Polystyrene Target Research Articles

High Optical Harmonics Generation on Solid Surfaces Irradiated by Mid-IR Femtosecond Laser Pulses

We obtained the spectra of high optical harmonics produced by subrelativistic femtosecond pulses on the surface of polystyrene, CaF2, BK7, and Al solid targets. High harmonics of up to the 51st order of radiation with central 3.85 µm wavelength were observed. The highest order harmonics were generated from the polystyrene target surface. The harmonics energy versus their numbers is shown to fit well a decaying power law with the exponent ranging from 4 to 8/3.

Benchmarking solid-to-plasma transition modeling for inertial confinement fusion laser-imprint with a pump-probe experiment

For laser direct-drive (LDD) fusion implosions, intense laser beams are used to directly illuminate the inertial confinement fusion (ICF) capsule. The laser beams' intensity nonuniformity (due to speckles) on the target can impose perturbation seeds which are subsequently amplified by Rayleigh-Taylor instability growth, thereby leading to degradation of ICF implosion performance. To devise methods to mitigate this issue, adequate understanding of the underlying so-called laser-imprinting process is required. Here, we report measurements and modeling of the initial plasma formation process which has been shown to affect the laser imprint. Specifically, we measured the transient transmission of a femtosecond probe pulse through a polystyrene target for different 100-picosecond pump pulse intensities pertaining to ICF conditions. The experimental data are used to benchmark a microphysics model of initial plasma formation that overall describes the observed dynamics, thus providing a validated solid-to-plasma modeling for laser-imprinting purposes in radiation-hydrodynamic codes to accurately simulate and design LDD targets.

Density evolution after shock release from laser-driven polystyrene (CH) targets in inertial confinement fusion

The evolution of the plasma density in the rarefaction wave formed after a laser-driven shock is released from a CH foil was measured using optical interferometry. It was found that the plasma density profile is very sensitive to the conditions at the back surface of the foil before the shock release. Dedicated experiments demonstrated that radiation preheat by coronal x rays caused early expansion of the back surface and faster expansion of the rarefaction wave. Radiation-hydrodynamics simulations with accurate modeling of radiation preheat from the plasma corona are in good agreement with the experimental results. The early expansion of material interfaces due to coronal x-ray preheat must be evaluated in designing and interpreting laser-driven inertial confinement fusion experiments.

Measurements of laser-imprint-induced shock velocity nonuniformities in plastic targets with the Nike KrF laser

We report results of direct-drive laser imprint experiments measuring velocity perturbation profiles of shock waves produced by the Nike krypton fluoride laser. A new high-resolution two-dimensional velocimeter system was successfully implemented on the Nike laser facility and used for sensitive optical measurements of the velocity perturbations. Planar polystyrene targets with and without a thin high-Z overcoat (400 Å Au or 600 Å Pd) were irradiated by four, eight, and sixteen Nike laser beams to examine laser imprint and its mitigation. The results from the uncoated targets showed that the shock velocity perturbations decreased with an increasing number of laser beams overlapped on target, precisely as anticipated by the beam averaging effect on laser imprint. In the experiment on the shocks driven in the high-Z coated targets, the shock velocity perturbations were further reduced by a factor of 2–6 compared to their counterparts in the uncoated experiment, with the amplitude of the velocity fluctuations measured as small as 20 m/s rms for shock velocities of 20 km/s. These experiments allowed more direct measurements of laser imprint effects without relying on the Rayleigh–Taylor hydrodynamic amplification, providing valuable quantitative data for calibrating radiation-hydrodynamic simulations of laser imprint.

Control of fast electron propagation in foam target by high-Z doping

The influence of high-Z dopant (bromine) in low-Z foam (polystyrene) target on laser-driven fast electron propagation is studied by the 3D hybrid particle-in-cell (PIC)/fluid code HEETS. It is found that the fast electrons are better confined in doped targets due to the increasing resistivity of the target, which induces a stronger resistive magnetic field which acts to collimate the fast electron propagation. The energy deposition of fast electrons into the background target is increased slightly in the doped target, which is beneficial for applications requiring long distance propagation of fast electrons, such as fast ignition.

