Fly-scan ptychography

Abstract

We report an experimental ptychography measurement performed in fly-scan mode. With a visible-light laser source, we demonstrate a 5-fold reduction of data acquisition time. By including multiple mutually incoherent modes into the incident illumination, high quality images were successfully reconstructed from blurry diffraction patterns. This approach significantly increases the throughput of ptychography, especially for three-dimensional applications and the visualization of dynamic systems.

Figure 1. Experimental setup for fly-scan ptychography measurement.

The collimated 635 nm laser is focused on a pinhole to generate the incident illumination. A test pattern was placed and scanned at a plane about 9.8 mm downstream of the pinhole. The diffraction patterns were collected by a camera placed 31 mm further downstream.

Figure 2. Fly-scan trajectory recorded by interferometers with 600 μm/s speed and 0.12 second exposure time per frame.

The motor movements along the fast (blue) and slow (cyan) scan axes are shown in the left panel. A zoomed-in view for the first scan line is displayed in the right panel. Each blue dot indicates the central location of a continuous motions during each data acquisition period. The solid green lines indicate the triggering time for the detector counting, and the dashed red lines indicate the completion time for data collection. The time interval from a solid green line to the next dashed red line defines the 0.12 second exposure time as indicated by the gray boxes in the inset, and the time interval from a dashed red line to the next solid green line is the 0.014 second dead time for detector readout.

Figure 3. The central part of collected diffraction patterns around the same sample position with different motor speed and the same exposure time: (a) 600 μm/s, (b) 450 μm/s, (c) 300 μm/s, (d) 150 μm/s.

With a faster scan speed, a larger sample area is scanned over a single exposure period, resulting in a more blurry diffraction pattern.

Figure 4. Reconstructed amplitude of the test pattern from diffraction datasets collected at different scan speeds with single (left colume) and multiple (right colume) illumination modes.

Figure 5. The top panel shows the three reconstructed illumination modes with the most powers for diffraction pattern collected at different scan speeds.

The bottom panel shows the power percentage of the recovered modes. With increased scan speed, more illumination power is removed from primary modes and redistributed into other modes. The inset in the bottom-left corner shows the propagation of the reconstructed illumination wave back to pinhole plane. The shape and dimension are consistent with SEM measurement of the pinhole.