Effect of external electric field on the terahertz transmission characteristics of electrolyte solutions*

Abstract

We fabricated a microfluidic chip with simple structure and good sealing performance, and studied the influence of the electric field on THz absorption intensity of liquid samples treated at different times by using THz time domain spectroscopy system. The tested liquids were deionised water and CuSO4, CuCl2, NaHCO3, Na2CO3 and NaCl solutions. The transmission intensity of the THz wave increases as the standing time of the electrolyte solution in the electric field increases. The applied electric field alters the dipole moment of water molecules in the electrolyte solution, which affects the vibration and rotation of the whole water molecules, breaks the hydrogen bonds in the water, increases the number of single water molecules and leads to the enhancement of the THz transmission spectrum.

Terahertz modulation characteristics of three nanosols under external field control based on microfluidic chip

“…It is well known that the transmission of THz wave in a material is influenced by the conductivity of the material itself. The real part of the conductivity affects the amplitude of the THz wave spectrum, whereas the imaginary part of the conductivity affects the transmission delay of THz waves ( Wang et al., 2022a , 2022b , 2022c ). Figure 1 D shows a plot of the real part of the TiO 2 nanosols’ complex conductivity.…”

“…To further analyze the mechanism that the real part of conductivity increases with the external optical pump power, we use the Drude model to fit the experimental data ( Wang et al., 2018 , 2022a , 2022b , 2022c ) and calculate the carrier density N as follows: where m denotes the effective electron mass, denotes the vacuum dielectric constant, e denotes the electron charge, and denotes the plasma frequency, which can be calculated as follows: where and denote the real and imaginary parts of the dielectric constant, respectively, and denotes the THz frequency.In this study, we select 0.59 THz as the research frequency. Through calculation, we obtained a plot of carrier density versus UV laser power, as shown by the red line in Figure 1 B.…”

“…To further analyze the mechanism that the real part of conductivity increases with the external optical pump power, we use the Drude model to fit the experimental data (Wang et al, 2018(Wang et al, , 2022a(Wang et al, , 2022b(Wang et al, , 2022c and calculate the carrier density N as follows:…”

“…Terahertz (THz) wave ( Cong et al., 2021 ; Tseng et al., 2020 ; Zhu et al., 2021 ; Lu et al., 2021 ) refers to an electromagnetic wave with a frequency of 0.1–10 THz and a wavelength of 0.03–3 mm, with a frequency band between millimeter waves and infrared light. Because of their wide bandwidth, low photon energy, and fingerprint spectral properties, THz waves have a wide range of application prospects in basic research fields, such as wireless communication, medical imaging, and biological diagnosis ( Li et al., 2022 ; Jia et al., 2022 ; Dong et al., 2022 ; Wang et al., 2022a , 2022b , 2022c ). Recently, THz sources ( Dong et al., 2021 ) and THz detectors ( Asgari et al., 2021 ) have made great progress, and solid-state THz modulation elements have developed rapidly with the increasing maturity of metasurface technology and semiconductor theory.…”

“…There is no obvious absorption peak in the THz frequency range. For a 2 mm thick COC material, the THz transmittance exceeds 90% ( Wang et al., 2022a , 2022b , 2022c ) ( Figure S1 ). Then, the THz wave modulation characteristics of TiO 2 , Ag, and Fe 3 O 4 nanosols under external ultraviolet (UV) field control, electric field (EF) control, and magnetic field (MF) control, respectively, were studied using the chip.…”