We demonstrate spectral modulation of third-harmonic generation from molecular alignment effects. The third harmonic spectrum is broadened or narrowed under different influences of cross-phase modulations originating ...We demonstrate spectral modulation of third-harmonic generation from molecular alignment effects. The third harmonic spectrum is broadened or narrowed under different influences of cross-phase modulations originating from various molecular alignment revivals. Furthermore, the spectrum and spatial distribution of the generated third harmonic pulse change dramatically in the presence of a preformed plasma. Under the influence of a preformed plasma, a narrower third harmonic spectrum is observed, and the conical third-harmonic pulse increases while the axial part decreases. The investigation provides an effective method to modulate the spectral characteristic and spatial distribution of third-harmonic generation from intense femtosecond filament.展开更多
A new liquid crystalline polyacetylene containing a phenyl benzoate mesogen (5) is synthesized,whose mesomorphic properties are found to be easily 'tunab1e' by simple mechanical perturbation. Thepolymerization...A new liquid crystalline polyacetylene containing a phenyl benzoate mesogen (5) is synthesized,whose mesomorphic properties are found to be easily 'tunab1e' by simple mechanical perturbation. Thepolymerization of 10- [ 4 - (4' -methoxyphenoxycarbonyl )phenoxycarbonyl] - 1 -decyne (4 ) in itiated by theWCl_6-Ph_4Sn/dioxane complex yields polymer 5 with a M_w of 28400. The molecular structure of 5 ischaracterized by NMR, IR, and UV spectroscopy and its liquid crystalline behavior is investigated by DSC,POM, and XRD analysis. Upon mechanical perturbation, 5 exhibits unusual agitation-induced high-strengthdisclinations, shear-induced inversion walls, and solidification-induced banded textures. Such phenomenahave been observed in the main-chain liquid crystalline polymers with rigid backbones, but have seldom beenreported for the side-chain liquid crystalline polymers with flexible backbones, suggesting that the rigidpolyacetylene backbone of 5 plays a constructive role in inducing the novel molecular alignments.展开更多
The field-free alignment of molecule Cl CN is investigated by using a terahertz few-cycle pulse(THz FCP)based on the time-dependent density matrix theory.It is shown that a high degree of molecular alignment can be ob...The field-free alignment of molecule Cl CN is investigated by using a terahertz few-cycle pulse(THz FCP)based on the time-dependent density matrix theory.It is shown that a high degree of molecular alignment can be obtained by changing the matching number of the THz FCPs in the adiabatic regime and the non-adiabatic regime.The matching number can affect both the maximum value of the alignment and the time at which it is achieved.It is also found that a higher degree of alignment can be achieved by using the THz FCP at lower intensity and there exists an optimal threshold of molecular alignment with the increase of the field amplitude.Also found is the frequency sensitive region in which the degree of maximum alignment can be enhanced greatly by modulating the center frequencies of different THz FCPs.The investigation demonstrates that comparing with a THz single-cycle pulse,a better result of the field-free alignment can be created by a THz FCP at a constant rotational temperature of molecule.展开更多
We demonstrate a deep-learning neural network(DNN) method for the measurement of molecular alignment by using the molecular-alignment-based cross-correlation polarization-gating frequency resolved optical gating(M-XFR...We demonstrate a deep-learning neural network(DNN) method for the measurement of molecular alignment by using the molecular-alignment-based cross-correlation polarization-gating frequency resolved optical gating(M-XFROG) technique.Our network has the capacity for direct measurement of molecular alignment from the FROG traces. In a proof-of-principle experiment, we have demonstrated our method in O^(2) molecules. With our method, the molecular alignment factor<cos^(2)θ>(t) of O_(2), impulsively excited by a pump pulse, was directly reconstructed. The accuracy and validity of the reconstruction have been verified by comparison with the simulations based on experimental parameters.展开更多
The dephasing of molecular alignment can lead to the deformation of the alignment signal during its periodic revivals.Most studies are concentrated on the first few rotational revival periods of the molecular alignmen...The dephasing of molecular alignment can lead to the deformation of the alignment signal during its periodic revivals.Most studies are concentrated on the first few rotational revival periods of the molecular alignment and neglect the dephasing effect.However,study of the alignment dephasing is still of great significance for both the long-term dynamics of the molecular alignment and the dephasing itself.In this work,we theoretically demonstrate that the dephasing effect is correlated with both the rotational temperature and the rotational revival period of the molecules.The results present that the dephasing is especially significant for those molecules with long rotational revival period at high rotational temperatures.The physics behind it is explored by taking advantage of the coherence of the rotational quantum state population.This work deepens our understanding of rotational dynamics and rotational spectroscopy in molecular alignment.展开更多
