The two-dimensional layered transition metal dichalcogenides provide new opportunities in future valley-based in- formation processing and also provide an ideal platform to study excitonic effects. At the center of va...The two-dimensional layered transition metal dichalcogenides provide new opportunities in future valley-based in- formation processing and also provide an ideal platform to study excitonic effects. At the center of various device physics toward their possible electronic and optoelectronic applications is understanding the dynamical evolution of various many- particle electronic states, especially exciton which dominates the optoelectronic response of TMDs, under the novel con- text of valley degree of freedom. Here, we provide a brief review of experimental advances in using helicity-resolved ultrafast spectroscopy, especially ultrafast pump-probe spectroscopy, to study the dynamical evolution of valley-related many-particle electronic states in semiconducting monolayer transitional metal dichalcogenides.展开更多
An ultrafast pump-probe spectroscopy system combined with a cryogenic diamond anvil cell(DAC) instrument is developed to investigate the photo-excitation dynamic properties of condensed materials under low temperature...An ultrafast pump-probe spectroscopy system combined with a cryogenic diamond anvil cell(DAC) instrument is developed to investigate the photo-excitation dynamic properties of condensed materials under low temperature and high pressure(LTHP) conditions.The ultrafast dynamics study is performed on Bi_(2)Sr_(2)CaCu_(2)O_(8+δ)(Bi-2212) thin film under LTHP conditions.The superconducting(SC) phase transition has been observed by analyzing the ultrafast dynamics of Bi-2212 as a function of pressure and temperature.Our results suggest that the pump-probe spectroscopy system combined with a cryogenic DAC instrument is an effective method to study the physical mechanism of condensed matter physics at extreme conditions,especially for the SC phase transition.展开更多
Ultrafast charge exchange recombination spectroscopy(UF-CXRS)has been developed on the EAST tokamak(Yingying Li et al 2019 Fusion Eng.Des.146522)to measure fast evolutions of ion temperature and toroidal velocity.Here...Ultrafast charge exchange recombination spectroscopy(UF-CXRS)has been developed on the EAST tokamak(Yingying Li et al 2019 Fusion Eng.Des.146522)to measure fast evolutions of ion temperature and toroidal velocity.Here,we report the preliminary diagnostic measurements after relative sensitivity calibration.The measurement results show a much higher temporal resolution compared with conventional CXRS,benefiting from the usage of a prismcoupled,high-dispersion volume-phase holographic transmission grating and a high quantum efficiency,high-gain detector array.Utilizing the UF-CXRS diagnostic,the fast evolutions of the ion temperature and rotation velocity during a set of high-frequency small-amplitude edgelocalized modes(ELMs)are obtained on the EAST tokamak,which are then compared with the case of large-amplitude ELMs.展开更多
Three decades ago,a highly nonlinear nonpertubative phenomenon,now well-known as the high harmonic generation(HHG),was discovered when intense laser irradiates gaseous atoms.As the HHG produces broadband coherent radi...Three decades ago,a highly nonlinear nonpertubative phenomenon,now well-known as the high harmonic generation(HHG),was discovered when intense laser irradiates gaseous atoms.As the HHG produces broadband coherent radiation,it becomes the most promising source to obtain attosecond pulses.The door to the attosecond science was opened ever since.In this review,we will revisit the incredible adventure to the attoworld.Firstly,the progress of attosecond pulse generation is outlined.Then,we introduce the efforts on imaging the structures or filming the ultrafast dynamics of nuclei and electrons with unprecedented attosecond temporal and Angstrom spatial resolutions,utilizing the obtained attosecond pulses as well as the high harmonic spectrum itself.展开更多
