Horizontal Propagation Deep Turbulence Test Bed.

摘要

The Navy is interested in horizontal laser propagation studies in a maritime environment near the ocean surface, for applications including imaging and high-energy laser propagation. The Naval Postgraduate School (NPS) in Monterey, California, and the Naval Research Laboratory (NRL) Wavefront Sensing and Control Division in Albuquerque, New Mexico, are collaborating in the development of a horizontal propagation testbed with adaptive optics for correction and simulation of atmospheric deep turbulence conditions. Atmospheric turbulence near the ocean surface is mostly dominated by scintillation, or intensity fluctuations, which degrade beam quality as propagation distance increases. While statistical data has been collected and analyzed for decades on the vertical turbulence profile, horizontal, deep turbulence data collection has begun only relatively recently. No theoretical model currently exists to describe horizontal turbulence that parallels the familiar Kolmogorov statistical model used in vertical AO applications, and investigations are underway to develop such models. The main purpose of the NPS testbed is to develop an adaptive optics system which is capable of simulating scintillation effects. Since it is known that branch points and scintillation are characteristic of the deep turbulence problem, the testbed developed for this research is used to simulate the effects of intensity fluctuations and intensity dropouts on the Shack-Hartmann WFS. This is accomplished by applying atmosphere on two separate Spatial Light Modulators (SLMs), both individually and simultaneously, and extending the beam path between them to observe the atmospheric disturbances produced. These SLMs allow the implementation of various atmospheric turbulence realizations, while the use of two in combination allows the simulation of a thick aberrator to more closely approximate horizontal turbulence behavior.