Holotomography: Quantitative phase tomography with micrometer resolution using hard synchrotron radiation x rays

TLDR

Hard X‑ray refractive index deviates slightly from unity, so beam phase changes on transmission; coherent propagation enables phase imaging, though phase is not directly proportional to intensity. A holographic reconstruction using images taken at multiple propagation distances yields quantitative phase maps and, combined with 3‑D reconstruction, produces holotomography of sample density. Holotomography provides micrometer‑resolution, quantitative density maps ideal for low‑absorption, radiation‑sensitive samples.

Abstract

Because the refractive index for hard x rays is slightly different from unity, the optical phase of a beam is affected by transmission through an object. Phase images can be obtained with extreme instrumental simplicity by simple propagation provided the beam is coherent. But, unlike absorption, the phase is not simply related to image brightness. A holographic reconstruction procedure combining images taken at different distances from the specimen was developed. It results in quantitative phase mapping and, through association with three-dimensional reconstruction, in holotomography, the complete three-dimensional mapping of the density in a sample. This tool in the characterization of materials at the micrometer scale is uniquely suited to samples with low absorption contrast and radiation-sensitive systems.