Femtosecond time-resolved coherent anti-Stokes Raman scattering （CARS） spectroscopy is used to investigate gaseous molecular dynamics. Due to the spectrally broad laser pulses, usually poorly resolved spectra result...Femtosecond time-resolved coherent anti-Stokes Raman scattering （CARS） spectroscopy is used to investigate gaseous molecular dynamics. Due to the spectrally broad laser pulses, usually poorly resolved spectra result from this broad spectroscopy. However, it can be demonstrated that by the electronic resonance enhancement optimization control a selective excitation of specific vibrational mode is possible. Using an electronically resonance-enhanced effect, iodine molecule specific CARS spectroscopy can be obtained from a mixture of iodine-air at room temperature and a pressure of 1 atm （corresponding to a saturation iodine vapour as low as about 35 Pa）. The dynamics on either the electronically excited state or the ground state of iodine molecules obtained is consistent with previous studies （vacuum, heated and pure iodine） in the femtoseeond time resolved CARS spectroscopy, showing that an effective method of suppressing the non-resonant CARS background and other interferences is demonstrated.展开更多
Internal solvation of protein was studied by site-directed mutagenesis, with which an intrinsically fluorescent probe,tryptophan, is inserted into the desired position inside a protein molecule for ultrafast spectrosc...Internal solvation of protein was studied by site-directed mutagenesis, with which an intrinsically fluorescent probe,tryptophan, is inserted into the desired position inside a protein molecule for ultrafast spectroscopic study. Here we review this unique method for protein dynamics research. We first introduce the frontiers of protein solvation, site-directed mutagenesis, protein stability and characteristics, and the spectroscopic methods. Then we present time-resolved spectroscopic dynamics of solvation dynamics inside cavities of active sites. The studies are carried out on a globular protein, staphylococcal nuclease. The solvation at sites inside the protein molecule＇s cavities clearly reveals characteristics of the local environment. These solvation behaviors are directly correlated to enzyme activity.展开更多
Terahertz time-domain spectroscopy （THz-TDS） is used to study the interaction between AlCl3 and o-xylene in a temperature range from 300 K to 368 K. For comparison, the three isomers of o-, m-, and p-xylene are meas...Terahertz time-domain spectroscopy （THz-TDS） is used to study the interaction between AlCl3 and o-xylene in a temperature range from 300 K to 368 K. For comparison, the three isomers of o-, m-, and p-xylene are measured by using THz-TDS. The o-xylene carries out isomerization reaction in the presence of catalyst AlCl3. The absorption coefficient of the mixed reaction solution is extracted and analyzed in the frequency range from 0.2 THz to 1.4 THz. The temperature dependence of the absorption coefficient, which is influenced by both the dissolution of AlCl3 and the production of the two other isomer resultants, is obtained, and it can indicate the process of the isomerization reaction. The results suggest that THz spectroscopy can be used to monitor the isomerization reaction and other reactions in chemical synthesis, petrochemical and biomedical fields.展开更多
Femtosecond pump probe spectroscopy is employed to study the photo-induced absorption feature in the single-walled carbon nanotube transient spectrum. The two advantages of the experiment, a chirality enriched sample ...Femtosecond pump probe spectroscopy is employed to study the photo-induced absorption feature in the single-walled carbon nanotube transient spectrum. The two advantages of the experiment, a chirality enriched sample and tuning the pump wavelength to the resonance of a specific nanotube species, greatly facilitate the identification of the photo-induced absorption signal of one tube species. It is found that a photo-induced absorption feature is located at one radial breathing mode to the blue side of the E11 state. This finding prompts a new explanation for the origin of the photo-induced absorption： the transition from the ground state to a phonon coupled state near the E ii state. The explanation suggests a superposition mechanism of the photo-bleach and photo-induced absorption signals, which may serve as a key to the interpretation of the complex pump probe transient spectrum of carbon nanotubes. The finding sheds some light on the understanding of the complex non-radiative relaxation process and the electronic structure of single-walled carbon nanotubes.展开更多
