THE FUTURE OF X-RAY HOLOGRAPHY

X-ray holography is a promising technique for high resolution study of biological, microelectronics and materials science specimens. It offe rs absorption and phase contrast, it is amenable to flash sources, and it is capable of three-dimensional imaging when coupled with tomograp hy. Soft X-rays are suited to microscopy of thin organic specimens and wet biological objects such as subcellular organelles. Major advances in X-ray sources, optics, and detectors have made possible Gabor and Fourier transform holography with 50 to 60-nm transverse resolution us ing 350-600 eV photons; 100-nm depth resolution by holographic tomogra phy has recently been demonstrated. X-ray holography at higher energie s (1-4 keV) may be feasible soon using third-generation synchrotron so urces. These methods might profitably be used to investigate denser ob jects than are accessible to soft X-rays, for example defects in micro circuits and adsorbates in zeolites. The future is likely to see progr ess in X-ray holography over an increasing range of photon energies, w ith elemental and chemical specificity, and with three-dimensional res olution below one micron.