|
Guest >> Sign In |
|
|
DIRECTED
ENERGY
PROFESSIONAL
SOCIETY
Abstract: 24-Systems-013
|
|
|
|
UNCLASSIFIED, PUBLIC RELEASE
Hot Operating Temperature (HOT) Diodes in Low SWaP Packages for Directed Energy Amplifiers
Multi kilowatt-class fiber lasers and amplifiers are becoming increasingly important building blocks for power-scaling laser systems in various architectures for high-energy laser (HEL) applications. Currently, state-of-the-art Yb-doped fiber lasers near 1060 nm operate with optical-to-optical power-conversion efficiency of about 85 %. State-of-the-art fiber-coupled pump diodes near 976 nm operate with about 50% electrical-to-fiber-coupled optical power conversion efficiency at 25°C heatsink temperature. Therefore, the total system electrical-to-optical power conversion efficiency is about 40%. As a result, a 100-kW fiber laser will generate ~114 kW of total heat from the diodes alone and ~14 kW at the fiber laser module with a total waste heat of ~128 kW. It is evident that ~90% of the waste heat is generated at the pump module, and, therefore, requires a SWaP-intensive Thermal Management System (TMS). The efficiency and the operating temperature of pump diodes play a pivotal role in improving the SWaP of the HEL system. Raising the operating temperature of laser diodes from 25°C to 50°C improves the efficiency of the vapor compression system in the TMS thereby reducing the SWaP of the HEL system itself. Laser diode themselves are, at least, 15% of the SWaP of HEL systems. Therefore, reducing the SWaP of laser diodes from the current ~1kg/W to less than 0.5 kg/W is also highly desirable. Past DoD funded programs have enabled demonstration of <0.5 kg/kW and <0.4 cm3/W laser diode pump modules at 25°C with ≥600W in 225µm and <0.22 NA fiber with >55% ex-fiber efficiency at TRL-4. Furthermore, there has also been past effort funded by JDETO to achieve wavelength-locked 55% efficient diodes at 50°C. Under a current ONR funded ManTech Program, nLIGHT is incorporating wavelength-stabilization in 50°C diodes in a low SWaP package to achieve 500W (threshold) and 550W (goal) with ~53% efficiency. We will report on the progress of our efforts.
UNCLASSIFIED, PUBLIC RELEASE
|