Chirality hold broad applications in life sciences,quantum devices,and various other areas.Traditionally,molecular chirality can be characterized by using steady-state circular dichroism spectroscopy.However,the techn...Chirality hold broad applications in life sciences,quantum devices,and various other areas.Traditionally,molecular chirality can be characterized by using steady-state circular dichroism spectroscopy.However,the techniques that can characterize excited state chirality are progressively capturing the public interest as it can provide the dynamic information for chirality generation and transfer.In this review,we focus on the theoretical background and the developmental history of femtosecond time-resolved circular dichroism spectroscopy(TRCD)techniques around the world.Additionally,we provide examples to showcase the utility of these techniques in the analysis of the dynamical molecular chemical structures,the investigation of molecular chirality generation,and the detection of electron spin dynamics in semiconductor quantum dots.展开更多
The S transform, which is a time-frequency representation known for its local spectral phase properties in signal processing, uniquely combines elements of wavelet transforms and the short-time Fourier transform （STF...The S transform, which is a time-frequency representation known for its local spectral phase properties in signal processing, uniquely combines elements of wavelet transforms and the short-time Fourier transform （STFT）. The fractional Fourier transform is a tool for non-stationary signal analysis. In this paper, we define the concept of the fractional S transform （FRST） of a signal, based on the idea of the fractional Fourier transform （FRFT） and S transform （ST）, extend the S transform to the time-fractional frequency domain from the time- frequency domain to obtain the inverse transform, and study the FRST mathematical properties. The FRST, which has the advantages of FRFT and ST, can enhance the ST flexibility to process signals. Compared to the S transform, the FRST can effectively improve the signal time- frequency resolution capacity. Simulation results show that the proposed method is effective.展开更多
Time-resolved electron spin resonance has been used to study quenching reactions between the antioxidant Vitamin C （VC） and the triplet excited states of 9,10-phenanthrenequinone （PAQ） in ethylene glycol-water （E...Time-resolved electron spin resonance has been used to study quenching reactions between the antioxidant Vitamin C （VC） and the triplet excited states of 9,10-phenanthrenequinone （PAQ） in ethylene glycol-water （EG-H2O） homogeneous and inhomogeneous reversed micelle solutions. Reversed micelle solutions were used to be the models of physiological environment of biological cell and tissue. In PAQ/EG-H2O homogeneous solution, the excited triplet of PAQ （3PAQ＊） abstracts hydrogen atom from solvent EG. In PAQ/VC/EG-H2O solution, 3pAQ＊ abstracts hydrogen atom not only from solvent EG but also from VC. The quenching rate constant of 3pAQ＊ by VC is close to the diffusion-controlled value of 1.41 × 108 L/（mol.s）. In hexadecyltrimethylammonium bromide （CTAB）/EG-H2O and aerosol OT （AOT）/EG- H2O reversed micelle solutions, 3pAQ＊ and VC react around the water-oil interface of the reversed micelle. Exit of 3pAQ＊ from the lipid phase slows down the quenching reaction. For Triton X-100 （TX-100）/EG-H2O reversed micelle solution, PAQ and VC coexist inside the hydrophilic polyethylene glycol core, and the quenching rate constant of 3pAQ＊ by VC is larger than those in AOT/EG-H2O and CTAB/EG-H2O reversed micelle solutions, even a little larger than that in EG-H2O homogeneous solution. The strong emissive chemically induced dynamic electron polarization of As＇- resulted from the effective TM spin polarization transfer in hydrogen abstraction of 3pAQ＊ from VC.展开更多
Junctions are an important structure that allows charge separation in solar cells and photocatalysts. Here, we studied the charge transfer at an anatase/rutile TiO2 phase junction using time-resolved photoluminescence...Junctions are an important structure that allows charge separation in solar cells and photocatalysts. Here, we studied the charge transfer at an anatase/rutile TiO2 phase junction using time-resolved photoluminescence spectroscopy. Visible （-S00 nm） and near-infrared （NIR, -830 nm） emissions were monitored to give insight into the photoinduced charges of anatase and rutile in the junction, respectively, New fast photoluminescence decay components appeared in the visible emission of futile-phase dominated TiO2 and in the NIR emission of many mixed phase TiO2samples. The fast decays confirmed that the charge separation occurred at the phase junction. The visible emission intensity from the mixed phase TiO2 increased, revealing that charge transfer from rutile to anatase was the main pathway. The charge separation slowed the microsecond time scale photolumines- cence decay rate for charge carriers in both anatase and rutile. However, the millisecond decay of the charge carriers in anatase TiO2 was accelerated, while there was almost no change in the charge carrier dynamics of rutile TiO2. Thus, charge separation at the anatase/rutile phase junction caused an increase in the charge carrier concentration on a microsecond time scale, because of slower electron-hole recombination. The enhanced photocatalytic activity previously observed at ana- tase/rutile phase junctions is likely caused by the improved charge carrier dynamics we report here. These findings may contribute to the development of improved photocatalytic materials.展开更多
