scholarly journals Spurious Absorption Frequency Appearance Due to Frequency Conversion Processes in Pulsed THz TDS Problems

Sensors ◽  
2020 ◽  
Vol 20 (7) ◽  
pp. 1859
Author(s):  
Vyacheslav A. Trofimov ◽  
Nan-Nan Wang ◽  
Jing-Hui Qiu ◽  
Svetlana A. Varentsova
Keyword(s):  
Nonlinear Response ◽  
Frequency Conversion ◽  
Pulse Propagation ◽  
Frequency Doubling ◽  
Absorption Frequency ◽  
Physical Experiments ◽  
Detection And Identification ◽  
Dangerous Substances ◽  
Spectral Intensities ◽  
Absorption Frequencies

The appearance of the spurious absorption frequencies caused by the frequency conversion process at the broadband THz pulse propagation in a medium is theoretically and experimentally discussed. The spurious absorption frequencies appear due to both the frequency doubling and generation of waves with sum or difference frequency. Such generation might occur because of the nonlinear response of a medium or its non-instantaneous response. This phenomenon is confirmed by the results of a few physical experiments provided with the THz CW signals and broadband THz pulses that are transmitted through the ordinary or dangerous substances. A high correlation between the time-dependent spectral intensities for the basic frequency and generated frequencies is demonstrated while using the computer simulation results. This feature of the frequency conversion might be used for the detection and identification of a substance.

scholarly journals A Possible Way for the Detection and Identification of Dangerous Substances in Ternary Mixtures Using THz Pulsed Spectroscopy

Sensors ◽  
2019 ◽  
Vol 19 (10) ◽  
pp. 2365 ◽  
Author(s):  
Vyacheslav A. Trofimov ◽  
Svetlana A. Varentsova
Keyword(s):  
Spectral Properties ◽  
Main Pulse ◽  
Ternary Mixtures ◽  
Thz Spectroscopy ◽  
Time Intervals ◽  
Detection And Identification ◽  
Dangerous Substances ◽  
Spectral Intensities ◽  
Absorption Frequencies ◽  
High Absorption

We discuss an effective tool for the detection and identification of substances in ternary mixtures with similar spectral properties using a broadband reflected THz signal. Nowadays, this is an urgent problem; its effective solution is still far off. Two ternary mixtures of the explosives (RDX+TNT+HMX and RDX+TNT+PETN) were used as the examples for demonstration of the efficiency of the method proposed. The identification is based on the pulsed THz spectroscopy. We follow the spectral intensities together with the use of integral correlation criteria. They use the spectral line dynamics of the THz pulse reflected from the substance under investigation and that of the standard THz signal from database. In order to increase the accuracy and reliability of the identification, we analyze the partial non-overlapping time intervals, containing the main pulse of the reflected THz signal and the sequential sub-pulses. The main pulse is shown to contain information about high absorption frequencies (ν > 2.6 THz) of the mixture components. In the sub-pulses, the absorption frequencies of the components are detected in the range of low (ν < 2.6 THz) and high (ν > 2.6 THz) frequencies. The opportunity of distinguishing the mixtures with similar spectral properties is also shown.

Detecting metal objects in magnetic environments using a broadband electromagnetic method

Geophysics ◽  
2003 ◽  
Vol 68 (6) ◽  
pp. 1877-1887 ◽  
Author(s):  
Haoping Huang ◽  
I. J. Won
Keyword(s):  
Magnetic Permeability ◽  
Field Studies ◽  
Unexploded Ordnance ◽  
Apparent Conductivity ◽  
Physical Experiments ◽  
Detection And Identification ◽  
Em Method ◽  
Magnetic Basement ◽  
Quadrature Response ◽  
Layered Half Space

We analyze the use of the broadband electromagnetic (EM) method in detecting metallic objects, such as unexploded ordnance (UXO), buried in magnetic environments. Magnetic rocks close to the sensor often contribute a larger in‐phase response than does the target at depth, making target detection and identification difficult. On the other hand, magnetic rocks contribute little quadrature response, which gives rise to the concept of using quadrature response and apparent conductivity to detect metallic objects in highly magnetic environments. To test this concept, we employed numeric models, physical experiments, and field studies. A layered half‐space simulated conductive overburden and magnetic basement. Sphere models are used for isolated magnetic rocks and metal targets. The responses of the layered earth, magnetic rocks, and metal objects were added to obtain the approximate total response. We then inverted the EM data into apparent magnetic permeability and conductivity. The EM response at the lowest frequency was used initially to estimate apparent magnetic permeability, which let us calculate the apparent conductivity using the EM data at all frequencies. The simulations and field examples show that broadband EM sensors can detect small metal targets in magnetic environments, mainly by the quadrature component of the responses and the apparent conductivity.

