SBIR-STTR Award

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.

Keywords:
Master Oscillator Beam Cleanup Power Amplifier Holography Mopa Spatial Filter Nonspatial Filters

The Phase II project proposed here will result in a Holographic Beam Shaper (HBS) that can be used to enhance the usable power of high energy cw or pulsed lasers. The beam shaper will be usable from the visible to near infrared (0.4 - 1.5 u). In particular, this device will increase, by more than 50%, the brightness of pulsed YAG amplifiers ( 1.064 u) as well as frequency doubled pulsed YAG amplifiers (0.532 u).To accommodate the high power levels, we will make large surface area holograms and encase them in a Cassegrian telescope system; thus, the beam will be expanded, pass through a large hologram where it will be shaped, and then be reduced to the desired size. This system will reduce irradiation levels to well below the damage threshold determined in Phase I. The HBS will be of widespread use in the world of optics, by virtue of its ability to create complex spatial patterns. Areas of applications include optical signal processing, optical computing, optical modulation, dye laser amplification using YAG lasers, non-linear optics, and instrumentation based on atom interferometry.