Foil Targets Research Articles

Control of ultra-intense single attosecond pulse generation in laser-driven overdense plasmas

Ultra-intense single attosecond pulse (AP) can be obtained from circularly polarized (CP) laser interacting with overdense plasma. High harmonics are naturally generated in the reflected laser pulses due to the laser-induced one-time drastic oscillation of the plasma boundary. Using two-dimensional (2D) planar particle-in-cell (PIC) simulations and analytical model, we show that multi-dimensional effects have great influence on the generation of AP. Self-focusing and defocusing phenomena occur in front of the compressed plasma boundary, which lead to the dispersion of the generated AP in the far field. We propose to control the reflected high harmonics by employing a density-modulated foil target (DMFT). When the target density distribution fits the laser intensity profile, the intensity of the attosecond pulse generated from the center part of the plasma has a flatten profile within the center range in the transverse direction. It is shown that a single 300 attosecond (1 as = 10(-18)s) pulse with the intensity of 1.4 × 10(21) W cm(-2) can be naturally generated. Further simulations reveal that the reflected high harmonics properties are highly related to the modulated density distribution and the phase offset between laser field and the carrier envelope. The emission direction of the AP generated from the plasma boundary can be controlled in a very wide range in front of the plasma surface by combining the DMFT and a suitable driving laser.

Velocity distribution in Recoil-Distance Doppler-Shift experiments

The Recoil-Distance Doppler-Shift (RDDS) or Plunger technique is a well established method to measure lifetimes of excited nuclear states in the pico-second range. In standard RDDS experiments, the velocities of the nuclei of interest emerging from a usually thin target foil are distributed around a mean velocity v¯=〈v〉v with a relatively narrow width and it is sufficient to assume that all nuclei move with the average velocity. In this paper we investigate the influence of a broader velocity distribution especially for lifetimes τ determined using the DDCM and its basic relation τ=−(R(x)−Rfeed(x))/(dR(x)/dx)v and simulated experimental data (R(x) decay curve of the level of interest, Rfeed(x) feeding decay curves). It turned out that it is favorable to use 〈1/v〉v instead of 1/〈v〉v. Further, deviations from the correct lifetimes practically vanish at target to stopper separations close to the maximum amplitude of the function dR(x)/dx. As a consequence in a plunger experiment target-to-stopper separations should be selected symmetrically around the maximum amplitude of the function dR(x)/dx in order to minimize the effect of a broad velocity distribution.

Preplasma effects on the generation of high-energy protons in ultraintense laser interaction with foil targets

It is shown that the intense quasistatic electric and magnetic fields self-generated near the axis of the laser-driven channel in an appropriately profiled preplasma during ultraintense laser interaction with a thin target can create dense relativistic electron bunches. The latter easily penetrate through the target and can greatly enhance the sheath field at the rear, resulting in significant increase in the laser-to-ion energy conversion efficiency and the maximum energy of the target normal sheath accelerated ions. Particle-in-cell simulations show that with a hydrogen targets a proton beam of peak energy ∼38 MeV and energy conversion efficiency ≥6.5% can be produced by a linearly polarized 5 × 1019 W/cm2 laser. An analytical model is also proposed and its results agree well with those of the simulations.

Measurements of 186Re production cross section induced by deuterons on natW target at ARRONAX facility

IntroductionThe ARRONAX cyclotron, acronym for “Accelerator for Research in Radiochemistry and Oncology at Nantes Atlantique” is a new facility installed in Nantes, France. A dedicated program has been launched on production of innovative radioisotopes for PET imaging and for β− and α targeted radiotherapy using protons or α particles. Since the accelerator is also able to deliver deuteron beams up to 35MeV, we have reconsidered the possibility of using them to produce medical isotopes. Indeed, in some cases, the use of deuterons allows higher production yield than protons. Methods186Re is a β− emitter which has chemical properties close to the widely used 99mTc and has been used in clinical trials for palliation of painful bone metastases resulting from prostate and breast cancer. 186Re production cross section has been measured between 9 and 23MeV using the ARRONAX deuteron beam and the stacked-foil technique.A novelty in our work is the use of a monitor foil behind each natW target foil in order to record efficiently the deuteron incident flux and energies all over the stack relying on the International Atomic Energy Agency (IAEA) recommended cross section of the natTi(d,x)48V reaction. Since a good optimization process is supposed to find the best compromise between production yield and purity of the final product, isotope of interest and contaminants created during irradiation are measured using gamma spectrometry. ResultsOur new sets of data are presented and compared with the existing ones and with results given by the TALYS code calculations. The thick target yield (TTY) has been calculated after the fit of our experimental values and compared with the IAEA recommended ones. ConclusionsPresented values are in good agreement with existing data. The deuteron production route is clearly the best choice with a TTY of 7.8MB/μAh at 30MeV compared to 2.4MBq/μAh for proton as projectile at the same energy. The TALYS code gives satisfactory results for 183,186Re isotopes.

