Science and technologies based on terahertz frequency electromagnetic radiation (100 GHz–30 THz) have developed rapidly over the last 30 years. For most of the 20th Century, terahertz radiation, then referred to as sub-millimeter wave or far-infrared radiation, was mainly utilized by astronomers and some spectroscopists. Following the development of laser based terahertz time-domain spectroscopy in the 1980s and 1990s the field of THz science and technology expanded rapidly, to the extent that it now touches many areas from fundamental science to 'real world' applications. For example THz radiation is being used to optimize materials for new solar cells, and may also be a key technology for the next generation of airport security scanners. While the field was emerging it was possible to keep track of all new developments, however now the field has grown so much that it is increasingly difficult to follow the diverse range of new discoveries and applications that are appearing. At this point in time, when the field of THz science and technology is moving from an emerging to a more established and interdisciplinary field, it is apt to present a roadmap to help identify the breadth and future directions of the field. The aim of this roadmap is to present a snapshot of the present state of THz science and technology in 2017, and provide an opinion on the challenges and opportunities that the future holds. To be able to achieve this aim, we have invited a group of international experts to write 18 sections that cover most of the key areas of THz science and technology. We hope that The 2017 Roadmap on THz science and technology will prove to be a useful resource by providing a wide ranging introduction to the capabilities of THz radiation for those outside or just entering the field as well as providing perspective and breadth for those who are well established. We also feel that this review should serve as a useful guide for government and funding agencies.

https://iopscience.iop.org/article/10.1088/1361-6463/50/4/043001/pdf

The 2017 terahertz science and technology roadmap

The 2016 terahertz science and technology roadmap

Terahertz (THz) imaging can see through otherwise opaque materials. However, because of the long wavelengths of THz radiation (λ = 400 μm at 0.75 THz), far-field THz imaging techniques suffer from low resolution compared to visible wavelengths. We demonstrate noninvasive, near-field THz imaging with subwavelength resolution. We project a time-varying, intense (>100 μJ/cm2) optical pattern onto a silicon wafer, which spatially modulates the transmission of synchronous pulse of THz radiation. An unknown object is placed on the hidden side of the silicon, and the far-field THz transmission corresponding to each mask is recorded by a single-element detector. Knowledge of the patterns and of the corresponding detector signal are combined to give an image of the object. Using this technique, we image a printed circuit board on the underside of a 115-μm-thick silicon wafer with ~100-μm (λ/4) resolution. With subwavelength resolution and the inherent sensitivity to local conductivity, it is possible to detect fissures in the circuitry wiring of a few micrometers in size. THz imaging systems of this type will have other uses too, where noninvasive measurement or imaging of concealed structures is necessary, such as in semiconductor manufacturing or in ex vivo bioimaging.

Noninvasive, near-field terahertz imaging of hidden objects using a single-pixel detector.

Terahertz time-domain spectroscopy (THz-TDS) is a powerful technique for material’s characterization and process control. It has been used for contact-free conductivity measurements of metals, semiconductors, 2D materials, and superconductors. Furthermore, THz-TDS has been used to identify chemical components such as amino acids, peptides, pharmaceuticals, and explosives, which makes it particularly valuable for fundamental science, security, and medical applications. This tutorial is intended for a reader completely new to the field of THz-TDS and presents a basic understanding of THz-TDS. Hundreds of articles and many books can be consulted after reading this tutorial. We explore the basic concepts of TDS and discuss the relationship between temporal and frequency domain information. We illustrate how THz radiation can be generated and detected, and we discuss common noise sources and limitations for THz-TDS. This tutorial concludes by discussing some common experimental scenarios and explains how THz-TDS measurements can be used to identify materials, determine complex refractive indices (phase delay and absorption), and extract conductivity.

Tutorial: An introduction to terahertz time domain spectroscopy (THz-TDS)

In order to store a graph or digraph in a computer, we need something other than the diagram or the formal definition. This something is the adjacency matrix, a matrix of O’s and l’s. The l’s correspond to the arcs of the digraph. Certain matrix operations will be seen to correspond to digraph concepts.

