Abstract
The Air Force Weapons Laboratory (AFWL) has been involved in the study of laser propagation from airborne platforms. A Line Spread Device (LSD) capable of yielding direct measure of a laser beam's Line Spread Function (LSF) was developed and employed in propagation tests conducted in a wind tunnel by AFWL to examine optimal acoustical suppression techniques for laser cavities exposed to simulated aircraft aerodynamic environments. Measurements were made on various aerodynamic fences and cavity air injection techniques that affect the LSF of a propagating laser. Using the quiescent tunnel as a control, the relative effect of each technique on laser beam quality was determined. The optical instrument employed enabled the comparison of relative beam intensity for each fence or mass injection. It was found that fence height had little effect on beam quality but fence porosity had a marked effect, i.e., 58% porosity alleviated cavity resonance and degraded the beam the least. Mass injection had little effect on the beam LSF. The use of a direct LSF measuring device proved to be a viable means of determining aerodynamic seeing qualities of flow fields. It could also be applied to static atmospheric seeing measurements through various gases and pollutants.
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