Experiment research on uniformity of multi-beam illumination

Abstract

Adaptive optics system can work with beacon produced by illumination the dim target with laser beam. But atmospheric turbulence distributed over the entire propagation path produces intensity scintillation of the illumination laser beam. The multi-beam illumination approach can improve the intensity uniformity by adding different intensity distributions produced by separate illumination beams passing through independent atmospheric paths. A 4 km horizontal propagation path was established to examine the illumination effect with multi-beam on the target. Individual laser beams were launched from a separate region of the transmitter telescope. The far-field irradiance profile was received by target-plane and recorded with a CCD camera operating in 1k Hz placed in front of the target-plane. The uniformity of target area was determined by the number of the illuminating beams and the turbulence strength. Data were recorded with 1, 3 or 6 incoherence lasers illumination and for a range of R0 parameter. We calculated the irradiance of a 8x8 cm² area in the target-plane to characterize uniformity of illumination. Results show a good reduction in intensity variance with number of illumination beams increasing and that the uniformity of illumination on target turns to worse when the atmosphere turbulence became worse. The back backscatter from the target-plane was received by another telescope nearby the transmitter side and imaged by a CCD camera. The images of the rough reflector showed that the image resolution and the illumination effects improved with the number of illuminating beams increasing.