Hot-air turbulence generator for multiconjugate adaptive optics

摘要

In this article, a simple low-cost, statistically repeatable, hot air optical turbulence generator based on the mixing of two air flows with different temperatures is described. Characterization results show that it is possible to create any turbulence strength up to C_N~2Δh ≈ 6 * 10~(-10) m~(1/3), allowing Fried's parameter as small as r_0 ≈ 1.7 mm for one crossing through the turbulator or r_0 ≈ 1.1 mm for two crossings. Outer scale of (L_0 ≈ 133 ± 60 mm) is found to be compatible to the turbulator chamber size (170 mm), and inner scale (l_0 ≈ 7.6 mm ± 3.8 mm) compatible with usual values measured by other authors for the free atmosphere. Power spectrum analysis of the centroid of the focused image shows a perfect and accurate agreement with Kolmogorov's theory, allowing to conclude that this device can be used with confidence to emulate good and easily controllable turbulence. In particular, this turbulator will be used with the MCAO test bench developed at the University of Victoria. By allowing two passes of the optical beam through the turbulator, without overlapping, two independent turbulent layers, set at equivalent altitudes of 5 and 15 km above the telescope entrance pupil, will be generated.