Controlled Generation of Double Emulsions for Laser Fusion Target Fabrication Using a Glass Capillary Microfluidic Device

We report the controllable generation of double emulsions for target fabrication using glass capillary microfluidic devices. Instead of a conventional triple-orifice droplet generator, user-friendly glass capillary devices are used to produce micrometer to millimeter-sized water-in-oil-in-water emulsions. The double emulsions have a relatively uniform size distribution with an average outer diameter of 1420 μm. The sizes of the emulsions can also be varied by changing the ratio of the inner, middle, and outer fluids. Increasing the flow rate ratio of the outer fluid to the other fluids [Qo/(Qm+Qi)] from 3 to 11, the outer radii of the emulsions decrease from 1120 to 950 μm. On the other hand, increasing the flow rate ratio of the middle fluid to the inner fluid (Qm/Qi) from 0.7 to 1.6, the aspect ratio of the emulsions increases from 4 to 8. Our experimental values are in good agreement with a simple theoretical model. These results suggest that our present method to control the generation of double emulsions can be used as an alternative approach to fabricate polystyrene targets for future laser fusion experiments.

Numerical simulations of the ablative Rayleigh-Taylor instability in planar inertial-confinement-fusion targets using the FastRad3D code

The ablative Rayleigh-Taylor (RT) instability is a central issue in the performance of laser-accelerated inertial-confinement-fusion targets. Historically, the accurate numerical simulation of this instability has been a challenging task for many radiation hydrodynamics codes, particularly when it comes to capturing the ablatively stabilized region of the linear dispersion spectrum and modeling ab initio perturbations. Here, we present recent results from two-dimensional numerical simulations of the ablative RT instability in planar laser-ablated foils that were performed using the Eulerian code FastRad3D. Our study considers polystyrene, (cryogenic) deuterium-tritium, and beryllium target materials, quarter- and third-micron laser light, and low and high laser intensities. An initial single-mode surface perturbation is modeled in our simulations as a small modulation to the target mass density and the ablative RT growth-rate is calculated from the time history of areal-mass variations once the target reaches a steady-state acceleration. By performing a sequence of such simulations with different perturbation wavelengths, we generate a discrete dispersion spectrum for each of our examples and find that in all cases the linear RT growth-rate γ is well described by an expression of the form γ=α [kg/(1+ϵ kLm)]1/2−βkVa, where k is the perturbation wavenumber, g is the acceleration of the target, Lm is the minimum density scale-length, Va is the ablation velocity, and ϵ is either one or zero. The dimensionless coefficients α and β in the above formula depend on the particular target and laser parameters and are determined from two-dimensional simulation results through the use of a nonlinear curve-fitting procedure. While our findings are generally consistent with those of Betti et al. (Phys. Plasmas 5, 1446 (1998)), the ablative RT growth-rates predicted in this investigation are somewhat smaller than the values previously reported for the same target and laser parameters. It is speculated that differences in the equation-of-state and opacity models are largely responsible for the discrepancy. Resolution of this issue awaits the development of better experimental diagnostics capable of measuring small-wavelength (5–20 μm) perturbation growth due to the ablative RT instability in the linear regime.

Experimental study on the incident-angle-dependent laser coupling features of polystyrene targets

Laser-produced plasmas have attracted great interest due to their potential utility in wide-ranging applications, especially in the field of inertial confinement fusion (ICF). For direct-driven ICF, laser coupling with polystyrene targets is a crucial and fundamental problem. In addition, oblique incidence is also a common phenomenon for laser facilities with multiple beams. It is necessary to evaluate the effects of oblique incidence on the laser coupling features relevant to the direct-driven ICF. Experiments using an intense nanosecond flat-top laser at around W cm–2 to irradiate polystyrene planar targets from three different incidence angles have been performed on the Shenguang-III prototype laser facility. The time-integrated absolute values of the full aperture backscatter (FABS), near backscatter scattering (NBS), and the x-ray conversion efficiency (CE) have been measured quantitatively. According to the experimental results, with the increase of the incidence angle, the percentage of the stimulated Brillouin backscatter and the overall x-ray CE decreased while the stimulated Raman backscatter fraction rose. Theoretical analyses based on hydrodynamic simulations and linear theory were qualitatively consistent with the experimental results. In addition, the specularly reflected light was also observed at 30° laser oblique incidence.

