The absorption spectrum of the cyclotrime-thylenetrinitramine(RDX)with four different particle sizes are measured in the frequency range from 0.1 THz to 2.5 THz by using the terahertz time-domain spectroscopy(THz-TDS)...The absorption spectrum of the cyclotrime-thylenetrinitramine(RDX)with four different particle sizes are measured in the frequency range from 0.1 THz to 2.5 THz by using the terahertz time-domain spectroscopy(THz-TDS),and the characteristic absorption peaks are acquired.All the samples are measured in a loose condition,which is very close to the real using environment of the RDX.The results show that the four kinds of samples have similar absorption peaks around the frequency of 0.82 THz,1.05THz,1.30 THz,1.46 THz,1.65 THz,and 1.95 THz.The sample with a large particle size obtains more peaks than the small one,while the peaks obtained from the sample with a small size are more protrudent.The reasons for these differences can be the refraction,scattering,and attenuation of the terahertz wave when it passes through the crystal samples.The theoretical terahertz spectrum of RDX was simulated by using density functional calculations,in which,the Becke&Perdew-Wang’s functional is used in a double numerical plus polarization method(BP/DNP).Good agreements between the experimental and computed results show that the three peaks located in the frequency of 1.30 THz,1.48 THz,and 1.96 THz are caused respectively by the twisting of three-nitrogen heterocyclic,the symmetrical oscillations of the double nitro groups,and the oscillations of a single nitro group.展开更多
The responsivity and the noise of a detector determine the sensitivity. Thermal energy usually affects both the responsivity and the noise spectral density. In this work, the noise characteristics and responsivity of ...The responsivity and the noise of a detector determine the sensitivity. Thermal energy usually affects both the responsivity and the noise spectral density. In this work, the noise characteristics and responsivity of an antenna-coupled AlGaN/GaN high-electron-mobility-transistor(HEMT) terahertz detector are evaluated at temperatures elevated from 300 K to 473 K. Noise spectrum measurement and a simultaneous measurement of the source–drain conductance and the terahertz photocurrent allow for detailed analysis of the electrical characteristics, the photoresponse, and the noise behavior. The responsivity is reduced from 59 mA/W to 11 mA/W by increasing the detector temperature from 300 K to 473 K. However,the noise spectral density maintains rather constantly around 1–2 pA/Hz^(1/2) at temperatures below 448 K, above which the noise spectrum abruptly shifts from Johnson-noise type into flicker-noise type and the noise density is increased up to one order of magnitude. The noise-equivalent power(NEP) is increased from 22 pW/Hz^(1/2) at 300 K to 60 pW/Hz^(1/2) at 448 K mainly due to the reduction in mobility. Above 448 K, the NEP is increased up to 1000 pW/Hz^(1/2) due to the strongly enhanced noise. The sensitivity can be recovered by cooling the detector back to room temperature.展开更多
The terahertz time-domain spectroscopy(THz-TDS)system and the related technology and the applications in Capital Normal University are presented.The most often used THz-TDS system as a spectroscopic measurement setup ...The terahertz time-domain spectroscopy(THz-TDS)system and the related technology and the applications in Capital Normal University are presented.The most often used THz-TDS system as a spectroscopic measurement setup in our lab is introduced in detail,including the THz radiation source,the THz detection method and its measurement,and the control system.THz spectra of various materials is summarized and discussed.These materials include but not limited to two kinds of typical matter—the illegal drugs and explosives.The biological macro-molecules,cosmetics and fine chemical materials,edible pigments and food additives,homocysteic acid and related compounds,heavy ions in soil,Chinese medicines,tobacco and crops,oil and chemical products,carbon nanotubes,superconductors,and various semiconductors and their heterojunctions,are presented.THz emissions from the InAs and InN semiconductors surface are compared.THz spectral investigation of metallic mesh structures is summarized.Finally,an outlook of THz spectroscopic applications is given.展开更多
An approach for solving the excitonic absorption in a semiconductor quantum well driven by an intense terahertz field is presented.The formalism relies on the stationary single-photon Schro¨dinger equation in the...An approach for solving the excitonic absorption in a semiconductor quantum well driven by an intense terahertz field is presented.The formalism relies on the stationary single-photon Schro¨dinger equation in the full quantum mechanical framework.The optical absorption dynamics in both weak and strong couplings are discussed and compared.The excitonic absorption spectra show the Autler-Townes doublets for the resonance terahertz field,a replica peak for the non-resonance terahertz field,and the electromagnetically induced transparency phenomenon for modulating the decay rate of the second electron state in the weak coupling.In particular,the electromagnetically induced transparency phenomenon window range is discussed.In the strong coupling region,the multi-order energy level resonance splitting due to the strong optical field is found.There are three(non-resonance terahertz field) or four(resonance terahertz field) peaks in the optical absorption spectra.This work provides a simple and convenient approach to deal with the optical absorption in the exciton system.展开更多