In this Letter, we study the molecular alignment and orientation driven by two elliptically polarized laser pulses.It is shown that the field-free molecular alignment can be achieved in a three-dimensional（3D） case,...In this Letter, we study the molecular alignment and orientation driven by two elliptically polarized laser pulses.It is shown that the field-free molecular alignment can be achieved in a three-dimensional（3D） case, while the field-free molecular orientation is only along the x and y directions, and that the field-free alignment and orientation along different axes are related to the populations of the rotational states. It is demonstrated that changing the elliptic parameter is efficient for controlling both in-pulse and post-pulse molecular alignment and orientation. The delay time also has an influence on the field-free molecular alignment and orientation.展开更多
This paper studies the molecular rotational excitation and field-free spatial alignment in a nonresonant intense laser field numerically and analytically by using the time-dependent SchrSdinger equation. The broad rot...This paper studies the molecular rotational excitation and field-free spatial alignment in a nonresonant intense laser field numerically and analytically by using the time-dependent SchrSdinger equation. The broad rotational wave packets excited by the femtosecond pulse are defined in conjugate angle space, and their coefficients are obtained by solving a set of coupled linear equations. Both single molecule orientation angles and an ensemble of O2 and CO molecule angular distributions are calculated in detail. The numerical results show that, for single molecule highest occupied molecular orbital （HOMO） symmetry σ tends to have a molecular orientation along the laser polarization direction and the permanent dipole moment diminishes the mean of the orientation angles; for an ensemble of molecules, angular distributions provide more complex and additional information at times where there are no revivals in the single molecule plot. In particular, at the revival peak instant, with the increase of temperature of the molecular ensemble, the anisotropic angular distributions with respect to the laser polarization direction of the πg orbital gradually transform to the symmetrical distributions regarding the laser polarization vector and for two HOMO configurations angular distributions of all directions are confined within a smaller angle when the temperature of the molecular ensemble is higher.展开更多
Controlling the alignment and packing structure of organic molecules on solid substrate surfaces at molecule level is essential to develop high-performance organic thin film(OTF)devices.Pentacene,which is a typical p-...Controlling the alignment and packing structure of organic molecules on solid substrate surfaces at molecule level is essential to develop high-performance organic thin film(OTF)devices.Pentacene,which is a typical p-type semiconductor material usually adopts lying-down geometry on metal substrates owning toπ-d coupling between pentacene and metal substrates.However,in this study,we found that pentacene molecules can be adsorbed on an anneal-treated Cu(111)surface with their long axis perpendicular to substrate surface.Highly ordered single-layer pentacene film with stand-up molecular geometry was achieved on this substrate.It was found that the functionalization of Cu surface with C=O groups due to annealing treatment should be accounted for standing-up geometry of pentacene on Cu substrate.This observation shed light on the tuning of the alignment and packing structure of organic molecules.展开更多
The propagation of femtosecond laser pulses in N2-filled hollow fibers is studied both theoretically and experimentally. The laser pulse aligns the N2 molecules and changes the refractive index, which meanwhile modula...The propagation of femtosecond laser pulses in N2-filled hollow fibers is studied both theoretically and experimentally. The laser pulse aligns the N2 molecules and changes the refractive index, which meanwhile modulates the spectrum of the pulse in turn. The dependence of the spectral modulation on the gas temperature is investigated. We find that both spectral broadening and frequency red-shift are enhanced at low temperature. The degree of enhancement is found to be dependent on the pulse duration. Based on our findings, we propose a method for femtosecond pulse spectral broadening and few-cycle pulse generation via the molecular alignment.展开更多
Through theoretical analysis,we show how aligning pulse durations affect the degree and the time-rate slope of nitrogen field-free alignment at a fixed pulse intensity.It is found that both the degree and the slope fi...Through theoretical analysis,we show how aligning pulse durations affect the degree and the time-rate slope of nitrogen field-free alignment at a fixed pulse intensity.It is found that both the degree and the slope first increase,then saturate,and finally decrease with the increasing pump duration.The optimal durations for the maximum degree and the maximum slope of the alignment are found to be different.Additionally,they are found to mainly depend on the molecular rotational period,and are affected by the temperature and the aligning pump intensities.The mechanism of molecular alignment is also discussed.展开更多
