We present optimization of laser plasma x-ray experimental conditions for ultrafast x-ray absorption spectroscopy measurements on broad range of transition metal oxides. First, the x-ray flux generated from a laser plasma source was optimized with an emphasis on the Bremsstrahlung by investigating the influence of the angle of the incidence of laser beam on a Cu tape target. The x-ray flux emitted in both the front and transmitted side of the target was found to be optimal at the incident angle of 15 ~ 25 degrees. Moreover the manipulation of the Bremsstrahlung peak energy by the laser focus distribution was discussed. In addition to the source optimization, we present a scheme to find the time-delay zero position in a pump-probe experiment together with a normalization scheme for x-ray source fluctuations. As a feasibility check, we present the transmitted spectra of two materials, Ni and NiO.

We present a detailed study of the electric and magnetic fields, which are created on plasma vacuum interfaces as a result of highly intense laser-matter interactions. For the field generation ultrathin polymer foils (30-50 nm) were irradiated with high intensity femtosecond (10(19)-10(20) W/cm(2)) and picosecond (similar to 10(17) W/cm(2)) laser pulses with ultrahigh contrast (10(10)-10(11)). To determine the temporal evolution and the spatial distribution of these fields the proton streak deflectometry method has been developed further and applied in two different imaging configurations. It enabled us to gather complementary information about the investigated field structure, in particular about the influence of different field components (parallel and normal to the target surface) and the impact of a moving ion front. The applied ultrahigh laser contrast significantly increased the reproducibility of the experiment and improved the accuracy of the imaging method. In order to explain the experimental observations, which were obtained by applying ultrashort laser pulses, two different analytical models have been studied in detail. Their ability to reproduce the streak deflectometry measurements was tested on the basis of three-dimensional particle simulations. A modification and combination of the two models allowed for an extensive and accurate reproduction of the experimental results in both imaging configurations. The controlled change of the laser pulse duration from 50 femtoseconds to 2.7 picoseconds led to a transition of the dominating force acting on the probing proton beam at the rear side of the polymer foil. In the picosecond case the (vxB)-term of the Lorentz force dominated over the counteracting E-field and was responsible for the direction of the net force. The applied proton deflectometry method allowed for an unambiguous determination of the magnetic field polarity at the rear side of the ultrathin foil.

The radiation pressure acceleration (RPA) of charged particles has been a challenging task in laser-driven proton/ion acceleration due to its stringent requirements in laser and target conditions. The realization of radiation-pressure-driven proton acceleration requires irradiating ultrathin targets with an ultrahigh contrast and ultraintense laser pulses. We report the generation of 93-MeV proton beams achieved by applying 800-nm 30-fs circularly polarized laser pulses with an intensity of 6.1×1020 W/cm2 to 15-nm-thick polymer targets. The radiation pressure acceleration was confirmed from the obtained optimal target thickness, quadratic energy scaling, polarization dependence, and three-dimensional particle-in-cell simulations. We expect this clear demonstration of RPA to facilitate the realization of laser-driven proton/ion sources delivering energetic and short-pulse particle beams for novel applications.

Laser-driven proton/ion acceleration is a rapidly developing research field attractive for both fundamental physics and applications such as hadron therapy, radiography, inertial confinement fusion, and nuclear/particle physics. Laser-driven proton/ion beams, compared to those obtained in conventional accelerators, have outstanding features such as low emittance, small source size, ultra-short duration and huge acceleration gradient of ∼1 MeV μm−1. We report proton acceleration from ultrathin polymer targets irradiated with linearly polarized, 30-fs, 1-PW Ti:sapphire laser pulses. A maximum proton energy of 45 MeV with a broad and modulated profile was obtained when a 10-nm-thick target was irradiated at a laser intensity of 3.3 × 1020 W/cm2. The transition from slow (I1/2) to fast scaling (I) of maximum proton energy with respect to laser intensity I was observed and explained by the hybrid acceleration mechanism including target normal sheath acceleration and radiation pressure acceleration in the acceleration stage and Coulomb-explosion-assisted free expansion in the post acceleration stage.

