Ion acceleration in multispecies targets driven by intense laser radiation pressure.

The acceleration of ions from ultrathin foils has been investigated by using 250 TW, subpicosecond laser pulses, focused to intensities of up to 3 × 10(20) W cm(-2). The ion spectra show the appearance of narrow-band features for protons and carbon ions peaked at higher energies (in the 5-10 MeV/nucleon range) and with significantly higher flux than previously reported. The spectral features and their scaling with laser and target parameters provide evidence of a multispecies scenario of radiation pressure acceleration in the light sail mode, as confirmed by analytical estimates and 2D particle-in-cell simulations. The scaling indicates that monoenergetic peaks with more than 100 MeV/nucleon are obtainable with moderate improvements of the target and laser characteristics, which are within reach of ongoing technical developments.

Dynamics of self-generated, large amplitude magnetic fields following high-intensity laser matter interaction.

The dynamics of magnetic fields with an amplitude of several tens of megagauss, generated at both sides of a solid target irradiated with a high-intensity (~10(19) W/cm(2)) picosecond laser pulse, has been spatially and temporally resolved using a proton imaging technique. The amplitude of the magnetic fields is sufficiently large to have a constraining effect on the radial expansion of the plasma sheath at the target surfaces. These results, supported by numerical simulations and simple analytical modeling, may have implications for ion acceleration driven by the plasma sheath at the rear side of the target as well as for the laboratory study of self-collimated high-energy plasma jets.

Monoenergetic energy doubling in a hybrid laser-plasma wakefield accelerator.

An ultracompact laser-plasma-generated, fs-scale electron double bunch system can be injected into a high-density driver/witness-type plasma wakefield accelerator afterburner stage to boost the witness electrons monoenergetically to energies far beyond twice their initial energy on the GeV scale. The combination of conservation of monoenergetic phase-space structure and fs duration with radial electric plasma fields E(r)∼100 GV/m leads to dramatic transversal witness compression and unprecedented charge densities. It seems feasible to upscale and implement the scheme to future accelerator systems.

Observation of magnetized soliton remnants in the wake of intense laser pulse propagation through plasmas.

Slowly evolving, regularly spaced patterns have been observed in proton projection images of plasma channels drilled by intense (≳10¹9 W cm⁻²) short (∼1 ps) laser pulses propagating in an ionized gas jet. The nature and geometry of the electromagnetic fields generating such patterns have been inferred by simulating the laser-plasma interaction and the following plasma evolution with a two-dimensional particle-in-cell code and the probe proton deflections by particle tracing. The analysis suggests the formation of rows of magnetized soliton remnants, with a quasistatic magnetic field associated with vortexlike electron currents resembling those of magnetic vortices.

[Retinal damage by perfluorocarbon liquids - a question of specific gravity? Intraocular pressure peaks and shearing forces]. / Retinale Schäden durch flüssige Perfluorkarbone - eine Frage des spezifischen Gewichts? Intraokulare Druckspitzen und Scherkräfte.

BACKGROUND: Perfluorocarbon liquids (PFCL) cause retinal damage when used as long-term ocular endotamponades. Whether these changes are related to the mechanical or to the chemical properties of PFCL is unclear. The purpose of this study was to evaluate pressure spikes or shearing forces during endotamponade with PFCL and standardised eye movements. MATERIAL AND METHODS: Part 1: In an eye model the resulting pressure forces of 6 PFCL were measured at four different sites during standardised eye movements. Part 2: Shearing forces were determined in a plexiglass eye model and the resulting tangential forces at the PFCL-retina interface were calculated. Part 3: Rabbit eyes were vitrectomised and filled with light and heavy fluorocarbons for 6 weeks. Subsequently, the retina were examined histologically and by immunohistochemistry. RESULTS: With increasing filling of the eye model, the maximum of the pressure peaks moved from the inferior wall of the eye model to the lateral eye walls. For perfluorodecalin (PFD) the highest pressure peak was 407 Pa with a 75 % filling of the vitreous cavity. The lowest pressure peak was 314 Pa with a 50 % filling of hexafluoropropene oxide. Shearing forces for standardised accelerations were dependent on viscosity and ranged between 0.87 mN/m(2) (perfluorohexyloctane) and 8055 mN/m(2) (hexafluoropropene oxide). Part 3: Histological and immunohistochemical analyses did not reveal pressure-related damage or any difference between the effects of the different tamponades in vivo. CONCLUSION: In comparison with physiological dynamic and static pressure peaks, the measured mechanical forces induced by intraocular PFCL tamponades are low. Specific gravity and mechanical damage by intraocular PFCL as a cause of retinal damage seem unlikely. Animal studies underline these findings.

