Design and applications of dual-wavelength digital holography wavefront sensor

The design and validation of a dual-wavelength digital holography wavefront sensor for quantitative simultaneous measurements of aero-optical wavefronts in subsonic compressible flow over two apertures is presented. The optical setup and processing methodology for reconstructing independently-reconstructed optical path difference (OPD) fields from interference patterns generated by two laser beams separated spatially along the streamwise axis are described in detail. The agreement and accuracy of the reconstructed wavefronts in a turbulent boundary layer flow are assessed, and the error between the OPD fields reconstructed from each beam is quantified using a normalized <i>L₂</i>-norm relative error metric. In addition, a time-delayed cross-correlation between the separated beams was computed to estimate the convective speed of aero-optical distortions in the boundary-layer-dominated flow. We demonstrate the consistent agreement between the two OPD fields, with errors being largely independent of flow speed, and convective speeds that scale predictably with freestream flow speed. These results validate dual-wavelength digital holography as a reliable method of high-resolution wavefront sensing in compressible flow environments.