In this paper, it is described that the time-frequency resolution of geophysical signals is affected by the time window function attenuation coefficient and sampling interval and how such effects are eliminated effect...In this paper, it is described that the time-frequency resolution of geophysical signals is affected by the time window function attenuation coefficient and sampling interval and how such effects are eliminated effectively. Improving the signal resolution is the key to signal time-frequency analysis processing and has wide use in geophysical data processing and extraction of attribute parameters. In this paper, authors research the effects of the attenuation coefficient choice of the Gabor transform window function and sampling interval on signal resolution. Unsuitable parameters not only decrease the signal resolution on the frequency spectrum but also miss the signals. It is essential to first give the optimum window and range of parameters through time-frequency analysis simulation using the Gabor transform. In the paper, the suggestions about the range and choice of the optimum sampling interval and processing methods of general seismic signals are given.展开更多
Spectrum analysis of the plasma has over the years been growing both in methods and instrument, which makes it become a widely used non-contact detection method, without disturbing the arc plasma itself. With noticeab...Spectrum analysis of the plasma has over the years been growing both in methods and instrument, which makes it become a widely used non-contact detection method, without disturbing the arc plasma itself. With noticeable developments in the industry application of the method, a need for careful analysis of the plasma with both time and space identification is desirable. Therefore, a spectral measurement system is developed in this paper for diagnosing arc plasma with time and space identification. With a new hollow probe scanning method, the instrument can be used to provide information like energy distribution of plasma, temperature within the arc plasma, which are of great significance with the requirement of space identification. Furthermore, the system can also be used to capture the instant state of the arc plasma with the synchronic triggering system, which uses high speed photo and electrical signal as the time criterion. The industry applications prove that the system works well for online detection of the arc plasma.展开更多
The ultrafast dynamics through conical intersections in 2,6-dimethylpyridine has been studied by femtosecond time-resolved photoelectron imaging coupled with time-resolved mass spectroscopy. Upon absorption of 266 nm ...The ultrafast dynamics through conical intersections in 2,6-dimethylpyridine has been studied by femtosecond time-resolved photoelectron imaging coupled with time-resolved mass spectroscopy. Upon absorption of 266 nm pump laser, 2,6-dimethylpyridine is excited to the S2 state with a ππ character from So state. The time evolution of the parent ion signals consists of two exponential decays. One is a fast component on a timescale of 635 fs and the other is a slow component with a timescale of 4.37 ps. Time-dependent photo- electron angular distributions and energy-resolved photoelectron spectroscopy are extracted from time-resolved photoelectron imaging and provide the evolutive information of S2 state. In brief, the ultrafast component is a population transfer from S2 to S1 through the S2/S1 conical intersections, the slow component is attributed to simultaneous IC from the S2 state and the higher vibrational levels of S1 state to So state, which involves the coupling of S2/S0 and S1/So conical intersections. Additionally, the observed ultrafast S2--＋S1 transition occurs only with an 18% branching ratio.展开更多
The nonlinear optical properties of Al-doped nc-Si-SiO2 composite films have been investigated using the time-resolved four-wave mixing technique with a femtosecond laser. The off-resonant third-order nonlinear suscep...The nonlinear optical properties of Al-doped nc-Si-SiO2 composite films have been investigated using the time-resolved four-wave mixing technique with a femtosecond laser. The off-resonant third-order nonlinear susceptibility is observed to be 1.0 × 10-10 esu at 800nm. The relaxation time of the optical nonlinearity in the films is as short as 60fs. The optical nonlinearity is enhanced due to the quantum confinement of electrons in Si nanocrystals embedded in the SiO2 films. The enhanced optical nonlinearity does not originate from Al dopant because there are no Al clusters in the films.展开更多
基金funded by the National Natural Science FoundationofChina(No.92156024and No.92356307 to Jinquan Chen)Menghui Jia thanks the Materials Characterization Center and the Office of Laboratory and Equipment of East China Normal University for funding support(ECNUETR2023-13).