Tumor cytotoxicity of human macrophages after incubation with synthetic analogues of 2-lysophosphatidylcholine.

Human alveolar macrophages as well as macrophages derived from Teflon culture of blood-borne monocytes were incubated with synthetic analogues of 2-lysophosphatidylcholine and then tested for their cytotoxic capacity against an allogeneic lymphoma cell line. Metabolic, rather stable analogues enhanced macrophage cytotoxicity significantly. This phenomenon was shown both in a growth-inhibition assay as well as in the 51Cr release assay. Macrophage activation was dose- and time-dependent and was potentiated at temperatures above 37 degrees C. Incubation of the macrophages with the active compounds induced characteristic changes in cell morphology as revealed by scanning electron microscopy.

Cytotoxic effector cell function at different stages of human monocyte-macrophage maturation.

Human blood-borne monocytes were cultured for up to 22 days on disposable Teflon foils. Within 8 days, these monocytes developed into mature macrophages. At various stages of differentiation, the cells were recovered from the hydrophobic membrane and were assayed for typical monocyte-macrophage enzymes and morphology, binding of monoclonal antibodies (OKM1, OKla1), Fc and transferrin receptors, phagocytic activity, lysozyme production, and ability to inhibit the growth of an allogeneic tumor target cell line (U937). A significant antitumor activity of mature macrophages was found, which developed along with the differentiation of the monocyte precursor cells. In addition, cytotoxic effector macrophages could be activated by lymphokine-rich medium and synthetic alkyl-lysophospholipids. After density gradient separation, light cells (less than 1.05 and less than 1.06 g/ml) showed enhanced cytotoxicity, whereas cells from the dense fraction (greater than 1.06 g/ml) with low base-line activity could be best activated for cytotoxicity by lymphokines. If monocyte-macrophages are involved in a natural surveillance mechanism, our results may indicate the importance of unimpaired macrophage maturation to generate effective host defense against tumor development.

Interferon-alpha alters the distribution of CFU-GM between the adherent and nonadherent compartments in long-term cultures of chronic myeloid leukemia marrow.

We studied the effect of recombinant interferon-alpha 2a (IFN alpha) on the interaction between stromal cells and granulocyte-macrophage colony-forming units (CFU-GM) from the marrow of normal individuals and chronic myeloid leukemia (CML) patients in chronic phase in long-term bone marrow cultures using preformed stromal layers. These stromal layers were established with marrow cells from normal allogeneic donors and grown to confluence in the presence or absence of IFN alpha at low concentration (100 U/ml). The number of CML CFU-GM localized within IFN alpha-treated stromal layers was significantly greater than the corresponding number localized within control stromal layers. Conversely, the distribution of normal CFU-GM between the adherent and nonadherent compartments was unaffected by IFN alpha treatment of the stromal layer. Preincubation of CML marrow cells with IFN alpha did not alter this distribution, so the observed effect of IFN alpha must be due to a primary action on stromal layers. Thus, in addition to its well known antiproliferative effect, IFN alpha enhances the capacity of marrow stromal cells to bind and/or retain CML progenitor cells, and the resulting restoration of normal regulatory control may be the basis for the selectivity of IFN alpha in CML.

Detection of the hybrid BCR/ABL messenger RNA in single CFU-GM colonies using the polymerase chain reaction.

In order to study which hemopoietic precursor cells express the hybrid BCR/ABL fusion mRNA we have developed a technique based on the polymerase chain reaction (PCR) for the examination of single hemopoietic colonies grown on semi-solid agar. The technique was developed by examining single CFU-GM colonies grown from newly diagnosed patients with chronic myeloid leukaemia (CML). RNA was isolated from individual 14 day colonies and reverse transcribed to a complementary DNA (cDNA) copy which formed the substrate for a PCR. We have studied 3 cases of CML using this method and have found that 5 out of 5, 9 out of 10 and 20 out of 23 colonies examined were positive. Thus we describe a simple and useful technique for the study of gene expression in a limited number of hemopoietic precursor cells.