Tritium-doping enhancement of polystyrene by ultraviolet laser and hydrogen plasma irradiation for laser fusion experiments

We investigate the tritium-doping enhancement of polystyrene by ultraviolet (UV) laser and hydrogen plasma irradiation. Tritium-doped polystyrene films are fabricated by the Wilzbach method with UV laser and hydrogen plasma. The 266-nm laser-irradiated, 355-nm laser-irradiated, and hydrogen plasma-irradiated polystyrene films exhibit higher PSL intensities and specific radioactivities than the non-irradiated sample. Tritium doping by UV laser irradiation can be largely affected by the laser wavelength because of polystyrene’s absorption. In addition, UV laser irradiation is more localized and concentrated at the spot of laser irradiation, while hydrogen plasma irradiation results to a more uniform doping concentration even at low partial pressure and short irradiation time. Both UV laser and plasma irradiations can nevertheless be utilized to fabricate tritium-doped polystyrene targets for future laser fusion experiments. With a high doping rate and efficiency, a 1% tritium-doped polystyrene shell target having 7.6×1011Bqg−1 specific radioactivity can be obtained at a short period of time thereby decreasing tritium consumption and safety management costs.

Instantaneous x-ray radiation energy from laser produced polystyrene plasmas for shock ignition conditions

Laser target energy coupling mechanism is crucial in the shock ignition (SI) scheme, and x-ray radiation energy is a non-negligible portion of the laser produced plasma energy. To evaluate the x-ray radiation energy amount at conditions relevant to SI scheme, instantaneous x-ray radiation energy is investigated experimentally with continuum phase plates smoothed lasers irradiating layer polystyrene targets. Comparative laser pulses without and with shock spike are employed. With the measured x-ray angular distribution, full space x-ray radiation energy and conversion efficiency are observed. Instantaneous scaling law of x-ray conversion efficiency is obtained as a function of laser intensity and time. It should be pointed out that the scaling law is available for any laser pulse shape and intensity, with which irradiates polystyrene planar target with intensity from 2 × 1014 to 1.8 × 1015 W/cm2. Numerical analysis of the laser energy transformation is performed, and the simulation results agree with the experimental data.

Neutron Generator Using Spherical Targets on a Rotating Disk Irradiated with an Ultraintense Laser at 1.25 Hz

A neutron generator is developed using 1-mm-diam spherical deuterated polystyrene targets on a rotating disk irradiated with an ultrahigh-intensity (>1018 W/cm2) diode-pumped laser. It consists of a rotating disk supplier, the targets, and a control system to irradiate the targets at 1.25 Hz. We adjusted the laser focus and position on the target to obtain the maximum neutron yield.

Implementation of focal zooming on the Nike KrF laser

In direct drive inertial confinement laser fusion, a pellet containing D-T fuel is imploded by ablation arising from absorption of laser energy at its outer surface. For optimal coupling, the focal spot of the laser would continuously decrease to match the reduction in the pellet's diameter, thereby minimizing wasted energy. A krypton-fluoride laser (λ = 248 nm) that incorporates beam smoothing by induced spatial incoherence has the ability to produce a high quality focal profile whose diameter varies with time, a property known as focal zooming. A two-stage focal zoom has been demonstrated on the Nike laser at the Naval Research Laboratory. In the experiment, a 4.4 ns laser pulse was created in which the on-target focal spot diameter was 1.3 mm (full width at half maximum) for the first 2.4 ns and 0.28 mm for the final 2 ns. These two diameters appear in time-integrated focal plane equivalent images taken at several locations in the amplification chain. Eight of the zoomed output beams were overlapped on a 60 μm thick planar polystyrene target. Time resolved images of self-emission from the rear of the target show the separate shocks launched by the two corresponding laser focal diameters.

