Subwavelength full-field terahertz ptychography via longitudinal shifts

Due to the unique characteristics of terahertz (THz) waves, THz complex-amplitude imaging, which reveals not only the absorption properties of the sample from the intensity image but also the relative thickness and the refractive index information by phase measurement, has been regarded as a prospective technology for applications ranging from biomedical to non-destructive testing.1,21. M. Wan, J. J. Healy, and J. T. Sheridan, “Terahertz phase imaging and biomedical applications,” Opt. Laser Technol. 122, 105859 (2020). https://doi.org/10.1016/j.optlastec.2019.1058592. S. Zhong, “Progress in terahertz nondestructive testing: A review,” Front. Mech. Eng. 14, 273–281 (2019). https://doi.org/10.1007/s11465-018-0495-9 THz systems can be divided into two major types: pulsed-wave and continuous-wave (CW). THz pulsed imaging based on THz time-domain spectroscopy (TDS) provides hyperspectral images with both amplitude and phase information by directly measuring the electric field of a THz pulse in the time domain. Although compressed sensing,33. S.-C. Chen, L.-H. Du, K. Meng, J. Li, Z.-H. Zhai, Q.-W. Shi, Z.-R. Li, and L.-G. Zhu, “Terahertz wave near-field compressive imaging with a spatial resolution of over λ/100,” Opt. Lett. 44, 21–24 (2019). https://doi.org/10.1364/ol.44.000021 two-dimensional electro-optical sampling,44. H. Zhong, A. Redo-Sanchez, and X.-C. Zhang, “Identification and classification of chemicals using terahertz reflective spectroscopic focal-plane imaging system,” Opt. Express 14, 9130–9141 (2006). https://doi.org/10.1364/oe.14.009130 asynchronous optical sampling,55. A. Bartels, R. Cerna, C. Kistner, A. Thoma, F. Hudert, C. Janke, and T. Dekorsy, “Ultrafast time-domain spectroscopy based on high-speed asynchronous optical sampling,” Rev. Sci. Instrum. 78, 035107 (2007). https://doi.org/10.1063/1.2714048 etc., can be adopted to reduce the long scanning time that is typically caused by the single-pixel detector and the optical delay line, THz wide-field, high-resolution, and rapid imaging based on TDS still needs further development.Alternatively, the phase can be retrieved from intensity measurements by coherent diffraction techniques,66. Y. Shechtman, Y. C. Eldar, O. Cohen, H. N. Chapman, J. Miao, and M. Segev, “Phase retrieval with application to optical imaging: A contemporary overview,” IEEE Signal Process. Mag. 32, 87–109 (2015). https://doi.org/10.1109/msp.2014.2352673 which have promoted THz full-field phase imaging with CW sources working at a fixed frequency.77. L. Valzania, Y. Zhao, L. Rong, D. Wang, M. Georges, E. Hack, and P. Zolliker, “THz coherent lensless imaging,” Appl. Opt. 58, G256–G275 (2019). https://doi.org/10.1364/ao.58.00g256 Over the past decade, a lot of work on THz digital holography has been done,8–228. M. S. Heimbeck and H. O. Everitt, “Terahertz digital holographic imaging,” Adv. Opt. Photonics 12, 1–59 (2020). https://doi.org/10.1364/aop.12.0000019. S.-H. Ding, Q. Li, Y.-D. Li, and Q. Wang, “Continuous-wave terahertz digital holography by use of a pyroelectric array camera,” Opt. Lett. 36, 1993–1995 (2011). https://doi.org/10.1364/ol.36.00199310. P. Zolliker and E. Hack, “THz holography in reflection using a high resolution microbolometer array,” Opt. Express 23, 10957–10967 (2015). https://doi.org/10.1364/oe.23.01095711. L. Rong, T. Latychevskaia, C. Chen, D. Wang, Z. Yu, X. Zhou, Z. Li, H. Huang, Y. Wang, and Z. Zhou, “Terahertz in-line digital holography of human hepatocellular carcinoma tissue,” Sci. Rep. 5, 8445 (2015). https://doi.org/10.1038/srep0844512. Z. Li, L. Li, Y. Qin, G. Li, D. Wang, and X. Zhou, “Resolution and quality enhancement in terahertz in-line holography by sub-pixel sampling with double-distance reconstruction,” Opt. Express 24, 21134–21146 (2016). https://doi.org/10.1364/oe.24.02113413. L. Valzania, P. Zolliker, and