The recent advent of coherent soft and hard X-ray sources has facilitated the development of imaging techniques that are capable of being inverted to the real space information extremely quickly. A research group at the SLAC National Accelerator Laboratory, USA, recently developed a novel technique for soft X-rays, based on differential holographic encoding, termed holography with extended reference by autocorrelation linear differential operation (HERALDO). The technique has achieved superior resolution over other similar lensless techniques, such as X-ray Fourier transform holography, while maintaining the signal-to-noise ratio and algorithmic simplicity. The spatial resolution was 16 nm, and this was obtained by synthesizing images in the Fourier domain from a single diffraction pattern, which allows resolution improvement beyond the reference fabrication limit. In addition to the capability of instant high-resolution reconstruction, the technique is found to be robust against data imperfections. It reduces artifacts arising from the commonly-missing central low-q data. For more information, see the paper, "High-Resolution X-Ray Lensless Imaging by Differential Holographic Encoding", D. Zhu et al., Phys. Rev. Lett. 105, 043901 (2010). For more information on the original idea of HERALDO, see the paper, "Holography with extended reference by autocorrelation linear differential operation", M. Guizar-Sicairos and J. R. Fienup, Optics Express, 15, 17592 (2007).