文摘Chirality hold broad applications in life sciences,quantum devices,and various other areas.Traditionally,molecular chirality can be characterized by using steady-state circular dichroism spectroscopy.However,the techniques that can characterize excited state chirality are progressively capturing the public interest as it can provide the dynamic information for chirality generation and transfer.In this review,we focus on the theoretical background and the developmental history of femtosecond time-resolved circular dichroism spectroscopy(TRCD)techniques around the world.Additionally,we provide examples to showcase the utility of these techniques in the analysis of the dynamical molecular chemical structures,the investigation of molecular chirality generation,and the detection of electron spin dynamics in semiconductor quantum dots.
基金supported by Scientific Research Fund of Sichuan Provincial Education Departmentthe National Nature Science Foundation of China (No. 40873035)
文摘The S transform, which is a time-frequency representation known for its local spectral phase properties in signal processing, uniquely combines elements of wavelet transforms and the short-time Fourier transform （STFT）. The fractional Fourier transform is a tool for non-stationary signal analysis. In this paper, we define the concept of the fractional S transform （FRST） of a signal, based on the idea of the fractional Fourier transform （FRFT） and S transform （ST）, extend the S transform to the time-fractional frequency domain from the time- frequency domain to obtain the inverse transform, and study the FRST mathematical properties. The FRST, which has the advantages of FRFT and ST, can enhance the ST flexibility to process signals. Compared to the S transform, the FRST can effectively improve the signal time- frequency resolution capacity. Simulation results show that the proposed method is effective.
基金ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China （No.20903004） and the Science Foundation of the Education Committee of Anhui Province （No.J2010A145）. We are grateful to professor Li-min Zhang for his help in transient absorptive spectrum measurement.
文摘Time-resolved electron spin resonance has been used to study quenching reactions between the antioxidant Vitamin C （VC） and the triplet excited states of 9,10-phenanthrenequinone （PAQ） in ethylene glycol-water （EG-H2O） homogeneous and inhomogeneous reversed micelle solutions. Reversed micelle solutions were used to be the models of physiological environment of biological cell and tissue. In PAQ/EG-H2O homogeneous solution, the excited triplet of PAQ （3PAQ＊） abstracts hydrogen atom from solvent EG. In PAQ/VC/EG-H2O solution, 3pAQ＊ abstracts hydrogen atom not only from solvent EG but also from VC. The quenching rate constant of 3pAQ＊ by VC is close to the diffusion-controlled value of 1.41 × 108 L/（mol.s）. In hexadecyltrimethylammonium bromide （CTAB）/EG-H2O and aerosol OT （AOT）/EG- H2O reversed micelle solutions, 3pAQ＊ and VC react around the water-oil interface of the reversed micelle. Exit of 3pAQ＊ from the lipid phase slows down the quenching reaction. For Triton X-100 （TX-100）/EG-H2O reversed micelle solution, PAQ and VC coexist inside the hydrophilic polyethylene glycol core, and the quenching rate constant of 3pAQ＊ by VC is larger than those in AOT/EG-H2O and CTAB/EG-H2O reversed micelle solutions, even a little larger than that in EG-H2O homogeneous solution. The strong emissive chemically induced dynamic electron polarization of As＇- resulted from the effective TM spin polarization transfer in hydrogen abstraction of 3pAQ＊ from VC.