E. Hack, “Topography of hidden objects using THz digital holography with multi-beam interferences,” Opt. Express 25, 11038–11047 (2017). https://doi.org/10.1364/oe.25.01103814. M. Yamagiwa, T. Ogawa, T. Minamikawa, D. G. Abdelsalam, K. Okabe, N. Tsurumachi, Y. Mizutani, T. Iwata, H. Yamamoto, and T. Yasui, “Real-time amplitude and phase imaging of optically opaque objects by combining full-field off-axis terahertz digital holography with angular spectrum reconstruction,” J. Infrared, Millimeter, Terahertz Waves 39, 561–572 (2018). https://doi.org/10.1007/s10762-018-0482-615. H. Huang, P. Qiu, S. Panezai, S. Hao, D. Zhang, Y. Yang, Y. Ma, H. Gao, L. Gao, Z. Zhang, and Z. Zheng, “Continuous-wave terahertz high-resolution imaging via synthetic hologram extrapolation method using pyroelectric detector,” Opt. Laser Technol. 120, 105683 (2019). https://doi.org/10.1016/j.optlastec.2019.10568316. Z. Li, Q. Yan, Y. Qin, W. Kong, G. Li, M. Zou, D. Wang, Z. You, and X. Zhou, “Sparsity-based continuous wave terahertz lens-free on-chip holography with sub-wavelength resolution,” Opt. Express 27, 702–713 (2019). https://doi.org/10.1364/oe.27.00070217. Z. Li, R. Zou, W. Kong, X. Wang, Q. Deng, Q. Yan, Y. Qin, W. Wu, and X. Zhou, “Terahertz synthetic aperture in-line holography with intensity correction and sparsity autofocusing reconstruction,” Photonics Res. 7, 1391–1399 (2019). https://doi.org/10.1364/prj.7.00139118. M. Yamagiwa, T. Minamikawa, F. Minamiji, T. Mizuno, Y. Tokizane, R. Oe, H. Koresawa, Y. Mizutani, T. Iwata, H. Yamamoto, and T. Yasui, “Visualization of internal structure and internal stress in visibly opaque objects using full-field phase-shifting terahertz digital holography,” Opt. Express 27, 33854–33868 (2019). https://doi.org/10.1364/oe.27.03385419. Z. Li, Q. Yan, Y. Qin, W. Kong, M. Zou, X. Zhou, Z. You, and P. Cheng, “Resolution enhancement in terahertz digital in-line holography by sparsity-based extrapolation,” J. Infrared, Millimeter, Terahertz Waves 42, 479–492 (2021). https://doi.org/10.1007/s10762-021-00796-520. D. Wang, D. Ma, K. Li, Y. Zhang, J. Zhao, Y. Wang, and L. Rong, “Dynamic full-field refractive index distribution measurements using total internal reflection terahertz digital holography,” Photonics Res. 10, 289–296 (2022). https://doi.org/10.1364/prj.44238821. Y. Zhang, J. Zhao, D. Wang, Y. Wang, and L. Rong, “Lensless Fourier-transform terahertz digital holography for real-time full-field phase imaging,” Photonics Res. 10, 323–331 (2022). https://doi.org/10.1364/prj.43576922. X. Jin, J. Zhao, D. Wang, L. Rong, Y. Wang, J. J. Healy, and S. Lin, “Iterative denoising phase retrieval method for twin-image elimination in continuous-wave terahertz in-line digital holography,” Opt. Lasers Eng. 152, 106986 (2022). https://doi.org/10.1016/j.optlaseng.2022.106986 with topics including twin-image suppression,12,16,2212. Z. Li, L. Li, Y. Qin, G. Li, D. Wang, and X. Zhou, “Resolution and quality enhancement in terahertz in-line holography by sub-pixel sampling with double-distance reconstruction,” Opt. Express 24, 21134–21146 (2016). https://doi.org/10.1364/oe.24.02113416. Z. Li, Q. Yan, Y. Qin, W. Kong, G. Li, M. Zou, D. Wang, Z. You, and X. Zhou, “Sparsity-based continuous wave terahertz lens-free on-chip holography with sub-wavelength resolution,” Opt. Express 27, 702–713 (2019). https://doi.org/10.1364/oe.27.00070222. X. Jin, J. Zhao, D. Wang, L. Rong, Y. Wang, J. J. Healy, and S. Lin, “Iterative denoising phase retrieval method for twin-image elimination in continuous-wave terahertz in-line digital holography,” Opt. Lasers Eng. 152, 106986 (2022). https://doi.org/10.1016/j.optlaseng.2022.106986 autofocusing,1717. Z. Li, R. Zou, W. Kong, X. Wang, Q. Deng, Q. Yan, Y. Qin, W. Wu, and X. Zhou, “Terahertz synthetic aperture in-line holography with intensity correction and sparsity autofocusing reconstruction,” Photonics Res. 7, 1391–1399 (2019). https://doi.org/10.1364/prj.7.001391 resolution enhancement,12,15,17,1912. Z. Li, L. Li, Y. Qin, G. Li, D. Wang, and X. Zhou, “Resolution and quality enhancement in terahertz in-line holography by sub-pixel sampling with double-distance reconstruction,” Opt. Express 24, 21134–21146 (2016). https://doi.org/10.1364/oe.24.02113415. H. Huang, P. Qiu, S. Panezai, S. Hao, D. Zhang, Y. Yang, Y. Ma, H. Gao, L. Gao, Z. Zhang, and Z. Zheng, “Continuous-wave terahertz high-resolution imaging via synthetic hologram extrapolation method using pyroelectric detector,” Opt. Laser Technol. 