Terahertz vibrational spectroscopy has recently been demonstrated as a novel noninvasive technique for the characterization of biological molecules. But the interpretation of the experimentally measured terahertz abso...Terahertz vibrational spectroscopy has recently been demonstrated as a novel noninvasive technique for the characterization of biological molecules. But the interpretation of the experimentally measured terahertz absorption bands requires robust computational method. In this paper, we present a statistical method for predicting the absorption peak positions of a macromolecule in the terahertz region. The essence of this method is to calculate the absorption spectra of a biological molecule based on multiple short scale molecular dynamics trajectories instead of using a long time scale trajectory. The method was employed to calculate the absorption peak positions of the protein, thioredoxin from Escherichia coli (E.coli), in the range of 10-25 cm -1 to verify the reliability of this statistical method. The predicted absorption peak positions of thioredoxin show good correlation with measured results demonstrating that the proposed method is effective in terahertz absorption spectra modeling. Such approach can be applied to predict characteristic spectral features of biomolecules in the terahertz region.展开更多
Several indole derivatives with different ‘3-' substituents have been investigated by terahertz(THz) time-domain spectroscopy. The low-frequency absorption spectra and refractive indices were obtained in the rang...Several indole derivatives with different ‘3-' substituents have been investigated by terahertz(THz) time-domain spectroscopy. The low-frequency absorption spectra and refractive indices were obtained in the range of 0.2 THz to 2.5 THz(7 cm–1 to 83 cm–1). These derivatives with different substituents present distinct features,which suggests that THz spectroscopy is sensitive to different structures and components of these chemicals. The density functional theory was employed to calculate the low-frequency vibrational properties of indole-3-carboxylic acid and indole-3-propionic acid based on their crystal structures,and the intermolecular interactions were involved. Meanwhile,the temperature dependence of the spectra agreed with the calculated results. The quantitative analysis of a ternary mixture was studied by taking the THz fingerprints into account,and the results demonstrate THz spectroscopy has great potential for the practical applications in biochemistry and pharmaceutics.展开更多
基金was supported by the National Natural Science Foundation of China under Grant No. U1330202 and 11204279the Foundation of Terahertz Research Center, CAEP under Grant No. T2014-005-0103
文摘The absorption spectrum of the cyclotrime-thylenetrinitramine(RDX)with four different particle sizes are measured in the frequency range from 0.1 THz to 2.5 THz by using the terahertz time-domain spectroscopy(THz-TDS),and the characteristic absorption peaks are acquired.All the samples are measured in a loose condition,which is very close to the real using environment of the RDX.The results show that the four kinds of samples have similar absorption peaks around the frequency of 0.82 THz,1.05THz,1.30 THz,1.46 THz,1.65 THz,and 1.95 THz.The sample with a large particle size obtains more peaks than the small one,while the peaks obtained from the sample with a small size are more protrudent.The reasons for these differences can be the refraction,scattering,and attenuation of the terahertz wave when it passes through the crystal samples.The theoretical terahertz spectrum of RDX was simulated by using density functional calculations,in which,the Becke&Perdew-Wang’s functional is used in a double numerical plus polarization method(BP/DNP).Good agreements between the experimental and computed results show that the three peaks located in the frequency of 1.30 THz,1.48 THz,and 1.96 THz are caused respectively by the twisting of three-nitrogen heterocyclic,the symmetrical oscillations of the double nitro groups,and the oscillations of a single nitro group.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFF0100501)the National Natural Science Foundation of China(Grant Nos.61771466,61775231,and 61611530708)+1 种基金the Six Talent Peaks of Jiangsu Province,China(Grant No.XXRJ-079)the Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant No.2017372)
文摘The responsivity and the noise of a detector determine the sensitivity. Thermal energy usually affects both the responsivity and the noise spectral density. In this work, the noise characteristics and responsivity of an antenna-coupled AlGaN/GaN high-electron-mobility-transistor(HEMT) terahertz detector are evaluated at temperatures elevated from 300 K to 473 K. Noise spectrum measurement and a simultaneous measurement of the source–drain conductance and the terahertz photocurrent allow for detailed analysis of the electrical characteristics, the photoresponse, and the noise behavior. The responsivity is reduced from 59 mA/W to 11 mA/W by increasing the detector temperature from 300 K to 473 K. However,the noise spectral density maintains rather constantly around 1–2 pA/Hz^(1/2) at temperatures below 448 K, above which the noise spectrum abruptly shifts from Johnson-noise type into flicker-noise type and the noise density is increased up to one order of magnitude. The noise-equivalent power(NEP) is increased from 22 pW/Hz^(1/2) at 300 K to 60 pW/Hz^(1/2) at 448 K mainly due to the reduction in mobility. Above 448 K, the NEP is increased up to 1000 pW/Hz^(1/2) due to the strongly enhanced noise. The sensitivity can be recovered by cooling the detector back to room temperature.
