T. Palchan

5.5-7.5 MeV Proton Generation by a Moderate-Intensity Ultrashort-Pulse Laser Interaction with H{sub 2}O Nanowire Targets

We report on the first generation of 5.5-7.5 MeV protons by a moderate-intensity short-pulse laser (∼5×10(17)  W/cm(2), 40 fsec) interacting with frozen H(2)O nanometer-size structure droplets (snow nanowires) deposited on a sapphire substrate. In this setup, the laser intensity is locally enhanced by the snow nanowire, leading to high spatial gradients. Accordingly, the nanoplasma is subject to enhanced ponderomotive potential, and confined charge separation is obtained. Electrostatic fields of extremely high intensities are produced over the short scale length, and protons are accelerated to MeV-level energies.

Efficient coupling of high intensity short laser pulses into snow clusters

Measurements of energy absorption of high intensity laser pulses in snow clusters are reported. Targets consisting of sapphire coated with snow nanoparticles were found to absorb more than 95% of the incident light compared to 50% absorption in flat sapphire targets.

Control of the filamentation distance and pattern in long-range atmospheric propagation

We use the double-lens setup [10, 11] to achieve a 20-fold delay of the filamentation distance of non-chirped 120 fs pulses propagating in air, from 16m to 330m. At 330m, the collapsing pulse is sufficiently powerful to create plasma filaments. We also show that the scatter of the filaments at 330m can be significantly reduced by tilting the second lens. To the best of our knowledge, this is the longest distance reported in the Literature at which plasma filaments were created and controlled. Finally, we show that the peak power at the onset of collapse is significantly higher with the double-lens setup, compared with the standard negative chirping approach.

Generation of fast ions by an efficient coupling of high power laser into snow nanotubes

Generation of fast ions in snow nanotubes irradiated by femtosecond laser pulses in the intensity range of 1016–1017W∕cm2 was investigated. The fast ion energy was measured through x-ray emission spectra of multicharged ions of oxygen. The profile of the He-β and Ly-α in He-like and H-like oxygen lines demonstrates a significant broadening, which may indicate generation of fast He-like and H-like ions with energies of up to 100keV.

Electron density in low density capillary plasma channel

A low density plasma channel of 1017cm−3 is created in a capillary discharge. The plasma channel is characterized through the hydrogen plasma spectra in the Balmer Hα line. The measured plasma density profiles were found to be in qualitative agreement with the hydrodynamic simulations. Guiding over many vacuum diffraction length using a plasma channel operating in the low density regime is demonstrated.

Application of snow nanograin targets for the generation of fast ions in femtosecond laser plasma

We have measured the energy of the directed motion of multiply charged ions produced when solid targets are exposed to low-contrast (10−3–10−2) femtosecond laser pulses with intensities 1015–1016 W cm−2. The measurements are based on the recording of spatially resolved X-ray spectra for H-and He-like oxygen ions in the target plane. Analysis of the Heβ and Lyα line profiles has revealed fractions of accelerated ions in plasma with energies from several to several tens of kiloelectronvolts. We show that using a layer of frozen nanometer-size water droplets as the targets leads to an effective absorption of laser pulses and a twofold rise in the energy (to 0.1 MeV) of He-like oxygen ions compared to the use of solid targets.

Generation of Multi‐MeV Protons by Interaction of Modest Laser Intensities with H2O “Snow” Nano‐Wire Targets

We report on the generation of protons with energies of 6 MeV when irradiating an H2O nano‐wire layer grown on a Sapphire plate with an intensity of 3×1017 W/cm2.

Interaction of high power laser with snow nanotubes

We found that snow nanotubes targets absorb more than 95% of the incident light of a high power laser. Fast ions were generated with energies up to 100 keV .

GUIDING OF HIGH LASER INTENSITIES IN LONG PLASMA CHANNELS

Plasma channels have been widely used to guide intense laser pulses over many Rayleigh lengths. Using optimized segmented capillary discharges, we demonstrated guided propagation of ultra short (100 fs) high intensity (1016 W/cm-2, limited by the laser system) pulses over distances up to 12.6 cm and intensities above 1018W/cm2 for 1.5cm boron nitride capillary. Both radial and longitudinal density profiles of plasma channels were studied under various discharge conditions. A new diagnostic technique is presented in which the transport of a guided laser pulse at different delay times from the initiation of the discharge is sampled on a single discharge shot. Using external, 10 nsec Nd YAG laser of several tenths of milijoules to ignite polyethylene capillaries we have demonstrated channels of various length in density range of 1017 - 1019cm-3 and up to 25% deep. The longitudinal profiles were found to be remarkably uniform in both short and long capillaries. The Boron Nitride capillary has provided a guiding medium that can withstand more than 1000 shots. Using these capillaries we have guided laser intensities above 1018W/cm2. The laser ignition of capillary discharge provided reliable almost jitter free approach. The concerns related to influence of relatively high current density flow through capillary on the injected electrons were studied extensively by us both theoretically and experimentally using a simple injection method. The method is based on the interaction of a high intensity laser pulse with a thin wire placed near capillary entrance. The influence of magnetic fields was found to be insignificant. Using this method we have studied transport of electrons though capillary discharge.