Moire interferometry of short wavelength Rayleigh-Taylor growth

One of the most critical quantities to be measured for better understanding of the ablative Rayleigh-Taylor (RT) instability is the cutoff wavelength below which the RT instability is stabilized. Unfortunately, this wavelengt h is expected to be below or close to spatial resolutions of most x-ray ima gers used in the RT experiments. We propose and test a new technique using moire' interferometry to convert short wavelength perturbations to longer w avelength perturbations. The RT target is backlit by x rays and imaged just like in conventional experiments, but a grid mask is inserted between the target and the x-ray imager. The grid mask is one dimensional grid with a p eriod slightly different from the wavelength of the RT target. It is set so that the grid and the RT perturbation groove are parallel to each other. W ith this operation, the long wavelength moire' interference is measured as the beat with the RT target. As an initial test, we use a grid mask with 10 mu m period coupled to RT targets with 8 and 12 mu m perturbation waveleng ths. The corresponding moire' interference wavelengths are 40 and 60 mu m,r espectively. (C) 1998 American Institute of Physics. [S0034-6748(99)69101-8 ].