DON27TZ02-NV009 — Domestic Manufacturing of Large Area Raman Laser Materials

Develop scalable domestic manufacturing technologies and processes for large Raman active optical crystals that will enable wavelength agile laser systems for Navy applications.

The Navy employs laser systems on air- and sea-borne vessels that serve a wide range of applications including laser range finding, target designation, shipboard and airborne LiDAR, and directed energy platforms. Future naval systems require improvements in spectral agility, optical efficiency, and power, with reductions to size and weight while maintaining operation in harsh maritime environments. Current laser architectures rely upon a limited set of mature gain and nonlinear optical materials including Nd- and Yb-doped yttrium aluminum garnet (YAG), potassium titanyl phosphate (KTP), lithium triborate (LBO), and barium borate (BBO). While these technologies provide reliable performance, wavelength conversion often requires multiple optical stages that increases system complexity, introduces alignment sensitivity, and can limit scalability to higher optical powers and larger apertures. Raman active optical materials offer a pathway toward compact and wavelength agile laser architectures capable of generating multiple output wavelengths from a single pump source. Such materials may enable simplified optical systems with reduced alignment complexity, improved robustness to vibration and shock, enhanced spectral diversity, and compact eye-safe laser sources. Many Raman laser crystals have been demonstrated to be grown to large sizes at high quality, but broader adoption of Raman active optical materials in these systems hinges on improving domestic production. Many candidate Raman laser materials are produced in small quantities at limited sizes and lack established domestic manufacturing capability and therefore development of domestic manufacturing technologies compatible with large crystal sizes is of importance for future naval laser systems. Candidate materials shall be compatible with bulk crystal growth processes capable of producing large aperture, high optical quality single crystals and offer a pathway toward crystal sizes of 50 mm and greater. This STTR topic seeks to develop a prototype manufacturing technology and process which can produce one or more Raman active materials at large crystal sizes with the potential to scale to high throughput. The prototype should minimize reliance on expensive precious metal crucibles. The prototype shall produce Raman active crystals that are large (> 5mm x 5mm x 25mm), achieve laser damage thresholds exceeding 10 J/cm², support self-Raman operation through rare earth doping, and meet the following optical quality criteria: Objective Threshold Notes Refractive Index Homogeneity: Threshold = <10 ppm; Objective = <5 ppm Transmitted Wavefront Distortion (at 50mm aperture): Threshold = Lamda/6; Objective = <Lambda/8 Surface Quality (Scratch-Dig): Threshold = 20-10; Objective = 10-5 (NOTE: The first number relates to the maximum allowable width of a scratch in micrometers, while the second number relates to the maximum allowable diameter of a dig or pit in hundredths of a millimeter.) Dislocation Density: Threshold = <10 cm^(-2); Objective = < 1 cm^(-2) Inclusion/Bulk Defect Density: Threshold = <5 inclusions greater than 1µm per cm^3; Objective = No detectable inclusions greater than 0.5µm per cm^3 Materials of interest include: Undoped and doped (Nd, Yb, Er, Tm) potassium gadolinium tungstate (KGW) and Potassium yttrium tungstate (KYW) [Refs 1,2,3] Undoped and doped (Nd, Yb, Er, Tm) Barium molybdate and Barium nitrate [Refs 4,5] Other Raman active tungstate, molybdate, nitrate, vanadate or related compelling Raman crystal systems Alternative material systems are encouraged provided performers demonstrate a credible pathway toward large aperture crystal production and significant Raman gain performance.

Develop a technical approach and concepts for manufacturing large and high-quality Raman active crystals. Develop and model a growth process and identify methods for optical characterization of grown crystals. Determine the technical feasibility of scaling the process to high throughput and provide a cost analysis. Produce a document containing the technical approach, concepts for manufacturing, growth model details and results, proposed optical characterization process, and approach to scale up the proposed manufacturing concept. Provide a Phase II development plan with performance goals and key technical milestones and that addresses technical risk reduction.

Based on the developed concepts in Phase I, develop and demonstrate the manufacturing prototype for growing large high-quality Raman active crystals. Fabricate one or more crystals and validate the prototype through characterization sufficient to establish technical feasibility and manufacturing viability. Characterize optical performance and laser damage thresholds. Use evaluation results to refine the prototype into an initial design that will meet the Naval Enterprise requirements. Prepare a Phase III development plan to transition the technology to Navy enterprise and commercial use.

Upon successful execution of Phase II and demonstration of a prototype manufacturing process that can produce large and high-quality Raman active crystals, support the ONR Navy ManTech program in transitioning the technology into program of record (PoR) manufacturing lines. Participate in the transition of manufacturing technologies and Raman active crystal materials into Navy laser systems supporting LIDAR, laser range finding, optical communications, and directed energy applications. Commercial applications include industrial laser systems, environmental sensing, autonomous vehicle LiDAR, medical imaging, telecommunications, spectroscopy, and advanced manufacturing.