Characterization of surface defects using a phase retrieval technique in a high-power laser system

Area of Science:

• Laser Physics and Optics
• Materials Science
• Optical Engineering

Background:

• Surface defects on optics in high-power laser systems can lead to significant light intensification.
• This intensification can induce damaging effects on downstream optical components.
• Accurate evaluation of defect-induced intensification is crucial for laser system integrity.

Purpose of the Study:

• To develop and validate a comprehensive method for evaluating light intensification caused by surface defects on laser optics.
• To model the amplitude and phase characteristics of defects.
• To predict the long-distance impact of these defects on downstream optics in high-energy laser systems.

Main Methods:

• Design of a dedicated measurement bench to quantify intensification from defects on various optics (e.g., KDP crystals, mirrors) up to 2000 mm propagation distance.
• Application of a multi-resolution single-beam multiple-intensity reconstruction phase retrieval algorithm to model defect amplitude and phase.
• Simulation of high-power laser systems to evaluate the impact of modeled defects on downstream optics.

Main Results:

• Experimental validation of the three-step method using a case study of damage on a Laser Mégajoule (LMJ) beam.
• Characterization of a specific defect and its intensification effects.
• Simulation of long-distance impact on the LMJ beam, compared with near-field measurements.

Conclusions:

• The proposed three-step method effectively measures, models, and predicts the impact of surface defects on laser optics.
• This approach is crucial for understanding and mitigating laser-induced damage in high-energy systems.
• The study provides a validated framework for optical defect analysis in large laser facilities.