7 results on '"Dongwen Zhang"'
Search Results
2. Dissociative multiple ionization of carbon dioxide dimers in intense femtosecond laser fields
- Author
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Pan Song, Yalei Zhu, Yan Yang, Xiaowei Wang, Congsen Meng, Jing Zhao, Jinlei Liu, Zhihui Lv, Dongwen Zhang, Zengxiu Zhao, and Jianmin Yuan
- Published
- 2022
3. Localized-plasma-assisted rotational transitions in the terahertz region
- Author
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Zhihui Lü, Chao Chang, Jinlei Liu, Yindong Huang, Jianmin Yuan, Xing Xu, Zhang Ziyi, Zengxiu Zhao, Wang Ruixing, Dongwen Zhang, Jing Zhao, and Xiang Zuoxian
- Subjects
Physics ,Infrared ,Terahertz radiation ,Nanoparticle ,Plasma ,Electron ,01 natural sciences ,Molecular physics ,010305 fluids & plasmas ,Ion ,Physics::Plasma Physics ,0103 physical sciences ,Molecule ,010306 general physics ,Absorption (electromagnetic radiation) - Abstract
Molecular spectroscopy is a powerful tool for accelerating advances in materials science, chemistry, biology, and astronomy. Typically, molecular spectroscopy uses nanotips or nanoparticles to locally detect the molecule properties in a sample resulting from absorption of infrared and terahertz radiations. Here, we present an alternative that transient localized plasma can be applied to enhance the molecular spectroscopy. Our experiments show a significant enhancement of rotational transitions in carbon monoxide plasma under the illumination of terahertz waves. We proposed a semiclassical model for this enhancement, dominated by the energy exchange from electrons to molecules or ions via a collision process in the localized plasma. Our findings gain more insight into the nonequilibrium dynamics in laser-generated localized plasma. We also propose that the localized plasma can be used to improve the sensitivity of molecular spectroscopy.
- Published
- 2021
4. Analysis of THz generation by multicolor laser pulses with various frequency ratios
- Author
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Zhaoyan Zhou, Zhihui Lv, Chi Lin, Dongwen Zhang, and Zengxiu Zhao
- Subjects
Physics ,Photon ,Photoemission spectroscopy ,business.industry ,Terahertz radiation ,Physics::Optics ,Sawtooth wave ,Laser ,01 natural sciences ,010305 fluids & plasmas ,law.invention ,Optics ,law ,Thz radiation ,0103 physical sciences ,010306 general physics ,business ,Quantum ,Mixing (physics) - Abstract
Terahertz (THz) generation in a gas medium is simulated by quantum calculations with multicolor intense laser pulses of various frequency ratios. By correlating THz radiation with the above-threshold-ionization photoelectron spectrum, we confirm that our previously proposed free-free transition model for the generation of THz radiation is also applicable to multicolor pulses. THz photon emissions can proceed through transitions between continuous states with similar energies that have opposite parities. This mechanism predicts that THz waves can be efficiently generated at special two-color laser frequency ratios when the multiphoton mixing condition is satisfied. Applying this model to multicolor fields (sawtooth wave shape), we provide a quantum-mechanical interpretation for the reason for THz radiation enhancement. A scheme combining multiple lasers to raise THz radiation satisfying multiphoton mixing conditions is also proposed.
- Published
- 2020
5. Dynamics of three-particle fragmentation of (CO2)23+ ions produced by intense femtosecond laser fields
- Author
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Zhihui Lv, Congsen Meng, Pan Song, Jianmin Yuan, Yongjun Li, Dongwen Zhang, Wenpu Dong, Xiaowei Wang, and Zengxiu Zhao
- Subjects
Physics ,Intermolecular force ,Coulomb explosion ,Kinetic energy ,01 natural sciences ,010305 fluids & plasmas ,Ion ,Crystallography ,symbols.namesake ,Fragmentation (mass spectrometry) ,Metastability ,Ionization ,0103 physical sciences ,symbols ,van der Waals force ,010306 general physics - Abstract
In a momentum coincidence measurement experiment, we studied the three-body fragmentation dynamics of carbon dioxide dimers in intense femtosecond laser fields. The three-dimensional momentum vectors and kinetic energies of the fragments were recorded in a cold-target recoil-ion momentum spectrometer. An analysis shows that ${({\mathrm{CO}}_{2})}_{2}{}^{3+}$ breaks up into ${\mathrm{CO}}_{2}{}^{+}+{\mathrm{CO}}^{+}+{\mathrm{O}}^{+}$ ions through both concerted and sequential fragmentation channels. These two fragmentation channels are consistent with the instantaneous and metastable dissociation channels in the dissociation dynamics of ${\mathrm{CO}}_{2}{}^{2+}$ ion breakup into ${\mathrm{CO}}^{+}$ and ${\mathrm{O}}^{+}$ ions. From Coulomb explosion imaging, our results show that, for the parallel sliding structure of the carbon dioxide dimer molecules, the angle between the C=O bond and the van der Waals bond is $48{}^{\ensuremath{\circ}}$, and the intermolecular nuclear distance $R({\mathrm{CO}}_{2}\text{\ensuremath{-}}{\mathrm{CO}}_{2})$ is 4.0 \AA{}. By tracing the direction of the fragmentation ions, the ${\mathrm{O}}^{+}$ was found to be produced from the C=O bond that is closer to the center of the C-C bond during direct dissociation. These results indicate that the dynamic characteristics of the monomer is retained and gives rise to new dynamics in the molecular cluster complexes. Finally, we have measured angular distributions of ion fragments produced by different dissociation channels of ${({\mathrm{CO}}_{2})}_{2}$, and the results reveal that the structure of the dimer and its relative orientation in the laser field govern the ionization dynamics.
