Reconstructed holographic interferogram

Stosswellenlabor RWTH, Aachen, Germany, and Tohoku University, Sendai, Japan

The original hologram was obtained through use of a ruby laser at 694 nm, pulse energy 1 J, pulse width 30 ns, and was captured on a holographic plate (10 cm x 15 cm). The hologram was reconstructed with a He-Ne laser (wavelength = 632.8 nm, 10 mW, cw) onto medium-format monochromatic film.
The photograph shows a shock wave traveling in a vertical direction, from bottom to top, with a speed of 770 m/s and diffracting around a cylinder. Apart from the primary diffracted and reflected shocks, this process generated a number of shear layers, vortices, and secondary shock waves. The cylinder had a diameter of 2 cm; the flow was generated in a shock tube with a square cross-section of 5.4 cm x 5.4 cm. The observed phenomenon is a shock wave in nitrogen (N2) of subatmospheric initial pressure (pi = 25 kPa).
The picture was taken under the supervision of Professor Hans Gršnig, RWTH, Aachen.