G. I. Dudnikova

High-energy ion generation by short laser pulses

This paper reviews the many recent advances at the Center for Ultrafast Optical Science (CUOS) at the University of Michigan in multi-MeV ion beam generation from the interaction of short laser pulses focused onto thin foil targets at intensities ranging from 1017 to 1019 W/cm2. Ion beam characteristics were studied by changing the laser intensity, laser wavelength, target material, and by depositing a well-absorbed coating. We manipulated the proton beam divergence using shaped targets and observed nuclear transformation induced by high-energy protons and deuterons. Qualitative theoretical approaches and fully relativistic two-dimensional particle-in-cell simulations modeled energetic ion generation. Comparison with experiments sheds light on ion energy spectra for multi-species plasma, the dependences of ion-energy on preplasma scale length and solid density plasma thickness, and laser-triggered isotope yield. Theoretical predictions are also made with the aim of studying ion generation for high-power lasers with the energies expected in the near future, and for the relativistic intensity table-top laser, a prototype of which is already in operation at CUOS in the limits of several-cycle pulse duration and a single-wavelength spot size.

Laser-triggered quasi-monoenergetic ion beams at a moderate intensity and pulse duration

Plasma produced by short laser pulses from thin homogeneous foils with light and heavy ions is capable of generating quasi-monoenergetic light ions. This happens for the tail of light ions near the front of heavy ions. It was found that this effect is well pronounced for a moderate laser intensity (∼1018 W/cm2) and pulse duration (∼1 ps) by using a 2D particle-in-cell simulation of the laser interaction with thin CD2 foils. Quasi-monoenergetic deuterons form a jet from the rear side of the foil with the energy ∼1 MeV. The conversion efficiency to these quasi-monoenergetic ions is 10−3.

Two-stage laser acceleration of ions

A scheme is proposed for producing a quasi-monoenergetic ion bunch by irradiating a foil with two subsequent ultrashort laser pulses—a prepulse followed by a stronger main pulse. Results are presented from numerical simulations that illustrate the scheme and determine the space-time and energy characteristics of the accelerated ions.

Numerical simulation of harmonics generation by ultrashort laser pulses

The interaction of ultrashort relativistically intense laser pulses with plasma resulting in the forward-directed harmonics generation from the rear side of a target is investigated by particle-in-cell simulation [1]. The dependences of the spectral characteristics of the electro-magnetic radiation on the laser intensity, the laser pulse duration, and the polarization of the laser light, as well as the laser radiation geometry and the plasma thickness and density, are considered.

Current sheets formed by Alfvén and magnetosonic pulses in the vicinity of the null line of the magnetic field

A study is made of the propagation of an Alfvén pulse and the superposition of an Alfvén and a magnetosonic pulse in the vicinity of the magnetic null line (the X point). It is shown that, on long time scales, the poloidal components of the velocity and magnetic field relax to steady-state distributions similar to those in the case of a magnetosonic pulse. In the essentially nonlinear problem under investigation, the steady-state distributions of the toroidal components of the velocity and magnetic field are found to be close to those in the corresponding linear problem. It is established that two-dimensional effects play an important role in the evolution of the forming current sheets.

Interaction of strong laser pulses with a thin slab of overdense plasma

Extremely large e.m. fields can be generated in plasmas by high intensity laser pulses. Several aspects of their generation and of their effect on the plasma and on the laser pulse have been discussed recently. In particular, the nonlinear interaction of an ultraintense laser pulse with a thin foil modifies the shape, the frequency content and the polarization of the pulse. A 2D3V particle in cell code has been developed and its characteristic features are described. Two examples of the results obtained are presented. These simulations show that the relativistic transparency of a thin foil leads to the sharpening of the laser pulse. In addition they show that a quasistatic magnetic field is generated at the foil surface.