Impact of Target Altitude Restrictions on Laser Performance

This report estimates the impact of Raman restrictions and shielding penalties separately and together. Its goal is an overall assessment of likely impact rather than a review of the details of missile trajectories, Raman physics, and shielding techniques, whose individual treatments matter less than their overall integration. Raman scattering could produce a factor of 23 reduction on the performance of repetitivepulse lasers with large fluences in each small pulse. Radio-frequency free-electron lasers (RF FELs), which have more frequent pulses with less energy in each, are impacted less. Shielding gives an independent penalty of about a factor of 2, but the combined effect of altitude and shielding penalizes lasers with large pulses by factors of 3-10. Those factors are significantly larger than any other factors differentiating between the two types of FELs.