Dual wavefront sensing design for supersonic wind tunnel experiments

The Air Force Research Laboratory Directed Energy Directorate is building a supersonic wind tunnel in order to characterize aero-optical effects. In order to gain access to the test section of interest, we must first send light through the access windows of the wind tunnel's test section. Thus, one of the initial challenges we face is being able to characterize the aberrations caused by the boundary-layer effects over the look-through windows separate from the aberrations caused by aero-optical effects over the test section of interest. As such, we are designing a dual wave-front sensor (WFS) setup in order to characterize these phenomena. The completed product will use a Shack-Hartmann (SH) WFS, in addition to a digital holography (DH) WFS. For all intents and purposes, the data obtained from the SH WFS will serve as the baseline for all experimentation, since it is the tried and true method for wavefront sensing in a wind tunnel environment. The DH WFS, on the other hand, is a unique method for wavefront sensing in a wind-tunnel environment. By providing us with access to an estimate of the complex-optical field, the DH WFS has the potential to transcend the capabilities of the SH WFS. In particular, we should be able to numerically propagate to various planes of interest in the optical train to characterize boundary layer effects over the look-through windows, separate from the aero-optical effects over the test section of interest. This paper reviews the requirements of our wind-tunnel environment and the design for this proposed dual WFS setup.