Effect of a Magnetic Field on Photocatalytic Degradation of Rhodamine B Over g-C3N4

2020 ◽  
Vol 12 (2) ◽  
pp. 156-162
Author(s):  
Ci Du ◽  
Tianjiao Hu ◽  
Zengyong Chu ◽  
Wenjian Wu ◽  
Xiaodong Li
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Photocatalytic Degradation ◽  
Infrared Absorption ◽  
Rhodamine B ◽  
Photocatalytic Efficiency ◽  
Bending Vibration ◽  
Absorption Frequency ◽  
The Magnetic Field ◽  
Absorption Frequencies

Magnetic fields have potential applications in photocatalysis. However, there is limited research on the effect of magnetic fields on heterogeneous photocatalysis, and the action mechanism remains unclear. In this study, the photocatalytic degradation of rhodamine B over g-C3N4 in an aqueous solution was investigated, and the adsorption and photocatalytic activity were analyzed in the absence and presence of a magnetic field. Furthermore, the infrared absorption frequency of the bending vibration of water was measured in real-time. The results show that the adsorption and photocatalytic efficiencies were positively correlated with the magnetic field intensity in the range of 0∼2 T, while high-intensity magnetic fields (4∼8 T) played an inhibitory role. In addition, the infrared absorption frequencies of water exhibited a red-shift under 1 T and 2 T magnetic fields at 37 °C, while the absorption frequencies under 4 T and 8 T magnetic fields were the same as that in the absence of magnetic fields. The effects of the magnetic field on the g-C3N4 photocatalytic efficiency and water infrared absorption frequency were similar, suggesting that the effect of the magnetic field on the water structure may be one factor affecting the g-C3N4 photocatalytic efficiency.

Experimental analysis of overall thermal properties of Nd:La2CaB10O19crystals

2012 ◽  
Vol 45 (6) ◽  
pp. 1182-1186 ◽  
Author(s):  
Jianxiu Zhang ◽  
Yang Wu ◽  
Guochun Zhang ◽  
Yin Li ◽  
Yicheng Wu
Keyword(s):  
Thermal Expansion ◽  
Rare Earth ◽  
Frequency Conversion ◽  
Frequency Doubling ◽  
Nonlinear Frequency ◽  
Rare Earth Ion ◽  
Nonlinear Frequency Conversion ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients ◽  
Measured Specific Heat

Pure or rare-earth-ion-doped La2CaB10O19(LCB) is a promising optical material for nonlinear frequency conversion, laser and self-frequency doubling applications. In this paper, the thermophysical properties of Nd3+-doped LCB (Nd:LCB) crystals were measured and compared with those of pure and of Yb3+- and Er3+-doped LCB, as well as other borate nonlinear optical crystals. The melting points of rare-earth-doped LCB crystals are lower than that of pure LCB. Thermal expansion coefficients along thea,b,c,c*,a*, 〈110〉 and 〈110〉* directions have been measured, and the principal expansion coefficients were calculated to be 1.85 × 10−6, 4.13 × 10−6and 8.79 × 10−6 K−1. The measured specific heat of Nd:LCB is lower than that of pure LCB, resulting in a larger internal temperature gradient under irradiation by a pulsed laser beam. The measured thermal expansion anisotropy of Nd:LCB is stronger than that of pure LCB. The thermal conductivities of Nd:LCB along thecandc* directions are smaller than those along other crystallographic directions.

scholarly journals Design and Thermal Analysis of Temperature Control Experiment Box for Final Optic Assembly

2021 ◽  
Vol 2083 (2) ◽  
pp. 022052
Author(s):  
Changqi Chen ◽  
Tianshu Xi ◽  
Yanan Zhang
Keyword(s):  
Thermal Analysis ◽  
Temperature Control ◽  
Frequency Conversion ◽  
Control Experiment ◽  
Radiation Heat Transfer ◽  
Frequency Doubling ◽  
Laser Frequency ◽  
Inertial Confinement ◽  
Control Research ◽  
Set Up

Abstract The Final Optic Assembly (FOA) is one of the key components of the inertial confinement nuclear fusion device. The temperature change in the FOA is related to the laser frequency conversion efficiency of the frequency doubling crystal. In order to research the temperature control of FOA, this paper considers the internal atmosphere and internal structure of FOA, designed and fabricated a vacuum temperature control experiment box, and set up heat sources inside the box to simulate the internal heating of the FOA. This article uses different radiation heat transfer models to analysis the temperature field of the vacuum experiment box. Compare the thermal simulation results of the S2S model and the DO model, and compare them with the actual temperature of the vacuum experiment box under the same boundary conditions. The results show that the S2S model fits well with the experimental results and is more suitable for thermal analysis of FOA, which is of great significance to the follow-up FOA temperature control research.

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