Review

Shearography and its applications – a chronological review
Rajpal Sirohi
Published Published online: 01 January 2022 , doi: 10.37188/lam.2022.001
This paper presents the activities in the field of shearography in chronological order and highlights the great potential of this holographic measurement technology. After a brief introduction, the basic theory of shearography is presented. Shear devices, phase-shift arrangements, and multiplexed shearography systems are described. Finally, the application areas where shearography has been accepted and successfully used as a tool are presented.
Holography, and the future of 3D display
Pierre-Alexandre Blanche
Published Published online: 01 December 2021 , doi: 10.37188/lam.2021.028
The pioneers of holography, Gabor, Leith, Upatnieks, and Denisyuk, predicted very early that the ultimate 3D display will be based on this technique. This conviction was rooted on the fact that holography is the only approach that can render all optical cues interpreted by the human visual system. Holographic 3D displays have been a dream chased after for many years, facing challenges on all fronts: computation, transmission, and rendering. With numbers such as 6.6 × 1015 flops required for calculations, 3 × 1015 b/s data rates, and 1.6 × 1012 phase pixels, the task has been daunting. This article is reviewing the recent accomplishments made in the field of holographic 3D display. Specifically, the new developments in machine learning and neural network algorithms demonstrating that computer-generated holograms approach real-time processing. A section also discuss the problem of data transmission that can arguably be solved using clever compression algorithms and optical fiber transmission lines. Finally, we introduce the last obstacle to holographic 3D display, which is is the rendering hardware. However, there is no further mystery. With larger and faster spatial light modulators (SLMs), holographic projection systems are constantly improving. The pixel count on liquid crystal on silicon (LCoS) as well as microelectromechanical systems (MEMS) phase displays is increasing by the millions, and new photonic integrated circuit phased arrays are achieving real progress. It is only a matter of time for these systems to leave the laboratory and enter the consumer world. The future of 3D displays is holographic, and it is happening now.
The language of holography
James D. Trolinger
Published Published online: 01 December 2021 , doi: 10.37188/lam.2021.034
Holography has evolved over its 70+ years of history across widespread and diverse communities and locations. This has produced a complex language that is sometimes inconsistent, confusing, and incorrect, resulting in a general public that often appears widely confused and/or ignorant regarding what holograms actually are and are not. Today’ s holographers employ many types of recording media to record all types of waves, such as light, sound, radar, and simulated waves, and for many different applications and purposes. This study examines the language of holography along with its origins, problems, and possible solutions, while recognizing that certain “errors” in the language are so embedded in society that simple and ideal fixes may be beyond reach. This leaves us with certain questions, as follows. First, can the correct language be restored and should we undertake the task, or are we stuck with every three-dimensional image being called a hologram? Is it our duty to better educate the public with a more useful and consistent language, or should we just go with the flow? In this work, beginning with the insights provided by the pioneers of the field, we attempt to set the stage for a more useful holography language and definitions, specialized so as to be understandable and usable by various audiences, including those interested in non-optical holography. Such knowledge can help the general public to take greater interest and enjoyment in holography; this would also be beneficial to those more involved in holography. Accordingly, this article offers advice for achieving this result.
Deep-nanometer-scale terahertz spectroscopy using a transistor geometry with metal nanogap electrodes
Ya Zhang, Shaoqing Du, Kazuhiko Hirakawa
Published Published online: 01 November 2021 , doi: 10.37188/lam.2021.031
Terahertz (THz) spectroscopy is a powerful tool for characterizing electronic properties and vibronic excitations in various types of solids, liquids, and gases, and it has been extensively used not only for basic science but also for industrial applications. Recently, it has become necessary to understand electronic and vibronic excitations at the nanometer (nm) scale to realize state-of-the-art quantum nanodevices and the synthesis of new molecules for medicine. However, it is challenging to perform THz spectroscopy at the nm scale because the diffraction limit of electromagnetic waves hinders tight focusing of THz radiation at the nm scale. Here, we introduce a novel technique for THz spectroscopy using metal nanogap electrodes. Metal nanogap electrodes integrated with a THz antenna are employed to capture sensing targets, such as a single semiconductor quantum dot (QD) or molecule. Even extremely weak THz absorption can be detected with high sensitivity by measuring the THz-induced photocurrent through the sensing target. Taking advantage of THz-induced photocurrent spectroscopy, the electronic structures in single QDs as well as the vibrational states in single molecules are systematically investigated. The present characterization technology for nm-scale systems provides a key scientific foundation for creating nanodevices with new functions.
Recent Advances in the Fabrication of Highly Sensitive Surface-Enhanced Raman Scattering Substrates: Nanomolar to Attomolar Level Sensing
Shi Bai, Koji Sugioka
Published Published online: 30 June 2021 , doi: 10.37188/lam.2021.013
Surface-enhanced Raman scattering (SERS) techniques have rapidly advanced over the last two decades, permitting multidisciplinary trace analyses and the potential detection of single molecules. This paper provides a comprehensive review of recent progress in strategies for the fabrication of highly sensitive SERS substrates, as a means of achieving sensing on the attomolar scale. The review examines widely used performance criteria, such as enhancement factors. In addition, femtosecond laser-based techniques are discussed as a versatile tool for the fabrication of SERS substrates. Several approaches for enhancing the performance of SERS sensing devices are also introduced, including photo-induced, transient, and liquid-interface assisted strategies. Finally, substrates for real-time sensing and biological applications are also reviewed to demonstrate the powerful analytical capabilities of these methods and the significant progress in SERS research.
Metasurfaces for manipulating terahertz waves
Xiaofei Zang, Bingshuang Yao, Lin Chen, Jingya Xie, Xuguang Guo, et al.
Published Published online: 30 June 2021 , doi: 10.37188/lam.2021.010
Terahertz (THz) science and technology have attracted significant attention based on their unique applications in non-destructive imaging, communications, spectroscopic detection, and sensing. However, traditional THz devices must be sufficiently thick to realise the desired wave-manipulating functions, which has hindered the development of THz integrated systems and applications. Metasurfaces, which are two-dimensional metamaterials consisting of predesigned meta-atoms, can accurately tailor the amplitudes, phases, and polarisations of electromagnetic waves at subwavelength resolutions, meaning they can provide a flexible platform for designing ultra-compact and high-performance THz components. This review focuses on recent advancements in metasurfaces for the wavefront manipulation of THz waves, including the planar metalens, holograms, arbitrary polarisation control, special beam generation, and active metasurface devices. Such ultra-compact devices with unique functionality make metasurface devices very attractive for applications such as imaging, encryption, information modulation, and THz communications. This progress report aims to highlight some novel approaches for designing ultra-compact THz devices and broaden the applications of metasurfaces in THz science.