Metal-organic frameworks(MOFs),which are self-assembled porous coordination materials,have garnered considerable attention in the fields of optoelectronics,photovoltaic,photochemistry,and photocatalysis due to their d...Metal-organic frameworks(MOFs),which are self-assembled porous coordination materials,have garnered considerable attention in the fields of optoelectronics,photovoltaic,photochemistry,and photocatalysis due to their diverse structures and excellent tunability.However,the performance of MOF-based optoelectronic applications currently falls short of the industry benchmark.To enhance the performance of MOF materials,it is imperative to undertake comprehensive investigations aimed at gaining a deeper understanding of photophysics and sequentially optimizing properties related to photocarrier transport,recombination,interaction,and transfer.By utilizing femtosecond laser pulses to excite MOFs,time-resolved optical spectroscopy offers a means to observe and characterize these ultrafast microscopic processes.This approach adds the time coordinate as a novel dimension for comprehending the interaction between light and MOFs.Accordingly,this review provides a comprehensive overview of the recent advancements in the photophysics of MOFs and additionally outlines potential avenues for exploring the time domain in the investigation of MOFs.展开更多
Dynamic topological photonics is a novel research field, combining the time-domain optics and topological physics.In this review, the recent progress and realization platforms of dynamic topological photonics have bee...Dynamic topological photonics is a novel research field, combining the time-domain optics and topological physics.In this review, the recent progress and realization platforms of dynamic topological photonics have been well introduced.The definition, measurement methods and the evolution process of the dynamic topological photonics are demonstrated to better understand the physical diagram. This review is meant to bring the readers a different perspective on topological photonics, grasp the advanced progress of dynamic topology, and inspire ideas about future prospects.展开更多
Pressure can reduce the distances among atoms, thereby modifying the overall optical characteristics of molecules.In this article, the excited state behavior of perylene is carefully observed under isotropic pressure ...Pressure can reduce the distances among atoms, thereby modifying the overall optical characteristics of molecules.In this article, the excited state behavior of perylene is carefully observed under isotropic pressure and non-complexing condition. In a steady state, absorption peak shows red shift and spectral width are broadened with pressure increasing,which is ascribed to the π-electron delocalization between molecules. In a transient state, the transition dynamics presents a wavelike tendency with pressure increasing because the shift of self-tapping exciton state is contrary to that of Y-state with pressure increasing. The results conduce to understanding the influence of inter-molecule interaction on excited state behavior with inter-molecule distance decreasing, which contributes to studying the materials under extreme condition.展开更多
Cs_(2)TiBr_(6) nanocrystals(NCs)are a type of promising optoelectronic materials,owing to their high photoelectric properties and non-toxicity.Here,we synthesize the colloidal Cs_(2)TiBr_(6)NCs using a hot-injection a...Cs_(2)TiBr_(6) nanocrystals(NCs)are a type of promising optoelectronic materials,owing to their high photoelectric properties and non-toxicity.Here,we synthesize the colloidal Cs_(2)TiBr_(6)NCs using a hot-injection approach.The temperaturedependent absorption data shows that its energy band changes about 30 me V with temperature,reflecting that its energy band structure is much stable.The excitation intensity-dependent transient absorption data confirms its linear absorption cross-sections and carrier recombination rate constants,involving monomolecular and bimolecular recombination,which are all superior to those of conventional perovskite bromide counterparts.In addition,its nonlinear absorption cross-sections are also measured based on femtosecond Z-scan.Our results suggest that Cs_(2)TiBr_(6)NCs can be extensively applied in the field of optoelectronics,owing to its excellent carrier dynamics and nonlinear optical properties.展开更多
Utilizing infrared spectroscopy,we study the charge dynamics of the topological superconductor candidate Sr_(x)Bi_(2)Se_(3).The frequency-dependent reflectivity R(ω)demonstrates metallic feature and the scattering ra...Utilizing infrared spectroscopy,we study the charge dynamics of the topological superconductor candidate Sr_(x)Bi_(2)Se_(3).The frequency-dependent reflectivity R(ω)demonstrates metallic feature and the scattering rate of the free carriers decreases with temperature decreasing.The plasma edge shows a slight blue shift upon cooling,similar to the behavior of Cu_(x)Bi_(2)Se_(3).As the carrier concentration n obtained by Hall resistivity increases slightly with the decreasing temperature,the effective mass is proved to increase as well,which is in contrast with that of Cu_(x)Bi_(2)Se_(3).We also perform the ultrafast pump-probe study on the Sr_(0.2)Bi_(2)Se_(3)compounds.Resembling its parent compound Bi_(2)Se_(3),three distinct relaxation processes are found to contribute to the transient reflectivity.However,the deduced relaxation times are quite different.In addition,the electron-optical-phonon coupling constant is identified to beλ=0.88.展开更多
