In present paper reference beam and shear dual-hologram methods conjointly using only Mach-Zehnder holograms made
more successful measuring characteristic densities, density gradients and studying a jet structure: weak shocks following
by expansion waves. The effect of fast transition to a transonic regime accompanying the disintegration of a jet was
observed and densities in transition region were evaluated. As a whole, method of dual-hologram interferometry has
showed their self-descriptiveness, flexibility and utility for optical diagnostics of a weak gas dynamic micro object - the
supersonic air micro jet. Finally, experimental data obtained from the both techniques were numerically compared.
Preliminary results of optical diagnostics of bow shocks in a supersonic wind tunnel by applying dual-hologram shear interferometry technique are discussed. A strong refraction effect of the probing beam penetrating a region in the vicinity of a bow shock over a blunt nose cone model has been discovered. On a signal hologram the effect leads to the disappearance of holographic fringes in a narrow region attached to the shock wave front. A reconstructed interferogram in this region, being illuminated only by the comparison wave, manifests the absent of an interference pattern.
Computer simulations were performed for a part of the probing beam penetrating the area of high-density steep-gradients of compressed air attaching to the central part of the shock front of a bow shock. The compressed area was modeled as a hyperbolic cap. The bow shock was assumed axisymmetric. The simulations made it possible to determine angles of deflections and found conformity with reconstructed interferograms (shadowgraph).
It is concluded that in the above indicated region of bow shocks probing light is deviated refractively into some angles, which could be large enough for light rays to be blocked out and never arrive at detector (photo film). In the case, when interferometric fringes disappear the effect of strong refraction makes it impossible measuring of air density gradients in some critical region.