Potential mechanisms of action of interferon-alpha in CML.

Treatment with interferon-alpha (IFN-alpha) adequately controls the leukemic cell mass in the majority of newly diagnosed patients with chronic myeloid leukemia (CML). However, the degree of response ranges from no 'hematologic' response to complete suppression of the leukemic clone. The mechanism(s) by which IFN-alpha elicits these responses is unknown, but in vitro studies have indicated that IFN-alpha might function by (1) selective toxicity against the leukemic clone, (2) enhancement of 'immune' regulation, and (3) modulation of bone marrow microenvironmental regulation of hematopoiesis. Using in vitro clonogenic assays we were unable to demonstrate that IFN-alpha selectively inhibited the proliferation of CML progenitor cells. We also found no difference in the expression of LFA-3 on normal or CML CD34+ cells. However, by panning and co-culturing hematopoietic cells on monolayers of bone marrow stromal cells, grown with and without IFN-alpha, we found that IFN-alpha enhanced the adhesion of CML progenitors to stromal cells, whereas adhesion by normal progenitor cells was essentially unaffected. This enhanced adhesion by CML progenitor cells was associated with a reduction in neuraminic acid levels in the extracellular matrix overlying stromal cells. Therefore, it is possible that one of the mechanisms by which IFN-alpha exerts its regulatory effect on the leukemic clone is through enhancement of hematopoietic cell-microenvironmental cell interactions.

Characterization of two distinct, simultaneous hot electron beams in intense laser-solid interactions.

The transport of energetic electron beams generated from aluminum foils irradiated by ultraintense laser pulses has been studied by imaging coherent transition radiation from the rear side of the target. Two distinct beams of MeV electrons are emitted from the target rear side at the same time. This measurement indicates that two different mechanisms, namely resonance absorption and jxB heating, accelerate the electrons at the targets front side and drive them to different directions, with different temperatures. This interpretation is consistent with 3D-particle-in-cell simulations.

Directed acceleration of electrons from a solid surface by Sub-10-fs laser pulses.

Electrons have been accelerated from solid target surfaces by sub-10-fs laser pulses of 120 microJ energy which were focused to an intensity of 2x10;{16} W/cm;{2}. The electrons have a narrow angular distribution, and their observed energies exceed 150 keV. We show that these energies are not to be attributed to collective plasma effects but are mainly gained directly via repeated acceleration in the transient field pattern created by incident and reflected laser, alternating with phase-shift-generating scattering events in the solid.

Guiding, focusing, and collimated transport of hot electrons in a canal in the extended tip of cone targets.

Hot electrons are produced, guided into a beam, and transported over 60 microm in a small canal to the outside tip of a structured cone target. The diameter of the electron beam is defined by the inside tip diameter. This carries the potential to create electron beams of specific diameters propagating over specific distances of interest for several applications.

Generation of Mie size microdroplet aerosols with applications in laser-driven fusion experiments.

We have developed a tunable source of Mie scale microdroplet aerosols that can be used for the generation of energetic ions. To demonstrate this potential, a terawatt Ti:Al2O3 laser focused to 2 x 10(19) W/cm2 was used to irradiate heavy water (D2O) aerosols composed of micron-scale droplets. Energetic deuterium ions, which were generated in the laser-droplet interaction, produced deuterium-deuterium fusion with approximately 2 x 10(3) fusion neutrons measured per joule of incident laser energy.

Absorption of ultrashort laser pulses in strongly overdense targets.

Absorption measurements on solid conducting targets have been performed in s and p polarization with ultrashort, high-contrast Ti:sapphire laser pulses at intensities up to 5x10{16}W/cm{2} and pulse duration of 8 fs. The particular relevance of the reported absorption measurements lies in the fact that the extremely short laser pulse interacts with matter close to solid density during the entire pulse duration. A pronounced increase of absorption for p polarization at increasing angles is observed reaching 77% for an incidence angle of 80 degrees . Simulations performed using a 2D particle in cell code show a very good agreement with the experimental data for a plasma profile of L/lambda approximately 0.01.

Equation-of-state measurement of dense plasmas heated with fast protons.

