Short-Pulse Underdense Laser–Plasma Interactions

The Plasma and Ultrafast Physics Group studies short-pulse (<10-ps), high-power (>100-TW) laser beam propgation through underdense plasmas. This team works on laser systems around the county including the Jupiter Laser Facility at Lawrence Livermore National Laboratory, the Multi-Terawatt (MTW) Laser and the Optical Parametric Amplfier Line (OPAL) lasers at the University of Rochester. These experiments are intimate hands-on experiences that involve developing advanced diagnostics and several-week-long campaigns over multiple years.

Nonlinear Electron Plasma Waves

The dynamics of strongly driven electron plasma waves (EPW's) is a rich area of plasma physics that involves many complex phenomena that are difficult to predict in simulations or diagnose experimentally. As an electron plasma wave is driven to high amplitude, a multitude of effects can occur such as nonlinear frequency shifts, wave breaking, acceleration of high-energy electrons, and cascading to shorter-wavelength plasma waves.

Resonance condition: ωpump = ωseed + ωplasma

Experiments are carried out that focus on probing nonlinear electron plasma wave dynamics in the underdense plasma (UDP) target chamber of the MTW Laser. To control the amplitude of the electron plasma waves, two counter-propagating laser pulses (pump and seed), whose frequency difference equals the plasma frequency, are being developed. The pump pulse will be provided by the current 1053-nm, 25-ps, 75-J MTW laser and the seed pulse will be provided by the ultrashort optical parametric amplifier line (OPAL), which will deliver 50 mJ in 50 fs with a central wavelength tunable from 1100 nm to 1300 nm. To measure the plasma conditions and probe the amplitude and frequency of the driven electron plasma wave, optical Thomson scattering is used [1].

One prominent application, Raman amplification [2,3], is the use of large amplitude EPW's to transfer a large amount of energy from the pump to the seed, thereby amplifying the seed to powers in excess of the damage thresholds that currently limit optical parametric chirped-pulse–amplification (OPCPA) laser systems today.

High-intensity, short-pulse laser (magenta) driving a plasma wake (blue). Electrons that are trapped in this wake (green) are accelerated to relativistic energies.

Wakefield Acceleration/Betatron X-Rays

In laser wakefield acceleration [4] (LWFA) (figure on right), a high-intensity, short-pulse laser is propagated through an underdense plasma where it drives a relativistic plasma wave (a wake), which has accelerating gradients 1000 times higher than those of traditional radiofrequency particle accelerators. Electrons can become trapped in this plasma wake and accelerated to relativistic energies. PUPG is pursuing methods to utilize LWFA's driven with both OMEGA EP and MTW OPAL to develop x-ray sources [5–7] towards the eventual realization of an x-ray source for ICF, HEDS, and astrophysics research.

Relevant Publications