Wind tunnel simulations to detect and quantify the turbulent effects of a propagating He-Ne laser beam in air

Shivan Michael Augustine, Naven Chetty

Abstract

In this paper, we ascertain the effectiveness of our experimental setup in detecting and quantifying the turbulent effects experienced by a He-Ne laser beam as it passes through a wind tunnel. The beam propagated through a series of optical components as well as the in-house designed and manufactured wind tunnel under controlled laboratory conditions. The wind tunnel was built to fit within an existing setup, which has previously proven to be successful in detecting the turbulent effects from other turbulence models. For various wind speeds and temperature settings, the setup has been successful as it was able to detect and measure the atmospheric conditions within the turbulent environment and fully quantify the characteristics of the laser beam. With the use of highly accurate measuring devices, we were able to successfully measure the refractive index structure function (Cn2) and the coherence diameter (Fried’s parameter). Values for Cn2 ranged between 1.61 × 10–16 m–2/3 and 6.77 × 10–15 m–2/3, which can be classified under the moderate to strong turbulence regime. These results tie in well with various published works for similar atmospheric scenarios hence this setup was successfully able to fully detect and quantify the thermal turbulence and wind velocity effects on the laser beam using a point diffraction interferometer.

Keywords

Thermal turbulence; wind tunnel; Fried´s parameter; structure function; interferometer; laser beam propagation; turbulence strength

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