Improved AR Treatment for Mid-IR Laser Materials Based of Surface Relief Microstructures

Conventional multi-layer thin film anti-reflection (AR) coatings limit the output energy of laser systems designed for important mid-infrared (mid-IR) applications such as LIDAR, communications, and atmospheric monitoring. Mismatched thermal expansion between the lasing crystals and thin-film AR coatings leads to failed film adhesion and catastrophic physical damage at optical energies well below that which could be attained with an alternative AR treatment. As a result there is an urgent need for an AR treatment that can suppress reflections of broad-band mid-IR light from the crystal faces used in solid-state laser systems while simultaneously allowing for an increased light output over a longer operational period. An innovative type of high performance AR treatment for mid-IR lasers is proposed that promises an increased laser damage threshold for higher output energies over a longer lifetime. Based on surface relief microstructures fabricated directly into the faces of the lasing crystals, the AR treatment completely eliminates the limitations due to stress, thermal mismatch, adhesion, physical damage, complexity, narrow-band performance, polarization splitting, and cost associated with conventional multi-layer thin-film AR coatings. The proposed Phase I project will adapt the designs and methods developed in a recent MDA SBIR program that demonstrated a radiation-resistant micro-structured AR treatment for HgCdTe infrared FPAs, to demonstrate an improved AR treatment for high-power solid-state lasers generating mid-IR light. In addition, mid-IR laser manufacturers such as BAE Systems will be engaged and plans will be developed for integrating the improved AR treatment fabrication process into the laser manufacturing process as part of a Phase II effort.