Characterization of laser-driven shock waves in solids using a fiber optic pressure probe

Measurement of laser-driven shock wave pressure in solid blocks of polymethyl methacrylate is demonstrated using fiber optic pressure probes. Three probes based on a fiber Fabry-Perot, fiber Bragg grating, and interferometric fiber tip sensor are tested and compared. Shock waves are generated using a high-power laser focused onto a thin foil target placed in close proximity to the test blocks. The fiber Fabry-Perot sensor appears capable of resolving the shock front with a rise time of 91 ns. The peak pressure is estimated, using a separate shadowgraphy measurement, to be 3.4 GPa.

Measurements of electron-induced neutrons as a tool for determination of electron temperature of fast electrons in the task of optimization laser-produced plasma ions acceleration

High intensity laser-plasma interaction has attracted considerable interest for a number of years. The laser-plasma interaction is accompanied by generation of various charged particle beams, such as high-energy proton and ions with high charge to mass ratio (Q/M; same as multi-charged ions). Results of simultaneous novel measurements of electron-induced photonuclear neutrons (photoneutron), which are a diagnostic of the laser-plasma interaction, are proposed to use for optimization of the laser-plasma ion generation. The proposed method is demonstrated by the laser irradiation with the intensity of 1 × 10(21) W/cm(2) on the metal foil target. The photoneutrons are measured by using NE213 liquid scintillation detectors. Heavy-ion signal is registered with the CR-39 track detector simultaneously. The measured signals of the electron-induced photoneutrons are well reproduced by using the Particle and Heavy Ion Transport code System. The results obtained provide useful approach for analyzing the various laser based ion beams.

Generation of Secondary Particles From Subnanosecond Laser Irradiation of Targets at Intensities of <formula formulatype="inline"><tex Notation="TeX">$10^{16}~{\rm W}~{\rm cm}^{-2}$</tex></formula>

Emission of several tens of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm mA}/{\rm cm}^{2}$</tex></formula> currents carried by MeV-protons is reported for plasmas produced by a beam of the 3-TW kJ-class Prague Asterix Laser System (PALS) focused onto foil targets of various thicknesses. The maximum proton energy of 4.2 MeV is observed at a modest irradiance <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(I{\lambda}^{2}\sim 2\times 10^{16}~{\rm W}~{\rm cm}^{-2}\mu{\rm m}^{2})$</tex> </formula> . According to the maximum ion energy scaling <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$E_{M}\sim (I{\lambda}^{2})^{0.4}$</tex></formula> found for picosecond lasers such a value should be reached at <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$I{\lambda}^{2}\sim 3\times 10^{18}~{\rm W}~{\rm cm}^{-2}~\mu{\rm m}^{2}$</tex> </formula> . Enhancement of the maximum proton energy can be explained by nonlinear interaction of the PALS laser beam with the generated plasma. Nonlinear effects also result in enhancement in the yield of fusion neutrons from <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm CD}_{2}$</tex></formula> plasma. The obtained yield of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$4\times 10^{5}$</tex></formula> DD-neutrons per laser energy is comparable to those obtained by the use of ps- and fs-lasers irradiating targets with <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$I{\lambda}^{2}\sim 10^{19}~{\rm W}~{\rm cm}^{-2}~\mu{\rm m}^{2}$</tex></formula> .

High-intensity laser-driven proton acceleration enhancement from hydrogen containing ultrathin targets

Laser driven proton acceleration experiments from micron and submicron thick targets using high intensity (2 × 1021 W/cm2), high contrast (10−15) laser pulses show an enhancement of maximum energy when hydrogen containing targets were used instead of non-hydrogen containing. In our experiments, using thin (&amp;lt;1μm) plastic foil targets resulted in maximum proton energies that were consistently 20%–100% higher than when equivalent thickness inorganic targets, including Si3N4 and Al, were used. Proton energies up to 20 MeV were measured with a flux of 107 protons/MeV/sr.

Improved generation of ion fluxes by a long laser pulse using laser-induced cavity pressure acceleration

Generation of ion fluxes in the laser-induced cavity pressure acceleration (LICPA) scheme is investigated by the time-of-flight method and compared with the one in the conventional laser-planar target interaction scheme. It is shown that the ion current density and intensity of the ion flux produced in the LICPA scheme from CD2 foil target irradiated by a 0.3-ns laser pulse of intensity ∼1014–1015 W/cm2 are by an order of magnitude higher and the mean and maximum ion energies by a factor 4–5 higher than those for the conventional scheme.

