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Non-uniform, variable-density fields, resulting from compressibility effects in turbulent flows, are the source of aero-optical distortions which cause significant reductions in optical system performance. Adaptive-Optics (AO) is a technique used to correct for such spatially and temporally varying aberrations on an optical beam by applying a conjugate waveform correction to the beam. Traditional AO systems are bandwidth limited by real-time processing issues and wavefront sensor limitations. This paper presents an alternative AO approach using a phase-locked-loop control strategy. By using flow control to regularize the shear layer and its corresponding optical wavefront, the bandwidth necessary to make realtime corrections is effectively reduced by producing a more periodic and predictable optical signal. A feedback control approach has been simulated numerically performing real-time corrections to an aberrating wavefront due to propagation through a free shear layer. Several cases were studied for a variety of upper and lower Mach numbers. The numerical results show significant increases in the time-averaged Strehl ratio for the cases where the regularized wavefront contained a single dominant frequency. Further increases in the Strehl ratios were achieved after additionally removing tip/tilt. It was noted that tip/tilt error must be removed post AO corrections rather than prior in order to maintain a traveling wavefront necessary for this control strategy. In the highest Mach number case studied, regularization of the shear layer produced an optical wavefront containing both fundamental and subharmonic frequencies. Higher Mach number cases, such as this, may require the use of two frequency control which is currently being investigated further. Nomenclature OPL= Optical Path Length OPD = Optical Path Difference n = index-of-refraction p = pressure ρ = density u = velocity in x direction, along the streamwise direction v = velocity in y direction, perpendicular to the flow direction T = temperature T ad = initial temperature calculated using the adiabatic relation p ∞ = free stream pressure γ = specific heat ratio θ = jitter angle f n = optical natural frequency Λ n = optical coherence length U c = convective velocity

A comparison of common optical wavefront measurement techniques is presented as an inter-calibration of these techniques. The sensors compared are the one-dimensional Small-Aperture Beam Technique (SABT) sensor, the one-dimensional Malley Probe, and two traditional two-dimensional Shack-Hartmann type sensors: one by Wavefront Sciences, and the other by Xinetics. The comparison was performed on a known, periodic, and repeatable optical aberration generated by a two-dimensional heated jet. The results showed good agreement between all tested wavefront sensors. The typically underappreciated effect of aperture sizing on the optical aberrations is also examined.