Fig. 7. Percentage of available power at the ground based site which is intercepted within a specified receptor radius. The percentage of available laser power intercepted by the receptor as a function of the receptor radius is shown in Figure 7 for several conditions. Considering diffraction spreading only, the two dashed curves show the functional behavior for the uniform or constant-intensity distribution and the Gaussian intensity distribution. These distributions bound the range of expected laser beam profiles, although the Gaussian profile more closely approximates the intensity distribution observed for large laser devices employing unstable resonators. The solid curve shows the beam spread of a Gaussian beam including the effects of diffraction, pointing error, and turbulence; turbulence-induced spreading accounts for less than 1% of the calculated spot diameter. If a smaller receptor spot size is required, then better pointing stability is preferred rather than a larger primary mirror since 0P > 6d. For the present specifications, a 50-m-diameter receptor will intercept — 99% of the available power at the ground site. Thermal Blooming. Thermal blooming is a nonlinear propagation mechanism common to high-power infrared lasers in which self-induced spreading, distortion, and bending of the laser beam occur as a result of molecular and aerosol absorption within the beam bath. Absorption leads to heating of the air causing density and,
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