Ion beam induced luminescence: Relevance to radiation induced bystander effects

The aim of this work is quantify the light emitted as a result of charged particle interaction in materials which may be of relevance to radiation induced “bystander effects” studies. We have developed a system which employs single photon counting to measure the light emitted from samples irradiated under vacuum by a charged particle beam. The system uses a fast photomultiplier tube with a peak cathode response at 420nm. It has been tested in a proof-of-principle experiment using polystyrene targets. Light output, as a result of irradiation, was measured. The luminescence yield appears to have a non-linear behavior with the incident ion fluence: it rises exponentially to an asymptotic value. The target was irradiated with beam energies varying from 1 to 2MeV and showed saturation at or before an incident fluence rate of 3×1013H+/cm2s. The average saturation value for the photon output was found to be 40×106cps. Some measurements were performed using filters to study the emission at specific wavelengths. In the case of filtered light measurements, the photon output was found to saturate at 28×103, 10×106, and 35×106cps for wavelengths of 280±5nm, 320±5nm and 340±5nm respectively. The light output reaches a maximum value because of damage induced in the polymer. Our measurements indicate a “damage cross section” of the order of 10−14cm2. The average radiant intensity was found to increase at wavelengths of 280 and 320nm when the proton energy was increased. This was not found to occur at 340nm. In conclusion, the light emission at specific wavelengths was found to depend upon the incident proton fluence and the proton energy. The wavelengths of the emitted light measured in this study have significance for the understanding of radiation induced bystander effects.

Energetic deuterons generated from an aluminum-coated deuterated polystyrene target driven by a femtosecond laser

To improve the efficiency of laser-induced deuteron generation used for neutron generation via D-D nuclear reaction, we investigated the angular dependences of deuterons and electrons with respect to the target normal and the time-of-flight (TOF) intensity distributions of particles for thick deuterated polystyrene solid-targets with and without coating a thin aluminum layer on the front surfaces of the targets. The peak deuteron energies of 90–213 keV, which were measured for polystyrene targets with thicknesses of 50–130 µm in the target’s rear normal direction, were increased to 132–227 keV for the double-layer target with a front surface coated with 0.3-μm thickness of aluminum. These correspond to 6.9–45.8% improvements in the peak deuteron energy.

Shock-Timing Experiment Using a Two-Step Radiation Pulse with a Polystyrene Target

A shock-timing experiment plays an important role in inertial confinement fusion studies, and the timing of multiple shock waves is crucial to the performance of inertial confinement fusion ignition targets. We present an experimental observation of a shock wave driven by a two-step radiation pulse in a polystyrene target. The experiment is carried out at Shen Guang III Yuan Xing (SGIIIYX) laser facility in China, and the generation and coalescence of the two shock waves, originating from each of the two radiation steps, is clearly seen with two velocity interferometers. This two-shock-wave coalescence is also simulated by the radioactive hydrodynamic code of a multi-1D program. The experimental measurements are compared with the simulations and quite good agreements are found, with relatively small discrepancies in shock timing.

Measurement ofK+production cross section by 8 GeV protons using high-energy neutrino interactions in the SciBooNE detector

The SciBooNE Collaboration reports K+ production cross section and rate measurements using high-energy daughter muon neutrino scattering data off the SciBar polystyrene (C8H8) target in the SciBooNE detector. The K+ mesons are produced by 8 GeV protons striking a beryllium target in Fermilab Booster Neutrino Beam line (BNB). Using observed neutrino and antineutrino events in SciBooNE, we measure d2σdpdΩ=(5.34±0.76) mb/(GeV/c×sr) for p+Be→K++X at mean K+ energy of 3.9 GeV and angle (with respect to the proton beam direction) of 3.7 degrees, corresponding to the selected K+ sample. Compared to Monte Carlo predictions using previous higher energy K+ production measurements, this measurement, which uses the NUANCE neutrino interaction generator, is consistent with a normalization factor of 0.85±0.12. This agreement is evidence that the extrapolation of the higher energy K+ measurements to an 8 GeV beam energy using Feynman scaling is valid. This measurement reduces the error on the K+ production cross section from 40% to 14%.12 MoreReceived 14 May 2011DOI:https://doi.org/10.1103/PhysRevD.84.012009© 2011 American Physical Society

Aptameric system for the highly selective and ultrasensitive detection of protein in human serum based on non-stripping gold nanoparticles