The angular distribution of CH3I is investigated experimentally using a single Fourier transform-limited laser pulse and a pulse train, where a 90-fs 800-nm linearly polarized laser field with a moderate intensity of ...The angular distribution of CH3I is investigated experimentally using a single Fourier transform-limited laser pulse and a pulse train, where a 90-fs 800-nm linearly polarized laser field with a moderate intensity of 2.8 × 10^13 W/cm2 is used. The dynamic alignment is demonstrated in a single pulse experiment. Moreover, a pulse train is used to optimize the molecular alignment, and the alignment degree is almost identical to that with the single pulse. The results are analysed by using chirped femtosecond laser pulses, and it demonstrates that the structure of pulse train rather than its effective duration is crucial to the molecular alignment.展开更多
Using the classical ensemble method, we investigate nonsequential double ionization （NSDI） of diatomic molecules by elliptically polarized laser pulses. The results show that the ellipticity of the laser field has a...Using the classical ensemble method, we investigate nonsequential double ionization （NSDI） of diatomic molecules by elliptically polarized laser pulses. The results show that the ellipticity of the laser field has a strong suppression effect on NSDI probabilities both in parallel and perpendicular alignments. The double ionization （DI） channel is commonly dominated by NSDI, and the NSDI channel changes with ellipticity. As ellipticity increases, more and more NSDIs occur through recollision excitation with subsequent field ionization （RESI）. Moreover, like the case of linear polarization, the two electrons involved in NSDI for perpendicularly aligned molecules are more likely to emit into the opposite hemispheres as compared to the case of parallel alignment. Additionally, this alignment effect increases as ellipticity increases.展开更多
Molecular similarity has long been a hot topic, which has been evaluated and compared by various approaches and plays a significant role in protein-ligand and protein-protein interactions recognition. There are curren...Molecular similarity has long been a hot topic, which has been evaluated and compared by various approaches and plays a significant role in protein-ligand and protein-protein interactions recognition. There are currently many types of molecular similarity evaluation methods with their own advantages and disadvantages. Molecular finger- prints are the most common methods for molecular similarity evaluation which only concern about rapid 2D com- mon substructure retrieval but lack the ability to encode the information about 3D conformers. 3D molecular de- scriptor based methods bear the advantages of representing the structure information of a conformer, but the de- scriptors are not guaranteed to describe the molecules precisely. Molecular alignment based methods try to super- impose two molecules and evaluate the similarity using the optimal poses which are generally more precise than the molecular descriptor but require a time-consuming optimization process. Pharmacophore based methods only focus on the chemical features about a molecule and are not capable of dealing with the molecular shape similarity. In or- der to evaluate the performance of molecular similarity based screening, many kinds of metrics are available, e.g., visual representation, quantitative measurements and scaffold hopping ability measurements. Further applications of molecular similarity include construction of molecule interaction network or generation of diverse compounds li- brary.展开更多
This study shows the unexpected and counterintuitive possibility of simultaneously orienting a molecule while delocalizing its molecular axis in a plane in field-free conditions.The corresponding quantum states are ch...This study shows the unexpected and counterintuitive possibility of simultaneously orienting a molecule while delocalizing its molecular axis in a plane in field-free conditions.The corresponding quantum states are characterized,and different control strategies using shaped terahertz(THz)laser pulses are proposed to reach such states at zero and nonzero temperatures.The robustness against temperature effects of a simple control procedure combining a laser and a THz pulse is shown.Such control strategies can be applied not only to linear molecules but also to symmetric top molecules.展开更多
基金supported by the National Key Scientific Instrument Project,China(Grant No.2012YQ150092)the National Basic Research Program of China(Grant No.2011CB808105)+3 种基金the National Natural Science Foundation of China(Grant No.11434005)China Postdoctoral Science Foundation(Grant No.2014M560348)the National Natural Science Foundation of China(Grant No.11504237)the Shanghai Municipal Science and Technology Commission,China(Grant No.14JC1401600)
文摘We demonstrate spectral modulation of third-harmonic generation from molecular alignment effects. The third harmonic spectrum is broadened or narrowed under different influences of cross-phase modulations originating from various molecular alignment revivals. Furthermore, the spectrum and spatial distribution of the generated third harmonic pulse change dramatically in the presence of a preformed plasma. Under the influence of a preformed plasma, a narrower third harmonic spectrum is observed, and the conical third-harmonic pulse increases while the axial part decreases. The investigation provides an effective method to modulate the spectral characteristic and spatial distribution of third-harmonic generation from intense femtosecond filament.
