Single-Axis Ptychographic Coherent Diffractive Imaging for Spectroscopic and Wavefront Retrieval

TL;DR

AP-CDI presents a single-axis, lensless ptychographic imaging framework that jointly reconstructs sample transmission and spectrally varying probe fields from incoherent, axially scanned diffraction data. It formulates a forward model and an efficient gradient-based phase retrieval algorithm that operates under partially coherent illumination to recover multispectral wavefronts and dispersion properties with reduced data volume. The method is validated through quasi-monochromatic, spectral-multiplexing, lens-dispersion analyses, and spatiospectral imaging of ultrafast beams, showing accurate chromatic aberration quantification and robust performance under low SNR. Implemented on GPUs, AP-CDI achieves real-time-like reconstruction speeds and offers a compact, scalable platform for multispectral quantitative imaging, optical metrology, and ultrafast beam diagnostics.

Abstract

We present a novel axial ptychographic coherent diffractive imaging (AP-CDI) technique designed to overcome the critical throughput bottleneck of conventional methods. By replacing the 2D raster scan with a simple 1D axial scan, our approach reduces the number of required diffraction patterns by approximately an order of magnitude while maintaining high-fidelity reconstruction. We have experimentally validated this concept, successfully performing simultaneous spectroscopic imaging of a sample and quantitative wavefront characterization of the illumination, thereby accurately quantifying the chromatic aberration of a broadband field. This capability establishes AP-CDI as a highly efficient and versatile tool for real-time, multi-modal imaging, with immediate potential in ultrafast science, material characterization, and live-cell bio-imaging.

Figures (7)

• Figure 1: Axial ptychographic imaging system. The sample is mounted on a motorized translation stage and moved incrementally along the optical axis. The beam sequentially illuminates the sample at each position to generate exit waves, while the detector simultaneously acquires the corresponding diffraction patterns. (a) Spectrum of the femtosecond source. (b) Diffraction data of the probe beam acquired without the sample. (c) Diffraction data set acquired during axial movement of the sample.
• Figure 2: Axial Phase Retrieval Algorithm. Each iteration of the algorithm comprises $N$ cycles executing this process, successively updating the estimates of the object and probe by utilising diffraction patterns from exits on different object planes.
• Figure 3: Experimental results obtained using the USAF 1951 standard resolution test chart as the sample under quasi-monochromatic source conditions. (a) Amplitude of the reconstructed object transmission function, with the enlarged red region showing more details of the sample. (b) Phase of the reconstructed object transmission function. (c) Amplitude of the reconstructed probe function at the aperture plane, where contamination of the optical elements causes the reconstructed spot to deviate from an ideal Gaussian profile. (d) Phase of the reconstructed probe function at the aperture plane, which deviates from an ideal plane wave due to contamination.
• Figure 4: Spectrum multiplexing experimental results of the collimated beam after passing through the aperture. (a) and (b) show the amplitude distributions of the object function reconstructed from the green and red light channels respectively; (c) and (d) display the corresponding amplitude distributions of the probe function; (e) and (f) present the phase distributions of the object function, exhibiting significant differences; (g) and (h) depict the phase distributions of the probe function.
• Figure 5: Spectrum multiplexing experimental results after the collimated beam passes through a convex lens. (a) and (b) show the reconstructed object function amplitude distributions for the green and red light channels respectively; the red light spot is larger, illuminating a greater area of the sample. (c) and (d) show the amplitude distributions of the corresponding probe functions; (e) and (f) display the probe function phases; (g) and (h) present the unwrapped phase results for the yellow regions in (e) and (f); (i) and (j) depict phase profiles along the marked lines in (g) and (h).