Cooling Laser Media in a Turbulent or Instable Flow: Index-Leveling for Forced-Flow Face-Cooling of High-Power Amplifiers

In the design of laser amplifiers capable of delivering high pulse energies and substantial repetition rates, the dimensions of the active media often increase significantly, sometimes resulting in an optical diameter that exceeds the length of the solid-state medium used for amplification. This presents a challenge in thermal management, making it increasingly difficult to avoid direct face-cooling of the active slab. Currently, many facilities utilize such techniques to produce high-energy laser beams at high repetition rates [1], [2]. However, the implementation of a transparent fluid flowing through the laser field requires meticulous engineering to ensure laminar flow. Excessively high Reynolds numbers (typically Re ≥ 1000) can induce turbulence, leading to refractive index gradients across the laser beam's path. These gradients compromise wavefront quality, causing light scintillation and reducing the final Strehl ratio of the laser system.