基金This project was in part supported by the Hong Kong Research Grants Council(HKUST597/95P&6149/97P)
文摘A new liquid crystalline polyacetylene containing a phenyl benzoate mesogen (5) is synthesized,whose mesomorphic properties are found to be easily 'tunab1e' by simple mechanical perturbation. Thepolymerization of 10- [ 4 - (4' -methoxyphenoxycarbonyl )phenoxycarbonyl] - 1 -decyne (4 ) in itiated by theWCl_6-Ph_4Sn/dioxane complex yields polymer 5 with a M_w of 28400. The molecular structure of 5 ischaracterized by NMR, IR, and UV spectroscopy and its liquid crystalline behavior is investigated by DSC,POM, and XRD analysis. Upon mechanical perturbation, 5 exhibits unusual agitation-induced high-strengthdisclinations, shear-induced inversion walls, and solidification-induced banded textures. Such phenomenahave been observed in the main-chain liquid crystalline polymers with rigid backbones, but have seldom beenreported for the side-chain liquid crystalline polymers with flexible backbones, suggesting that the rigidpolyacetylene backbone of 5 plays a constructive role in inducing the novel molecular alignments.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12274265 and 11874241)the Taishan Scholar Project of Shandong Province,China。
文摘The field-free alignment of molecule Cl CN is investigated by using a terahertz few-cycle pulse(THz FCP)based on the time-dependent density matrix theory.It is shown that a high degree of molecular alignment can be obtained by changing the matching number of the THz FCPs in the adiabatic regime and the non-adiabatic regime.The matching number can affect both the maximum value of the alignment and the time at which it is achieved.It is also found that a higher degree of alignment can be achieved by using the THz FCP at lower intensity and there exists an optimal threshold of molecular alignment with the increase of the field amplitude.Also found is the frequency sensitive region in which the degree of maximum alignment can be enhanced greatly by modulating the center frequencies of different THz FCPs.The investigation demonstrates that comparing with a THz single-cycle pulse,a better result of the field-free alignment can be created by a THz FCP at a constant rotational temperature of molecule.
基金supported by the National Key Research and Development Program of China(No.2019YFA0308300)the National Natural Science Foundation of China(Nos.91950202,12225406,12074136,and 12021004)the Natural Science Foundation of Hubei Province(No.2021CFB330).
文摘We demonstrate a deep-learning neural network(DNN) method for the measurement of molecular alignment by using the molecular-alignment-based cross-correlation polarization-gating frequency resolved optical gating(M-XFROG) technique.Our network has the capacity for direct measurement of molecular alignment from the FROG traces. In a proof-of-principle experiment, we have demonstrated our method in O^(2) molecules. With our method, the molecular alignment factor<cos^(2)θ>(t) of O_(2), impulsively excited by a pump pulse, was directly reconstructed. The accuracy and validity of the reconstruction have been verified by comparison with the simulations based on experimental parameters.
基金supported by the National Natural Science Foundation of China(No.12004199).
