Jing Xu's research while affiliated with University of California, Santa Barbara and other places

... The terahertz CD spectra related to these vibration modes are excellent to probe biomolecules' soft oscillatory motions. [8][9][10] Measuring the CD signals requires accurate polarimetry of electromagnetic waves. [11,12] However, in the terahertz region, this kind of technique is still rare because of lacking devices that can modulate the polarization states of terahertz waves. ...

... Biological polymers show low spectral features in the THz region corresponding to functionally relevant, global and subglobal collective modes with periods on the picosecond timescale. THz spectroscopy can also be used to analyse the dynamics of biopolymers in water [97]. Compared to FTIR spectroscopy, THz spectroscopy can provide information on the low-frequency vibrational modes of biopolymers, such as the collective vibrational modes of amino acids, proteins and carbohydrates, which are not accessible with FTIR spectroscopy [60]. ...

... Here, this idea is extended to the study of the dielectric function of dilute aqueous solutions and demonstrated for a typical salt, sodium chloride. Most previous reports of successful THz-TDS measurements on NaCl solutions are at concentrations of about one Molar (1 M) [55,[90][91][92][93][94][95][96][97][98]. For example, one of the highest precision measurements to date [16] did not report a detectable difference between pure water and 0.1 M NaCl at THz frequencies. ...

... Since the seminal work of Esaki and Tsu [33] the study of Bloch oscillations in electrically biased semiconductor superlattices draws the particular attention of physicists as the fundamental mechanism to provide electromagnetic radiation at terahertz frequencies [34][35][36][37][38]. ...

... 6,7 Serving as non-destructive, nonionizing, and remote analytical spectroscopies, THz waves are capable of capturing vibrations and phonon modes present in crystalline molecules and biomolecular assemblies. 3,8,9 Although many physical and chemical phenomena have been revealed by the continuous development of THz spectroscopies and technology over the last decade, the average radiation power of THz sources remains relatively weak, typically a few milliwatts. This limitation significantly restricts their current applications to only probing the linear response of materials. ...

... Due to water being the most common constituent present in various parts of the leaf, a THz response obtained in both the transmission and reflection can provide a sharp contrast. This occurs, in particular, due to the strong absorption of THz radiation by liquid water [17,18] in the vein structures, with relatively higher transparency occurring in regions of the leaf consisting mostly of cell groups, which contain a much lower concentration of liquid water (the flat component of the leaf, the lamina) [19]. Additionally, the reason for their transparency to THz waves lies in the fact that their cell walls are mostly made of cellulose which has a relatively lower absorption in the THz range [12]. ...

... Proteins also exhibit collective vibrational modes that couple very well with frequencies in the THz frequency band [12]. These modes provide information about protein conformational changes, ligand binding and oxidation states [13]. The aforementioned interactions can therefore trigger unique changes in vibration that can be used in detection and diagnoses [14]. ...

... Terahertz technology has been gradually noticed in the field of non-destructive testing of insulating material because of its unique response of H-bond structure change and high transmittance to insulating oil terahertz radiation (T-Ray), which refers to electromagnetic radiation between infrared radiation and microwave over the frequency range of 0.1 to 10 THz and a wavelength range of 30 µm to 3 mm. Terahertz time-domain spectroscopy (THz-TDS) has a sensitive response to the H-bond structure of cellulose [21][22][23][24][25][26]. The decrease in DP of insulating paper leads to changes in the structure and strength of the H-bond network [27]. ...