The 8th International Conference on Matter and Radiation at Extremes (ICMRE2025)

Beam smoothing technology plays a pivotal role in inertial confinement fusion (ICF) by enabling precise control of laser speckle characteristics to mitigate laser-plasma instabilities (LPI). Among existing techniques, polarization smoothing (PS) has demonstrated significant LPI suppression effectiveness in OMEGA and NIF experiments. Conventional PS implementations employing KDP crystals for polarization rotation face limitations in damage threshold and production scalability. This study presents a novel stress-induced polarization smoothing (SPS) technique utilizing fused quartz, offering comparable PS performance with enhanced damage resistance.

The proposed SPS technology achieves beam depolarization through controlled stress birefringence in fused quartz. Unlike KDP-based PS requiring enough far-field spot offset, our approach generates self-consistently separation of far-field speckles in orthogonal polarization states via stress-gradient-induced optical axis variations. The technique features a customized clamping mechanism that creates designed non-uniform stress distributions, enabling development of stress-engineered polarization optical elements.

The LPI experiment results by using this optical element show that depolarization rate of beam(@351nm) by stressed-induced polarization element is 19%, in which the Stimulated Brillouin Scattering(SBS) energy is reduced by 30% compared with single-polarization case. Theoretical analysis and LPI simulations predict equivalent suppression performance to conventional KDP-based PS when reaching 50% depolarization. The stress-induced polarization provide a great potential for developing robust beam smoothing solutions in higher-power laser system.
 

Beam Smoothing, Laser Plasma Interaction