We study two-photon resonant nondegenerate four-wave mixing （NFWM） in a Doppler broadened system. It is found that because the induced polarization is sensitive to the atomic velocity, there exists interference betw...We study two-photon resonant nondegenerate four-wave mixing （NFWM） in a Doppler broadened system. It is found that because the induced polarization is sensitive to the atomic velocity, there exists interference between polarizations of atoms with different velocities, leading to significant modification of the NFWM spectra. This polarization interference can be controlled through applying an additional coupling field.展开更多
The absorption responses of blank silicon and black silicon（silicon with micro/nano-conical surface structures） wafers to an 808-nm continuous-wave（CW） laser are investigated at room temperature by terahertz time-...The absorption responses of blank silicon and black silicon（silicon with micro/nano-conical surface structures） wafers to an 808-nm continuous-wave（CW） laser are investigated at room temperature by terahertz time-domain spectroscopy. The transmission of the blank silicon shows an appreciable change, from ground state to the pump state, with amplitude varying up to 50%, while that of the black silicon（BS） with different cone sizes is observed to be more stable. Furthermore,the terahertz transmission through BS is observed to be strongly dependent on the size of the conical structure geometry.The conductivities of blank silicon and BS are extracted from the experimental data with and without pumping. The non-photo-excited conductivities increase with increasing frequency and agree well with the Lorentz model, whereas the photo-excited conductivities decrease with increasing frequency and fit well with the Drude–Smith model. Indeed, for BS, the conductivity, electron density and mobility are found to correlate closely with the size of the conical structure.This is attributed to the influence of space confinement on the carrier excitation, that is, the carriers excited at the BS conical structure surface have a stronger localization effect with a backscattering behavior in small-sized microstructures and a higher recombination rate due to increased electron interaction and collision with electrons, interfaces and grain boundaries.展开更多
基金Project supported by the National Basic Research Program of China(Grant Nos.2012CB921300 and 2014CB920900)the National Key Research and Development Program of China(Grant No.2016YFA0300802)+1 种基金the National Natural Science Foundation of China(Grant Nos.11274015,11674013,and 21405109)the Recruitment Program of Global Experts,China,and Beijing Natural Science Foundation,China(Grant No.4142024)
文摘The two-dimensional layered transition metal dichalcogenides provide new opportunities in future valley-based in- formation processing and also provide an ideal platform to study excitonic effects. At the center of various device physics toward their possible electronic and optoelectronic applications is understanding the dynamical evolution of various many- particle electronic states, especially exciton which dominates the optoelectronic response of TMDs, under the novel con- text of valley degree of freedom. Here, we provide a brief review of experimental advances in using helicity-resolved ultrafast spectroscopy, especially ultrafast pump-probe spectroscopy, to study the dynamical evolution of valley-related many-particle electronic states in semiconducting monolayer transitional metal dichalcogenides.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 12274168 and 12074141)。
文摘An ultrafast pump-probe spectroscopy system combined with a cryogenic diamond anvil cell(DAC) instrument is developed to investigate the photo-excitation dynamic properties of condensed materials under low temperature and high pressure(LTHP) conditions.The ultrafast dynamics study is performed on Bi_(2)Sr_(2)CaCu_(2)O_(8+δ)(Bi-2212) thin film under LTHP conditions.The superconducting(SC) phase transition has been observed by analyzing the ultrafast dynamics of Bi-2212 as a function of pressure and temperature.Our results suggest that the pump-probe spectroscopy system combined with a cryogenic DAC instrument is an effective method to study the physical mechanism of condensed matter physics at extreme conditions,especially for the SC phase transition.
