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Published in Anna M. Doro-on, Handbook of Systems Engineering and Risk Management in Control Systems, Communication, Space Technology, Missile, Security and Defense Operations, 2023
According to Reddy (2009), quantum cascade lasers (QCLs) are a new class of semiconductor lasers that are unipolar and can work effectively in mid-infrared and terahertz spectral regions, even at room temperatures. QCLs are thus ideal light sources for probing the strong fundamental vibration-rotational absorption bands of most gaseous molecules in nature, which have tell-tale spectral finger prints in these spectral regions (Reddy 2009). Combined with sensitive laser spectroscopic techniques like cavity ringdown spectroscopy (CRDS) and photoacoustic spectroscopy (PAS), QCLs provide ultra-sensitive detection capability to meet the challenge of standoff detection of lower concentration of IEDs and other hazardous chemicals in the field environment (Reddy 2009). Because of its low interference and non-ionizing characteristics, terahertz imaging is expected to be a powerful technique for safe, in vivo medical imaging, where the use of a longer wavelength allows for deeper penetration in the investigated material (Reddy 2009). QCLs in the mid-infrared to far-infrared, including at THz region, are going to play a pivotal role in the investigation of new science and revisiting the most viable technologies (Reddy 2009).
Review of Nanoscale Spectroscopy in Medicine
Published in Sarhan M. Musa, Nanoscale Spectroscopy with Applications, 2018
Chintha C. Handapangoda, Saeid Nahavandi, Malin Premaratne
Different imaging parameters, such as the pulse height, pulse width, and time delay, can be used to construct terahertz images. In addition, the time post-pulse, which is the ratio of the electric field amplitude at some time after the pulse minimum to the electric field amplitude minimum, can be used (Woodward et al. 2003). The time at which the electric field is sampled after the pulse minimum can be adjusted to maximize the image contrast (Bowen 2011). Oh et al. (2009) have shown that gold nanorods can be used as nanoparticle contrast agents to increase the terahertz contrast of cancer cells (Bowen 2011). One disadvantage of terahertz imaging is the limited penetration depth into body tissues due to the high water content (Bowen 2011). At 0.5 THz, the penetration depth into skin is around 0.5 mm. However, the penetration depth into fatty tissue (typical of breast tissue) is much higher, around 6.5 mm (Bowen 2011). Nevertheless, an inter op era five terahertz probe can be used during surgery to indicate the extent of a tumor, as a high proportion of cancers lie in the outer regions of organs (Ashworth et al. 2008, Bowen 2011). The introduction of image and spectral artefacts is a complication associated with terahertz imaging and spectroscopy of inhomogeneous samples (Bowen 2011).
Imaging Based on Absorption and Ion Detection Methods
Published in Helmut H. Telle, Ángel González Ureña, Laser Spectroscopy and Laser Imaging, 2018
Helmut H. Telle, Ángel González Ureña
Terahertz imaging has been applied to a vast range of medical applications, ranging from the detection of cancers (breast, colon, skin, etc.), to monitoring of phenomena in the skin, to detecting the onset of dental caries, to name but a few. A wider insight into terahertz imaging for applications in biology and medicine and a thorough introduction into the underlying physical processes and practical instrumentational issues can be found, e.g., in the book by Yin et al. (2012). Here, the two examples described in the following sections can give only a small flavor of the versatility of biomedical terahertz imaging.
Multi-functional graphene-based tunable beam splitter in terahertz band
Published in Waves in Random and Complex Media, 2022
Beam splitter is an important element that has been widely applied in various optical equipment, such as optical switch [1,2], magneto-optical data storage [3], imaging systems [4,5], sensors [6–8], etc. Among which, the beam splitter with one-port output, also known as the polarizer, is the key element of large-scale photonic integrated circuits [9], and the dual-port and three-port output beam splitter has been demonstrated that can be applied in signal processing [10,11], fiber laser [12], pulse detection [13], and so on. Recently, due to the simple structure and outstanding performance of the micro-nano gratings, the beam splitters based on grating structure [14–16] have attracted attentions from researchers around the world. Simultaneously, owing to the unique characteristics exhibited in terahertz band (frequency range of 0.1–10 THz), e.g. good transparency to cloth and plastic products, excellent reflection performance to metal materials, and extremely low damage to human health, terahertz imaging technology has been greatly sought after by many researchers around the world. Refs. [17,18] depict several optical devices for terahertz imaging at 2.52 THz, which is the radiation frequency of far-infrared CO2 lasers [18]. Ref. [17] carried out a SIFIR-50 from Coherent, Inc. as the THz source. Pumping by a CO2 laser, it can generate cw THz output and operate stably at 2.52 THz. Grating-based terahertz imaging systems have also been widely proposed in recent years [19]. For example, the authors in Ref. [19] proposed the terahertz referenceless wavefront sensing by means of computational shear-interferometry, in which the grating-based beam splitter structure plays an important part in the whole system. Therefore, it is necessary to propose a high-performance grating-based beam splitter.