A novel approach is proposed in this study for the development of an aptameric assay system for protein based on non-stripping gold nanoparticles (NPs)-triggered chemiluminescence (CL) upon target binding. The strategy chiefly depends on the formation of a sandwich-type immunocomplex among the capture antibody immobilized on the polystyrene microwells, target protein and aptamer-functionalized gold NPs. Introduction of target protein into the assay system leads to the attachment of gold NPs onto the surface of the microwells and thus the assembled gold NPs could trigger the reaction between luminol and AgNO(3) with a CL emission. Further signal amplification was achieved by a simple gold metal catalytic deposition onto the gold NPs. Such an amplified CL transduction allowed for the detection of model target IgE down to the 50 fM, which is better than most existing aptameric methods for IgE detection. This new protocol also provided a good capability in discriminating IgE from nontarget proteins such as IgG, IgA, IgM and interferon. The practical application of the proposed gold NPs-based immunoassay was successfully carried out for the determination of IgE in 35 human serum samples. Overall, the proposed assay system exhibits excellent analytical characteristics (e.g., a detection limit on the attomolar scale and a linear dynamic range of 4 orders of magnitude), and it is also straightforward to adapt this strategy to detect a spectrum of other proteins by using different aptamers. This new CL strategy might create a novel technology for developing simple biosensors in the sensitive and selective detection of target protein in a variety of clinical, environmental and biodefense applications.

Shock timing experiment in polystyrene target based on imaging velocity interferometer system for any reflector

The shock timing experiment in ablator material wave, where the shock wave transferring and catching up are investigated, can be simulated with an inertial confinement fusion planar target. The photo ionization effect caused by the X-ray from Hohlraum target is explained. With the simulation data, the block effects of Au and Cu for shock wave are analyzed. The shock velocity and the transfer time of two-shock wave in CH material are compared by using two radiation sources. The shock signals of acceleration and deceleration are obtained after adding Au block layer with thickness 5 μm to the Al layer. The shock signals of acceleration, deceleration and reloading for two shock wave experiment are achieved after adding Au layer with thickness 2 μm and Cu layer with thickness 3 μm. The experimental data show that the two conditions should be satisfied in order to obtain the two shock signals. The first condition is that the difference in radiation between two steps source should be large, and the second condition is that the shield layer should be the combination of high impedance Au and low impedance Cu. These experimental results show the shock timing ability of "Shenguang-Ⅲ", and give the reference design for planar target in shock timing technique.

Phase-contrast imaging using ultrafast x-rays in laser-shocked materials

High-energy x-rays, >10 keV, can be efficiently produced from ultrafast laser target interactions with many applications to dense target materials in inertial confinement fusion and high-energy density physics. These same x-rays can also be applied to measurements of low-density materials inside high-density Hohlraum environments. In the experiments presented, high-energy x-ray images of laser-shocked polystyrene are produced through phase contrast imaging. The plastic targets are nominally transparent to traditional x-ray absorption but show detailed features in regions of high density gradients due to refractive effects often called phase contrast imaging. The 200 TW Trident laser is used both to produce the x-ray source and to shock the polystyrene target. X-rays at 17 keV produced from 2 ps, 100 J laser interactions with a 12 μm molybdenum wire are used to produce a small source size, required for optimizing refractive effects. Shocks are driven in the 1 mm thick polystyrene target using 2 ns, 250 J, 532 nm laser drive with phase plates. X-ray images of shocks compare well to one-dimensional hydro calculations.

XPS depth profiling of polystyrene etched by electrospray droplet impact

AbstractThe molecular‐level depth profiling of polystyrene (PS) has been performed by using a newly designed electrospray droplet impact (EDI) gun. The multiple charged water droplets with kinetic energy of ∼106 eV were irradiated to a bulk and a spin‐coated PS. When a PS target is etched by EDI, the ablation of the sample is suppressed to minimal, i.e. the shallow surface etching with nonrecognizable damage on the surface is realized. It was found that XPS spectra for PS were independent on the irradiation time by EDI. This indicates that EDI is a unique technique for the surface etching of synthetic polymer materials without resulting in any damage to the etched surface. Copyright © 2010 John Wiley & Sons, Ltd.