Review

A review of common-path off-axis digital holography: towards high stable optical instrument manufacturing
Jiwei Zhang, Siqing Dai, Chaojie Ma, Teli Xi, Jianglei Di, et al.
Published Published online: 01 August 2021 , doi: 10.37188/lam.2021.023

Digital holography possesses the advantages of wide-field, non-contact, precise, and dynamic measurements for the complex amplitude of object waves. Today, digital holography and its derivatives have been widely applied in interferometric measurements, three-dimensional imaging, and quantitative phase imaging, demonstrating significant potential in the material science, industry, and biomedical fields, among others. However, in conventional off-axis holographic experimental setups, the object and reference beams propagate in separated paths, resulting in low temporal stability and measurement sensitivity. By designing common-path configurations where the two interference beams share the same or similar paths, environmental disturbance to the two beams can be effectively compensated. Therefore, the temporal stability of the experimental setups for hologram recording can be significantly improved for time-lapsing measurements. In this review, we categorise the common-path models as lateral shearing, point diffraction, and other types based on the different approaches to generate the reference beam. Benefiting from compact features, common-path digital holography is extremely promising for the manufacture of highly stable optical measurement and imaging instruments in the future.

Review of laser powder bed fusion (LPBF) fabricated Ti-6Al-4V: process, post-process treatment, microstructure, and property
Sheng Cao, Yichao Zou, Chao Voon Samuel Lim, Xinhua Wu
Published Published online: 01 July 2021 , doi: 10.37188/lam.2021.020

Laser powder bed fusion (LPBF) is a timely important additive manufacturing technique that offers many opportunities for fabricating three-dimensional complex shaped components at a high resolution with short lead times. This technique has been extensively employed in manufacturing Ti-6Al-4V parts for aerospace and biomedical applications. However, many challenges, including poor surface quality, porosity, anisotropy in microstructure and property, and difficulty in tailoring microstructure, still exist. In this paper, we review the recent progress in post-process treatment and its influence on the microstructure evolution and material performance, including tensile, fatigue, fracture toughness, creep, and corrosion properties. The contradictions in simultaneously achieving high strength/ductility and strength/fracture toughness/creep resistance have been identified. Furthermore, research gaps in understanding the effects of the emerging bi-modal microstructure on fatigue properties and fracture toughness require further investigation.

Multi-material multi-photon 3D laser micro- and nanoprinting
Liang Yang, Frederik Mayer, Uwe H. F. Bunz, Eva Blasco, Martin Wegener
Published Published online: 01 May 2021 , doi: 10.37188/lam.2021.017
Three-dimensional (3D) laser micro- and nanoprinting based upon multi-photon absorption has made its way from early scientific discovery to industrial manufacturing processes, e.g., for advanced microoptical components. However, so far, most realized 3D architectures are composed of only a single polymeric material. Here, we review 3D printing of multi-materials on the nano- and microscale. We start with material properties that have been realized, using multi-photon photoresists. Printed materials include bulk polymers, conductive polymers, metals, nanoporous polymers, silica glass, chalcogenide glasses, inorganic single crystals, natural polymers, stimuli-responsive materials, and polymer composites. Next, we review manual and automated processes achieving dissimilar material properties in a single 3D structure by sequentially photo-exposing multiple photoresists as 3D analogs of 2D multicolor printing. Instructive examples from biology, optics, mechanics, and electronics are discussed. An emerging approach – without counterpart in 2D graphical printing – prints 3D structures combining dissimilar material properties in one 3D structure by using only a single photoresist. A controlled stimulus applied during the 3D printing process defines and determines material properties on the voxel level. Change of laser power and/or wavelength, or application of quasi-static electric fields allow for the seamless manipulation of desired materials properties.
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: 01 February 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.
Review of geometric error measurement and compensation techniques of ultra-precision machine tools
Zongchao Geng, Zhen Tong, Xiangqian Jiang
Published Published online: 01 April 2021 , doi: 10.37188/lam.2021.014
Inevitable machine motion errors change the cutting tool trajectory and degrade the machined surface quality. Compared to the mature error measurement technologies developed for traditional precision CNC machine tools, the increasing use of ultra-precision machine tools (UPMTs) has shown some distinctive characteristics in error modelling, measurement, and compensation. This paper attempts to summarise state-of-the-art research in the calibration of geometric errors of UPMTs. A general routine for a UPMT error calibration is proposed in this literature review. Various error modelling methods, instruments, and measurement methods applicable to the geometric error measurement of both the linear and rotary axes are discussed using typical case studies. With respect to these achievements, there is a real concern regarding the reproducibility of measurement sensors used for the calibration of UPMTs and it remains challenging to decompose the volumetric motion error of UPMTs. Owing to the high flexibility in practice, trial cutting and a sensitivity analysis-based error measurement and compensation provide a promising solution to achieve a fast UPMT calibration.
Extracellular scaffold design for ultra-soft microtissue engineering
Jiaqi Wang, Xiaowei Tang, Zitian Wang, Jiawei Li, Shaohua Ma
Published Published online: 01 February 2021 , doi: 10.37188/lam.2021.011
Soft and ultra-soft extracellular scaffolds constitute a major fraction of most human internal organs, except for the skeletal system. Modelling these organs in vitro requires a comprehensive understanding of their native scaffolding materials and proper engineering approaches to manufacture tissue architectures with microscale precision. This review focuses on the properties of soft and ultra-soft scaffolds, including their interactions with cells, mechanical properties (e.g. viscoelasticity), and existing microtissue engineering techniques. It also summarises challenges presented by the conflict between the properties of the materials demanded by cell behaviours and the capacities of engineering techniques. It proposes that leveraging the engineering ability of soft and ultra-soft scaffolds will promote therapeutic advances and regenerative medicine.
Metasurfaces for manipulating terahertz waves
Xiaofei Zang, Bingshuang Yao, Lin Chen, Jingya Xie, Xuguang Guo, et al.
Published Published online: 01 February 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.