Full-aperture random polarization smoothing for a low-coherence laser facility.

Area of Science:

• Optics and Photonics
• Laser Physics
• Materials Science

Background:

• Laser focal field polarization control is crucial for applications like inertial confinement fusion.
• Existing methods for polarization smoothing often face limitations such as near-field discontinuity or restricted applicability.

Purpose of the Study:

• To propose and validate new full-aperture random polarization smoothing techniques for low-coherence lasers.
• To achieve fast random polarization evolution in the laser focal field.
• To generate focal fields approximating unpolarized thermal light for suppressing laser plasma instabilities.

Main Methods:

• Development of two methods: one using a birefringent wedge and another using a flat birefringent plate.
• Designing crystal axis direction and wedge angle to control time delay and spatial displacement.
• Utilizing the low spatiotemporal coherence of the laser focal field for rapid polarization evolution.

Main Results:

• Both methods successfully introduce transient polarization evolution, avoiding near-field discontinuity and operating under high fluence.
• The birefringent wedge method slightly improved focal spot uniformity.
• The flat birefringent plate method achieved non-polarization with a degree of polarization (DOP) below 2%.
• Experimental validation of the birefringent wedge method reduced focal spot DOP from 1 to 0.27.

Conclusions:

• The proposed full-aperture random polarization smoothing methods are effective in generating rapidly evolving, randomized focal polarization.
• These techniques can produce focal fields closely resembling unpolarized thermal light.
• The developed methods hold promise for suppressing laser plasma instabilities in high-power laser systems.