Effect of Focusing Plane on Laser Blow-off Shock Waves from Confined Aluminum and Copper Foils

We present results on the dynamics of laser-induced blow-off shockwave generation from the rear side of 20 µm thick aluminum and copper foil confined with a glass (BK7) substrate. These foils are irradiated by 10 ns, 532 nm laser pulses of energy 25 – 200 mJ corresponding to the intensity range 0.2 – 10 GW/cm2. The plasma temperature at the glass-foil interface is observed to play an important role in the coupling of laser energy to the foil. From our experiments and 1D hydrodynamic simulations, we confirm that moving the glass-foil interface away from the focal plane led to (a) enhanced absorption of the laser beam by the foil resulting in ~ 30 % higher blow-off shock velocities (b) significant changes in the material ejection in terms of increased blow-off mass of the foil (c) lower plasma density and temperatures. The material ejection as well as blow-off shock velocity is higher for Al compared to Cu. The simulated shock evolution in ambient air shows a reasonably good agreement with the experimental results.

Phosphorous Incorporated-Silicon Nanoparticles Synthesized Using Double Tube Reactor and Inductive Coupled Plasma

Phosphorous (P) incorporated silicon nanoparticles (Si NPs) were synthesized by using inductive coupled plasma (ICP) and a specially designed double tube reactor.Their microstructures were investigated by injecting various amounts of PH3 gas during the synthesis. Injection of PH3 gas during the synthesis resulted in a change from crystalline to amorphous phase, a reduction of particle size as well as process yield. These results were attributed to a lower plasma density when higher amount of PH3 was injected.From EDS, SIMS and XPS analysis, it was revealed that P was successively incorporated in Si NPs.However, secondary phases such as P4 (red P) and P2O5were formed as amorphous ones in nanoscale when a relatively large amount of PH3 was injected.

Resonant enhancement of electron energy by frequency chirp during laser acceleration in an azimuthal magnetic field in a plasma

Electron acceleration by a chirped laser pulse in an azimuthal magnetic field in a plasma has been studied. The betatron resonance saturates and the electrons start losing energy beyond a specific point of time without a frequency chirp. The resonance can be maintained for a longer duration and the energy of the electrons can be enhanced if a suitable frequency chirp is introduced. The duration of interaction increases for a lower plasma density or a lower initial electron energy which causes increase in the electron energy gain. The value of magnetic field required for resonance increases with an increase in plasma density and with a decrease in initial electron energy.