High Power Coherent Beam Combined Laser Array

High-Energy Laser (HEL) systems are widely used in material processing and are increasingly important for next-generation weaponry. Current HEL technologies including fiber lasers, solid-state lasers, and spectral-beam-combined diode lasers are limited by excessive size, weight, and power consumption (SWaP) or by low beam quality. A promising alternative approach is to coherently combine beams from an array of semiconductor diode lasers. Semiconductor lasers have the highest electrical-to-optical (EO) efficiency of all laser types, and are compact, rugged, inexpensive, and available at a wide range of wavelengths. Unfortunately, diode lasers are plagued by either limited output power (single emitters) or low beam quality (diode bars). Coherent beam combination promises to resolve this dilemma by scaling up the desirable properties of low-power diode lasers – high EO efficiency, compactness, and high beam quality – up to the kW level. In the Phase I SBIR Effort, EOSPACE designed an architecture for a high-power, direct-diode, coherently-combined laser system. This laser system will reach tens of kW of output power while delivering improved SWaP compared to current HEL technologies. Tapered amplifiers will be used to maintain high beam quality throughout the system, improving the final output as well as maximizing coherent combining efficiency.  A compact, chip-based design will reduce system footprint and improve stability. The phase feedback control system will leverage lessons learned from decades of previous research in this field as well as EOSPACE’s practical experience in optical phase control. To improve the manufacturability and commercial viability of the proposed high-energy laser, EOSPACE’s design uses off-the-shelf components in a design planned for straightforward assembly. In Phase II we plan to build a prototype that will demonstrate every essential feature of the full-scale system. We will also carefully study the various tradeoffs in system design and performance on different metrics, paving the way for a coherently combined 60 kW diode laser system. Because EOSPACE performs nanofabrication, packaging, and RF/optical testing in-house, we will be able to rapidly iterate and improve the design multiple times during the prototype phase. During this Phase II effort we will be able to build a scaled-down version of the high-energy laser system and explore different approaches to beam combining and phase feedback, and optimize the architecture to meet the program’s goals. This Phase II SBIR effort will result in a demonstration of the high EO efficiency and beam quality of a diode-based coherently-combined laser system capable of reaching extreme output power for demanding applications in defense and manufacturing.