Stage 1 - P1 2016

The project implementation schedule

Phase no. 1

Responsible: Dr. O. BUDRIGA

Deadline: 13.05.2016

Title: "System and procedure for temporal profile characterization of ultraintense pulses in the proximity of the interaction chamber. Energy measurements and calibration of the transport system to the interaction place"

Abstract: This report is a preliminary stage in achieving the main objective of the theme within the project which proposes a complex system for characterizing high-intensity pulses from the interaction chamber. The activities carried out for this project were focused on several general directions aiming to fulfill the objectives. The results so far have role to help on identification of the main components in the amplification stages of the Petawatt laser system which play an important role in controlling the temporal profile of the pulses that reach the interaction chamber. The development of an ptoelectronic system targeted onto complex characterization of extremely intense laser pulses parameters requires high level experience in using specific devices in measuring such parameters as: temporal profile, energy, spectral mode profile and some procedures in advance for integrating such devices into the current laser system setup as installed at CETAL.

Phase no. 2

Responsible: Dr. G. DINESCU/ Dr. C. STANCU

Deadline: 13.05.2016

Title: "Plasma sources for selective attack of contaminant layer under reduced ionic bombardment and plasma-based systems for localized or large area treatment of surfaces"

Abstract: Two types of plasma sources were designed and realized: a plasma source with outer circular electrodes and a plasma source with central powered electrode. The basic ideas that lead to the design and subsequently to the realization of the plasma sources was following: i) designing of experimental systems based on similar geometry of plasma in front of the surfaces to be cleaned; ii) avoid the plasma contact with metallic surfaces (electrodes or chamber walls) to avoid the risk of contamination of the surfaces to be cleaned after sputtering processes that may occur due to metals; iii) operation of the plasma sources in low ionic bombardment in order to avoid the damage risk of the optical qualities of the optical surfaces.

Phase no. 3

Responsible: Dr. M. GANCIU

Deadline: 15.07.2016

Title: "Development, testing and calibration of diagnosis systems intended for large amplitude electromagnetic pulses generated during interactions of high power lasers with targets"

Abstract: Development, testing and calibration of diagnosis systems intended for large amplitude electromagnetic pulses - EMP (or transient electromagnetic disturbances), which are the outcome of the interaction between a very intense laser pulse and different type of targets (solid or gas), requires design and testing of electromagnetic pulse simulators that exhibit characteristics as close as possible to reality, or enable intensity scaling while maintaining temporal characteristics. We report design and testing of such system by using a filamentary discharge in nitrogen flux at standard ambient temperature and pressure conditions and speeds in the range of tens of m/s, optimized for repetition frequencies of around 30 kHz. The system we designed delivers EMPs with rise times < 1 ns and time durations of around 5 – 10 ns, depending on the discharge geometry. The switched voltage range is 3 – 8 kV, depending on the electrode geometry and gas pressure, for a speed which is optimized for the maximum overvoltage applied between the electrodes that generate the filamentary discharge. Inter-electrode capacity at the moment of the discharge initiation is around 10 pF. Both capacitive and inductive coupling electronic probes have been tested. The experimental setup is compact, transportable and can be easily mounted within the interaction chamber of a PW class laser system, for different type of targets. The high repetition rate enables performing accurate measurements, even outside the interaction chamber region where the signal can be sensibly attenuated. Such an approach allows optimizations of the electromagnetic shielding of diagnosis, drive, and control systems, for intense EMPs associated to the interaction between very intense laser beams and matter. These optimizations, which are performed for low energies of the test pulses, have no effect whatosever on the operation of the tested system within parameters.

