Optical turbulence on 1-km horizontal path with short and medium IR Gaussian laser beams

Abstract

We have investigated effects of optical turbulence on laser beams with wavelengths of λ = 1064 nm and 2036 nm. The two laser beams (one diode and one thulium fiber laser) were expanded to 7 cm diameter through a common telescope by means of an off-axis parabolic mirror. The two approximately Gaussian beams were focused along a 1-km-long horizontal path (about 1 m above ground) onto a roughened metal plate. The beam spots were recorded by two separate cameras with band-pass filters. The laser beams were pulsed at 50 Hz and synchronized with the camera shutters. Altogether 76 runs of 20 s length (resulting in 1000 single frames each) were recorded during the days of Oct. 12 to 14, 2022 at ONERAs test site in Fauga-Mauzac in southern France. Turbulence conditions during that time varied from C2n as low as a few 10−16 m−2/3 to as high as several 10−13 m−2/3. We discuss our findings for both wavelengths in terms of long-term (20 s) beam spot size, short-term (fraction of ms) beam spot size as well as spatial and temporal beam wander. We also find departure from Gaussian beam shape in average at increasing turbulence level. Comparison of experimental data with some selected models is provided.