Active Laser Protection System

The use of commercial off-the-shelf laser systems as weapons is increasingly becoming real. Battery operated visible and infrared lasers can be purchased with powers near 1-watt, sufficient to cause permanent eye damage. Future threats may include frequency agile lasers. It is critical that countermeasure systems provide laser eye protection (LEP) across the visible and IR waveband. Self-activating (passive) devices where protection is activated by the incoming radiation (optical limiting) are the best approach to counter frequency agile and short pulse laser threats. An ideal optical limiter will have high linear transmittance for low-input-energy light and low transmittance for input energies above a user-specified threshold. An ideal optical limiter will have a picosecond, broadband response (e.g., the visible spectrum), and a large dynamic range. This performance is a challenging problem for LEP where MPE is in the J/cm2 range for visible light. Optical limiting with a nonlinear process usually requires a focal plane for this dynamic range. We propose to build optical limiters from metal-dielectric thin-film stacks using nonlinear properties of metals and/or semiconductors. These stacks are very thin and built using standard thin-film equipment on common substrates. They can be integrated into optical systems with little modification of the optics.