120, 105683 (2019). https://doi.org/10.1016/j.optlastec.2019.10568317. Z. Li, R. Zou, W. Kong, X. Wang, Q. Deng, Q. Yan, Y. Qin, W. Wu, and X. Zhou, “Terahertz synthetic aperture in-line holography with intensity correction and sparsity autofocusing reconstruction,” Photonics Res. 7, 1391–1399 (2019). https://doi.org/10.1364/prj.7.00139119. Z. Li, Q. Yan, Y. Qin, W. Kong, M. Zou, X. Zhou, Z. You, and P. Cheng, “Resolution enhancement in terahertz digital in-line holography by sparsity-based extrapolation,” J. Infrared, Millimeter, Terahertz Waves 42, 479–492 (2021). https://doi.org/10.1007/s10762-021-00796-5 real-time imaging,14,2114. M. Yamagiwa, T. Ogawa, T. Minamikawa, D. G. Abdelsalam, K. Okabe, N. Tsurumachi, Y. Mizutani, T. Iwata, H. Yamamoto, and T. Yasui, “Real-time amplitude and phase imaging of optically opaque objects by combining full-field off-axis terahertz digital holography with angular spectrum reconstruction,” J. Infrared, Millimeter, Terahertz Waves 39, 561–572 (2018). https://doi.org/10.1007/s10762-018-0482-621. Y. Zhang, J. Zhao, D. Wang, Y. Wang, and L. Rong, “Lensless Fourier-transform terahertz digital holography for real-time full-field phase imaging,” Photonics Res. 10, 323–331 (2022). https://doi.org/10.1364/prj.435769 and biomedical application.1111. L. Rong, T. Latychevskaia, C. Chen, D. Wang, Z. Yu, X. Zhou, Z. Li, H. Huang, Y. Wang, and Z. Zhou, “Terahertz in-line digital holography of human hepatocellular carcinoma tissue,” Sci. Rep. 5, 8445 (2015). https://doi.org/10.1038/srep08445 Off-axis holography can obtain the complex-amplitude wave-front free from twin-image but at the expense of the space-bandwidth product (SBP) due to the requirement for spectral filtering during reconstruction. The introduction of an additional reference beam increases the distance between the sample and the detector, regardless of the Mach–Zehnder structure1818. M. Yamagiwa, T. Minamikawa, F. Minamiji, T. Mizuno, Y. Tokizane, R. Oe, H. Koresawa, Y. Mizutani, T. Iwata, H. Yamamoto, and T. Yasui, “Visualization of internal structure and internal stress in visibly opaque objects using full-field phase-shifting terahertz digital holography,” Opt. Express 27, 33854–33868 (2019). https://doi.org/10.1364/oe.27.033854 or the triangular geometry,1414. M. Yamagiwa, T. Ogawa, T. Minamikawa, D. G. Abdelsalam, K. Okabe, N. Tsurumachi, Y. Mizutani, T. Iwata, H. Yamamoto, and T. Yasui, “Real-time amplitude and phase imaging of optically opaque objects by combining full-field off-axis terahertz digital holography with angular spectrum reconstruction,” J. Infrared, Millimeter, Terahertz Waves 39, 561–572 (2018). https://doi.org/10.1007/s10762-018-0482-6 making it difficult to achieve high-resolution imaging with a large numerical aperture (NA). Since commercial spatial light modulators are not available in THz, the reconstruction results suffer from non-uniform illumination. In comparison, the Gabor in-line holography can provide subwavelength lateral resolution with a higher NA, which is beneficial to its compact optical configuration and full utilization of SBP. So far, the best lateral resolution (40 µm, 0.7λ@5.24 THz) in THz digital holography has been achieved by THz on-chip in-line holography.1616. Z. Li, Q. Yan, Y. Qin, W. Kong, G. Li, M. Zou, D. Wang, Z. You, and X. Zhou, “Sparsity-based continuous wave terahertz lens-free on-chip holography with sub-wavelength resolution,” Opt. Express 27, 702–713 (2019). https://doi.org/10.1364/oe.27.000702 The uneven illumination and the fixed noise from the detector can be suppressed by normalization,2323. T. Latychevskaia and H.