Wave-Front Measurements of a Supersonic Boundary Layer Using Laser Induced Breakdown

The aero-optical effect of a flat-plate adiabatic boundary layer has been measured using the light generated by a laser-induced breakdown spark. The measurements were performed in a blowdown wind tunnel at freestream Mach numbers of 3 and 4.38. The tests showed that the aero-optical effect of boundary layers with rms optical path difference as low as 0.05 μm could be accurately measured using the laser-induced breakdown spark, including their deflection-angle spatial spectra. The results demonstrate that, using the laser-induced breakdown spark as a source of illumination, it is possible to make accurate measurements of low-amplitude aero-optical effects in a manner that is self-contained, nonintrusive, and suitable for a flight-test environment.