-ray photons of at least 10 keV energy. The parameters of generated X-ray emission were studied. It was found that after propagation through 40 cm thick air layer X-ray spectra consisted of pronounced Kα and Kβ characteristic lines and relatively small Bremsstrahlung continuum. Since transversal source size has an order of a few tens of micrometers, such a source can be used for absorption imaging of micro-objects in standard laboratory conditions. That can be particularly important for diagnostic of medical and biological samples in vivo.

An improved high luminosity, easily spectrally tunable backlighting scheme based on a spherically bent crystal is considered in this paper. Contrary to the traditional backlighting scheme, we used crystal far from normal incidence, and the backlighter source was inside the Rowland circle. With the presented configuration, we obtained a spatial resolution up to 8 µm in the desired direction with an X-ray backlighting energy close to 5 keV. Detailed discussions and ray-tracing calculations show that with this convenient scheme resolution down to 5 µm can be achieved. A dedicated application to high energy density physics is presented: the radiography of shock compressed matter.

We used X-ray spectroscopy as a diagnostic tool for investigating the properties of laser-cluster interactions at the stage in which non-adiabatic cluster expansion takes place and a quasi-homogeneous plasma is produced. The experiment was carried out with a 10 TW, 65 fs Ti:Sa laser focused on CO2 cluster jets. The effect of different laser-pulse contrast ratios and cluster concentrations was investigated. The X-ray emission associated to the Rydberg transitions allowed us to retrieve, through the density and temperature of the emitting plasma, the time after the beginning of the interaction at which the emission occurred. The comparison of this value with the estimated time for the “homogeneous” plasma formation shows that the degree of adiabaticity depends on both the cluster concentration and the pulse contrast. Interferometric measurements support the X-ray data concerning the plasma electron density.

X-ray spectra of plasma produced by the interaction of Ti:Sa laser pulses (duration from 60 fs to 1 ps, and energy from 15 mJ to 128 mJ) with foil and solid Teflon and AL targets are investigated. It is shown experimentally and theoretically that the use of low contrast (10−2 – 10−4) short laser pulses, essentially promotes the conditions for generation of fast multi-charged ions. This effect is caused by self-focusing of the main laser pulse in a preplasma produced by intense laser prepulses. Modeling of the observed spectral line shape gives evidence of a considerable (about 3%) amount of multi-charged He-like F ions with energy E ∼ 1 MeV at rather low values of laser intensity IL ≈ 6 × 1016 W cm−2.

High energy heavy ions were generated in laser produced plasma at moderate laser energy, with a large focal spot size of 0.5 mm diameter. The laser beam was provided by the 10 GW GSI-NHELIX laser systems, and the ions were observed spectroscopically in status nascendi with high spatial and spectral resolution. Due to the focal geometry, plasma jet was formed, containing high energy heavy ions. The velocity distribution was measured via an observation of Doppler shifted characteristic transition lines. The observed energy of up to 3 MeV of F-ions deviates by an order of magnitude from the well-known Gitomer (Gitomer et al., 1986) scaling, and agrees with the higher energies of relativistic self focusing.

Below is the complete Reference citation for Hoffmann et al. (2005).

Hoffmann, D.H.H., Blazevic, A., Ni, P., Rosmej, O., Roth, M., Tahir, N., Tauschwitz, A., Udrea, S., Varentsov, D., Weyrich, K. & Maron, Y. (2005). Present and future perspectives for high energy density physics with intense heavy ion and laser beams. Laser Part. Beams23, 47–53.

The study of heavy ion stopping dynamics using associated K-shell projectile and target radiation was the focus of the reported experiments. Ar, Ca, Ti, and Ni projectile ions with the initial energies of 5.9 and 11.4 MeV/u were slowed down in quartz and arogels. Characteristic radiation of projectiles and target atoms induced in close collisions was registered. The variation of the projectile ion line Doppler shift due to the ion deceleration measured along the ion beam trajectory was used to determine the ion velocity dynamics. The dependence of the ion velocity on the trajectory coordinate was measured over 70–90% of the ion beam path with a spatial resolution of 50–70 μm. The choice of SiO2 aerogel with low mean densities of 0.04–0.15 g/cm3 as a target material, made it possible to stretch the ion stopping range by more than 20–50 times in comparison with solid quartz. It allowed for resolving the dynamics of the ion stopping process. Experimentally, it has been proven that the fine porous nano-structure of aerogels does not affect the ion energy loss and charge state distribution. The strong increase of the ion stopping range in aerogels made it possible to resolve fast ion radiation dynamics. The analysis of the projectile Kα-satellites structure allows supposing that ions propagate in solid in highly exicted states. This can provide an experimental explanation for so called gas-solid effect.

High-resolution K-shell spectra of a plasma created by superintense laser irradiation of micron-sized Ar clusters have been measured with an intensity above 1019 W/cm2 and a pulse duration of 30 fs. The total photon flux of 2 × 108 photons/pulse was achieved for Heα1 resonant line of Ar (λ = 3.9491 Å, 3.14 keV). In parallel with X-ray measurements, energy distributions of emitted ions have been measured. The multiply charged ions with kinetic energies up to 800 keV were observed. It is found that hot electrons produced by high contrast laser pulses allow the isochoric heating of clusters and shift the ion balance toward the higher charge states, which enhances both the X-ray line yield of the He-like argon ion and the ion kinetic energy.

The high precision X-ray spectroscopy studies of plasma created from the CO2 clusters in gas jet targets by the ultrashort laser pulses (35 and 60 fs duration) were performed at the intensities IL ∼ 1017–1018 W cm−2. The spectral line shape of the H-like and He-like oxygen ions gains an asymmetry with increasing the laser pulse intensity. Theoretical modeling of the line shape shows that the asymmetry can be explained by absorption of the Doppler-shifted line radiation from the essential fraction of ions (over 10−3) with energies above 1 MeV due to photoionization of inner shells of carbon ions. The results obtained demonstrate measurement capabilities of the X-ray spectral measurements of multicharged ions accelerated during the interaction with a laser radiation.

The X-ray spectral distribution of swift heavy Ti and Ni ions (11 MeV/u) observed inside aerogels (ρ = 0.1 g/cm3) and dense solids (quartz, ρ = 2.23 g/cm3) indicates a strong presence of simultaneous 3–5 charge states with one K-hole. We show that the theoretical analysis can be split into two tasks: first, the treatment of complex autoionizing states together with the originating spectral distribution, and, second, a charge-state distribution model. Involving the generalized line profile function theory, we discuss attempts to couple charge-state distributions.