-W. Fink, “Solution to the twin image problem in holography,” Phys. Rev. Lett. 98, 233901 (2007). https://doi.org/10.1103/physrevlett.98.233901 also known as empty beam correction,2424. J. Hagemann, A.-L. Robisch, D. R. Luke, C. Homann, T. Hohage, P. Cloetens, H. Suhonen, and T. Salditt, “Reconstruction of wave front and object for inline holography from a set of detection planes,” Opt. Express 22, 11552–11569 (2014). https://doi.org/10.1364/oe.22.011552 which is a crude approximation so that reconstruction errors may be expected in the subsequent phase retrieval process.24,2524. J. Hagemann, A.-L. Robisch, D. R. Luke, C. Homann, T. Hohage, P. Cloetens, H. Suhonen, and T. Salditt, “Reconstruction of wave front and object for inline holography from a set of detection planes,” Opt. Express 22, 11552–11569 (2014). https://doi.org/10.1364/oe.22.01155225. C. Homann, T. Hohage, J. Hagemann, A.-L. Robisch, and T. Salditt, “Validity of the empty-beam correction in near-field imaging,” Phys. Rev. A 91, 013821 (2015). https://doi.org/10.1103/physreva.91.013821 However, two major limitations hinder the application of the technique. First, ever since its invention, it has been troubled by the twin-image artifacts, for which computational algorithms, such as object-constraint-based iterative phase retrieval,2323. T. Latychevskaia and H.-W. Fink, “Solution to the twin image problem in holography,” Phys. Rev. Lett. 98, 233901 (2007). https://doi.org/10.1103/physrevlett.98.233901 sparse optimization,16,2616. Z. Li, Q. Yan, Y. Qin, W. Kong, G. Li, M. Zou, D. Wang, Z. You, and X. Zhou, “Sparsity-based continuous wave terahertz lens-free on-chip holography with sub-wavelength resolution,” Opt. Express 27, 702–713 (2019). https://doi.org/10.1364/oe.27.00070226. W. Zhang, L. Cao, D. J. Brady, H. Zhang, J. Cang, H. Zhang, and G. Jin, “Twin-image-free holography: A compressive sensing approach,” Phys. Rev. Lett. 121, 093902 (2018). https://doi.org/10.1103/PhysRevLett.121.093902 and deep learning,27,2827. Y. Rivenson, Y. Zhang, H. Günaydın, D. Teng, and A. Ozcan, “Phase recovery and holographic image reconstruction using deep learning in neural networks,” Light: Sci. Appl. 7, 17141 (2018). https://doi.org/10.1038/lsa.2017.14128. F. Wang, Y. Bian, H. Wang, M. Lyu, G. Pedrini, W. Osten, G. Barbastathis, and G. Situ, “Phase imaging with an untrained neural network,” Light: Sci. Appl. 9, 77 (2020). https://doi.org/10.1038/s41377-020-0302-3 have been proposed. Second, it requires the size restriction of the sample in the illuminated field of view for reliable reconstruction,2929. T. Latychevskaia and H.-W. Fink, “Reconstruction of purely absorbing, absorbing and phase-shifting, and strong phase-shifting objects from their single-shot in-line holograms,” Appl. Opt. 54, 3925–3932 (2015). https://doi.org/10.1364/ao.54.003925 which is an important obstacle for application to extended or dense objects. This issue can be overcome by multi-plane phase retrieval,30,3130. N. V. Petrov, J.-B. Perraud, A. Chopard, J.-P. Guillet, O. A. Smolyanskaya, and P. Mounaix, “Terahertz phase retrieval imaging in reflection,” Opt. Lett. 45, 4168–4171 (2020). https://doi.org/10.1364/ol.39793531. A. Chopard, E. Tsiplakova, N. Balbekin, O. Smolyanskaya, J.-B. Perraud, J.-P. Guillet, N. V. Petrov, and P. Mounaix, “Single-scan multiplane phase retrieval with a radiation of terahertz quantum cascade laser,” Appl. Phys. B 128, 63 (2022). https://doi.org/10.1007/s00340-022-07787-x but non-uniform illumination remains a problem.3131. A. Chopard, E. Tsiplakova, N. Balbekin, O. Smolyanskaya, J.-B. Perraud, J.