文摘The dephasing of molecular alignment can lead to the deformation of the alignment signal during its periodic revivals.Most studies are concentrated on the first few rotational revival periods of the molecular alignment and neglect the dephasing effect.However,study of the alignment dephasing is still of great significance for both the long-term dynamics of the molecular alignment and the dephasing itself.In this work,we theoretically demonstrate that the dephasing effect is correlated with both the rotational temperature and the rotational revival period of the molecules.The results present that the dephasing is especially significant for those molecules with long rotational revival period at high rotational temperatures.The physics behind it is explored by taking advantage of the coherence of the rotational quantum state population.This work deepens our understanding of rotational dynamics and rotational spectroscopy in molecular alignment.
基金supported by the National Natural Science Foundation of China(No.11674198)the Taishan Scholar Project of Shandong Province
文摘In this Letter, we study the molecular alignment and orientation driven by two elliptically polarized laser pulses.It is shown that the field-free molecular alignment can be achieved in a three-dimensional（3D） case, while the field-free molecular orientation is only along the x and y directions, and that the field-free alignment and orientation along different axes are related to the populations of the rotational states. It is demonstrated that changing the elliptic parameter is efficient for controlling both in-pulse and post-pulse molecular alignment and orientation. The delay time also has an influence on the field-free molecular alignment and orientation.
基金supported by the Program of Excellent Team in Harbin Institute of Technologythe Program for New Century Excellent Talents in University (NCET)National Natural Science Foundation of China (Grant Nos 10774033,60878018 and 10674036)
文摘This paper studies the molecular rotational excitation and field-free spatial alignment in a nonresonant intense laser field numerically and analytically by using the time-dependent SchrSdinger equation. The broad rotational wave packets excited by the femtosecond pulse are defined in conjugate angle space, and their coefficients are obtained by solving a set of coupled linear equations. Both single molecule orientation angles and an ensemble of O2 and CO molecule angular distributions are calculated in detail. The numerical results show that, for single molecule highest occupied molecular orbital （HOMO） symmetry σ tends to have a molecular orientation along the laser polarization direction and the permanent dipole moment diminishes the mean of the orientation angles; for an ensemble of molecules, angular distributions provide more complex and additional information at times where there are no revivals in the single molecule plot. In particular, at the revival peak instant, with the increase of temperature of the molecular ensemble, the anisotropic angular distributions with respect to the laser polarization direction of the πg orbital gradually transform to the symmetrical distributions regarding the laser polarization vector and for two HOMO configurations angular distributions of all directions are confined within a smaller angle when the temperature of the molecular ensemble is higher.
基金Project supported by the Natural Science Foundation of Zhejiang Province,China(Grant No.LY19F040005)the National Natural Science Foundation of China(Grant Nos.61474077 and 51802355).
文摘Controlling the alignment and packing structure of organic molecules on solid substrate surfaces at molecule level is essential to develop high-performance organic thin film(OTF)devices.Pentacene,which is a typical p-type semiconductor material usually adopts lying-down geometry on metal substrates owning toπ-d coupling between pentacene and metal substrates.However,in this study,we found that pentacene molecules can be adsorbed on an anneal-treated Cu(111)surface with their long axis perpendicular to substrate surface.Highly ordered single-layer pentacene film with stand-up molecular geometry was achieved on this substrate.It was found that the functionalization of Cu surface with C=O groups due to annealing treatment should be accounted for standing-up geometry of pentacene on Cu substrate.This observation shed light on the tuning of the alignment and packing structure of organic molecules.
基金Project supported by the National Natural Science Foundation of China(Grants Nos.11074014 and 11121091)
文摘The propagation of femtosecond laser pulses in N2-filled hollow fibers is studied both theoretically and experimentally. The laser pulse aligns the N2 molecules and changes the refractive index, which meanwhile modulates the spectrum of the pulse in turn. The dependence of the spectral modulation on the gas temperature is investigated. We find that both spectral broadening and frequency red-shift are enhanced at low temperature. The degree of enhancement is found to be dependent on the pulse duration. Based on our findings, we propose a method for femtosecond pulse spectral broadening and few-cycle pulse generation via the molecular alignment.
