Abstract-Terahertz Time-Domain Polarimetry for Principal Optical Axes of Anisotropic Crystals

 

Alexander Mamrashev, Fedor Minakov, Nazar Nikolaev, Valery Antsygin, 

https://www.mdpi.com/2304-6732/8/6/213/pdf

We propose a method for measuring the terahertz properties for two principal optical axes of anisotropic crystals without optical activity using terahertz time-domain spectroscopy (THzTDS). The method put forward in this paper utilizes the inherent polarization sensitivity of the THz-TDS electro-optic detection system. We demonstrate the practical application of the method by measuring the temperature dependence of the refractive index and the absorption coefficient of a lithium triborate crystal for three optical axes.

Abstract-Enhancing Absorption Bandwidth through Vertically Oriented Metamaterials

Aaron J. Pung,  Michael D. Goldflam,  D. Bruce Burckel,  Igal Brener, Michael B. Sinclair, Salvatore Campione

https://www.mdpi.com/2076-3417/9/11/2223

Metamaterials research has developed perfect absorbers from microwave to optical frequencies, mainly featuring planar metamaterials, also referred to as metasurfaces. In this study, we investigated vertically oriented metamaterials, which make use of the entire three-dimensional space, as a new avenue to widen the spectral absorption band in the infrared regime between 20 and 40 THz. Vertically oriented metamaterials, such as those simulated in this work, can be experimentally realized through membrane projection lithography, which allows a single unit cell to be decorated with multiple resonators by exploiting the vertical dimension. In particular, we analyzed the cases of a unit cell containing a single vertical split-ring resonator (VSRR), a single planar split-ring resonator (PSRR), and both a VSRR and PSRR to explore intra-cell coupling between resonators. We show that the additional degrees of freedom enabled by placing multiple resonators in a unit cell lead to novel ways of achieving omnidirectional super absorption. Our results provide an innovative approach for controlling and designing engineered nanostructures.

Abstract-Multi-functional Device with Switchable Functions of Absorption and Polarization Conversion at Terahertz Range

Lin Peng, Xing Jiang, Si-min Li,

https://nanoscalereslett.springeropen.com/articles/10.1186/s11671-018-2811-z

Terahertz electromagnetic (EM) wave components usually have a single function, such as they can only convert the polarization state of an incident wave or absorb the incident energy, which would be a limitation for their applications. To make a breakthrough, a multi-functional device (MFD) is proposed in this paper, and it is capable of switching between absorption mode and polarization conversion mode. The device has a low-profile and simple structure, and it is constructed by graphene-based absorbing metasurface (AM) and gold-based polarization conversion metasurface (PCM). By controlling the chemical potential (μc) of the graphene, the leading role is transferred between the AM and the PCM, which leads to steerable absorption and polarization conversion (PC) modes. For the PC mode, the simulated polarization conversion ratio (PCR) is larger than 0.9 in the 2.11–3.63-THz band (53.0% at 2.87 THz). For the absorption mode, the simulated absorptivity is larger than 80% in the 1.59–4.54-THz band (96.4% at 3.06 THz). The physical mechanisms and operating characteristics of the MFD are discussed. This research has potential applications in terahertz imaging, sensors, photodetectors, and modulators.

Abstract-Frequency Modulation and Absorption Improvement of THz Micro-bolometer with Micro-bridge Structure by Spiral-Type Antennas