-P. Guillet, N. V. Petrov, and P. Mounaix, “Single-scan multiplane phase retrieval with a radiation of terahertz quantum cascade laser,” Appl. Phys. B 128, 63 (2022). https://doi.org/10.1007/s00340-022-07787-x In recent years, ptychography, which can simultaneously reconstruct the complex-valued distributions of both the illumination probe and the object, has been demonstrated in the THz band.32–3432. L. Valzania, T. Feurer, P. Zolliker, and E. Hack, “Terahertz ptychography,” Opt. Lett. 43, 543–546 (2018). https://doi.org/10.1364/ol.43.00054333. L. Rong, C. Tang, Y. Zhao, F. Tan, Y. Wang, J. Zhao, D. Wang, and M. Georges, “Continuous-wave terahertz reflective ptychography by oblique illumination,” Opt. Lett. 45, 4412–4415 (2020). https://doi.org/10.1364/ol.40050634. L. Rong, F. Tan, D. Wang, Y. Zhang, K. Li, J. Zhao, and Y. Wang, “High-resolution terahertz ptychography using divergent illumination and extrapolation algorithm,” Opt. Lasers Eng. 147, 106729 (2021). https://doi.org/10.1016/j.optlaseng.2021.106729 Since it does not require a reference beam and can image extended samples, it has become an attractive and indispensable imaging tool. A typical realization of ptychography is based on multiple overlapped diffraction patterns through the scan of a localized probe on the object, resulting in a low imaging throughput. Based on a compact and divergent probe and the extrapolation algorithm, the resolution of THz ptychography has reached 178 µm (1.5λ).3434. L. Rong, F. Tan, D. Wang, Y. Zhang, K. Li, J. Zhao, and Y. Wang, “High-resolution terahertz ptychography using divergent illumination and extrapolation algorithm,” Opt. Lasers Eng. 147, 106729 (2021). https://doi.org/10.1016/j.optlaseng.2021.106729 At the present time, the requirement for a “compact probe” has proved to be overly restrictive,3535. T. B. Edo, D. J. Batey, A. M. Maiden, C. Rau, U. Wagner, Z. D. Pešić, T. A. Waigh, and J. M. Rodenburg, “Sampling in x-ray ptychography,” Phys. Rev. A 87, 053850 (2013). https://doi.org/10.1103/physreva.87.053850 and near-field ptychography with extended illumination has been implemented in the visible and x-ray regions.36–4036. M. Stockmar, P. Cloetens, I. Zanette, B. Enders, M. Dierolf, F. Pfeiffer, and P. Thibault, “Near-field ptychography: Phase retrieval for inline holography using a structured illumination,” Sci. Rep. 3, 1927 (2013). https://doi.org/10.1038/srep0192737. A.-L. Robisch and T. Salditt, “Phase retrieval for object and probe using a series of defocus near-field images,” Opt. Express 21, 23345–23357 (2013). https://doi.org/10.1364/oe.21.02334538. A.-L. Robisch, K. Kröger, A. Rack, and T. Salditt, “Near-field ptychography using lateral and longitudinal shifts,” New J. Phys. 17, 073033 (2015). https://doi.org/10.1088/1367-2630/17/7/07303339. S. Jiang, J. Zhu, P. Song, C. Guo, Z. Bian, R. Wang, Y. Huang, S. Wang, H. Zhang, and G. Zheng, “Wide-field, high-resolution lensless on-chip microscopy via near-field blind ptychographic modulation,” Lab Chip 20, 1058–1065 (2020). https://doi.org/10.1039/c9lc01027k40. S. Jiang, C. Guo, P. Song, N. Zhou, Z. Bian, J. Zhu, R. Wang, P. Dong, Z. Zhang, J. Liao, J. Yao, B. Feng, M. Murphy, and G. Zheng, “Resolution-enhanced parallel coded ptychography for high-throughput optical imaging,” ACS Photonics 8, 3261–3271 (2021). https://doi.org/10.1021/acsphotonics.1c01085 When the illumination is an extended plane wave, the lateral translation of the sample only brings the movement of the diffraction pattern without changing at all, which exhibits little diversity. Therefore, a diffuser36,39,4036. M. Stockmar, P. Cloetens, I. Zanette, B. Enders, M. Dierolf, F. Pfeiffer, and P. Thibault, “Near-field ptychography: Phase retrieval for inline holography using a structured illumination,” Sci. Rep. 3, 1927 (2013). https://doi.org/10.1038/srep0192739. S. Jiang, J. Zhu, P. Song, C. Guo, Z. Bian, R. Wang, Y. Huang, S. Wang, H. Zhang, and G. Zheng, “Wide-field, high-resolution lensless on-chip microscopy via near-field blind ptychographic modulation,” Lab Chip 20, 1058–1065 (2020). https://doi.org/10.1039/c9lc01027k40. S. Jiang, C. Guo, P. Song, N. Zhou, Z. Bian, J. Zhu, R. Wang, P. Dong, Z. Zhang, J. Liao, J. Yao, B. Feng, M. Murphy, and G. Zheng, “Resolution-enhanced parallel coded ptychography for high-throughput optical imaging,” ACS Photonics 8, 3261–3271 (2021). https://doi.org/10.1021/acsphotonics.1c01085 or longitudinal shifts of the sample37,3837. A.