基金supported by the National Natural Science Foundation of China (21203185, 21373209)the National Basic Research Program of China (2014CB239400)
文摘Junctions are an important structure that allows charge separation in solar cells and photocatalysts. Here, we studied the charge transfer at an anatase/rutile TiO2 phase junction using time-resolved photoluminescence spectroscopy. Visible （-S00 nm） and near-infrared （NIR, -830 nm） emissions were monitored to give insight into the photoinduced charges of anatase and rutile in the junction, respectively, New fast photoluminescence decay components appeared in the visible emission of futile-phase dominated TiO2 and in the NIR emission of many mixed phase TiO2samples. The fast decays confirmed that the charge separation occurred at the phase junction. The visible emission intensity from the mixed phase TiO2 increased, revealing that charge transfer from rutile to anatase was the main pathway. The charge separation slowed the microsecond time scale photolumines- cence decay rate for charge carriers in both anatase and rutile. However, the millisecond decay of the charge carriers in anatase TiO2 was accelerated, while there was almost no change in the charge carrier dynamics of rutile TiO2. Thus, charge separation at the anatase/rutile phase junction caused an increase in the charge carrier concentration on a microsecond time scale, because of slower electron-hole recombination. The enhanced photocatalytic activity previously observed at ana- tase/rutile phase junctions is likely caused by the improved charge carrier dynamics we report here. These findings may contribute to the development of improved photocatalytic materials.
基金This work was funded by National Natural Science Foundation of China-（No. 40474044）.
文摘In this paper, it is described that the time-frequency resolution of geophysical signals is affected by the time window function attenuation coefficient and sampling interval and how such effects are eliminated effectively. Improving the signal resolution is the key to signal time-frequency analysis processing and has wide use in geophysical data processing and extraction of attribute parameters. In this paper, authors research the effects of the attenuation coefficient choice of the Gabor transform window function and sampling interval on signal resolution. Unsuitable parameters not only decrease the signal resolution on the frequency spectrum but also miss the signals. It is essential to first give the optimum window and range of parameters through time-frequency analysis simulation using the Gabor transform. In the paper, the suggestions about the range and choice of the optimum sampling interval and processing methods of general seismic signals are given.
基金Research Project Supported by Shanxi Scholarship Council of China(No.2012-69)Selected Research Project by Department of Human Resources and Social Security of Shanxi
文摘Spectrum analysis of the plasma has over the years been growing both in methods and instrument, which makes it become a widely used non-contact detection method, without disturbing the arc plasma itself. With noticeable developments in the industry application of the method, a need for careful analysis of the plasma with both time and space identification is desirable. Therefore, a spectral measurement system is developed in this paper for diagnosing arc plasma with time and space identification. With a new hollow probe scanning method, the instrument can be used to provide information like energy distribution of plasma, temperature within the arc plasma, which are of great significance with the requirement of space identification. Furthermore, the system can also be used to capture the instant state of the arc plasma with the synchronic triggering system, which uses high speed photo and electrical signal as the time criterion. The industry applications prove that the system works well for online detection of the arc plasma.
基金This work was supported by the National Natural Science Foundation of China （No.10704083）,the Innovation Foundation of Chinese Academyof Sciences （No.KJCX1-YW-N30）, and the Public Science and Technology Program of Shenzhen （No.SY200806260026A）.
文摘The ultrafast dynamics through conical intersections in 2,6-dimethylpyridine has been studied by femtosecond time-resolved photoelectron imaging coupled with time-resolved mass spectroscopy. Upon absorption of 266 nm pump laser, 2,6-dimethylpyridine is excited to the S2 state with a ππ character from So state. The time evolution of the parent ion signals consists of two exponential decays. One is a fast component on a timescale of 635 fs and the other is a slow component with a timescale of 4.37 ps. Time-dependent photo- electron angular distributions and energy-resolved photoelectron spectroscopy are extracted from time-resolved photoelectron imaging and provide the evolutive information of S2 state. In brief, the ultrafast component is a population transfer from S2 to S1 through the S2/S1 conical intersections, the slow component is attributed to simultaneous IC from the S2 state and the higher vibrational levels of S1 state to So state, which involves the coupling of S2/S0 and S1/So conical intersections. Additionally, the observed ultrafast S2--＋S1 transition occurs only with an 18% branching ratio.
文摘The nonlinear optical properties of Al-doped nc-Si-SiO2 composite films have been investigated using the time-resolved four-wave mixing technique with a femtosecond laser. The off-resonant third-order nonlinear susceptibility is observed to be 1.0 × 10-10 esu at 800nm. The relaxation time of the optical nonlinearity in the films is as short as 60fs. The optical nonlinearity is enhanced due to the quantum confinement of electrons in Si nanocrystals embedded in the SiO2 films. The enhanced optical nonlinearity does not originate from Al dopant because there are no Al clusters in the films.