Particle-in-cell simulations of the absorption of an ultrashort and ultraintense laser pulse at structured targets are presented. The targets consist of a bunch of parallel or tapered carbon nanowires. Such targets are effective in generating large currents of relativistic electrons, propagating along the wires and following their curvature. Focusing the electron beam into one wire makes it possible to reduce the transverse size of the electron cloud in comparison to the diameter of the laser pulse. The density of the energy flux of the hot electrons in such a bunch, propagating along one nanowire, is in the excess of several times the intensity of the laser pulse.

The radiation pressure acceleration (RPA) of charged particles has been considered a challenging task in laser particle acceleration. Laser-driven proton/ion acceleration has attracted considerable interests due to its underlying physics and potential for applications such as high-energy density physics, ultrafast radiography, and cancer therapy. Among critical issues to overcome the biggest challenge is to produce energetic protons using an efficient acceleration mechanism. The proton acceleration by radiation pressure is considerably more efficient than the conventional target normal sheath acceleration driven by expanding hot electrons. Here we report the generation of 93-MeV proton beams achieved by applying 30-fs circularly polarized laser pulses with an intensity of 6.1 x 1020 W/cm2 to ultrathin targets. The radiation pressure acceleration was confirmed from the obtained optimal target thickness, quadratic energy scaling, polarization dependence, and 3D-PIC simulations. We expect this fast energy scaling to facilitate the realization of laser-driven proton/ion sources delivering stable and short particle beams for practical applications.

If regions of localized strong fields at plasma-vacuum interfaces are probed longitudinally with laser accelerated proton beams their velocity distribution changes sensitively and very fast. Its measured variations provide indirectly a higher temporal resolution as deduced from deflection geometries which rely on the explicit temporal resolution of the proton beam at the position of the object to probe. With help of reasonable models and comparative measurements changes of proton velocity can trace the field dynamics even at femtosecond time scale. In longitudinal probing, the very low longitudinal emittance together with a broad band kinetic energy distribution of laser accelerated protons is the essential prerequisite of the method. With a combination of energy and one-dimensional spatial resolution, we resolve fast field changes down to 100 fs. The used pump probe setup extends previous schemes and allows discriminating simultaneously between electric and magnetic fields in their temporal evolution.

A tabletop, short-pulse laser-based hard X-ray (Kα) source equipped with an advanced X-ray optics and dedicated for high-resolution spectroscopy and time-resolved diffraction is described. Operation of the source together with a high-resolution spectrometer containing a large-aperture highly annealed pyrolytic graphite gave a resolution E/ΔE of ~1,800 for the spectral range around Kα line of Cu. The estimated total flux of the 8.05-keV photons was equal to 5.9 × 1010 ph/s in 4π sr. Performance boost of the source caused by X-ray optics relied on the significant increase in the Cu-Kα photon flux on both, the sample (4.7 × 106 ph/s) and the detector (3.4 × 103 ph/s). A spectral brightness of 1.4 × 107 ph/s/mm2/mrad2 was derived from the source parameters for the Kα line. Better performance due to high collecting power and reflectivity of the spectrometer enabled application of the cross-correlation technique with an Ni foil. An upper bound of emission duration of 323 ± 47 fs was obtained in this measurement. X-ray absorption near-edge spectroscopy on an Ni sample with an acquisition time of only 15 min confirmed the increased capability of the setup also for continuous spectrum (bremsstrahlung).

Two-step laser acceleration of protons with two foils and two laser pulses is modelled and optimized. It is shown that a nearly mono-energetic distribution of proton bunches can be realized by a suitable parameter choice. Two-step acceleration schemes make it possible to obtain both higher efficiency and energy as compared to the acceleration with only one laser pulse of an energy equal to the sum of the energy of the two pulses. With the aid of our analytical model, the optimal distance between the two targets, the delay between the two laser pulses, and the parameters of the laser pulses are determined. Estimates and results of the modelling are proven with 2D PIC simulations of the acceleration of proton bunches moving through the second target.

