X-Ray Ptychography with a Laboratory Source

X-ray ptychography has revolutionized nanoscale phase contrast imaging at large-scale synchrotron sources in recent years. We present here the first successful demonstration of the technique in a small-scale laboratory setting. An experiment was conducted with a liquid metal-jet x-ray source and a single photon-counting detector with a high spectral resolution. The experiment used a spot size of $5\mu \mathrm{m}$ to produce a ptychographic phase image of a Siemens star test pattern with a submicron spatial resolution. The result and methodology presented show how high-resolution phase contrast imaging can now be performed at small-scale laboratory sources worldwide.

Figure 1

Experimental configuration. Ptychography setup (not to scale) showing the experimental layout as implemented at SMALL, Sheffield, UK.

Figure 2

The x-ray source spectrum as recorded with the SLcam. The gallium K-alpha peak (9.25 keV) along with the double pileup (18.5 keV) and triple pileup peaks (27.75 keV) are shown in blue. The K-alpha escape peak in silicon (7.51 keV) is shown in green and the K-beta (10.26 keV) is shown in red.

Figure 3

Source and illumination stability. (a) Fluctuation of total intensity measured by integrating the total flux on the detector during the scan. The value is normalized by the mean value. (b) Beam position and tilt correction as recovered during the ptyrex reconstruction. The origin of the arrow represents the recalculated position, the direction of the arrow represents the direction of the tilt correction, and the length of the arrow is proportional to the modulus of the angular tilt. The color map of both (a) and (b) represents the modulus of the angular tilt at each scan position, highlighting the correlation between intensity fluctuations and angular tilt corrections. The two points removed during the reconstruction are marked as black dots both in (a) and (b).

Figure 4

The ptychography reconstruction. (a) Phase image of the Siemens star test target with a reconstructed pixel size of 116 nm. (b) Modulus of the beam profile at the sample plane. (c) Line plot from the dashed black line in (a). The raw data are represented by the solid black line and the 10 pixel moving average is represented by the solid red line. (d) Fourier ring correlation of the two split exposure reconstructions showing $1.08\mu {\mathrm{m}}^{-1}$ spatial frequency (corresponding to 930 nm). Two diffractograms recorded in two different scan positions are shown in (e) and (f). (g), the difference (e)–(f), shows clearly the interference fringes.