Stage 2 - P1
Phase no. 6
Responsible: Dr. F. JIPA
Title: "The realization of matrix holder for micro-targets"
Abstract: In this work we report a manufacturing procedure of a (solid) target holder, designed to allow the fabrication of 3D micro-structures (micro-targets) on the surface of aluminum foils (with a thickness of few micrometers) used for particles acceleration after the interaction with ultra-intense laser pulses. The (solid) target holder having a length of 2 inches and a width of 1 inch is composed of two flat layers provided with holes of different diameters arranged in a matrix configuration. The thin aluminum foil is inserted between the two layers and it is fitted with connectors. A photoresist material is deposited directly on the aluminum foil surface through the holes in the holder layers in order to create 3D cone shape structures by direct laser writing technique. The structures fabricated on the aluminum foil surface (cone shape structures) have the height and the base diameter equal to 100 μm and they are positioned with the tip in contact with the thin foil. The method presented in this research activity report has been submitted as a patent application to the State Office for Inventions and Trademarks.
Phase no. 7
Responsible: Dr. Sandu ION
Title: "The study of relation between selfassembly of some nanomaterials and their geometric constrains"
Abstract: By depositing liquid drops and thin films which contain nano-objects onto a substrate and let them to evaporate, we found that the drop or film architecture can dramatically influence the quality of single layer self-assembled nano-objects. We found that a colloidal drop which is geometric constrained to be flat (by a scaffold), arranges its nanoparticles in single layer ribbons without dislocations. This make them suitable as devices in Bragg diffraction phenomena or as lithographic masks. During experiments we studied the influence of parameters such as: substrate nature (polymer, glass, metal, silicon), substrate roughness, solvent nature (water, ethanol), substrate tilt, the role of stabilizing substances (Triton), nanoobjects nature (Fe2O3, TiO2, SnO2, C nanoparticles, polystirene nanosphere) nanoparticle size and nanophere size (0.7 - 20 μm), the nature, dimension and architecture of scaffold (wires of Cu, steel and polymer with diameters varieing between 100 - 2000 μm), substrate temperature, external medium temperature and relative humidity (40 - 90 %). The best results were obtained for (Polistyrene nanosphere, d = 0.7 μm, water and triton as stabilization agent, low concentrations of nanospheres (c = 0.1 %), parallel Cu wires distanced at 1 mm). The resulting ribbons size was of 50 x 25000 μm. We found that some ionic salts (K2CrO4) crystallize (from aqueous solutions) as single crystal grids (interspacing 5 - 20 μm) when they are evaporated as diluted (c < 1 % wt.) liquid thin films (d = 2 μm, geometric constrained) on a hot plate (T = 300 - 500 0C). We found no differences in static, evaporation, and crystallization of some drops deposited on an ''infinite'', flat substrate and onto the superior surface of cylindrical pillars. The information obtained during the study of geometric constrain on the self-assembly phenomenon may lead to the fabrication of some performing and still cheap devices.
Phase no. 8
Responsible: Dr. F. SPINEANU
Title: "Theoretical modeling of coherent X ray sources for developing angstrom size wavelength light pulses with tens of femtoseconds duration"
Abstract: Lasing at nanometer (N. Rohringer et al., Nature (London) 481, 2012) and angstrom (H. Yoneda et al., Nature 524, 2015) scale have been recently demonstrated thus allowing new possibilities for experiments concerning nonlinear photon-electron scattering (C. Weninger et al., Phys.Rev.Lett. 111, 2013), observation of electrons dynamics on their natural time scale, and extending the energy domain for plasma diagnostics in extreme conditions (fusion plasma, astrophysical plasma or laboratory laser-produced plasma). Fine-structure transitions belonging to heavy ions in highly ionized plasmas are investigated through the interactions of these accelerated relativistic particles and coherent X rays with very short wavelengths. The X-ray Free Electron Laser (XFEL) plays a key role at the borderline between atomic physics and nuclear physics allowing different oportunities for new high frequency light sources (very short wavelength).
In the present work we make use of the generalized Maxwell-Bloch approach (C. Weninger and N. Rohringer, PRA 90, 2014) in order to simulate the amplification of radiation within a plasma column resulting from the photo-ionization of the neon gas performed with the help of the XFEL pulse similar to the experiment performed in 2012. The spontaneous emission is modeled using a stochastic term characterized by a correlation function which reproduces the correct Lorentian line-shape of the transition. The numerical simulation of the amplification process allows spatial and temporal monitorization of the population inversion, laser gain, laser pulse (temporal profile, brightness, duration, frequency band) and pumping radiation attenuation along its propagation in the lasing medium.
Phase no. 9
Responsible: Dr. C. TICOS
Title: "Electron acceleration regimes in the plasma produced by a hiperintense laser"
Abstract: The acceleration regime of the electrons in the plasma produced by a hiperintense laser depends on the plasma parameters and laser pulse duration. In the present phase the different regimes of electron acceleration were identified and numerically evaluated by highlighting the main features and realization conditions. The efficiency of the electron acceleration procces is characterized by the numerical investigation of the acceleration length and the energy gain specific to each regime.
The main characteristics of the accelerated electron beams such as the energy distribution, and the angular dispersion due to the magnetic field by using a magnetic spectrometer were determined. The simulations took into account the initial spatial distribution of the beam and its energy spectrum as well. An electron magnetic spectrometer was designed in order to measure a broad range of energies, from 1 to 200 MeV in a single shot, by employing simultaneously two detectors located in perpendicular planes. The proposed spectrometer was analytically and numerically investigated obtaining the preliminary results for the experimental realization of the setup.
Phase no. 10
Responsible: Dr. O. BUDRIGA
Title: "System and procedure for the characterization of the spatial profile of the ultra-intense laser pulses in the interaction zone. Intensity contrast measurements at picosecond and nanoscond time scale"
Abstract: The temporal intensity profile of the ultra-intense laser pulses was measured in different configurations at the interaction chamber level using a third-order autocorrelator TUNDRA. This type of measurement is a method for the evaluation of the intensity contrast at hundreds of picosecond time scale. For the evaluation of the intensity contrast at a nanosecond time scale, it was implemented a particular method which uses a fast photo-diode coupled with an oscilloscope. Another important parameter of the laser beam is the intensity spatial profile which was measured. A method was implemented at CETAL-PW laser system to control the beam focusability at the interaction chamber level. For this purpose we use a software which does a control loop of a system consisting in a deformable mirror and a Shack Hartmann sensor in order to compensate the wavefront errors introduced by the optical components.