Graphs and Matrices

The terahertz region lies between the microwave and infrared regions of the electromagnetic spectrum such that it is strongly attenuated by water and very sensitive to water content. Terahertz radiation has very low photon energy and thus it does not pose any ionization hazard for biological tissues. Because of these characteristic properties, there has been an increasing interest in terahertz imaging and spectroscopy for biological applications within the last few years and more and more terahertz spectra are being reported, including spectroscopic studies of cancer. The presence of cancer often causes increased blood supply to affected tissues and a local increase in tissue water content may be observed: this acts as a natural contrast mechanism for terahertz imaging of cancer. Furthermore the structural changes that occur in affected tissues have also been shown to contribute to terahertz image contrast. This paper introduces terahertz technology and provides a short review of recent advances in terahertz imaging and spectroscopy techniques. In particular investigations relating to the potential of terahertz imaging and spectroscopy for cancer diagnosis will be highlighted.

The potential of terahertz imaging for cancer diagnosis: A review of investigations to date

As investigations into potential applications of terahertz technology grow, there is an increasing need for improved terahertz optical components such as polarizers. To determine the optical properties of a sample accurately, the polarization properties of the light must also be known accurately. Many terahertz emitters will have both horizontal and vertical polarization components and often assumptions are made about device characteristics without measuring them-even the position of excitation beam on the photoconductive emitter can affect the resulting terahertz electric field and so the exact optical properties of a given device will vary depending on how they are configured. Polarizers operating at terahertz frequencies can be used to characterize the electric field accurately or remove unwanted components as long as the polarizer is of sufficiently high performance. In this paper we review the key properties of polarizers and look at recent advances in their design and development at terahertz frequencies.

Advances in Polarizer Technology for Terahertz Frequency Applications

Social media becomes increasingly popular among members of the public. The emergence of this new trend in the twenty-first century raises new opportunities for government agencies to extend their community networks for their operations. Here, we present a case study on how the Hong Kong Police Force should develop its social media public relations and policing strategies. In recent years, there is a growing trend that some opinions form quickly through social media with its quick viral cycle in Hong Kong. There are occasions where the conflicts between the Hong Kong Police Force and some members of the public are results of communication breakdown. Hence, it is becoming increasingly important for the law enforcement agencies, such as police, to properly engage with members of the public for public relations purpose. Plus, there have been a number of instances in the past few years, which materials involving confidential information related to the government agencies have been uploaded onto Web sites and blogs in Hong Kong. These situations do not only generate a lot of discussions among the online community in Hong Kong, but also engender public discussions from different angles as well as the safety of law enforcement officers. In this research, we use balanced scorecard to analyze the alternative strategies that the Hong Kong Police Force can use in social media. Based on our analysis, we develop strategic approaches, which are useful for law enforcement agencies and government agencies to develop their social media management and engagement policies.

Engaging and Developing the Community Through Social Media: A Pragmatic Analysis in Policing Context in Hong Kong

Purpose – This study aims to provide an analysis of Hong Kong's strengths and weaknesses in developing its technology and innovation industry. Design/methodology/approach – It briefly discussed the “extended open innovation” model on the basis of Chesbrough's “open innovation” model to explicitly highlight the elements associated with different stages throughout the whole spectrum of innovation processes. Findings – The model is then illustrated with Hong Kong's unique experience to gain insights for various stakeholders on how open innovation could be used beyond research and development activities and how Hong Kong could benefit from this paradigm shift. Originality/value – The extended open innovation model can be used as a framework to address the development of the technology and innovation industry.

Strengths and weaknesses of Hong Kong's technology and innovation industry with reference to the extended open innovation model

This paper studied the government Websites of 47 member nations of the United Nations in Asia. To investigate the extent of information availability and information reuse among these websites, data on number of pages, number of pages receiving incoming hyperlinks and number of pages containing outgoing hyperlinks of the government websites of each nation were gathered from major commercial search engines. The correlations of information availability and reuse with economics indicators, information technology advancement indicators, and democracy level indicators of these nations were examined. We further analyzed the information reuse within the government Websites by examining the hyperlinks interlinking among the Websites of all selected nations. We considered these government Websites as a hyperlinked network and used network analysis and visualization techniques to analyze and visualize the network structure. The results identified the role and significance of each nation in this government information network.

Calvin Chun Yu

Papers

The potential of terahertz imaging for cancer diagnosis: A review of investigations to date

Advances in Polarizer Technology for Terahertz Frequency Applications

Engaging and Developing the Community Through Social Media: A Pragmatic Analysis in Policing Context in Hong Kong

Strengths and weaknesses of Hong Kong's technology and innovation industry with reference to the extended open innovation model

Information Reuse among Government Websites in Asian Countries