Influence of proton beam Coulomb explosion in laser proton acceleration

To further understand proton acceleration driven by the interaction between ultra-intense laser pulse and foil targets, the influence of proton beam Coulomb explosion has been analyzed theoretically and investigated using two-dimensional particle-in-cell (2D-PIC) simulations. Employing different proton layer sizes in the simulations, it is found that proton beam Coulomb explosion plays an important role on proton acceleration, in particular on proton cut off energy. Proton dynamics including the effect of both sheath field and proton beam Coulomb explosion was proposed and discussed in detail. This work may serve to improve the understanding of proton acceleration driven by intense laser-foil interactions.

Ultra-bright, ultra-broadband hard x-ray driven by laser-produced energetic electron beams

We propose a new method of obtaining a compact ultra-bright, ultra-broadband hard X-ray source. This X-ray source has a high peak brightness in the order of 1022 photons/(s mm2 mrad2 0.1\%BW), an ultrashort duration (10 fs), and a broadband spectrum (flat distribution from 0.1 MeV to 4 MeV), and thus has wide-ranging potential applications, such as in ultrafast Laue diffraction experiments. In our scheme, laser-plasma accelerators (LPAs) provide driven electron beams. A foil target is placed oblique to the beam direction so that the target normal sheath field (TNSF) is used to provide a bending force. Using this TNSF-kick scheme, we can fully utilize the advantages of current LPAs, including their high charge, high energy, and low emittance.

Proton Acceleration Driven by High-Intensity Ultraviolet Laser Interaction with a Gold Foil

Proton acceleration induced by a high-intensity ultraviolet laser interaction with a thin foil target was studied on an ultra-short KrF laser amplifier called LLG50 in China Institute of Atomic Energy (CIAE). The ultraviolet laser produced pulses with a high-contrast of 109, duration of 500 fs and energy of 30 mJ. The p-polarized laser was focused on a 2.1 μm gold foil by an off-axis parabola mirror (OAP) at an incident angle of 45°. The laser intensity was 1.2×1017 W/cm2. The divergence angle for proton energy of 265 keV or higher was 30°, which was recorded by a CR39 detector covered with 2 μm aluminum foil in the target normal direction. The maximum proton energy recorded by a CR39 detector covered with a 4 μm aluminum foil was 440 keV, and the proton energy spectrum was measured by a proton spectrometer. The ultraviolet laser acquires a relatively lower hot electron temperature, which can be ascribed to the proportional relationship of Iλ2, but a higher hot electron density because of the higher laser absorption and critical density. Higher electron density availed to strengthen the sheath electric field, and increased the proton acceleration.

Thick backed carbon targets via mechanical rolling

For targets requiring thick backing foils, the straight-forward and usual method is to deposit the target material directly on the backing by thermal evaporation. In some instances the reverse is more desirable, adding a backing to an already existing target foil, for example. A recent study involving measurement of the lifetime of the first 2+ excited state in 36Ar by the Doppler shift attenuation method required 0.5 mg/cm2 natural carbon targets on thick (18 mg/cm2) gold and lead backings. Problems of delamination had arisen after beam irradiation using thick gold backings for these experiments. Carbon target foils were then prepared by mechanical rolling in direct contact with a thick lead backing using an intermediate layer of indium to assure good adhesion of the layers. Details of the method will be discussed.

Observation of Gigawatt-Class THz Pulses from a Compact Laser-Driven Particle Accelerator

We report the observation of subpicosecond terahertz (T-ray) pulses with energies ≥460 μJ from a laser-driven ion accelerator, thus rendering the peak power of the source higher even than that of state-of-the-art synchrotrons. Experiments were performed with intense laser pulses (up to 5×10(19) W/cm(2)) to irradiate thin metal foil targets. Ion spectra measured simultaneously showed a square law dependence of the T-ray yield on particle number. Two-dimensional particle-in-cell simulations show the presence of transient currents at the target rear surface which could be responsible for the strong T-ray emission.

Enhancement of temporal contrast in a femtosecond petawatt Ti:sapphire laser

Significant enhancement of temporal contrast is achieved in a femtosecond petawatt Ti:sapphire laser. A pulse cleaning technique, combining double-CPA, non-collinear optical parametrical amplification and second harmonics generation, is applied to improve the amplified spontaneous emission (ASE) contrast. Meanwhile, pre-pulse leaking from the regenerative amplifier is suppressed by double Pockels cells and a saturable absorber. Measurement results show that pre-pulse on nanosecond scale can be effectively suppressed and the ASE contrast can be improved from the original ∼10−8 to ∼2 × 10−12. Proton acceleration experimental results with a foil target also demonstrate a significant enhancement of temporal contrast.

