Angular Distribution Of Hot Electrons Research Articles

Laser-driven high-energy proton beam with homogeneous spatial profile from a nanosphere target

A high-energy, high-yield proton beam with a good homogeneous profile has been generated from a nanosphere target irradiated by a short (30-fs), intense ($7\ifmmode\times\else\texttimes\fi{}{10}^{20}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$) laser pulse. A maximum proton energy of 30 MeV has been observed with a high proton number of $7\ifmmode\times\else\texttimes\fi{}{10}^{10}$ in the energy range 5--30 MeV. A homogeneous spatial profile with a uniformity (standard deviation from an average value within 85% beam area) of 15% is observed with the nanosphere dielectric target. Particle-in-cell simulations show the enhancement of proton cutoff energy and proton number with the nanosphere target and reveal that the homogeneous beam profile is related with a broadened angular distribution of hot electrons, which is initiated by the nanosphere structure. The homogeneous spatial properties obtained with the nanosphere target will be advantageous in developing laser-driven proton sources for practical applications in which high-quality beams are required.

Soft x-ray emission, angular distribution of hot electrons, and absorption studies of argon clusters in intense laser pulses

High resolution soft x-ray spectra (3–40 nm) produced by the interaction of intense femtosecond laser pulses with argon clusters at an intensity of about 1×1016 W/cm2 are measured under different backing pressures. Soft x-ray spectra are strongly dependent on the initial size of cluster and plasma expanding process. We find that laser polarization has no evident effect on the soft x-ray emission from the lateral side. The measurement on angular distribution of hot electrons shows that the resonant absorption is the dominated mechanism. Both the x-ray yield and the laser energy absorption are more efficient when the radius of cluster is comparable with the plasma resonant length.

Measurements of energy and angular distribution of hot electrons and protons emitted from a p- and s-polarized intense femtosecond laser pulse driven thin foil target

The energy spectra and angular distributions of hot electrons as well as protons emitted from a 3-μm-thick tantalum foil irradiated by a 70-fs laser pulse with an intensity of ∼1018W∕cm2 are measured. Three hot electron flows are found, in the rear target normal, specular, and target surface directions. The angular distribution of hot electrons is found to depend on the polarization of the incident light. The measured energy spectrum of hot electrons in the rear target normal direction can explain the generated proton beam.

Influence of laser incidence angle on hot electrons generated in the interaction of ultrashort intense laser pulses with foil target

The effect of laser incidence angle on the angular distribution of hot electrons generated in the interaction of an ultrashort intense laser pulse with the foil target are investigated. A new emission peaked in the target surface direction is observed for the first time. With the increase of the incidence angle, the ratio of the number of surface electrons to the total electron number increases, while the number of transmitted electron through the target decreases. It is believed that the surface hot electrons are caused by the confinement of the quasi-static surface magnetic field and electric field.

Angular distribution of hot electrons emitted from ethanol droplets irradiated by ultrashort laser pulses

The angular distribution and the energy spectrum of hot electrons with energy over 50keV emitted from ethanol droplets irradiated by linearly polarized 150 fs laser pulses at the intensity of 10 16W/cm2 have been measured. The angular distribution of hot electrons is found to be dependent on the laser polarization. Two hot electron jets like double leaves symmetrically with respect to the laser propagation direction are observed within the polarization plane. The maximum energy of the hot electrons is found to be more than 750 keV. A model based on the resonance absorption can be used to interpret the above distribution. The calculation agrees well with the experimental results.

Experimental study for angular distribution of the hot electrons generated by femtosecond laser interaction with solid targets

The experimental results of angular distribution of hot electrons in the interaction of a 60 fs, 125 mJ, 800 nm, ∼1017 W cm−2 laser pulse with Al targets are reported. Three obvious peaks of hot electrons emission have been observed, as there is a weak normal component of the laser electric field. These emission peaks are located in the directions of the specular reflection of the laser, the target normal, and the backreflection of the laser, respectively. In the case of the P-polarized laser pulse, which has a strong normal component of the laser electric field, the peak in the backreflection of the laser disappeared, and only two obvious peaks of hot electron emissions existed. It shows that the different directions of hot electrons emission are dominated by different absorption or acceleration mechanisms. The experimental result of the hot electrons energy spectrum at the target normal shows that the effective temperature of hot electrons is about 190 keV, which is consistent with a scaling law of the resonance absorption.

Hot electrons generated by ultra-short pulse laser interacting with solid targets

Hot electrons produced by ultra-short pulse laser interacting with solid targets were studied systematically. When 800 nm, 8 × 1 0 15 W /cm 2 laser pulses interacted with solid targets, hot electron emission was found to be collimated in certain directions and the angular distribution of hot electrons depended on the energy absorption. The angular divergence of outgoing hot electrons was inversely proportional to the hot electron energy. The energy spectrum of hot electrons was found to be in a bi- Maxwellian distribution and the maximum energy was over 500 keV.

Hot Electron Ballistic Transport in Two Dimensional Structures

Quasi ballistic transport in a 2 dimension electron gas was explored and tunneling through an electrostatic barrier induced by metallic gates on the top of the heterostructure was demonstrated. For energies above 36 meV we observed the LO phonon emission, 1eading to a short mean free path. At energies below the phonon energy we find a mean free path of the order of 2 μm, about an order of magnitude longer than expected theoretically for electron interactions. The angular distribution of hot electrons injected from a point source was shown to be collimated and could be steered by controling the electrostatic profile of the injector. In addition we demonstrated operation of electrostatic 1ens which opens a new branch in semiconductor physics, namely, electronoptics in solids.

Hot electron transport in two dimensional electron gas

We demonstrate ballistic transport of hot electrons in a high mobility two dimensional electron gas (2DEG) over distances as large as two micrometers and tunneling through a barrier induced in the 2DEG. Various inelastic scattering mechanisms are studied experimentally. For electrons with excess energy larger than the longitudinal optical (LO) phonon energy quanta we show sequential emission of up to three phonons. Below that energy we find a surprisingly long mean free path, approximately an order of magnitude longer than expected theoretically for electron-electron scattering. The combination of a very short mean free path for LO phonon emission and the long mean free path below the phonon energy leads to a new type of periodic oscillations in the maximal energy of the collected electrons. Finally we report on a study of the angular distribution of hot electrons injected from a point contact and demonstrate electrostatic steering of the electronic beam.

Angular distribution of hot electrons incident on a laser-irradiated target

Angular distributions of bremsstrahlung emission are calculated for various energy and angular distributions of hot electrons incident on a laser-irradiated plastic target. These theoretical results are used to interpret experimental data of x-ray continuum emission from a C${\mathrm{O}}_{2}$-laser-produced plasma. It is shown that at low irradiance (${I}_{L}\ensuremath{\le}5\ifmmode\times\else\texttimes\fi{}{10}^{12}$ W/${\mathrm{cm}}^{2}$) the incident electrons are normal to the target surface but that at higher irradiance, the incident electrons' angular distribution (spatially integrated over the target surface) is semi-isotropic. The influence of the directional distribution of hot electrons on axial energy transport is also studied by comparing calculated continum x-ray spectra as well as energy-deposition profiles with experimental results.