High efficiency InP pump sources for reduced C-SWaP SWIR illuminators

Application of High Energy Lasers (HELs) as Directed Energy Weapons (DEWs) is an area of strategic importance to the US Air Force; yet there are several technical barriers remaining that hinder the practical deployment of this technology. In particular, the size, weight, and power consumption (SWAP) of DEW components need to be significantly reduced, especially on airborne platforms. High energy laser weapons require a track illumination laser (TIL) for target identification and tracking (pre-engagement) and aimpoint maintenance (during engagement).  It has recently been shown that the thermal management of the TIL carries a SWAP burden which is similar to, or perhaps even higher than, the HEL itself, and a SWAP reduction is critically needed. The typical TIL is a pulsed laser operating in the 15xx-16xx nm wavelength band, and it relies on a three-stage laser architecture: 980 nm fiber-coupled pump diodes are used to pump Er/Yb co-doped fiber laser, which in turn pumps an Er-doped crystal (such as Er:YAG) solid state laser. This system is highly inefficient (~9% wallplug conversion efficiency) and very large. A simple solution exists: direct resonant pumping of the Er:YAG solid state laser with high power diode pumps operating in the 15xx nm wavelength band can enable a dramatic reduction in the size and weight of the TIL.  This approach can reduce the overall quantum defect from ~40% to ~7%.  This enables a dramatic increase in wallplug conversion efficiency (from 9% up to ~24%) which in turn reduces the cooling requirements by >3X.  After initial prototype demonstration, this program will support improving the manufacturability and reliability of these InP diode pump modules in order to accelerate the transition of DEW technologies to support the warfighter.