Dynamic Imaging with X-ray Holography

Abstract

X-ray holography is a type of coherent diffractive imaging where the phase information is physically encoded in the diffraction pattern by means of interference with a reference beam. The image of the diffracting specimen is obtained by a single Fourier transform of the interference pattern. X-ray holography is particularly well-suited for high resolution dynamic imaging because, intrinsically, the reconstructed image does not drift and the images show high contrast. Therefore, the motion of features between two images can be determined with a precision of better than 3 nm, as demonstrated recently. In this chapter, the technical aspects of X-ray holography are discussed from an end user perspective, focusing on what is required to obtain a high quality image in a short time. Specifically, the chapter discusses the key challenges of the technique, such as sample design and fabrication, beam requirements, suitable end stations, and how to implement pump-probe dynamic imaging. Good imaging parameters were found using simulations and experiments, and it is demonstrated how a deviation from the optimum value affects the image quality.

Field-free deterministic ultrafast creation of magnetic skyrmions by spin–orbit torques

“…Imaging was performed at beamline P04 at PETRA III, DESY, Germany, using X-ray holography with circular polarized X-rays of 778 eV photon energy [29].…”

“…Imaging was performed at beamline P04 at PETRA III, DESY, Germany, using X-ray holography with circular polarized X-rays of 778 eV photon energy [29]. The reference holes had a diameter of 25 nm, 120 nm, and 110 nm in Figs.…”

“…2a,b). On the back side of the membrane, two holes were prepared in an opaque Au film, the larger one with 1 µm diameter defining the field of view (FOV) and the smaller one providing the reference beam for X-ray holographic imaging [28,29], allowing us to reconstruct images of the distribution of m z within the FOV. The magnetic state was imaged after a sequence of (i) saturating the film with a large z-axis bias field, (ii) reducing the field to a value where domains can exist but do not nucleate spontaneously, and (iii) injecting single rectangular-shaped SOT current pulses or unipolar pulse trains.…”

Coherent correlation imaging for resolving fluctuating states of matter

“…Three circular apertures were milled by focused-ion-beam lithography into this opaque layer, one with 720 nm in diameter defining the field of view and two reference holes 60 nm and 40 nm in diameter providing reference beams for holography. These hole diameters represent a geometry that was developed for time-resolved X-ray holography of out-of-plane magnetic domains [41][42][43] . They represent a good compromise between sensitivity for small changes (which is easier revealed with smaller object holes) and contextual information (for which larger field of views are preferred).…”

“…Images in Figs. 1, 3 were reconstructed by Fourier-transform holography (FTH) 42,45,46 , which is a linear operation and therefore best suited to illustrate the effect of limited signal-to-noise ratio (SNR) and blind averaging. The final, high-SNR images of the magnetic states and modes (Figs.…”