Coping with Atmospheric Turbulence in the Selection of Laser Hardening Technology for Fcs Targeting Systems

The FCS Laser-Hardened Vision STO seeks to develop an electro-optic targeting vision system that utilizes a combination of nonlinear and sacrificial materials to provide protection from damage by frequency-agile battlefield lasers at both long and short range. Evidently, the selection of sensor protection technologies for incorporation into the final targeting system will be based on their optical limiting performance under field conditions. While few optical limiting devices perform as well in the field as in the laboratory, some, notably an otherwise extremely promising prototype sacrificial mirror, exhibit a discrepancy that is particularly striking. In the case of a thin, passive limiting component (e.g., ablative mirror or dye cell) situated at a focal plane, the decrease in performance can be attributed to the randomly fluctuating axial displacement of the focal plane that is known to arise from the effects of atmospheric turbulence on a propagating laser beam. I present the results of a quantitative study of the effects of turbulence-induced focal shift on the performance of passive optical limiting devices. The results apply not only to the FCS targeting system, but to all laser eye and sensor protection devices that employ a thin, passive component whose optical limiting performance depends strongly on the input irradiance or the input fluence.