fluorecence microscopy study of cds quantum dots obtained by laser irradiation from a single source precursor in polymeric film

Abstract Recently the quantum dots (QDs) synthesis from single source precursors (SSPs) showed a potential interest for patterning formation of nano-composites. In this approach the SSPs have to be mixed with a matrix that afterwards is treated selectively to obtain the desired nanocomposite. The study of the generation of the QDs from the SSPs is, therefore, crucial for the definition of its behaviour within the polymeric matrix. The formation of the CdS QDs via thermolysis of the cadmium diethyldithiocarbamate (CdDDTC) was performed and studied in the presence of a non coordinating solvent such as octadecene (ODE) in presence of myristic acid (MA) as ligand. The precursor is then studied in combination with the poly(methyl methacrylate) (PMMA) polymer for the generation of the CdS QDs under the laser irradiation within a film. The effect of the laser has been studied both on neat PMMA and on the polymer/precursor blend film with the aid of the fluorescence microscope. The results are used to identify the optimal laser parameters to obtain the decomposition of the precursor and to evaluate the effect of the laser irradiation on the polymer

Optically Pumped Mid-Infrared Stimulated Emission of ZnSe:Cr Crystals

We demonstrate that ZnSe:Cr is an excellent solid state laser material for mid-infrared region with a broad amplification band from 2.2 μm to 3 μm, and with a high quantum efficiency of a radiative recombination. 46% external total efficiency and 56 mW threshold power were achieved, when pumped with a CW YAlO:Ho laser at resonant excitation conditions. Such laser system can have widespread applications in medicine as laser scalpels with regulated cutting depth. We further demonstrate a stimulated emission under Cr2+ to 1+ photo-ionization pumping. The latter opens chances for laser emission under carrier injection conditions

Optically Pumped Mid-Infrared Stimulated Emission of ZnSe:Cr Crystals

We demonstrate that ZnSe:Cr is an excellent solid state laser material for mid-infrared region with a broad amplification band from 2.2 μm to 3 μm, and with a high quantum efficiency of a radiative recombination. 46% external total efficiency and 56 mW threshold power were achieved, when pumped with a CW YAlO:Ho laser at resonant excitation conditions. Such laser system can have widespread applications in medicine as laser scalpels with regulated cutting depth. We further demonstrate a stimulated emission under Cr2+ to 1+ photo-ionization pumping. The latter opens chances for laser emission under carrier injection conditions

Laser printed nano-gratings: orientation and period peculiarities

Understanding of material behaviour at nanoscale under intense laser excitation is becoming critical for future application of nanotechnologies. Nanograting formation by linearly polarised ultra-short laser pulses has been studied systematically in fused silica for various pulse energies at 3D laser printing/writing conditions, typically used for the industrial fabrication of optical elements. The period of the nanogratings revealed a dependence on the orientation of the scanning direction. A tilt of the nanograting wave vector at a fixed laser polarisation was also observed. The mechanism responsible for this peculiar dependency of several features of the nanogratings on the writing direction is qualitatively explained by considering the heat transport flux in the presence of a linearly polarised electric field, rather than by temporal and spatial chirp of the laser beam. The confirmed vectorial nature of the light-matter interaction opens new control of material processing with nanoscale precision.Partial support via ARC Discovery DP120102980 is acknowledged

Symmetric and asymmetric shocked gas jets for laser-plasma experiments

International audienceShocks in supersonic flows offer both high density and sharp density gradients that are used, for instance, for gradient injection in laser-plasma accelerators. We report on a parametric study of oblique shocks created by inserting a straight axisymmetric section at the end of a supersonic “de Laval” nozzle. The effect of different parameters, such as the throat diameter and straight section length on the shock position and density, is studied through computational fluid dynamics (CFD) simulations. Experimental characterizations of a shocked nozzle are compared to CFD simulations and found to be in good agreement. We then introduce a newly designed asymmetric shocked gas jet, where the straight section is only present on one lateral side of the nozzle, thus providing a gas profile well adapted for density transition injection. In this case, full-3D fluid simulations and experimental measurements are compared and show excellent agreement

Demonstration of stable long-term operation of a kilohertz laser-plasma accelerator

International audienceWe report on the stable and continuous operation of a kilohertz laser-plasma accelerator. Electron bunches with 2.6 pC charge and 2.5 MeV peak energy were generated via injection and trapping in a downward plasma density ramp. This density transition was produced in a specially designed asymmetrically shocked gas jet. The reproducibility of the electron source was also assessed over a period of a week and found to be satisfactory with similar values of the beam charge and energy. Particle in cell simulations confirm the role of the shock and the density transition in the electron injection mechanism. These results show that the reproducibility and stability of the laser-plasma accelerator are greatly enhanced on the long-term scale when using a robust scheme for density gradient injection

Optimization and stabilization of a kilohertz laser-plasma accelerator

Laser–plasma acceleration at kilohertz repetition rates has recently been shown to work in two different regimes with pulse lengths of either 30 fs or 3.5 fs. We now report on a systematic study in which a large range of pulse durations and plasma densities were investigated through continuous tuning of the laser spectral bandwidth. Indeed, two laser–plasma accelerator (LPA) processes can be distinguished, where beams of the highest quality, with a charge of 5.4 pC and a spectrum peaked at 2–2.5 MeV, are obtained with short pulses propagating at moderate plasma densities. Through particle-in-cell (PIC) simulations, the two different acceleration processes are thoroughly explained. Finally, we proceed to show the results of a 5-h continuous and stable run of our LPA accelerator accumulating more than 18 ???? 106 consecutive shots, with a charge of 2.6 pC and a peaked 2.5 MeV spectrum. A parametric study of the influence of the laser driver energy through PIC simula- tions underlines that this unprecedented stability was obtained thanks to micro-scale density gradient injection. Together, these results repre- sent an important step toward stable laser–plasma accelerated electron beams at kilohertz repetition rates