Statistical analysis of atmospheric beam propagation, and single-photon counting

by | Nov 22, 2017 | Seminar Talks

Speaker: Agata Pawlikowska and Brian Flemming, Leonardo MW Ltd

Title: Statistical analysis of atmospheric beam propagation, and single-photon counting

Abstract: Lasers can be used in a wide variety of applications such as range-finding, LIDAR, target identification and laser communication. However, the performance of a laser beam projected through the atmosphere can be badly affected by optical turbulence. Lightwave radiation passing through an optically-turbulent atmosphere encounters regions of differing refractive index, which act like weak lenses causing an apparently random distortion of the advancing wave-front and a corresponding deterioration in the quality of any projected image. Optical turbulence is characterised as a random process. The physics of wave-front propagation through a turbulent atmosphere is complex and is strictly applicable to weak turbulence regimes only. Computer simulation is a cost-effective alternative to expensive field trials, but the output requires to be validated against observed experimental data.The first part of the discussion provides a short overview of the relevant physics and of the problems to be encountered when devising a suitable statistical analysis of scintillated beam profiles for validation purposes. Understanding the impact of turbulence on the performance of optical systems which rely on long distance transmission and detection of electromagnetic radiation through the atmosphere is critical in assessment of long-range lidar performance. In this work we experimentally determine parameters which characterise optical turbulence with a new approach using single-photon detection. We have used an array of 32 × 32 InGaAs/InP single-photon avalanche diode (SPAD) detectors operating at a wavelength of 1550 nm. In the second part of this presentation we discuss a comparative method of refractive index structure parameter (Cn2) calculation, which shows a close match with the results obtained using a commercial scintillometer.