Development of a Thin-Film Evaporative Cooling System for a High Energy Thulium Holmium: Lutetium Lithium Flouride Solid-State Laser Oscillator Crystal

Abstract

The feasibility and critical design parameters for the development of a thin-film evaporative cooling concept for a high energy, pulsed solid-state laser oscillator were investigated. The scope of the investigation was broad, and a multidisciplinary approach was employed. No contra-indicators for the feasibility of the proposed system were revealed. A 1-dimensional two-fluid was developed to model the hydrodynamic flow and heat transfer assuming a constant wall heat flux. This analysis produced nominal pressure drops for the flow required, indicating nominal power will be required to transport fluid across the crystal surface. Interfacial experiments reveal that the laser crystal material has a surface energy of approximately 30 mN/m, and is highly dispersive in nature. Design rules to allow for the orthotropic thermal expansion of the crystal rod surrounded by a thin metal sleeve were developed to support the design of a hermetic crystal-metal seal. The results indicate that commercially pure nickel produces minimal joint stresses for large thermal excursions.