Nonspatial Filtering of Master Oscillator Power Amplifiers (MOPA)

We propose to design and demonstrate beam cleanup for the Master Oscillator (MO) which will allow the Power Amplifier (PA) to operate efficiently and produce a high energy beam useful as a Directed Energy Weapon (DEW). The method we describe is totally new to the DEW field. Of course for low power lasers, we can focus the beam down and pass the clean part through a pinhole spatial filter. The "noisy" part is absorbed, so only a perfect beam emerges. The problem is that for even a few watts of laser power, metal pinholes melt and diamond pinholes shatter. At MO power levels, the pinhole method is clearly absurd. Our approach, developed with BMDO for visible light lasers up to a few watts, is to use the angular selectivity of a thick hologram to clean up the beam. It works well. Neither focusing nor absorption is required, so extension to MO power levels seems plausible. We will explore two main issues: handling of useable MO power levels and extension to nonvisible wavelengths as required by many (but not all) candidate MOs. The team includes the company which makes the holographic filters, a consultant involved in its invention, and a consultant with decades of HEL experience.