Abstract-Broadband terahertz spectroscopy of paper and banknotes

Author links open overlay panelGuanhua Ren, Zhongjie Zhu, Jianbing Zhang, Hongwei Zhao, Yanfeng Li, Jiaguang Han,

 

https://www.sciencedirect.com/science/article/abs/pii/S0030401820306842


Paper and paper products banknotes play an important role in daily life. Two terahertz (THz) time-domain spectrometers (TDS) with combined spectral coverage from 0.5 to 10 THz were used to characterize the optical properties of several types of paper and banknotes. We found that the paper and banknotes show remarkable fingerprints in the terahertz regime, which are highly related to the vibrational modes of the main component of paper and banknotes — celluloses. Meanwhile, THz transmission imaging measurements had been performed and shown the capability of imaging the key anti-counterfeit labels of banknotes such as watermarks, security threads and optically variable inks. The presented study here indicates that the THz spectroscopy together with the imaging method could provide a visible, contactless and nondestructive alternative to delineating paper and paper product banknotes.

Abstract-Terahertz spectroscopy of enantiomeric and racemic pyroglutamic acid

Zhipeng Wu, Zhongjie Zhu, Chao Cheng, Jianbing Zhang, Gong Yan, Mingzhu Xu, Shaoping Lia, Hongwei Zhao,

https://www.sciencedirect.com/science/article/pii/S1386142519308996

The low-frequency vibrational properties of D-, L- and DL-pyroglutamic acid (PGA) have been investigated with the terahertz time-domain spectroscopy (THz-TDS) from 0.5 to 4.5 THz. The enantiomers (D- and L-PGA) present similar absorption spectra, while the spectrum of racemate (DL-PGA) is obviously different. The temperature-dependent THz spectra of different PGA were recorded in the range of 293–83 K. The spectral changes during the cooling process suggest that D- and L-PGA undergo a structural phase transition, and no phase change of DL-PGA was found. The results indicate that THz spectroscopy is highly sensitive to the crystal structure of molecules. The density functional theory (DFT) calculations based on the crystal structures were performed to simulate the sample's THz spectra. It was demonstrated that the characteristic resonant absorption peaks of the enantiomeric and racemic PGA in the low-frequency THz region originate from the different vibrations, which corresponding to the specific structures and intermolecular interactions. The conformational diversity and fluctuation may help to understand the properties of PGA in biochemistry and functional material.

Abstract-Far-infrared terahertz properties of L-cysteine and its hydrochloride monohydrate

Guanhua Ren, Siqi Zong, Zhongjie Zhu, Chao Cheng. Ligang Chen,  Lu. Zhou, Jianbing Zhang, Liyuan Liu, Jiaguang Han, Hongwei Zhao

https://www.sciencedirect.com/science/article/pii/S1386142519308662

As the building blocks of proteins, amino acids serve vital metabolic functions in addition to protein synthesis and thus attract enormous interest. Here we reported the far-infrared optical properties of L-cysteine (Lcys) and its hydrochloride monohydrate (LCHM) characterized by terahertz time-domain spectroscopy. The Lcys and LCHM exhibit quite distinct characteristics in the terahertz region due to diverse collective vibrations of the molecules, which is further confirmed by the solid-state density functional theory (DFT) calculations. The presented studies indicate that the intermolecular hydrogen bonds play a critical role in the far-infrared terahertz response of Lcys and LCHM.