A laser wakefield acceleration facility using SG-II petawatt laser system.

Area of Science:

• Plasma Physics
• Laser-driven Particle Acceleration

Background:

• Laser Wakefield Acceleration (LWFA) typically requires cm-scale interaction lengths.
• Achieving this often involves focusing powerful lasers in long underdense plasmas with large f-number optics.

Purpose of the Study:

• To present a new PW-class LWFA instrument at the SG-II laser facility.
• To investigate electron beam generation under specific focusing and plasma conditions.

Main Methods:

• Utilized a 1-PW, 30-fs laser pulse focused with f/23 optics to a 230 µm spot.
• Employed Nomarski interferometry for online plasma density probing with a 30 fs probe beam.
• Investigated electron beam production at varying gas pressures (plasma densities).

Main Results:

• Achieved a peak laser intensity of 2.6 × 10¹⁸ W/cm², a mild-relativistic level.
• Observed electron beams exclusively when relativistic self-focusing occurred.
• Relativistic self-focusing required plasma densities exceeding 3 × 10¹⁸ cm^-3, despite the laser's large aspect ratio.

Conclusions:

• Electron beam generation in this LWFA setup is contingent on achieving relativistic self-focusing.
• High plasma densities are necessary to overcome the limitations of the laser pulse's aspect ratio and initiate self-focusing.