The radiation pressure acceleration (RPA) of charged particles has been considered a challenging task in laser particle acceleration. Laser-driven proton/ion acceleration has attracted considerable interests due to its underlying physics and potential for applications such as high-energy density physics, ultrafast radiography, and cancer therapy. Among critical issues to overcome the biggest challenge is to produce energetic protons using an efficient acceleration mechanism. The proton acceleration by radiation pressure is considerably more efficient than the conventional target normal sheath acceleration driven by expanding hot electrons. Here we report the generation of 93-MeV proton beams achieved by applying 30-fs circularly polarized laser pulses with an intensity of 6.1 x 1020 W/cm2 to ultrathin targets. The radiation pressure acceleration was confirmed from the obtained optimal target thickness, quadratic energy scaling, polarization dependence, and 3D-PIC simulations. We expect this fast energy scaling to facilitate the realization of laser-driven proton/ion sources delivering stable and short particle beams for practical applications.

Physical processes in laser–matter interaction used to be determined by generation of fast electrons resulting from efficient conversion of the absorbed laser radiation. Composite materials offer the possibility to control the absorption by choice of the host material and dopants. Reported here strong absorption of ultrashort laser pulse in a composite carbon-based nanomaterial including single-walled carbon nanotubes (SWCNTs) or multilayer graphene was measured in the intensity range between 1012 and 1016 W cm−2. A protein (lysozyme) was used as the host. The maximum absorption of femtosecond laser pulse has reached 92–96 %. The optical damage thresholds of the coatings were registered at an intensity of (1.1 ± 0.5) × 1013 W cm−2 for the embedded SWCNTs and at (3.4 ± 0.3) × 1013 W cm−2 for the embedded graphene. Encapsulated variant of the dispersed nanomaterial was investigated as well. It was found that supernatant protein in the coating material tends to dominate the absorption process, independently of the embedded nanomaterial. The opposite was observed for the encapsulated material.

A simple model of dynamics of a collisional X-ray laser is given applying Maxwell-Bloch equations in a uniform approximation. The main considered parameters include polarization and coherence of the emitted radiation. Speckle pattern, typical for a radiation source of partial coherence, especially, if involving process of the amplified spontaneous emission (ASE), are used as an alternative source of information on the processes occurring in the active medium of an X-ray laser. A level of partial coherence is deduced by statistical analysis of the speckle pattern generated in the output beam of the laser. It is shown that plasma fluctuation and non-Gaussian character of the statistics are needed to reproduce the transverse coherence values reported in the experiment.

The scenario of “electron capture and loss” has been recently proposed for the formation of negative ion and neutral atom beams with up to MeV kinetic energy [S. Ter-Avetisyan, et al., Appl. Phys. Lett. 99, 051501 (2011)]. Validation of these processes and of their generic nature is here provided in experiments where the ion source and the interaction medium have been spatially separated. Fast positive ions accelerated from a laser plasma sourceare sent through a cold spray where their charge is changed. Such formed neutral atom or negative ion has nearly the same momentum as the original positive ion. Experiments are released for protons,carbon, and oxygen ions and corresponding beams of negative ions and neutral atoms have been obtained. The electron capture and loss phenomenon is confirmed to be the origin of the negative ion and neutral atom beams. The equilibrium ratios of different chargecomponents and cross sections have been measured. Our method is general and allows the creation of beamsof neutral atoms and negative ions for different species which inherit the characteristics of the positive ion source.

We present observations of intense beams of energetic negative hydrogen ions and fast neutral hydrogen atoms in intense (5 × 1019 W/cm2) laser plasma interaction experiments, which were quantified in numerical calculations. Generation of negative ions and neutral atoms is ascribed to the processes of electron capture and loss by a laser accelerated positive ion in the collisions with a cloud of droplets. A comparison with a numerical model of charge exchange processes provides information on the cross section of the electron capture in the high energy domain.

Particle acceleration using ultraintense, ultrashort laser pulses is one of the most attractive topics in relativistic laser-plasma research. We report proton and/or ion acceleration in the intensity range of 5×10(19) to 3.3×10(20) W/cm2 by irradiating linearly polarized, 30-fs laser pulses on 10-to 100-nm-thick polymer targets. The proton energy scaling with respect to the intensity and target thickness is examined, and a maximum proton energy of 45 MeV is obtained when a 10-nm-thick target is irradiated by a laser intensity of 3.3×10(20) W/cm2. The proton acceleration is explained by a hybrid acceleration mechanism including target normal sheath acceleration, radiation pressure acceleration, and Coulomb explosion assisted-free expansion. The transition of proton energy scaling from I(1/2) to I is observed as a consequence of the hybrid acceleration mechanism. The experimental results are supported by two- and three-dimensional particle-in-cell simulations.