基金supported by the National Magnetic Confinement Fusion Science Program of China (No. 2019YFE 03030004)National Natural Science Foundation of China (Nos. 11535013 and 11975232)
文摘Ultrafast charge exchange recombination spectroscopy(UF-CXRS)has been developed on the EAST tokamak(Yingying Li et al 2019 Fusion Eng.Des.146522)to measure fast evolutions of ion temperature and toroidal velocity.Here,we report the preliminary diagnostic measurements after relative sensitivity calibration.The measurement results show a much higher temporal resolution compared with conventional CXRS,benefiting from the usage of a prismcoupled,high-dispersion volume-phase holographic transmission grating and a high quantum efficiency,high-gain detector array.Utilizing the UF-CXRS diagnostic,the fast evolutions of the ion temperature and rotation velocity during a set of high-frequency small-amplitude edgelocalized modes(ELMs)are obtained on the EAST tokamak,which are then compared with the case of large-amplitude ELMs.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12021004 and 91950202)
文摘Three decades ago,a highly nonlinear nonpertubative phenomenon,now well-known as the high harmonic generation(HHG),was discovered when intense laser irradiates gaseous atoms.As the HHG produces broadband coherent radiation,it becomes the most promising source to obtain attosecond pulses.The door to the attosecond science was opened ever since.In this review,we will revisit the incredible adventure to the attoworld.Firstly,the progress of attosecond pulse generation is outlined.Then,we introduce the efforts on imaging the structures or filming the ultrafast dynamics of nuclei and electrons with unprecedented attosecond temporal and Angstrom spatial resolutions,utilizing the obtained attosecond pulses as well as the high harmonic spectrum itself.
基金supported by the National Natural Science Foundation of China (Grant Nos.60878018 and 61008023)the Natural Scientific Research Innovation Foundation in Harbin Institute of Technology,China (Grant No.HIT.NSRIF.2009009)the Science and Technology Innovation Foundation,Harbin,China (Grant No.RC2007QN017030)
文摘Femtosecond time-resolved coherent anti-Stokes Raman scattering （CARS） spectroscopy is used to investigate gaseous molecular dynamics. Due to the spectrally broad laser pulses, usually poorly resolved spectra result from this broad spectroscopy. However, it can be demonstrated that by the electronic resonance enhancement optimization control a selective excitation of specific vibrational mode is possible. Using an electronically resonance-enhanced effect, iodine molecule specific CARS spectroscopy can be obtained from a mixture of iodine-air at room temperature and a pressure of 1 atm （corresponding to a saturation iodine vapour as low as about 35 Pa）. The dynamics on either the electronically excited state or the ground state of iodine molecules obtained is consistent with previous studies （vacuum, heated and pure iodine） in the femtoseeond time resolved CARS spectroscopy, showing that an effective method of suppressing the non-resonant CARS background and other interferences is demonstrated.
基金Project supported by the National Basic Research Program of China(Grant Nos.2013CB921904,2009CB930504,and 2013CB328700)the National Natural Science Foundation of China(Grant Nos.11074016,11121091,10934001,61177020,11134001,and 10828407)
文摘Internal solvation of protein was studied by site-directed mutagenesis, with which an intrinsically fluorescent probe,tryptophan, is inserted into the desired position inside a protein molecule for ultrafast spectroscopic study. Here we review this unique method for protein dynamics research. We first introduce the frontiers of protein solvation, site-directed mutagenesis, protein stability and characteristics, and the spectroscopic methods. Then we present time-resolved spectroscopic dynamics of solvation dynamics inside cavities of active sites. The studies are carried out on a globular protein, staphylococcal nuclease. The solvation at sites inside the protein molecule＇s cavities clearly reveals characteristics of the local environment. These solvation behaviors are directly correlated to enzyme activity.
基金Project supported by the National Basic Research Program of China(Grant No.2013CB328706)the Specially Funded Program on National Key Scientific Instruments and Equipment Development,China(Grant No.2012YQ14005)+1 种基金the Beijing National Science Foundation,China(Grant No.4122064)the Science Foundation of the China University of Petroleum(Beijing)(Grant Nos.QZDX-2010-01 and KYJJ2012-06-27)
文摘Terahertz time-domain spectroscopy （THz-TDS） is used to study the interaction between AlCl3 and o-xylene in a temperature range from 300 K to 368 K. For comparison, the three isomers of o-, m-, and p-xylene are measured by using THz-TDS. The o-xylene carries out isomerization reaction in the presence of catalyst AlCl3. The absorption coefficient of the mixed reaction solution is extracted and analyzed in the frequency range from 0.2 THz to 1.4 THz. The temperature dependence of the absorption coefficient, which is influenced by both the dissolution of AlCl3 and the production of the two other isomer resultants, is obtained, and it can indicate the process of the isomerization reaction. The results suggest that THz spectroscopy can be used to monitor the isomerization reaction and other reactions in chemical synthesis, petrochemical and biomedical fields.