- Published
- 2019
6. Theoretical study of terahertz generation from atoms and aligned molecules driven by two-color laser fields
- Author
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Jinlei Liu, Chao Meng, Yindong Huang, Wenbo Chen, Jianmin Yuan, Dongwen Zhang, Zengxiu Zhao, and Zhaoyan Zhou
- Subjects
Physics ,Field (physics) ,Atomic Physics (physics.atom-ph) ,Terahertz radiation ,Far-infrared laser ,FOS: Physical sciences ,Physics::Optics ,Laser ,Atomic and Molecular Physics, and Optics ,Physics - Atomic Physics ,Terahertz spectroscopy and technology ,law.invention ,Photomixing ,law ,Ultrafast laser spectroscopy ,Physics::Atomic Physics ,Electric potential ,Atomic physics - Abstract
We study the generation of terahertz radiation from atoms and molecules driven by an ultrashort fundamental laser and its second harmonic field by solving time-dependent Schr\"odinger equation (TDSE). The comparisons between one-, two-, and three- dimensional TDSE numerical simulations show that initial ionized wave-packet and its subsequent acceleration in the laser field and rescattering with long-range Coulomb potential play key roles. We also present the dependence of the optimum phase delay and yield of terahertz radiation on the laser intensity, wavelength, duration, and the ratio of two-color laser components. Terahertz wave generation from model hydrogen molecules are further investigated by comparing with high harmonic emission. It is found that the terahertz yield is following the alignment dependence of ionization rate, while the optimal two-color phase delays varies by a small amount when the alignment angle changes from 0 to 90 degrees, which reflects alignment dependence of attosecond electron dynamics. Finally we show that terahertz emission might be used to clarify the origin of interference in high harmonic generation from aligned molecules by coincidently measuring the angle-resolved THz yields.
- Published
- 2015
7. Terahertz emission of atoms driven by ultrashort laser pulses
- Author
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Zhaoyan Zhou, Zengxiu Zhao, Jianmin Yuan, and Dongwen Zhang
- Subjects
Physics ,Field (physics) ,Far-infrared laser ,Physics::Optics ,Field strength ,Laser ,Atomic and Molecular Physics, and Optics ,law.invention ,Photomixing ,X-ray laser ,law ,Ultrafast laser spectroscopy ,Physics::Atomic Physics ,Atomic physics ,Terahertz time-domain spectroscopy - Abstract
Terahertz (THz) emissions of an isolated atom in an ultrashort (100 fs) laser field are simulated by solving the time-dependent Schr\"odinger equation. From numerical calculations with one- and three-dimensional hydrogen atom models and a short-range shallow potential model, it can be concluded that continuum THz emissions occur more readily following transitions involving intermediate states above rather than those well below the ionization threshold of the system. Line-shaped THz emissions from transitions between high-lying Rydberg states are also found. The models are also used to describe the observed enhanced terahertz emissions with a superposed second-order harmonic laser field or a spatially constant electric field. The dependence of the THz field strength on the intensities of the fundamental laser field and the superposed field is also examined. Strong field approximation is extended to analyze the general features of THz emissions resulting from continuum free-free transitions of an electron in strong laser fields. These calculations contribute to an understanding of the THz emission processes when strong laser fields interact with atomic and molecular systems that have larger ionization potentials and where multiphoton processes are involved in order to generate THz emissions effectively.
- Published
- 2009
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