Abstract-Fast terahertz reflective confocal scanning imaging with a quantum cascade laser and a photodetector

F. C. Qiu, Y. Z. Fu, C. Wang, Z. Y. Tan, Z. L. FuW. J. Wan, J. C. Cao

https://link.springer.com/article/10.1007/s00340-019-7198-8

For the terahertz imaging systems, the fast detection of terahertz light is deemed as a key technology. We present a fast terahertz reflective confocal scanning imaging system employing a fast terahertz quantum-well photodetector (QWP) and a fast rotating translational platform. The excellent performance of the terahertz QWP indicates that the device can rapidly detect the 4.3 THz radiation generated from a pulsed electrically pumped terahertz quantum cascade laser, which is used as the terahertz source of the imaging system. Two 200 μm pinholes are placed in the two focuses to filter out the scattered light and improve the resolution of the imaging system, we achieve a lateral resolution better than 110 μm and an axial resolution of about 320 μm. The terahertz two-dimension images of some objects are obtained within 5 s with a high contrast. The three-dimensional sections of the object demonstrate the great axial selectivity of the terahertz imaging system.

Abstract-Measurement of Absorption Coefficient of Paraformaldehyde and Metaldehyde with Terahertz Spectroscopy

J. Zhang, T. Xia, Q. Chen, Q. Sun, Y. Deng, C. Wang, 

https://link.springer.com/article/10.1007/s10812-018-0616-6

The characteristic absorption spectra of paraformaldehyde and metaldehyde in the terahertz frequency region are obtained by terahertz time-domain spectroscopy (THz-TDS). In order to reduce the absorption of terahertz (THz) wave by water vapor in the air and the background noise, the measurement system was filled with dry air and the measurements were conducted at the temperature of 24°C. Meanwhile, the humidity was controlled within 10% RH. The THz frequency domain spectra of samples and their references from 0 to 2.5 THz were analyzed via Fourier transform. The refractive index and absorption coefficients of the two aldehydes were calculated by the model formulas. From 0.1 to 2.5 THz, there appear two weak absorption peaks at 1.20 and 1.66 THz in the absorption spectra of paraformaldehyde. Only one distinct absorption peak emerges at 1.83 THz for metaldehyde. There are significant differences between the terahertz absorption coefficients of paraformaldehyde and metaldehyde, which can be used as "fingerprints" to identify these substances. Furthermore, the relationship between the average absorption coefficients and mass concentrations was investigated and the average absorption coefficient–mass concentration diagrams of paraformaldehyde and metaldehyde were shown. For paraformaldehyde, there is a linear relationship between the average absorption coefficient and the natural logarithm of mass concentration. For metaldehyde, there exists a simpler linear relationship between the average absorption coefficient and the mass concentration. Because of the characteristics of THz absorption of paraformaldehyde and metaldehyde, the THz-TDS can be applied to the qualitative and quantitative detection of the two aldehydes to reduce the unpredictable hazards due to these substances.

Abstract-Multipath propagation channel modeling and capacity analysis for terahertz indoor communications

C. Liu, C. Wang, and J. C. Cao

https://www.osapublishing.org/jot/abstract.cfm?uri=jot-84-1-53&origin=search

The eventual practical deployment of a terahertz indoor communication system for ultra-high-speed wireless links requires a unified and proper channel model. By considering the peculiarity of terahertz radiation, we develop a deterministic multipath propagation channel model based on Kirchhoff scattering theory and ray tracing techniques, which incorporates the propagation models for the line-of-sight, reflected, and scattered paths. This work also provides a novel evaluation methodology to quantify the proposed channel model for system performance investigation. Numerical simulations are carried out with experimental measurements. The results demonstrate the validity of the proposed model and reveal the importance of the non-line-of-sight propagation paths, especially the scattered rays. Spatial characteristics of the terahertz propagation have also been fully investigated for the diversity antenna steering and beamforming schemes. Finally, channel capacity and delay spread effects are evaluated and analyzed in detail, and huge potential on ultra-high-speed wireless communications over 20 Gbps has been demonstrated in the terahertz band for indoor scenarios.

© 2017 Optical Society of America

Abstract-Extended mode in blocked impurity band detectors for terahertz radiation detection

K. S. Liao¹, N. Li¹, C. Wang¹, L. Li¹, Y. L. Jing¹, J. Wen¹, M. Y. Li¹, H. Wang¹,X. H. Zhou^1,a), Z. F. Li¹ and W. Lu^1,b)
 http://scitation.aip.org/content/aip/journal/apl/105/14/10.1063/1.4897275
a) Electronic mail: xhzhou@mail.sitp.ac.cn
b) Electronic mail: luwei@mail.sitp.ac.cn
Appl. Phys. Lett. 105, 143501 (2014); http://dx.doi.org/10.1063/1.4897275

We demonstrate the existence of an interfacial barrier in blocked impurity band (BIB) detectorsusing temperature-dependent dark current and corresponding theoretical calculations. Considering the effects of the interfacial barrier, the calculated photoresponse is in good agreement with the experimental results. A dual-excitation model, including the direct excitation over the full barrier and excitation to the band minimum with subsequent tunneling into the blocking layer, is proposed to quantitatively explain the observed photoresponse extension. A concept of extended-mode detection is developed to suggest the option for some selective photoresponse in the terahertz region and open the possibility of extending BIB photoresponse to lower frequency.