16 August 2010 Optical aberrations in gas lenses
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Gas lenses work on the basis that aerodynamic media can be used to generate a graded refractive index distribution which can be used to focus a laser beam. An example is a spinning pipe gas lens (SPGL). It is a steel pipe whose walls are heated to a preselected temperature and then rotated along the axis to any desired speed to generate a cooler core of incoming air. A laser beam propagating through these lenses is focussed in space. However, experimental observation has shown that distortions are generated in the beam. We provide a computational fluid dynamics (CFD) model of the lens and experimental results of the Zernike aberrations measured using a Shack-Hartmann wavefront sensor which show that the aerodynamic medium in the lens have a deleterious effect on laser beam quality (M2). The effect on the SPGL is that the beam deterioration increases with rotation speed and temperature though the worst M2 measured at speed 20 Hz and temperature 155 °C was ~3.5 which is fairly good.
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C. Mafusire, A. Forbes, M. M. Michaelis, G. Snedden, "Optical aberrations in gas lenses", Proc. SPIE 7789, Laser Beam Shaping XI, 778908 (16 August 2010); doi: 10.1117/12.862855; https://doi.org/10.1117/12.862855

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