Scaling hot-electron generation to high-power, kilojoule-class laser-solid interactions

Area of Science:

• Plasma Physics
• High-Energy-Density Physics
• Laser-Matter Interaction

Background:

• Understanding laser energy coupling to hot electrons is critical for inertial confinement fusion (ICF) and other high-energy-density physics applications.
• Previous studies have investigated this coupling, but the influence of laser pulse duration requires further clarification.

Purpose of the Study:

• To quantify the laser-energy-coupling efficiency to hot electrons in thin-foil targets irradiated by high-power, short laser pulses.
• To investigate the temporal characteristics of laser energy coupling.
• To determine the dependence of this coupling efficiency on laser pulse duration.

Main Methods:

• Irradiation of thin-foil targets with high-power (1–210 TW), 10-ps laser pulses at intensities exceeding 10^18 W/cm^2.
• Utilized K-photon spectroscopy to measure emitted K-photon energy.
• Employed time-resolved X-ray emission measurements.
• Compared experimental K-photon emission data with target-heating calculations.

Main Results:

• A laser-energy-coupling efficiency to hot electrons (η(L-e)) of 20 ± 10% was determined.
• Time-resolved X-ray emission indicated that laser energy couples to hot electrons throughout the entire laser pulse duration.
• The coupling efficiency (η(L-e)) was found to be independent of laser pulse duration for pulses between 1 and 10 ps.

Conclusions:

• Efficient coupling of laser energy to hot electrons occurs in thin-foil targets under the studied conditions.
• The coupling process is sustained over the laser pulse duration.
• Laser pulse duration, within the 1–10 ps range, does not significantly affect the laser-to-hot-electron energy coupling efficiency.