Wavefront Aberration in a Laser Beam Induced by Supersonic Flow Field Around a Wedge
Aero-optical experiment is conducted in Mach 7 shock tunnel. To investigate the influence of shock wave and boundary layer on the optical wave, 12° wedge model with window on the surface is designed and used. Vibration of the facility is reduced by isolating the test section table from the facility. Also the nozzle shear layer is avoided by installing another wedge structure on the incident laser beam. Diode laser beam with 635 nm wavelength is shot through the flow field, and two-dimensional Shack-Hartmann sensor measured the wavefront of the laser beam. The flow characteristics are acquired by shadowgraph image and pressure measurement. The angle of the laser beam is varied to study the effect of the line of sight. From the measured wavefront, point spread function is calculated to quantify the bore sight error and Strehl ratio. As the line of sight is lowered, bore sight error increased, and Strehl ratio decreased. Thus, lower line of sight is influenced more by the flow.