Betatron-like resonance in ultra-intense laser mass-limited foil interaction

With the help of three-dimensional particle-in-cell simulations, we study the electron dynamics in radiation pressure acceleration of a mass-limited foil target. When a mass-limited foil is irradiated by a circularly polarized laser pulse, the wing parts of the laser overtake the foil from the foil boundaries. In the laser propagation direction, electrons are significantly accelerated by the laser radiation pressure. In the laser polarization direction, electrons are subjected to a strong radial space-charge force and oscillate in the overtaking laser field. Under their combined actions, electrons execute a betatron-like oscillation and a spatially helix electron bunch is thus formed. A simple analytical model is proposed for interpreting the high electron energies and large oscillating amplitudes. It is shown that, when the electron oscillation frequency coincides with the laser frequency as witnessed by the electron, betatron-like resonance occurs, resulting in hundreds of MeV electron generation.

Spectral Efficiency of Extreme Ultraviolet Emission from CO2 Laser-Produced Tin Plasma Using a Grazing Incidence Flat-Field Spectrograph

A grazing incidence flat-field spectrograph using a concave grating was constructed to measure extreme ultraviolet (EUV) emission from a CO2 laser-produced tin plasma throughout the wavelength region of 5 nm to 20 nm for lithography. Spectral efficiency of the EUV emission around 13.5 nm from plate, cavity, and thin foil tin targets was studied. By translating the focusing lens along the laser axis, the dependence of EUV spectra on the amount of defocus was investigated. The results showed that the spectral efficiency was higher for the cavity target in comparison to the plate or foil target, while it decreased with an increase in the defocus distance. The source's spectra and the EUV emission intensity normalized to the incident pulse energy at 45° from the target normal were characterized for the in-band (2% of bandwidth) region as a function of laser energy spanning from 46 mJ to 600 mJ for the pure tin plate target. The energy normalized EUV emission was found to increase with the increasing incident pulse energy. It reached the optimum value for the laser energy of around 343 mJ, after which it dropped rapidly.

A spectrometer on chemical vapour deposition-diamond basis for the measurement of the charge-state distribution of heavy ions in a laser-generated plasma

This article reports on the development and the first applications of a new spectrometer which enables the precise and time-resolved measurement of both the energy loss and the charge-state distribution of ion beams with 10 < Z < 30 at energies of 4-8 MeV/u after their interaction with a laser-generated plasma. The spectrometer is based on five 20 × 7 mm(2) large and 20 μm thick polycrystalline diamond samples produced via the Chemical Vapour Deposition (CVD) process and was designed with the help of ion-optical simulations. First experiments with the spectrometer were successfully carried out at GSI using (48)Ca ions at an energy of 4.8 MeV/u interacting with a carbon plasma generated by the laser irradiation of a thin foil target. Owing to the high rate capability and the short response time of the spectrometer, pulsed ion beams with 10(3)-10(4) ions per bunch at a bunch frequency of 108 MHz could be detected. The temporal evolution of the five main charge states of the calcium ion beams as well as the corresponding energy loss values could be measured simultaneously. Due to the outstanding properties of diamond as a particle detector, a beam energy resolution ΔEE ≈ 0.1% could be reached using the presented experimental method, while a precision of 10% in the energy loss and charge-state distribution data was obtained.

Hybrid proton acceleration scheme using relativistic intense laser light

Ion acceleration phenomena at relativistic intense laser interaction with thin foil targets are studied to find an efficient laser-target interaction concept at the conditions, where neither the ponderomotive pressure of the laser light nor the hot electron pressure is negligible. Particle in cell simulations and the analytical model are allowing to predict optimum laser-target parameters and suggesting a significant increase of proton energy if a hybrid proton acceleration scheme is used. In the proposed scenario, the laser polarisation is changed during the acceleration process: First with circularly polarised laser light the target is accelerated as a whole by the ponderamotive pressure, and then with linearly polarised laser light the electrons are heated which additionally increases the accelerating field. The calculations are in good agreement with experimental findings.

Effects of Ions Charge-Mass Ratio on Energy and Energy Spread of Accelerated Ions in Laser Driven Plasma

Effects of ions charge-mass ratio on energy and energy spread of accelerated ions in laser driven plasma are investigated in detail by proposing a simple double-layer model for a foil target driven by an ultrastrong laser. The radiation pressure acceleration mechanism plays an important role on the studied problem. For the ions near the plasma mirror, i.e. electrons layer, the dependence of ions energy on their charge-mass ratio is derived theoretically. It is found that the larger the charge-mass ratio is, the higher the accelerated ions energy gets. For those ions far away from the layer, the dependence of energy and energy spread on ions charge-mass ratio are also obtained by numerical performance. It exhibits that, as ions charge-mass ratio increases, not only the accelerated ions energy but also the energy spread will become large.