Characterizing the modulation transfer function for X-ray radiography in high energy density experiments.

The Modulation Transfer Function () is an established means for characterizing imaging performance of X-ray radiography systems. We report on experiments using high energy, laser-driven X-ray radiography systems that assess performance using values measured with the knife-edge projection method. The broadband, hard X-ray systems under study use line-projection imaging produced by narrowing the laser-generated X-ray source with a slit. We find that good contrast resolution can be achieved (the = 0.5 at 75 m wavelength) and that this performance is reproduced on different laser facilities. We also find that the is sensitive both to the thickness of the line-projection slit and to the backing material thickness under the knife-edge. Both these sensitivities are due to a common mechanism, namely induced changes in the spectrally-averaged spatial widths of the X-ray source. The same line-projection system is also used on experimental campaigns measuring Rayleigh-Taylor instability growth by dynamically imaging sinusoidal, high micro-targets with wavelengths of 100 m or less. By applying the measured values to correct the ripple target contrast measurements, we can predict ripple growth to approximately 10% accuracy.