Beams of energetic negative ions and neutral atoms are obtained from water and ethanol spray targets irradiated by high intensity (5x10(19) W/cm(2)) and ultrashort (50 fs) laser pulses. The resulting spectra were measured with the Thomson parabola spectrometer, which enabled absolute measurements of both: positive and negative ions. The generation of a beam of energetic neutral hydrogen atoms was confirmed with CR-39 track detectors and their spectral characteristics have been measured using time of flight technique. Generation is ascribed to electron-capture and -loss processes in the collisions of laser-accelerated high-energy protons with spray of droplets. The same method can be applied to generate energetic negative ions and neutral atoms of different species.

We report on the absolute calibration of a microchannel plate (MCP) detector, used in conjunction with a Thomson parabola spectrometer. The calibration delivers the relation between a registered count numbers in the CCD camera (on which the MCP phosphor screen is imaged) and the number of ions incident on MCP. The particle response of the MCP is evaluated for positive, negative, and neutral particles at energies below 1 MeV. As the response of MCP depends on the energy and the species of the ions, the calibration is fundamental for the correct interpretation of the experimental results. The calibration method and arrangement exploits the unique emission symmetry of a specific source of fast ions and atoms driven by a high power laser.

Ultrafast X-ray absorption spectroscopy (UXAS) offers the opportunity to investigate function-structure relationships of complex organic molecules or biological functional subunits without the need of crystallization. Of special interest from the viewpoint of structural biology is the region of K-edges of transition metals between 5 and 10 keV. Regardless of successful application of time-resolved diffraction techniques to investigations of crystal dynamics using synchrotron and laboratory based sources there are only very few examples for application of UXAS to revealing the structural dynamics in biomolecular systems. This is mainly caused by the lack of broadband ultrafast x-ray sources as well as of appropriate optics adapted to these sources. Due to the long-data-recording time in UXAS experiments the sample integrity is mainly determined by the average power of the pump pulses inducing the structural changes. Using a fixed energy of the pump pulse the latter one is determined by the repetition rate of the pump laser. In this paper we discuss the prospects of UXAS comparing fs laser plasma sources with different repetition rates in combination with tailor-made optics based on highly annealed pyrolytic graphite (HAPG).

We have developed a 0.1-Hz-repetition-rate, 30-fs, 1.5-PW Ti:sapphire laser system for the research on high field physics. In this paper, we describe the design and output performance of the PW Ti:sapphire laser and its applications in the generation of relativistic high order harmonic generation and the acceleration of charged particles (protons and electrons). In the experiment on relativistic harmonic generation, the harmonic order dramatically extended up to 164th that corresponds to 4.9 nm in wavelength, and the dramatic extension was explained by the oscillatory flying mirror model. Recently, we could accelerate protons up to 45 MeV from a 10-nm polymer target and show the change in the acceleration mechanism from target normal sheath acceleration to radiation pressure acceleration. The femtosecond high power laser system is a good candidate for developing a compact electron accelerator as well. The generation of multi-GeV electron beam was observed from an injection scheme when a PW laser pulse was focused by a long focal length spherical mirror.

Results of energy deposition measurement in interaction between an ultra-short laser pulse and nanostructured target are described. As a target we used carbon nanotubes and multilayer graphene deposited on a sapphire wafer surface and embedded in a layer of protein. A 25 fs, p-polarised pulses from a 1 kHz-Ti;sapphire laser of energy up to 3 mJ were focused to give intensity up to 2x10(16) W/cm(2) on a target positioned within an integrating sphere. The absorption measured showed a level in excess of 80 %, increasing with the intensity. The results suggest that the host material (lysozyme) is responsible for the breakdown while the embedded material contributes dominantly to the absorption.