基金Project supported by the National Natural Science Foundation of China (Grants Nos. 10634020,11074014 and 10821062)
文摘Through theoretical analysis,we show how aligning pulse durations affect the degree and the time-rate slope of nitrogen field-free alignment at a fixed pulse intensity.It is found that both the degree and the slope first increase,then saturate,and finally decrease with the increasing pump duration.The optimal durations for the maximum degree and the maximum slope of the alignment are found to be different.Additionally,they are found to mainly depend on the molecular rotational period,and are affected by the temperature and the aligning pump intensities.The mechanism of molecular alignment is also discussed.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10774056 and 10974070)the Fundamental Research Funds for the Central Universities, China (Grant No. 200903371)the Specialized Research Fund for the Doctoral Program of Higher Education, China (Grant No. 20100061110045)
文摘The angular distribution of CH3I is investigated experimentally using a single Fourier transform-limited laser pulse and a pulse train, where a 90-fs 800-nm linearly polarized laser field with a moderate intensity of 2.8 × 10^13 W/cm2 is used. The dynamic alignment is demonstrated in a single pulse experiment. Moreover, a pulse train is used to optimize the molecular alignment, and the alignment degree is almost identical to that with the single pulse. The results are analysed by using chirped femtosecond laser pulses, and it demonstrates that the structure of pulse train rather than its effective duration is crucial to the molecular alignment.
基金Project supported by the Fund for Excellent Youths of Education Department of Hubei Province,China(Grant No.Q20133001)the Natural Science Foundation of Hubei Province,China(Grant No.2013CFB015)the Special Fund of Theoretical Physics,China(Grant No.11347189)
文摘Using the classical ensemble method, we investigate nonsequential double ionization （NSDI） of diatomic molecules by elliptically polarized laser pulses. The results show that the ellipticity of the laser field has a strong suppression effect on NSDI probabilities both in parallel and perpendicular alignments. The double ionization （DI） channel is commonly dominated by NSDI, and the NSDI channel changes with ellipticity. As ellipticity increases, more and more NSDIs occur through recollision excitation with subsequent field ionization （RESI）. Moreover, like the case of linear polarization, the two electrons involved in NSDI for perpendicularly aligned molecules are more likely to emit into the opposite hemispheres as compared to the case of parallel alignment. Additionally, this alignment effect increases as ellipticity increases.
基金the Fundamental Research Funds for the Central Universities,the National Natural Science Foundation of China，the Special Fund for Major State Basic Research Project，the Shanghai Committee of Science and Technology，the 863 Hi-Tech Program of China (No.2012AA020308).Honglin Li is also sponsored by Program for New Century Excellent Talents in University
文摘Molecular similarity has long been a hot topic, which has been evaluated and compared by various approaches and plays a significant role in protein-ligand and protein-protein interactions recognition. There are currently many types of molecular similarity evaluation methods with their own advantages and disadvantages. Molecular finger- prints are the most common methods for molecular similarity evaluation which only concern about rapid 2D com- mon substructure retrieval but lack the ability to encode the information about 3D conformers. 3D molecular de- scriptor based methods bear the advantages of representing the structure information of a conformer, but the de- scriptors are not guaranteed to describe the molecules precisely. Molecular alignment based methods try to super- impose two molecules and evaluate the similarity using the optimal poses which are generally more precise than the molecular descriptor but require a time-consuming optimization process. Pharmacophore based methods only focus on the chemical features about a molecule and are not capable of dealing with the molecular shape similarity. In or- der to evaluate the performance of molecular similarity based screening, many kinds of metrics are available, e.g., visual representation, quantitative measurements and scaffold hopping ability measurements. Further applications of molecular similarity include construction of molecule interaction network or generation of diverse compounds li- brary.
文摘This study shows the unexpected and counterintuitive possibility of simultaneously orienting a molecule while delocalizing its molecular axis in a plane in field-free conditions.The corresponding quantum states are characterized,and different control strategies using shaped terahertz(THz)laser pulses are proposed to reach such states at zero and nonzero temperatures.The robustness against temperature effects of a simple control procedure combining a laser and a THz pulse is shown.Such control strategies can be applied not only to linear molecules but also to symmetric top molecules.