-L. Robisch and T. Salditt, “Phase retrieval for object and probe using a series of defocus near-field images,” Opt. Express 21, 23345–23357 (2013). https://doi.org/10.1364/oe.21.02334538. A.-L. Robisch, K. Kröger, A. Rack, and T. Salditt, “Near-field ptychography using lateral and longitudinal shifts,” New J. Phys. 17, 073033 (2015). https://doi.org/10.1088/1367-2630/17/7/073033 are introduced to provide measurement diversity. Extended illumination has several advantages. The field of view (FOV) is large, which improves the imaging throughput. Especially in the on-chip structure, the entire sensor area can be used as the imaging FOV. With a spatially confined probe, it is difficult to collect the low-frequency components in the bright-field and the dark-field features lying at high scattering angles at the same time. Conversely, in the extended illumination geometry, the whole detector is illuminated and the required dynamic range for the detector is reduced. Nevertheless, extended illumination has not been adopted in THz ptychography.In this paper, by combining the idea of multi-plane phase retrieval and ptychography, we demonstrate subwavelength resolution, full-field, and lensless THz ptychography. Two contributions are reported: (1) In order to suppress the infrared noise during data acquisition, an optical chopper is introduced and an algorithm based on digital phase-locked is proposed to deal with the raw data, which simplifies the process compared to the conventional method of background subtraction. (2) The full-field, lensless ptychography with extended illumination by longitudinal scanning is proposed, along with a reconstruction algorithm based on the single-beam multiple-intensity phase reconstruction (SBMIR)4141. G. Pedrini, W. Osten, and Y. Zhang, “Wave-front reconstruction from a sequence of interferograms recorded at different planes,” Opt. Lett. 30, 833–835 (2005). https://doi.org/10.1364/ol.30.000833 and the extended ptychographical iterative engine (ePIE).4242. A. M. Maiden and J. M. Rodenburg, “An improved ptychographical phase retrieval algorithm for diffractive imaging,” Ultramicroscopy 109, 1256–1262 (2009). https://doi.org/10.1016/j.ultramic.2009.05.012 Different from the typical ptychography, the diversity of the diffraction pattern is provided by longitudinal shifts of the sample instead of its lateral movements, and an extended illumination rather than a localized probe is adopted to realize full-field recording. This implementation requires fewer diffraction patterns, which improves the imaging throughput by nearly an order of magnitude over conventional THz ptychography while maintaining a large FOV for imaging. The proposed method does not limit the sample size as in-line holography does, while it mitigates the problem of uneven illumination compared to multi-plane phase retrieval. Thanks to the lensless, single-beam mode, and full-field illumination, this approach can achieve the highest NA by placing the object as close as possible to the detector and allows us to use the entire sensor area as the imaging FOV. We verify it on the extended samples, and the experiment on the USAF 1951 shows that the lateral resolution achieves 88 µm (0.74λ) at 2.52 THz. With these features, this method is more practical than previous solutions and helps to promote the application of THz imaging.

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