Phase no. 4

Responsible: Dr. F. SPINEANU

Deadline: 15.07.2016

Title: "High power laser pulse filamentation during propagation"

Abstract: The propagation of laser beams through madia with nonlinear polarization has many practical applications. The processes that are involved are at the limit of extreme (cuasi-singular) concentration of intensity and the transversal modulational instability, the saturation and defocusing effect of the plasma generated through avalanche and multi-photon (MPI) ionization are competing leading to complicated pattern of intensity. This is optical turbulence and the previous studies complementing the experiments were based on numerical simulations. We have identified the mechanism that underlies the creation of the apparent random field as the manifestation of the dynamics “activator-inhibitor”. The first attempt to implement this model consisted in finding a unique connection, the “complex Landau- Ginzburg equation”, a common ground for the nonlinear Schrodinger equation (optical propagation) and reaction-diffusion systems (activator-inhibitor). The present study is a deeper level of investigation. We exhibit the integrable nature of the elementary self-focusing propagation (“gas Chaplygin with anomalous polytropic”). Then we show that the intensity dynamics is extended on physical basis to include potential barrier separating two states of equilibria, the drive due to competing Kerr and MPI nonlinearities We exhibit the variational structure (according to Goldstein approach) and calculate the width of a branch of the cluster of high intensity. Our result is smaller but satisfactorily in the range of the experimental observations.

Phase no. 5

Responsible: Dr. T. DASCALU

Deadline: 03.08.2016

Title: "Study of the physical and technological parameters which determine the obtaining of rare-earth doped ceramic materials with high transparency"

Abstract: Nd doped yttrium aluminum garnet NdxY3-xAl5O12 (x= 0.5; 1.0 and 1.5-at.%) polycrystalline ceramic samples were obtained by solid-state reaction and vacuum sintering method using high purity nanopowders of Al2O3, Y2O3 and Nd2O3 as starting materials. The raw materials were mixed in stoichiometric proportions and homogenized in ethanol medium for 24 h. 0.5-wt.% TEOS combined with 0.1-wt.% MgO were used as sintering aids, in order to obtain dense ceramic pellets by decreasing the inter- and intra- particle porosity. Polyethylene glycol (PEG400) was used as dispersant at 0.3-wt.%, and was added to the suspension in the last 2 h of homogenization. The slurry was dried using spray drying technique (Mini Spray Dryer B-290, Buchi) equipped with Inert Loop B-295 for the removal of organic solvent. Spray-dried powders were shaped into pellets with a diameter of about 12 mm and thickness of 1.5 mm by uniaxialy pressing in a metallic dye at 10 MPa followed by cold isostatic pressing (CIP) at 245 MPa / 20 min. Before sintering, samples were calcinated in air at 800oC for 6 h for the complete removal of the organic additives. Sintering was conducted at 1730 - 1760oC for 12 h under high vacuum (4x10-6 mbar) in a furnace with a tungsten-molybdenum chamber. Annealing cycles were performed in air at 1450oC for 10 h in order to promote the oxidation of the phases reduced during sintering under high vacuum.
The phase structure, microstructure and optical properties of prepared ceramics as a function of sintering temperature were investigated. For 0.5-at.% Nd:YAG, 1.0-at.% Nd:YAG and 1.5-at.% Nd:YAG ceramic samples sintered at 1730oC and 1740oC / 12 h, the XRD pattern exibits a mixture of a cubic major phase of Y3Al5O12 (YAG - ICDD 01-079-1891) with an orthorhombic phase of YAlO3 (YAP - ICDD 04-002-0534). At higher temperatures of sintering at 1750oC and 1760oC / 12 h, all the diffraction peaks are representative of the corresponding desired garnet phase of Y3Al5O12 (YAG - ICDD 01-079-1891), with cubic symmetry (Ia3d space group).
The SEM morphology of fractured surface of 0.5-at.% Nd:YAG, 1.0-at.% Nd:YAG and 1.5-at.% Nd:YAG ceramic samples sintered at lower temperatures than 1750oC, exibit a high degree of inter- and intragranular porosity. The densification of ceramic bodies increase with increasing of sintering temperature at 1760oC / 12 h, reaching values of the grain size up to 14 μm. The optical properties (investigated by optical spectroscopy techniques) are improved with increasing the sintering temperature. Thus, the highest transmission (the lowest scattering) was obtained for 1.0-at.% Nd:YAG ceramic sample sintered at 1760oC / 12 h.