Holography technologies have been rapidly evolving in the recent years due to surprising crossover of concepts and methods across different fields. This special issue was planned to capture some of the latest advances in the broad area of holography. We received contributions from leading researchers across the globe on all the important facets of holography technologies with a total of 85 authors. One of the significant aspects of this special issue is the roadmap type articles on two main branches of holography and imaging, namely incoherent digital holography (IDH) [1] and chaos-inspired imaging technologies (CI2-Tech) [2].

The roadmap on IDH covered all the important subfields with a valuable historical overview of development connecting all the subfields with technology and time. In this roadmap, many top researchers contributed in their respective specialty areas: the basic principles and milestones of optical scanning holography by Zhang and Poon, Fresnel incoherent correlation holography and coded aperture correlation holography (COACH) by Rosen and Anand, compressive computational imaging with Fresnel zone aperture by Wu and Cao, application of phase-shifting interferometry technique to IDH by Tahara, Koujin, Matsuda, Ishii, Kozawa, Okamoto, and Oi, 3D infinite depth of field imaging using bimodal IDH by Nobukawa, holographic camera using geometric phase lens and 4-pol camera by Choi, 3D radiometric temperature measurement using IDH by Imbe and high-speed 3D motion picture by Tahara, Kozawa, Ishii, Okamoto, and Oi, were presented. We believe that this will be a useful material for a freshman to quickly understand the area of IDH and for an expert to review the future challenges [1].

The roadmap on CI2-Tech is fundamentally different from IDH as this area “CI2-Tech” has been newly identified as an area of interest in this special issue due to myriad of publications on this topic recently. Chaos has always been seen as a problem to be minimized if not eliminated in most areas of research. In the recent years, imaging technologies which exploit chaos as a means to enhance imaging capabilities is on the rise. Surprisingly, these techniques were not only powerful but also diverse in methods and applications. Like the roadmap on IDH, the roadmap on CI2-Tech also received contributions from leading researchers across the globe. In this roadmap, both fundamental and applied research was contributed by the researchers: interferenceless COACH by Rosen, COACH with synthetic point spread functions by Rosen, Anand and Juodkazis, optical imaging through turbid media by Xie, Liu, Liang and Zhou, microscopy with chaotic light with regular and single pixel camera and extended depth of imaging through scatterers by Osten, Ludwig, Pedrini, Schindle, Singh, and Takeda, amplitude and phase imaging with random light by Rakesh Kumar Singh and Sarkar, quantitative phase imaging using incoherent light by Baek, Hugonnet, Lee, and Park, deep learning aided imaging through turbid media by Yang and Situ, speckle correlation based imaging and learning based focusing and imaging by Horisaki and super-resolution deep imaging with speckle illumination by Aguiar and Gigan [2].

The other articles published in the special issue were diverse and exciting. The research group led by Juodkazis – Smith, Ng, Han, Katkus, Anand and Glazebrook, reported an interdisciplinary research work connecting computational imaging and advanced manufacturing [3]. The research group led by Forbes consisting of Rodríguez‑Fajardo, Guzman, Mouane,Wamwangi, Sideras‑Haddad and Roux reported a novel interferometry-based topography measurement method that is capable of measuring reflective as well as partially reflective surfaces [4]. A rapid computer generated holography calculation method based on deep learning was reported to overcome the limitations of Gerchberg-Saxton algorithm by the research group led by Ito—Ishii, Shimobaba, Blinder, Birnbaum, Schelkens and Kakue [5]. The research group led by Awatsuji—Inoue, Sasaki, Nishio, and Kubota presented a useful numerical analysis of light-in-flight holography systems [6]. Wavefront analysis in in-line and off-axis holography configurations with a plane wave and conical wave have been compared with a deep learning network by the research group led by Petrov—Khonina, Khorin, Serafimovich, Dzyuba and Georgieva [7]. The performances of de-noising algorithms from the point of noise statistics have been analyzed by Montrésor and Picart [8]. The research group led by Kumar—Dwivedi, Pensia, and Singh reported an interesting application of a portable digital holographic camera to inspect the wear of machine tools [9]. The research group led by Ferraro—Sirico, Miccio, Wang, Memmolo, Xiao, Che, Xin and Pan presented an extensive research on strategies to minimize aberrations in holographic microscopy systems [10]. Mirsky and Shaked reported single shot six-pack holography technique that enables acquisition of six off-axis holograms with improved field of view [11].

We believe that the collection of articles in the special issue will be treasured in holography. We also hope that this special issue will be useful in understanding the latest developments in the area of holography. Before we conclude, we express our sincere thanks to the leading researchers and authors who contributed to the special issue. We thank Cindy Zitter, Fabio Santos and Malwina Strenkowska for their invaluable support. Above all we thank the Editor-in-Chief, Jacob I. Mackenzie of Applied Physics B who has offered his continuous support, encouragement, strategic advices and guidance from the beginning—pre-announcement of the special issue to the current date. Happy Reading!!!

  1. 1.

    Assoc. Prof. Jacob I. Mackenzie (Editor-in-Chief of Applied Physics B)

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We are very proud of our Collections series in Applied Physics B, they provide a focused snapshot of present and past in their topics, a fabulous information source for scientists to come back to when wanting to reprise themselves of the state of the art in the field. This special issue is no exception, it contains two Roadmap feature articles that set out visions for imaging methodologies that will inspire readers to push into new frontiers. These papers are aptly supported by the accompanying contributed papers heralding key advances in various holography and imaging modalities. I’d personally like to congratulate the Editors of this collection and hope our readers benefit from the pearls of knowledge therein.

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    Prof. Peeter Saari (Emeritus Professor, Institute of Physics, University of Tartu)

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Without doubt, this special issue is interesting and useful both for researchers who work in the field of holography and imaging, as well as for PhD students specializing in these fields. But in addition, those who, like me, have dealt with holography at some earlier point in their research careers will also find it enjoyable to read and realize what a tremendous development this field has undergone.

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    Prof. Aydogan Ozcan (Chancellor’s Professor and HHMI Professor, UCLA)

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This is a very exciting special issue on holographic imaging field, which has been going through a true renaissance over the last several years, driven by machine learning and the optimization tools behind deep learning. I believe the readers will very much enjoy going over these recent contributions to holography and its applications to imaging.