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Super High Efficiency Diode Sources (SHEDS)
Program Manager: Dr. Joseph Mangano
Overview
It is the goal of the Super High Efficiency Diode Sources (SHEDS) Program to achieve 80% electrical-to-optical efficiency in the generation of light from stacks of semiconductor diode laser bars. The spectral range of interest for this program is 880nm to 980nm, the range for pumping directly into the upper laser level of Nd and Yb:YAG lasers. Aluminum-free materials are considered the best to use for these devices. Due to the narrow linewidth of some of the transitions being pumped, the linewidth of the radiation over the whole bar must be on the order of 1-2 nm and must have the same peak wavelength within plus or minus 0.5 nm from each bar in the stack. Wavelength stabilization must also be provided to prevent thermal drift of the diode bar wavelength outside of the range of high absorption of the laser transition. The power level of 500W/cm2 per diode bar operating continuously is sought. A peak power of 2000W/cm2 is sought for operating the bars in a quasi-continuous wave (CW) mode with a duty cycle of no less than 25%. These bars will be used for pumping slabs and disks as opposed to fibers.
Vision Statement
Future DoD solid-state laser weapons call for 100-kW of optical power from solid state lasers. With a typical optical to optical conversion efficiency of 20%, such a solid-state laser system would require roughly 500-kW of diode pump power. Current diode laser technology is capable of converting electrical power to optical power at roughly 50% efficiency. The SHEDS program seeks to develop laser diode device design and technology that will result in 80% conversion efficiency. Such a breakthrough in laser diode technology would reduce the electrical power requirements by almost 40% and reduce the weight of the thermal management system by almost 4000 kg (assumes 10 kg per kW for state of the art thermal management systems).
In addition to highly efficient pumps for solid-state lasers, there are many other defense applications of SHEDS sources. These include: Tactical weapons, illuminators, designators, optical countermeasures, multi-spectral scene projection, foliage penetrating radar, precision fusing for detonation, laser radar interceptor, 3-D imaging radar for UAVs, low cost chemical & biological detectors, underwater imaging/mine detection. As a particular example, SHEDS sources have a unique capability for IR countermeasures to protect against heat seeking missiles for both military and commercial aircraft. The high peak power, high rep rate capability of these devices will allow multiple wavelengths to be produced from sub-arrays whose spectral distribution can cover the sensor bands of heat-seeking missiles with a distribution in wavelength that can simulate the spectral signatures of aircraft (or ground vehicles) together with modulation rates that would be effective for the electronic part of the jamming.