基金supported by the National Natural Science Foundation of China under Grant No. 50971094, 61171051Beijing Key Project of Science and Technology Development under Grant No. KZ201310028032
文摘The terahertz time-domain spectroscopy(THz-TDS)system and the related technology and the applications in Capital Normal University are presented.The most often used THz-TDS system as a spectroscopic measurement setup in our lab is introduced in detail,including the THz radiation source,the THz detection method and its measurement,and the control system.THz spectra of various materials is summarized and discussed.These materials include but not limited to two kinds of typical matter—the illegal drugs and explosives.The biological macro-molecules,cosmetics and fine chemical materials,edible pigments and food additives,homocysteic acid and related compounds,heavy ions in soil,Chinese medicines,tobacco and crops,oil and chemical products,carbon nanotubes,superconductors,and various semiconductors and their heterojunctions,are presented.THz emissions from the InAs and InN semiconductors surface are compared.THz spectral investigation of metallic mesh structures is summarized.Finally,an outlook of THz spectroscopic applications is given.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10647132)the Science Foundation from the Education Department of Hunan Province,China (Grant No. 10A100)
文摘An approach for solving the excitonic absorption in a semiconductor quantum well driven by an intense terahertz field is presented.The formalism relies on the stationary single-photon Schro¨dinger equation in the full quantum mechanical framework.The optical absorption dynamics in both weak and strong couplings are discussed and compared.The excitonic absorption spectra show the Autler-Townes doublets for the resonance terahertz field,a replica peak for the non-resonance terahertz field,and the electromagnetically induced transparency phenomenon for modulating the decay rate of the second electron state in the weak coupling.In particular,the electromagnetically induced transparency phenomenon window range is discussed.In the strong coupling region,the multi-order energy level resonance splitting due to the strong optical field is found.There are three(non-resonance terahertz field) or four(resonance terahertz field) peaks in the optical absorption spectra.This work provides a simple and convenient approach to deal with the optical absorption in the exciton system.
基金Supported by National Science Foundation of China(Nos.60907044,91027020 and 11005148)
文摘Terahertz vibrational spectroscopy has recently been demonstrated as a novel noninvasive technique for the characterization of biological molecules. But the interpretation of the experimentally measured terahertz absorption bands requires robust computational method. In this paper, we present a statistical method for predicting the absorption peak positions of a macromolecule in the terahertz region. The essence of this method is to calculate the absorption spectra of a biological molecule based on multiple short scale molecular dynamics trajectories instead of using a long time scale trajectory. The method was employed to calculate the absorption peak positions of the protein, thioredoxin from Escherichia coli (E.coli), in the range of 10-25 cm -1 to verify the reliability of this statistical method. The predicted absorption peak positions of thioredoxin show good correlation with measured results demonstrating that the proposed method is effective in terahertz absorption spectra modeling. Such approach can be applied to predict characteristic spectral features of biomolecules in the terahertz region.
基金supported by the National Basic Research Program of China under Grant No.2014CB339806
文摘Several indole derivatives with different ‘3-' substituents have been investigated by terahertz(THz) time-domain spectroscopy. The low-frequency absorption spectra and refractive indices were obtained in the range of 0.2 THz to 2.5 THz(7 cm–1 to 83 cm–1). These derivatives with different substituents present distinct features,which suggests that THz spectroscopy is sensitive to different structures and components of these chemicals. The density functional theory was employed to calculate the low-frequency vibrational properties of indole-3-carboxylic acid and indole-3-propionic acid based on their crystal structures,and the intermolecular interactions were involved. Meanwhile,the temperature dependence of the spectra agreed with the calculated results. The quantitative analysis of a ternary mixture was studied by taking the THz fingerprints into account,and the results demonstrate THz spectroscopy has great potential for the practical applications in biochemistry and pharmaceutics.
基金Supported by the National Natural Science Foundation of China(21171119,11574408,81573822,21376008)the Beijing Natural Science Foundation(2172017)+1 种基金the Fundamental Research Funds for the Central Universities in China University of Geosciences(2-9-2021-008)the R&D Program of Beijing Municipal Education Commission(KM202210028015)。