• Jun Gou, 
• Qingchen Niu, 
• Kai Liang, 
• Jun Wang, Yadong Jian,

https://link.springer.com/article/10.1186/s11671-018-2484-7

Antenna-coupled micro-bridge structure is proven to be a good solution to extend infrared micro-bolometer technology for THz application. Spiral-type antennas are proposed in 25 μm × 25 μm micro-bridge structure with a single separate linear antenna, two separate linear antennas, or two connected linear antennas on the bridge legs, in addition to traditional spiral-type antenna on the support layer. The effects of structural parameters of each antenna on THz absorption of micro-bridge structure are discussed for optimized absorption of 2.52 THz wave radiated by far infrared CO2 lasers. The design of spiral-type antenna with two separate linear antennas for wide absorption peak and spiral-type antenna with two connected linear antennas for relatively stable absorption are good candidates for high absorption at low absorption frequency with a rotation angle of 360*n (n = 1.6). Spiral-type antenna with extended legs also provides a highly integrated micro-bridge structure with fast response and a highly compatible, process-simplified way to realize the structure. This research demonstrates the design of several spiral-type antenna-coupled micro-bridge structures and provides preferred schemes for potential device applications in room temperature sensing and real-time imaging.

Abstract-Grating-coupled surface plasmons on InSb: a versatile platform for terahertz plasmonic sensing (Conference Presentation)

Diyar Talbayev, Shuai Lin

Tulane Univ. (United States)

Jiangfeng Zhou, Khagendra Bhattarai

Univ. of South Florida (United States)

Proc. SPIE 10210, Next-Generation Spectroscopic Technologies X, 102100X (June 9, 2017); doi:10.1117/12.2263717

http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=2632318

Detection and identification of molecular materials based on their THz frequency vibrational resonances remains an open technological challenge. The need for such technology is illustrated by its potential uses in explosives detection (e.g., RDX) or identification of large biomolecules based on their THz-frequency vibrational fingerprints. The prevailing approaches to THz sensing often rely on a form of waveguide spectroscopy, either utilizing geometric waveguides, such as metallic parallel plate, or plasmonic waveguides made of structured metallic surfaces with sub-wavelength corrugation. The sensitivity of waveguide-based sensing devices is derived from the long (1 cm or longer) propagation and interaction distance of the THz wave with the analyte. We have demonstrated that thin InSb layers with metallic gratings can support high quality factor “true” surface plasmon (SP) resonances that can be used for THz plasmonic sensing. We find two strong SP absorption resonances in normal-incidence transmission and investigate their dispersion relations, dependence on InSb thickness, and the spatial distribution of the electric field. The sensitivity of this approach relies on the frequency shift of the SP resonance when the dielectric function changes in the immediate vicinity of the sensor, in the region of deeply sub-wavelength thickness. Our computational modeling indicates that the sensor sensitivity can exceed 0.25 THz per refractive index unit. One of the SP resonances also exhibits a splitting when tuned in resonance with a vibrational mode of an analyte, which could lead to new sensing modalities for the detection of THz vibrational features of the analyte.

 © (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Abstract-Tunable terahertz coherent perfect absorption in a monolayer graphene

Yuancheng Fan, Fuli Zhang, Qian Zhao, Zeyong Wei, and Hongqiang Li  »View Author Affiliations

Optics Letters, Vol. 39, Issue 21, pp. 6269-6272 (2014)

http://dx.doi.org/10.1364/OL.39.006269

http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-39-21-6269

Coherent perfect absorber (CPA) was proposed as the time-reversed counterpart to laser: a resonator containing lossy medium instead of gain medium can absorb the coherent optical fields completely. Here, we exploit a monolayer graphene to realize the CPA in a nonresonant manner. It is found that quasi-CPA point exists in the terahertz regime for suspending monolayer graphene, and the CPA can be implemented with the assistance of proper phase modulation among two incident beams at the quasi-CPA frequencies. The graphene-based CPA is found of broadband angular selectivity: CPA point splits into two frequency bands for the orthogonal s and p polarizations at oblique incidence, and the two bands cover a wide frequency range starting from zero frequency. Furthermore, the coherent absorption can be tuned substantially by varying the gate-controlled Fermi energy. The findings of CPA with nonresonant graphene sheet can be generalized for potential applications in terahertz/infrared detections and signal processing with two-dimensional optoelectronic materials.

© 2014 Optical Society of America