Possibility of single biomolecular imaging with coherent amplification of weak scattering X-ray photons

Abstract

The number of photons available by coherent X-ray scattering from a single biomolecule is considerably less because of the extremely small elastic-scattering cross-section and low damage threshold. Even with a high X-ray flux of 3 x 10to 12 photons per 100-nm-diameter spot and an ultrashort pulse of 10 fs driven by a future X-ray free electron laser (X-ray FEL), it has been predicted that only a few 100 photons will be available by scattering from a single lysozyme molecule. In this paper I propose a new method: instead of directly observing the photons scattered from the sample, we amplify the scattered waves by superimposing an intense coherent reference pump wave on it and record the resulting interference pattern using a planar X-ray detector, similar to technique followed in holography. Using a nanosized gold particle as a reference pump wave source, we can collect 10 to 4 ~ 10 to 5 photons in single shot imaging where the signal from a single biomolecule is amplified and recorded as 2D diffraction intensity data. To recover the phase information and reconstruct the image, the iterative phase retrieval technique will be applicable. However, the technical difficulty is how to precisely reconstruct faint image of the single bio-molecular in Angstrom resolution, whose intensity is much lower than the bright gold particle linked to it. In order to solve this problem, I propose a new scheme that combines the iterative phase-retrieval on reference pump wave and digital Fourier transform holography.