文摘Femtosecond pump probe spectroscopy is employed to study the photo-induced absorption feature in the single-walled carbon nanotube transient spectrum. The two advantages of the experiment, a chirality enriched sample and tuning the pump wavelength to the resonance of a specific nanotube species, greatly facilitate the identification of the photo-induced absorption signal of one tube species. It is found that a photo-induced absorption feature is located at one radial breathing mode to the blue side of the E11 state. This finding prompts a new explanation for the origin of the photo-induced absorption： the transition from the ground state to a phonon coupled state near the E ii state. The explanation suggests a superposition mechanism of the photo-bleach and photo-induced absorption signals, which may serve as a key to the interpretation of the complex pump probe transient spectrum of carbon nanotubes. The finding sheds some light on the understanding of the complex non-radiative relaxation process and the electronic structure of single-walled carbon nanotubes.
基金Project supported by the Science Challenge Project(Grant No.TZ2018001)the National Natural Science Foundation of China(Grant Nos.11872058 and 21802036)the Project of State Key Laboratory of Environment-friendly Energy Materials,and Southwest University of Science and Technology(Grant No.21fksy07)。
文摘Metal-organic frameworks(MOFs),which are self-assembled porous coordination materials,have garnered considerable attention in the fields of optoelectronics,photovoltaic,photochemistry,and photocatalysis due to their diverse structures and excellent tunability.However,the performance of MOF-based optoelectronic applications currently falls short of the industry benchmark.To enhance the performance of MOF materials,it is imperative to undertake comprehensive investigations aimed at gaining a deeper understanding of photophysics and sequentially optimizing properties related to photocarrier transport,recombination,interaction,and transfer.By utilizing femtosecond laser pulses to excite MOFs,time-resolved optical spectroscopy offers a means to observe and characterize these ultrafast microscopic processes.This approach adds the time coordinate as a novel dimension for comprehending the interaction between light and MOFs.Accordingly,this review provides a comprehensive overview of the recent advancements in the photophysics of MOFs and additionally outlines potential avenues for exploring the time domain in the investigation of MOFs.
基金Project supported by the National Key Research and Development Program of China (Grant No.2018YFB2200403)the National Natural Science Foundation of China (Grant Nos.91950204 and 92150302)。
文摘Dynamic topological photonics is a novel research field, combining the time-domain optics and topological physics.In this review, the recent progress and realization platforms of dynamic topological photonics have been well introduced.The definition, measurement methods and the evolution process of the dynamic topological photonics are demonstrated to better understand the physical diagram. This review is meant to bring the readers a different perspective on topological photonics, grasp the advanced progress of dynamic topology, and inspire ideas about future prospects.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2018YFA0305900 and 2017YFA0403704)the National Natural Science Foundation of China(Grant Nos.61575079,51632002,11804113,and 51720105007)+1 种基金the Natural Science Foundation of Jilin Province,China(Grant No.20180101230JC)the Program for Changjiang Scholars and Innovative Research Team in University,China(Grant No.IRT 15R23).
文摘Pressure can reduce the distances among atoms, thereby modifying the overall optical characteristics of molecules.In this article, the excited state behavior of perylene is carefully observed under isotropic pressure and non-complexing condition. In a steady state, absorption peak shows red shift and spectral width are broadened with pressure increasing,which is ascribed to the π-electron delocalization between molecules. In a transient state, the transition dynamics presents a wavelike tendency with pressure increasing because the shift of self-tapping exciton state is contrary to that of Y-state with pressure increasing. The results conduce to understanding the influence of inter-molecule interaction on excited state behavior with inter-molecule distance decreasing, which contributes to studying the materials under extreme condition.
