Figure 1.

Comparison of step-scan and fly-scan ptychography. In step-scan mode (a), the probe moves relative to the sample in a move-settle-acquire sequence, where the detector doesn’t acquire data during the move-settle overhead time t_o; then the diffraction pattern is collected over an exposure time of t_e, after which the detector becomes inactive for a dead time t_d for data transfer. In fly-scan mode (b), the probe moves relative to the sample in a scan line with a constant speed while data is acquired over exposure times t_e followed by brief detector dead times t_d. Insets show both step-scan and fly-scan beam footprints (assuming a round probe with a diameter d) with s representing the probe motion distance during exposure time t_e. (c) The diffraction intensities measured from a gold test sample in the two scan modes with t_e= 100 ms and s = 100 nm (experimental details are in Sec. 2). Speckle visibility is reduced in fly-scan mode. Figure based on.¹⁷