Using an ultrafast pulse of mega-electron-volt energy protons accelerated from a laser-irradiated foil, we have heated solid density aluminum plasmas to temperatures in excess of 15 eV. By measuring the temperature and the expansion rate of the heated Al plasma simultaneously and with picosecond time resolution we have found the predictions of the SESAME Livermore equation-of-state (LEOS) tables to be accurate to within 18%, in this dense plasma regime, where there have been few previous experimental measurements.

Production of dense plasmas with sub-10-fs laser pulses.

Close to solid state density plasmas with peak electron temperatures of about 190 eV have been generated with sub-10-fs laser pulses incident on solid targets. Extreme ultraviolet (XUV) spectroscopy is used to investigate the K shell emission from the plasma. In the spectra, a series limit for the H- and He-like resonance lines becomes evident which is explained by pressure ionization in the dense plasma. The spectra are consistent with computer simulations calculating the XUV emission and the expansion of the plasma.

Study of electron-beam propagation through preionized dense foam plasmas.

The transport of an intense electron-beam produced by the Vulcan petawatt laser through dense plasmas has been studied by imaging with high resolution the optical emission due to electron transit through the rear side of coated foam targets. It is observed that the MeV-electron beam undergoes strong filamentation and the filaments organize themselves in a ringlike structure. This behavior has been modeled using particle-in-cell simulations of the laser-plasma interaction as well as of the transport of the electron beam through the preionized plasma. In the simulations the filamentary structures are reproduced and attributed to the Weibel instability.

Enhancement of spontaneous and lymphokine activated human macrophage cytotoxicity by hyperthermia.

Human macrophages grown on hydrophobic teflon membranes from blood-born monocytes were incubated at hyperthermic temperatures for various time periods and then tested for their ability to inhibit the growth of an allogeneic lymphoma cell line (U 937). Incubation at 40.5 degrees C greatly enhanced macrophage cytotoxicity. This effect of hyperthermia developed slowly with an optimal incubation period of 48 h. In addition, lymphokine activation of macrophages for cytotoxicity appeared to be more effective at elevated temperatures.

Human macrophage maturation and heterogeneity: analysis with a newly generated set of monoclonal antibodies to differentiation antigens.

We have analyzed the expression of late differentiation antigens during terminal in vitro maturation of human macrophages (M phi) from blood monocytes (MO) in comparison to their distribution among mature M phi residing in various tissue sites. By immunizing mice with M phi derived from blood MO by culture on hydrophobic Teflon foils, monoclonal antibodies (mAbs) were developed (MAX.1, MAX.2, MAX.3, MAX.11) that reacted with lineage-restricted differentiation antigens. These antigens were expressed exclusively on M phi or were markedly increased after in vitro differentiation. The only overlap to another hemopoietic cell lineage was observed with MAX.3, which is shared by platelets and megakaryocytes. In the course of M phi maturation in vitro, the MAX.1 and MAX.3 antigens are detected within the cytoplasm two days before they appear on the cell surface. In contrast, the MAX.11 antigen is expressed simultaneously in the cytoplasm and at the cell surface, is found in varying degrees on a minor portion of blood MO and U937 cells, and is expressed rapidly at high density during early M phi differentiation in vitro. Among conventional mAbs that do not react with MO we found those against the transferrin (TF)-receptor, the BA-2, and the PCA1 antigen to label M phi. M phi matured in vivo and isolated from body fluids were positive with some but not all MAX mAbs. Distinctive patterns were observed with pulmonary M phi, exudate M phi from pleural and peritoneal effusions, synovial fluids, and early lactation milk. M phi from the alveolar space, for example, constantly expressed the MAX.2 antigen but not the MAX.3 antigen. Pleural effusion M phi, however, did not react with the MAX.1 mAb, but in most cases, it did react with the MAX.3 mAb. The detection of novel differentiation antigens, all expressed on monocyte-derived M phi but differently expressed on site-specific M phi in situ, underlines the remarkable heterogeneity among human M phi. The expression of these antigens is flexible because those MAX antigens that were not expressed in situ could be induced if cells from distinct tissue sites were cultured in vitro for several days. MAX mAbs may be of potential value to study both the sequential stages of maturation within the M phi lineage as well as differential developments induced by various culture conditions in parallel to environmental factors in vivo.