Optical zooming based on focusing grating in direct drive ICF

Area of Science:

• Physics
• Optics
• Plasma Physics

Background:

• Direct drive inertial confinement fusion (ICF) requires efficient energy transfer for target compression.
• Cross-beam energy transfer (CBET) is a significant loss mechanism in ICF.
• Optical zooming offers a potential solution to mitigate CBET and improve hydrodynamic efficiency.

Purpose of the Study:

• To propose and experimentally validate a novel optical zooming scheme for ICF.
• To reduce laser spot size on target using a focusing grating.
• To enhance hydrodynamic efficiency by minimizing CBET.

Main Methods:

• A focusing grating was employed to focus broadband laser pulses.
• The scheme was experimentally tested with a 40-mm × 40-mm grating and wavelengths from 1052.43 nm to 1053.23 nm.
• Simulations were performed for a full-sized 360-mm × 360-mm grating with 3rd harmonic light (350.81 nm to 351.08 nm).

Main Results:

• A peak-valley defocusing wavefront distribution of 0.73 µm was achieved experimentally.
• Simulations predicted a focal spot reduction of 21.8% for the full-sized grating.
• The focal spot size decreased from 375 µm to 294 µm using a 300 µm shaping continuous phase plate.

Conclusions:

• The proposed optical zooming scheme effectively reduces laser spot size.
• This technique shows promise for mitigating CBET in ICF.
• The method has the potential to significantly increase hydrodynamic efficiency in ICF experiments.