基金Project supported by the National Natural Science Foundation of China(Grant No.61804063)the Natural Science Foundation of Jilin Province,China(Grant No.20190201208JC)。
文摘Cs_(2)TiBr_(6) nanocrystals(NCs)are a type of promising optoelectronic materials,owing to their high photoelectric properties and non-toxicity.Here,we synthesize the colloidal Cs_(2)TiBr_(6)NCs using a hot-injection approach.The temperaturedependent absorption data shows that its energy band changes about 30 me V with temperature,reflecting that its energy band structure is much stable.The excitation intensity-dependent transient absorption data confirms its linear absorption cross-sections and carrier recombination rate constants,involving monomolecular and bimolecular recombination,which are all superior to those of conventional perovskite bromide counterparts.In addition,its nonlinear absorption cross-sections are also measured based on femtosecond Z-scan.Our results suggest that Cs_(2)TiBr_(6)NCs can be extensively applied in the field of optoelectronics,owing to its excellent carrier dynamics and nonlinear optical properties.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12074042 and 11704033)the National Key Research and Development Program of China(Grant Nos.2021YFA1400400 and 2016YFA0302300)the Fundamental Research Funds for the Central Universities。
文摘Utilizing infrared spectroscopy,we study the charge dynamics of the topological superconductor candidate Sr_(x)Bi_(2)Se_(3).The frequency-dependent reflectivity R(ω)demonstrates metallic feature and the scattering rate of the free carriers decreases with temperature decreasing.The plasma edge shows a slight blue shift upon cooling,similar to the behavior of Cu_(x)Bi_(2)Se_(3).As the carrier concentration n obtained by Hall resistivity increases slightly with the decreasing temperature,the effective mass is proved to increase as well,which is in contrast with that of Cu_(x)Bi_(2)Se_(3).We also perform the ultrafast pump-probe study on the Sr_(0.2)Bi_(2)Se_(3)compounds.Resembling its parent compound Bi_(2)Se_(3),three distinct relaxation processes are found to contribute to the transient reflectivity.However,the deduced relaxation times are quite different.In addition,the electron-optical-phonon coupling constant is identified to beλ=0.88.
基金Supported. by the National Natural Science Foundation of China under Grant Nos 10174096, 10374113 and 60178013.
文摘We study two-photon resonant nondegenerate four-wave mixing （NFWM） in a Doppler broadened system. It is found that because the induced polarization is sensitive to the atomic velocity, there exists interference between polarizations of atoms with different velocities, leading to significant modification of the NFWM spectra. This polarization interference can be controlled through applying an additional coupling field.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11574408,11504439,61627814,and 61675238)the National Key Research and Development Program of China(Grant No.2017YFB0405402)+1 种基金the National Instrumentation Program of China(Grant No.2012YQ14000508)the Young-talent Plan of State Affairs Commission,China(Grant No.2016-3-02)
文摘The absorption responses of blank silicon and black silicon（silicon with micro/nano-conical surface structures） wafers to an 808-nm continuous-wave（CW） laser are investigated at room temperature by terahertz time-domain spectroscopy. The transmission of the blank silicon shows an appreciable change, from ground state to the pump state, with amplitude varying up to 50%, while that of the black silicon（BS） with different cone sizes is observed to be more stable. Furthermore,the terahertz transmission through BS is observed to be strongly dependent on the size of the conical structure geometry.The conductivities of blank silicon and BS are extracted from the experimental data with and without pumping. The non-photo-excited conductivities increase with increasing frequency and agree well with the Lorentz model, whereas the photo-excited conductivities decrease with increasing frequency and fit well with the Drude–Smith model. Indeed, for BS, the conductivity, electron density and mobility are found to correlate closely with the size of the conical structure.This is attributed to the influence of space confinement on the carrier excitation, that is, the carriers excited at the BS conical structure surface have a stronger localization effect with a backscattering behavior in small-sized microstructures and a higher recombination rate due to increased electron interaction and collision with electrons, interfaces and grain boundaries.
